Change search
Refine search result
12 1 - 50 of 79
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Andersson, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Plant patch structure influences plant fitness via antagonistic and mutualistic interactions but in different directions2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 4, p. 1175-1182Article in journal (Refereed)
    Abstract [en]

    Plant patch structure and environmental context can influence the outcome of antagonistic and mutualistic plant-insect interactions, leading to spatially variable fitness effects for plants. We investigated the effects of herbivory and pollen limitation on plant reproductive performance in 28 patches of the self-compatible perennial herb Scrophularia nodosa and assessed how such effects varied with plant patch size, plant density and tree cover. Both antagonistic and mutualistic interactions had strong effects on plant reproductive performance. Leaf feeding from herbivores reduced both fruit production and seed germination, and leaf herbivory increased with plant patch size. Experimentally hand-pollinated flowers produced more seeds than open-pollinated flowers, and pollen limitation was more severe in patches with fewer plants. Our study on S. nodosa is one of few which documents that plant patch structure influences the outcome of both antagonistic and mutualistic plant-insect interactions. The results thus provide an example of how variation in plant patch structure and environmental factors can lead to spatially variable fitness effects from mutualistic and antagonistic interactions.

  • 2.
    Andersson, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Immigration of olfactory searching insects into host plant patches: testing scaling rules for olfactory information2011In: Arthropod-Plant Interactions, ISSN 1872-8855, E-ISSN 1872-8847, Vol. 5, p. 269-277Article in journal (Refereed)
    Abstract [en]

    Herbivorous insects are commonly faced with host plants being distributed in scattered patches across a landscape. Immigration rates into habitat patches may strongly depend on the sensory cues used in the patch location process, and immigration rates of insects can be predicted based on the scaling of sensory cues. Here, we tested recent estimates of the scaling of olfactory information to patch size, which predicts a scaling coefficientf z = -0.5 (A^z, where A = patch size, z = scaling coefficient). We predicted that immigration rates of olfactory searching insects into patches of different sizes should scale according to the estimated slope. We investigated attraction of the weevils Cionus tuberculosus and Cionus scrophulariae to odors from figwort Scrophularia nodosa and quantified immigration rates of weevils into differently sized patches. We also investigated oviposition rates of the sawfly Tenthredo scrophulariae. The slope in the regression between density and patch size for herbivores was then compared with the predicted scaling coefficient. Using olfactometers, we found that weevils were attracted to figwort odors. Weevil densities were significantly affected by patch size, and the slope in the relationship between density and patch size was z = -0.53. The slope in the relationship between larval densities of sawflies and patch size was less negative with a slope of z = -0.15, indicating differences in search behavior compared with the weevils. The density–patch size relationship for the weevils closely matched the predicted slope and supported the previous estimations of the scaling of olfactory informationto patch size.

  • 3.
    Andersson, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    What shapes local density?: The importance of migration rates and local growth for density-patch size relationships in two Cionus weevils2012In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 37, no 1, p. 90-98Article in journal (Refereed)
    Abstract [en]

    1. The relative effect of migration and local growth on the spatio-temporal density-distribution of two co-existing herbivorous weevils, Cionus scrophulariae L. and C. tuberculosus Scop., in 32 host plant Scrophularia nodosa L. patches of varying sizes was investigated. 2. Predictions of the temporal development of the slope in the density-patch size relationships were derived from a basic population model with scale-dependent migration rates. The model indicated that the slopes in the density-patch size relationships during the early season should be reflected by the net scaling of immigration and emigration rates, whereas the slopes during the later season should increase as a result of local growth. 3. Emigration rates of the weevils were estimated in a field experiment, were the weevils coexisted in space and time. These results were then combined with a previous estimate of immigration rates in order to determine the net scaling of migration rates. 4. The emigration rate differed between species, caused by different movement rates in small patches, which could explain differences in the general slope of the density-patch size relationships of the weevils in the natural figwort patches throughout the summer. The slopes in the relationships in the early season were largely predicted by the net scaling of migration rates. The slope also increased in the later season for C. tuberculosus, whereas the slope decreased for C. scrophulariae. 5. It was concluded that the understanding of both inter- and intra-specific variations in density-patch size relationships of insect herbivores can be improved using population models incorporating scale-dependent migration and local growth.

  • 4.
    Andersson, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Löfstedt, Christer
    Lund Univ, Dept Biol..
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Insect density-plant density relationships: a modified view of insect responses to resource concentrations2013In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 173, no 4, p. 1333-1344Article in journal (Refereed)
    Abstract [en]

    Habitat area is an important predictor of spatial variation in animal densities. However, the area often correlates with the quantity of resources within habitats, complicating our understanding of the factors shaping animal distributions. We addressed this problem by investigating densities of insect herbivores in habitat patches with a constant area but varying numbers of plants. Using a mathematical model, predictions of scale-dependent immigration and emigration rates for insects into patches with different densities of host plants were derived. Moreover, a field experiment was conducted where the scaling properties of odour-mediated attraction in relation to the number of odour sources were estimated, in order to derive a prediction of immigration rates of olfactory searchers. The theoretical model predicted that we should expect immigration rates of contact and visual searchers to be determined by patch area, with a steep scaling coefficient, mu = -1. The field experiment suggested that olfactory searchers should show a less steep scaling coefficient, with mu a parts per thousand -0.5. A parameter estimation and analysis of published data revealed a correspondence between observations and predictions, and density-variation among groups could largely be explained by search behaviour. Aphids showed scaling coefficients corresponding to the prediction for contact/visual searchers, whereas moths, flies and beetles corresponded to the prediction for olfactory searchers. As density responses varied considerably among groups, and variation could be explained by a certain trait, we conclude that a general theory of insect responses to habitat heterogeneity should be based on shared traits, rather than a general prediction for all species.

  • 5.
    Andersson, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Löfstedt, Christer
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    How insects sense olfactory patches: the spatial scaling of olfactory information2013In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 122, no 7, p. 1009-1016Article in journal (Refereed)
    Abstract [en]

    When searching for resources in heterogeneous environments, animals must rely on their abilities to detect the resources via their sensory systems. However, variation in the strength of the sensory cue may be mediated by the physical size of the resource patch. Patch detection of insects are often predicted by the scaling of sensory cues to patch size, where visual cues has been proposed to scale proportional to the diameter of the patch. The scaling properties of olfactory cues are, however, virtually unknown. Here, we investigated scaling rules for olfactory information in a gradient of numbers of odour sources, relevant to odour-mediated attraction under field conditions. We recorded moth antennal responses to sex pheromones downwind from pheromone patches and estimated the slope in the scaling relationship between the effective length of the odour plumes and the number of odour sources. These measurements showed that the effective plume length increased proportional to the square root of the number of odour sources. The scaling relationship, as estimated in the field experiment, was then evaluated against field data of the slope in the relationship between trap catch and release rate of chemical attractants for a wide range of insects. This meta-analysis revealed an average slope largely consistent with the estimated scaling relationship between the effective plume length and the number of odour sources. This study is the first to estimate the scaling properties of olfactory cues empirically and has implications for understanding and predicting the spatial distributions of insects searching by means of olfactory cues in heterogeneous environments.

  • 6.
    Andersson, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Löfstedt, Christer
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Insect density-plant density relationships – a modified view of insect responses to resource concentrationsArticle in journal (Refereed)
  • 7.
    Belivanov, Yordan K.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The time scale of isotope signals in spiders: molting the remains of a previous diet2015In: Entomologia Experimentalis et Applicata, ISSN 0013-8703, E-ISSN 1570-7458, Vol. 156, no 3, p. 271-278Article in journal (Refereed)
    Abstract [en]

    Stable isotope analysis (SIA) has emerged as an important tool for understanding consumer diets and diet shifts. However, although the general idea behind SIA is clear, the interpretation of data is often fraught with problems because tissue turnover and fractionations are not known. We investigated shifts in stable isotope composition of spiders following a diet shift, using mealworms fed either maize (C4) or wheat (C3) flour. Mealworms had different carbon isotope composition depending on their diet and this difference was reflected in spider body parts. In the experiment, we first fed the spiders on a diet of either maize-fed or wheat-fed mealworms and then switched diet at the time of the second molt. Spiders were then sampled repeatedly until the next molt. We sampled both legs and abdomens, as these are presumed to have different turnover of tissue, and also molt remains were sampled when this was relevant. The data indicated that the spider legs had a turnover of about 20days, whereas the spider abdomens had a turnover of about 8days. Molt remains had the slowest turnover and reflected the diet at the previous molt, when the exoskeleton was formed. Both these observations indicate that SIA may be successfully used for elucidating diet shifts. More problematic was the fact that fractionation of carbon isotope ratios varied with body parts and diets. When spiders were fed maize-mealworms then the fractionation was larger for abdomens, but when the spiders were fed wheat-mealworms then the fractionation was larger for legs. The mechanisms underlying this pattern are unclear and deserve further attention.

  • 8. Birkhofer, Klaus
    et al.
    Bylund, Helena
    Dalin, Peter
    Ferlian, Olga
    Gagic, Vesna
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Klapwijk, Maartje
    Mestre, Laia
    Roubinet, Eve
    Schroeder, Martin
    Stenberg, Johan A.
    Porcel, Mario
    Björkman, Christer
    Jonsson, Mattias
    Methods to identify the prey of invertebrate predators in terrestrial field studies2017In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 7, no 6, p. 1942-1953Article, review/survey (Refereed)
    Abstract [en]

    Predation is an interaction during which an organism kills and feeds on another organism. Past and current interest in studying predation in terrestrial habitats has yielded a number of methods to assess invertebrate predation events in terrestrial ecosystems. We provide a decision tree to select appropriate methods for individual studies. For each method, we then present a short introduction, key examples for applications, advantages and disadvantages, and an outlook to future refinements. Video and, to a lesser extent, live observations are recommended in studies that address behavioral aspects of predator-prey interactions or focus on per capita predation rates. Cage studies are only appropriate for small predator species, but often suffer from a bias via cage effects. The use of prey baits or analyses of prey remains are cheaper than other methods and have the potential to provide per capita predation estimates. These advantages often come at the cost of low taxonomic specificity. Molecular methods provide reliable estimates at a fine level of taxonomic resolution and are free of observer bias for predator species of any size. However, the current PCR-based methods lack the ability to estimate predation rates for individual predators and are more expensive than other methods. Molecular and stable isotope analyses are best suited to address systems that include a range of predator and prey species. Our review of methods strongly suggests that while in many cases individual methods are sufficient to study specific questions, combinations of methods hold a high potential to provide more holistic insights into predation events. This review presents an overview of methods to researchers that are new to the field or to particular aspects of predation ecology and provides recommendations toward the subset of suitable methods to identify the prey of invertebrate predators in terrestrial field research.

  • 9. Björkman, Maria
    et al.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Hopkins, Richard J.
    Ramert, Birgitta
    Evaluating the enemies hypothesis in a clover-cabbage intercrop: effects of generalist and specialist natural enemies on the turnip root fly (Delia floralis)2010In: Agricultural and Forest Entomology, ISSN 1461-9555, E-ISSN 1461-9563, Vol. 12, no 2, p. 123-132Article in journal (Refereed)
    Abstract [en]

    The relative importance of the resource concentration hypothesis and the enemies hypothesis was investigated for the turnip root fly Delia floralis in a cabbage-red clover intercropping system compared with a cabbage monoculture. Delia floralis egg densities were measured as well as the activity-densities of generalist predators in a field experiment during two growing seasons. In the second year, a study of egg predation with artificially placed eggs was conducted, in addition to a predator exclusion experiment, to estimate total predation during the season. Parasitization rates were estimated from samples of pupae. Delia floralis oviposition was greater in the monoculture during both years. The predator activity-densities differed between treatments and study years. The known natural enemies of Delia spp., Bembidion spp. and Aleochara bipustulata showed a strong response to a cultivation system with higher activity-densities in the monoculture. The response, however, appeared to be caused primarily by habitat preferences and not by D. floralis egg densities. The reduction in the number of D. floralis pupae in the intercropping may be explained by a disruption in oviposition behaviour caused by the presence of clover because neither predation, nor parasitization rates differed between cultivation systems.

  • 10. Björkman, Maria
    et al.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Rämert, Birgitta
    Neighboring monocultures enhance the effect of intercropping in turnip root flies (Delia floralis).2007In: Entomologia Experimentalis et Applicata, Vol. 124, p. 319-326Article in journal (Refereed)
    Abstract [en]

    Knowledge of insect behaviour is essential for accurately interpreting studies of diversification and to develop diversified agroecosystems that have a reliable pest-suppressive effect. In this study, we investigated the egg-laying behaviour of the turnip root fly, Delia floralis (Fall.) (Diptera: Anthomyiidae), in an intercrop-monoculture system. We examined both the main effect of intercropping and the effect on oviposition in the border zone between a cabbage monoculture [Brassica oleracea L. var. capitata (Brassicaceae)] and a cabbage-red clover intercropping system [Trifolium pratense L. (Fabaceae)]. To investigate the border-effect, oviposition was measured along a transect from the border between the treatments to the centre of experimental plots. Intercropping reduced the total egg-laying of D. floralis with 42% in 2003 and 55% in 2004. In 2004, it was also found that the spatial distribution of eggs within the experimental plots was affected by distance from the adjoining treatment. The difference in egg-laying between monoculture and intercropping was most pronounced close to the border, where egg-laying was 68% lower on intercropped plants. This difference in egg numbers decreased gradually up to a distance of 3.5 m from the border, where intercropped plants had 43% fewer eggs than the corresponding monocultured plants. The reason behind this oviposition pattern is most likely that flies in intercropped plots have a higher probability of entering the monoculture if they are close to the border than if they are in the centre of a plot. When entering the monoculture, flies can pursue their egg-laying behaviour without being disrupted by the clover. As the final decision to land is visually stimulated, flies could also be attracted to fly from the intercropped plots into the monoculture, where host plants are more visually apparent. Visual cues could also hinder flies in a monoculture from entering an intercropped plot. Other possible patterns of insect attack due to differences in insect behaviour are discussed, as well as the practical application of the results of this study.

  • 11. Björkman, Maria
    et al.
    Hopkins, Richard
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Rämert, Birgitta
    Effects of plant competition and herbivore density on the development of the turnip root fly (Delia floralis) in an intercropping system2009In: Arthropod-plant interactions, ISSN 1872-8855, Vol. 3, p. 55-62Article in journal (Refereed)
    Abstract [en]

    In this study, interactive effects of plant competition and herbivory on plant quality and herbivore development were examined in a greenhouse experiment where cabbage plants [Brassica oleracea L. var. capitata (Brassicaceae)] were intercropped with red clover [Trifolium pratense L. (Fabaceae)]. Cabbages were grown with two red clover densities and attack rates by the root feeding herbivore the turnip root fly, Delia floralis Fall. (Diptera: Anthomyiidae). Above ground and below ground cabbage biomass was reduced through intercropping and larval damage. Intercropping also resulted in lower nitrogen and higher carbon root levels compared with levels in the roots of monocultured cabbage. Furthermore, both root nitrogen and carbon levels increased with herbivory. Root neutral detergent fibre (NDF) and lignin content increased in response to both increased plant competition and higher egg densities. For lignin, an interaction effect was observed in the form of elevated levels in intercropped plants subjected to larval damage, while levels in roots of monocultured cabbage remained unchanged. The quality changes brought about by clover competition affected D. floralis development negatively, which resulted in reduced pupal weight. In addition, increased egg density also decreased larval growth. The effects on the development of D. floralis in relation to host plant quality are discussed.

  • 12. Bukovinszky, Tibor
    et al.
    Gols, Rieta
    Kamp, Andre
    de Oliveira-Domingues, Filipe
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Jongema, Yde
    Bezemer, T. Martijn
    Dicke, Marcel
    van Dam, Nicole M.
    Harvey, Jeffrey A.
    Combined effects of patch size and plant nutritional quality on local densities of insect herbivores2010In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 11, no 5, p. 396-405Article in journal (Refereed)
    Abstract [en]

    Plant-insect interactions occur in spatially heterogeneous habitats. Understanding how such interactions shape density distributions of herbivores requires knowledge on how variation in plant traits (e.g. nutritional quality) affects herbivore abundance through, for example, affecting movement rates and aggregation behaviour. We studied the effects of plant patch size and herbivore-induced differences in plant nutritional quality on local densities of insect herbivores for two Brassica oleracea cultivars, i.e. white cabbage and Brussels sprouts. Early season herbivory as a treatment resulted in measurable differences in glucosinolate concentrations in both cultivars throughout the season. Herbivore induction and patch size both influenced community composition of herbivores in both cultivars, but the effects differed between species. Flea beetles (Phyllotreta spp.) were more abundant in large than in small patches, and this patch response was more pronounced on white cabbage than on Brussels sprouts. Herbivore-induction increased densities in all patches. Thrips tabaci was also more abundant in large patches and densities of this species were higher on Brussels sprouts than on white cabbage. Thrips densities were lower on induced than on control plants of both cultivars and this negative effect of induction tended to be more pronounced in large than in small patches. Densities of the cabbage moth (Mamestra brassicae) were lower on Brussels sprouts than on white cabbage and lower on herbivore-induced than on uninduced plants, with no effect of patch size. No clear effects of patch size and induction were found for aphids. This study shows that constitutive and herbivore-induced differences in plant traits interact with patch responses of insect herbivores.

  • 13. Dahlgren, Jonas
    et al.
    Oksanen, Lauri
    Oksanen, Tarja
    Olofsson, Johan
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Lindgren, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Plant defences to no avail?: Responses of plants of varying edibility to food web manipulations in a low arctic scrubland2009In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, no 8, p. 1189-1203Article in journal (Refereed)
    Abstract [en]

    Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin, all plants are edible for some herbivores. Hence, the copious abundance of plant biomass, typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles, so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass. Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids? Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators, to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method. Results: In the absence of predators, vole densities increased 3.7-fold and the community-level plant biomass was decimated. The least palatable plant group, evergreen ericoids, suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles. Conclusions: Our results corroborate the Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation. The fate of plants in predator-free systems with browsing vertebrates depends primarily on the accessibility of each plant during the limiting season. Evergreen ericoids then form the most sensitive functional group.

  • 14. Dahlgren, Jonas
    et al.
    Oksanen, Lauri
    Oksanen, Tarja
    Olofsson, Johan
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Lindgren, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Plant defenses to no avail? responses of plants with varying edibility to food web manipulations in a low arctic scrubland2009In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, p. 1189-1203Article in journal (Refereed)
    Abstract [en]

    Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin, all plants are edible for some herbivores. Hence, the copious abundance of plant biomass, typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles, so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass.

    Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids?

    Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators, to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method.

    Results: In the absence of predators, vole densities increased 3.7-fold and the communitylevel plant biomass was decimated. The least palatable plant group, evergreen ericoids, suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles.

    Conclusions: Our results corroborate Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation. The fate of plants in predator-free systems with browsing vertebrates depends primarily on the accessibility of each plant during the limiting season. Evergreen ericoids then form the most sensitive functional group.

  • 15.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Borgström, Sara
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Boyd, Emily
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. University of Reading, England.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Dalen, Love
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ermold, Matti
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hedlund, Johanna
    Stockholm University, Faculty of Science, Department of Zoology.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Jaramillo, Fernando
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lagerholm, Vendela K.
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Moor, Helen
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Nykvist, Björn
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Stockholm University, Stockholm Environment Institute.
    Pasanen-Mortensen, Marianne
    Stockholm University, Faculty of Science, Department of Zoology.
    Plue, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Prieto, Carmen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    van der Velde, Ype
    Stockholm University, Faculty of Science, Department of Physical Geography. Wageningen University & Research Center, Netherlands.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Interacting effects of change in climate, human population, land use, and water use on biodiversity and ecosystem services2015In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 20, no 1, article id UNSP 23Article in journal (Refereed)
    Abstract [en]

    Human population growth and resource use, mediated by changes in climate, land use, and water use, increasingly impact biodiversity and ecosystem services provision. However, impacts of these drivers on biodiversity and ecosystem services are rarely analyzed simultaneously and remain largely unknown. An emerging question is how science can improve the understanding of change in biodiversity and ecosystem service delivery and of potential feedback mechanisms of adaptive governance. We analyzed past and future change in drivers in south-central Sweden. We used the analysis to identify main research challenges and outline important research tasks. Since the 19th century, our study area has experienced substantial and interlinked changes; a 1.6 degrees C temperature increase, rapid population growth, urbanization, and massive changes in land use and water use. Considerable future changes are also projected until the mid-21st century. However, little is known about the impacts on biodiversity and ecosystem services so far, and this in turn hampers future projections of such effects. Therefore, we urge scientists to explore interdisciplinary approaches designed to investigate change in multiple drivers, underlying mechanisms, and interactions over time, including assessment and analysis of matching-scale data from several disciplines. Such a perspective is needed for science to contribute to adaptive governance by constantly improving the understanding of linked change complexities and their impacts.

  • 16.
    Fors, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Liblikas, Ilme
    Andersson, Petter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Borg-Karlson, Anna-Karin
    Cabezas, Nancy
    Mozuraitis, Raimondas
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Chemical communication and host search in Galerucella leaf beetles2015In: Chemoecology, ISSN 0937-7409, E-ISSN 1423-0445, Vol. 25, no 1, p. 33-45Article in journal (Refereed)
    Abstract [en]

    Herbivore insects use a variety of search cues during host finding and mate recognition, including visual, gustatory, and olfactory stimuli, leaving multiple traits for evolution to act upon. However, information about differences or similarities in search pattern amongst closely related insect herbivore species is still scarce. Here, we study the production of and the response to pheromone in Galerucella (Coleoptera: Chrysomelidae) to investigate the beetles' search behaviour. Males of G. pusilla and G. calmariensis, two closely related species, are known to produce the aggregation pheromone dimethylfuran-lactone when feeding on their host plant, whereas no pheromones have been identified in other Galerucella species. We show that dimethylfuran-lactone is produced also by males of G. tenella, a species phylogenetically close to G. pusilla and G. calmariensis, whereas the more distantly related species G. lineola and G. sagittariae were not found to produce the same compound. To investigate the beetles' behavioural response to dimethylfuran-lactone, the pheromone was synthesized using a partly novel method and tested in olfactometers, showing that G. pusilla, G. calmariensis, and G. tenella were all attracted to the pheromone, whereas G. lineola and G. sagittariae did not respond. This suggests that the production of and the response to pheromone could be linked to the phylogenetic relatedness between the species.

  • 17.
    Fors, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Markus, Robert
    Theopold, Ulrich
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Ericson, Lars
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Geographic variation and trade-offs in parasitoid virulence2016In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 85, no 6, p. 1595-1604Article in journal (Refereed)
    Abstract [en]

    1. Host-parasitoid systems are characterized by a continuous development of new defence strategies in hosts and counter-defence mechanisms in parasitoids. This co-evolutionary arms race makes host-parasitoid systems excellent for understanding trade-offs in host use caused by evolutionary changes in host immune responses and parasitoid virulence. However, knowledge obtained from natural host-parasitoid systems on such trade-offs is still limited.

    2. In this study, the aim was to examine trade-offs in parasitoid virulence in Asecodes parviclava (Hymenoptera: Eulophidae) when attacking three closely related beetles: Galerucella pusilla, Galerucella calmariensis and Galerucella tenella (Coleoptera: Chrysomelidae). A second aim was to examine whether geographic variation in parasitoid infectivity or host immune response could explain differences in parasitism rate between northern and southern sites.

    3. More specifically, we wanted to examine whether the capacity to infect host larvae differed depending on the previous host species of the parasitoids and if such differences were connected to differences in the induction of host immune systems. This was achieved by combining controlled parasitism experiments with cytological studies of infected larvae.

    4. Our results reveal that parasitism success in A. parviclava differs both depending on previous and current host species, with a higher virulence when attacking larvae of the same species as the previous host. Virulence was in general high for parasitoids from G. pusilla and low for parasitoids from G. calmariensis. At the same time, G. pusilla larvae had the strongest immune response and G. calmariensis the weakest. These observations were linked to changes in the larval hemocyte composition, showing changes in cell types important for the encapsulation process in individuals infected by more or less virulent parasitoids.

    5. These findings suggest ongoing evolution in parasitoid virulence and host immune response, making the system a strong candidate for further studies on host race formation and speciation.

  • 18.
    Fors, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Markus, Robert
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Theopold, Ulrich
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Differences in Cellular Immune Competence Explain Parasitoid Resistance for Two Coleopteran Species2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 9, article id e108795Article in journal (Refereed)
    Abstract [en]

    The immune defence of an organism is evolving continuously, causing counteradaptations in interacting species, which in turn affect other ecological and evolutionary processes. Until recently comparative studies of species interactions and immunity, combining information from both ecological and immunological fields, have been rare. The cellular immune defense in insects, mainly mediated by circulating hemocytes, has been studied primarily in Lepidoptera and Diptera, whereas corresponding information about coleopteran species is still scarce. In the study presented here, we used two closely related chrysomelids, Galerucella pusilla and G. calmariensis (Coleoptera), both attacked by the same parasitoid, Asecodes parviclava (Hymenoptera). In order to investigate the structure of the immune system in Galerucella and to detect possible differences between the two species, we combined ecological studies with controlled parasitism experiments, followed by an investigation of the cell composition in the larval hemolymph. We found a striking difference in parasitism rate between the species, as well as in the level of successful immune response (i.e. encapsulation and melanisation of parasitoid eggs), with G. pusilla showing a much more potent immune defense than G. calmariensis. These differences were linked to differences in the larval cell composition, where hemocyte subsets in both naive and parasitised individuals differed significantly between the species. In particular, the hemocytes shown to be active in the encapsulation process; phagocytes, lamellocytes and granulocytes, differ between the species, indicating that the cell composition reflects the ability to defend against the parasitoid.

  • 19.
    Fors, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mozuraitis, Raimondas
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Nature Research Centre, Lithuania.
    Blažytė‐Čereškienė, Laima
    Verschut, Thomas A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Selection by parasitoid females among closely related hosts based on volatiles: Identifying relevant chemical cues2018In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 8, no 6, p. 3219-3228Article in journal (Refereed)
    Abstract [en]

    Parasitoid fitness is influenced by the ability to overcome host defense strategies and by the ability of parasitoid females to select high-quality host individuals. When females are unable to differentiate among hosts, their fitness will decrease with an increasing abundance of resistant hosts. To understand the effect of mixed host populations on female fitness, it is therefore necessary to investigate the ability of female parasitoids to select among hosts. Here, we used behavioral assays, headspace volatile collection, and electrophysiology to study the ability of Asecodes parviclava to use olfactory cues to select between a susceptible host (Galerucella calmariensis) and a resistant host (Galerucella pusilla) from a distance. Our studies show that parasitoid females have the capacity to distinguish the two hosts and that the selection behavior is acquired through experiences during earlier life stages. Further, we identified two volatiles (-terpinolene and [E]--ocimene) which amounts differ between the two plant-herbivore systems and that caused behavioral and electrophysiological responses. The consequence of this selection behavior is that females have the capacity to avoid laying eggs in G.pusilla, where the egg mortality is higher due to much stronger immune responses toward A.parviclava than in larvae of G.calmariensis.

  • 20.
    Fors, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Verschut, Thomas
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Host search and host preference in Asecodes parviclavaManuscript (preprint) (Other academic)
  • 21.
    Hamback, Per A
    Stockholm University, Faculty of Science, Department of Botany.
    Density-dependent processes in leaf beetles feeding on purple loosestrife: aggregative behaviour affecting individual growth rates2010In: Bulletin of entomological research, ISSN 0007-4853, E-ISSN 1475-2670, Vol. 100, no 5, p. 605-611Article in journal (Refereed)
    Abstract [en]

    Aggregative responses are commonly observed in insects, including chrysomelids, affecting both individual and population growth rates. In two closely related chrysomelid beetles (Galerucella calmariensis and G. pusilla) feeding on purple loosestrife (Lythrum salicaria), recent studies suggest that male-produced pheromones may cause both inter- and intraspecific attraction. This paper further examines the causes and consequences of feeding aggregations in these species. Olfactometer studies confirm previous findings, showing cross-species attraction to damaged plants, but suggest that also damaged induced plant volatiles may be involved. In addition, the studies suggest that the cross-species attraction observed in previous studies have asymmetric effects on the two beetles. Galerucella pusilla was more attracted to damage by G. calmariensis than to damage by conspecifics. Laboratory and field data suggest that feeding aggregations in these species increase pupal mass, at least at low to intermediate larval densities. This positive feedback may have important consequences for the spatiotemporal dynamics and as a consequence on the role of the two chrysomelid beetles on biological control of purple loosestrife.

  • 22.
    Hamback, Peter A.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Björkman, Maria
    Stockholm University, Faculty of Science, Department of Botany.
    Hopkins, Richard J.
    Patch size effects are more important than genetic diversity for plant-herbivore interactions in Brassica crops2010In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 35, no 3, p. 299-306Article in journal (Refereed)
    Abstract [en]

    2. This paper examines the effect of intraspecific genetic diversity within Brassica fields on two Brassica specialists, cabbage root fly, and diamondback moth, and on a parasitoid attacking diamondback moths. Genetic diversity was manipulated both in a replacement and an additive design. 3. Both herbivore densities and parasitism rates were higher in smaller plots, with limited responses to increased within-plot diversity. All species showed variable densities across genotypes, and preference hierarchies were species specific. 4. Responses to plot size in root flies scaled with the diameter-to-area ratio, suggesting that patch detectability affected local density, whereas responses by diamondback moths and parasitoids deviated from this ratio. These species differences could be traced to differences in the residence time within patches, where diamondback moths typically spend longer and more variable time periods in patches than root flies. 5. The lack of response to genetic diversity by both herbivores suggests that egg-laying rates are affected by decisions on the plant and not by attraction from a distance, neither to the plant itself nor the patch. Patterns of differential attack may then be due to different acceptability for studied genotypes. 6. Future theories on insect responses to spatial heterogeneity should focus on species traits and how traits interact with information landscapes in the field.

  • 23.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    A green or a prickly world?2010In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 327, p. 1583-1584Article in journal (Refereed)
    Abstract [en]

    Is the world a green place where plant biomass abounds for herbivores to devour, or a prickly place where herbivores struggle to locate the few edible plant pieces? The answer to this question has crucial consequences for broad ecological and evolutionary questions. On page 1642 of this issue, Mooney et al. (1) show how evolutionary trade-offs among plant traits affect responses to herbivores and higher trophic levels.

  • 24.
    Hambäck, Peter A.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Dahlgren, Johan P.
    Stockholm University, Faculty of Science, Department of Botany.
    Andersson, Petter
    Stockholm University, Faculty of Science, Department of Botany.
    Rabasa, Sonja G.
    Bommarco, Riccardo
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Plant trait-mediated interactions between early and late herbivores on common figwort (Scrophularia nodosa) and effects on plant seed set2011In: Ecoscience, ISSN 1195-6860, Vol. 18, no 4, p. 375-381Article in journal (Refereed)
    Abstract [en]

    This study examined the interactive effects of early and late season herbivory on the growth and reproductive output of figwort (Scrophularia nodosa). The early season herbivore is a pentatomid bug that feeds on and kills the apical meristem, while the late season herbivores are 2 weevil species and a sawfly that all feed on leaves and flowers. The direct effect of early season meristem damage on plant reproduction was quite limited, although meristem damage did cause increased branching. This change in plant morphology may entail that early season herbivores have profound indirect effects on plant reproduction by affecting the abundance of and damage caused by late season herbivores. Comparisons of plants with and without early season meristem damage, natural and artificial, also suggest that plants with meristem damage are significantly shorter throughout most of the summer and receive less damage late in season. However, the reduced damage translated to increased flowering but not to increased fruit production, suggesting that the plants were able to compensate for late season damage. In the end, and despite damage, figwort was well able to tolerate the observed meristem and leaf damage.

  • 25.
    Hambäck, Peter A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Inouye, Brian D.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Florida State University, Tallahassee, USA.
    Andersson, Petter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Underwood, Nora
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Florida State University, Tallahassee, USA.
    Effects of plant neighborhoods on plant-herbivore interactions: resource dilution and associational effects2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 5, p. 1370-1383Article in journal (Refereed)
    Abstract [en]

    Effects of neighboring plants on herbivore damage to a focal plant (associational effects) have been documented in many systems and can lead to either increased or decreased herbivore attack. Mechanistic models that explain the observed variety of herbivore responses to local plant community composition have, however, been lacking. We present a model of herbivore responses to patches that consist of two plant types, where herbivore densities on a focal plant are determined by a combination of patch-finding, within-patch redistribution, and patch-leaving. Our analyses show that the effect of plant neighborhood on herbivores depends both on how plant and herbivore traits combine to affect herbivore movement and on how experimental designs reveal the effects of plant density and plant relative frequency. Associational susceptibility should be the dominant pattern when herbivores have biased landing rates within patches. Other behavioral decision rules lead to mixed responses, but a common pattern is that in mixed patches, one plant type experiences associational resistance while the other plant experiences associational susceptibility. In some cases, the associational effect may shift sign along a gradient of plant frequency, suggesting that future empirical studies should include more than two plant frequencies to detect nonlinearities. Finally, we find that associational susceptibility should be commonly observed in experiments using replacement designs, whereas associational resistance will be the dominant pattern when using additive designs. Consequently, outcomes from one experimental design cannot be directly compared to studies with other designs. Our model can also be translated to other systems with foragers searching for multiple resource types.

  • 26.
    Hambäck, Peter A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Weingartner, Elisabet
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ericson, Lars
    Fors, Lisa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Cassel-Lundhagen, Anna
    Stenberg, Johan A.
    Bergsten, Johannes
    Bayesian species delimitation reveals generalist and specialist parasitic wasps on Galerucella beetles (Chrysomelidae): sorting by herbivore or plant host2013In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 13, article id 92Article in journal (Refereed)
    Abstract [en]

    Background: To understand the ecological and evolutionary consequences of species interactions in food webs necessitates that interactions are properly identified. Genetic analyses suggest that many supposedly generalist parasitoid species should rather be defined as multiple species with a more narrow diet, reducing the probability that such species may mediate indirect interactions such as apparent competition among hosts. Recent studies showed that the parasitoid Asecodes lucens mediate apparent competition between two hosts, Galerucella tenella and G. calmariensis, affecting both interaction strengths and evolutionary feedbacks. The same parasitoid was also recorded from other species in the genus Galerucella, suggesting that similar indirect effects may also occur for other species pairs. Methods: To explore the possibility of such interactions, we sequenced mitochondrial and nuclear genetic markers to resolve the phylogeny of both host and parasitoid and to test the number of parasitoid species involved. We thus collected 139 Galerucella larvae from 8 host plant species and sequenced 31 adult beetle and 108 parasitoid individuals. Results: The analysis of the Galerucella data, that also included sequences from previous studies, verified the five species previously documented as reciprocally monophyletic, but the Bayesian species delimitation for A. lucens suggested 3-4 cryptic taxa with a more specialised host use than previously suggested. The gene data analyzed under the multispecies coalescent model allowed us to reconstruct the species tree phylogeny for both host and parasitoid and we found a fully congruent coevolutionary pattern suggesting that parasitoid speciation followed upon host speciation. Conclusion: Using multilocus sequence data in a Bayesian species delimitation analysis we propose that hymenopteran parasitoids of the genus Asecodes that infest Galerucella larvae constitute at least three species with narrow diet breath. The evolution of parasitoid Asecodes and host Galerucella show a fully congruent coevolutionary pattern. This finding strengthens the hypothesis that the parasitoid in host search uses cues of the host rather than more general cues of both host and plant.

  • 27.
    Hambäck, Peter A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Weingartner, Elisabeth
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dalén, Love
    Wirta, Helena
    Roslin, Tomas
    Spatial subsidies in spider diets vary with shoreline structure: Complementary evidence from molecular diet analysis and stable isotopes2016In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, no 23, p. 8431-8439Article in journal (Refereed)
    Abstract [en]

    Inflow of matter and organisms may strongly affect the local density and diversity of organisms. This effect is particularly evident on shores where organisms with aquatic larval stages enter the terrestrial food web. The identities of such trophic links are not easily estimated as spiders, a dominant group of shoreline predator, have external digestion. We compared trophic links and the prey diversity of spiders on different shore types along the Baltic Sea: on open shores and on shores with a reed belt bordering the water. A priori, we hypothesized that the physical structure of the shoreline reduces the flow between ecosystem and the subsidies across the sea-land interface. To circumvent the lack of morphologically detectable remains of spider prey, we used a combination of stable isotope and molecular gut content analyses. The two tools used for diet analysis revealed complementary information on spider diets. The stable isotope analysis indicated that spiders on open shores had a marine signal of carbon isotopes, while spiders on reedy shores had a terrestrial signal. The molecular analysis revealed a diverse array of dipteran and lepidopteran prey, where spiders on open and reedy shores shared a similar diet with a comparable proportion of chironomids, the larvae of which live in the marine system. Comparing the methods suggests that differences in isotope composition of the two spider groups occurred because of differences in the chironomid diets: as larvae, chironomids of reedy shores likely fed on terrestrial detritus and acquired a terrestrial isotope signature, while chironomids of open shores utilized an algal diet and acquired a marine isotope signature. Our results illustrate how different methods of diet reconstruction may shed light on complementary aspects of nutrient transfer. Overall, they reveal that reed belts can reduce connectivity between habitats, but also function as a source of food for predators.

  • 28.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Andersson, Petter
    Stockholm University, Faculty of Science, Department of Botany.
    Bukovinszky, Tibor
    Netherlands Institute of Ecology.
    Trait-mediated effects modify patch-size density relationships in insect herbivores and parasitoids2012In: Trait-mediated indirect interactions:  Ecological and evolutionary perspecitves / [ed] T. Ohgushi, O.J. Schmitz and R.D. Holt, Cambridge, UK: Cambridge University Press, 2012, p. 466-488Chapter in book (Refereed)
  • 29.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Björkman, Maria
    Stockholm University, Faculty of Science, Department of Botany.
    Rämert, Birgitta
    Hopkins, Richard
    Scale-dependent responses in cabbage herbivores affect attack rates in spatially heterogenous systems2009In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 10, p. 228-236Article in journal (Refereed)
    Abstract [en]

    Herbivorous insects face a dilemma when selecting suitable hosts in a complex environment, and their sensory capability may often reduce the female capacity for proper selection. As a consequence, eggs are often deposited on inferior hosts, affecting both insect and host plant fitness. We examined the attack rates of three cabbage herbivores in monocultures and biculture plots of different Brassica oleracea genotypes, with different spatial heterogeneity. The main goals of the study were to improve our understanding of the spatial scales involved in herbivore search processes and to examine the possibility of using spatial heterogeneity for manipulating pest attack rates in cabbage cropping systems. The results showed that the host selection behaviour of the small white butterfly (Pieris rapae) was strongly dependent on spatial heterogeneity. The difference in egg density between plant genotypes was larger when contrasting plants were growing in close proximity than in monoculture. This suggests that P. rapae is able to differentiate among genotypes from a small distance, while selection is compromised at larger spatial scales. The two other herbivores in the study (Mamestra brassicae and Delia radicum) did not respond to heterogeneity at any spatial scale, but showed a constant preference hierarchy. This suggests that host selection in these species occurs after direct plant contact. The difference in species’ responses to spatial heterogeneity has consequences both for selection gradients in natural communities and for the potential to reduce pest attack in polyculture systems.

  • 30.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Gilbert, James
    Schneider, Katie
    Martinson, Holly
    Kolb, Gundula
    Stockholm University, Faculty of Science, Department of Botany.
    Fagan, William
    Effects of body size, trophic mode and larval habitat on Diptera stoichiometry: a regional comparison2009In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 118, p. 615-623Article in journal (Refereed)
    Abstract [en]

    Ecological stoichiometry has emerged as a tool for exploring nutrient demand and evolutionary responses to nutrient limitation. Previous studies of insects have found predictable variability in stoichiometry, both in relation to body size and trophic mode, at ordinal levels or higher. Our study further examines the evolutionary and ecological lability in these traits by comparing the effects of body size, trophic mode (larval and adult) and larval habitat on the stoichiometry of insects within one order (Diptera). The study also expands on previous work by analyzing trophic mode both at coarse (detritivore, herbivore, predator) and fine (high- vs low- nutrient quality resources within trophic categories) scales and by comparing nutrient stoichiometry in two geographical regions, Sweden and Arizona. As predicted, adults feeding on nectar or pollen had the lowest body N content in the dataset. Additionally, for Diptera with predatory larvae, species low N diets had lower body N content than those with high N diets. However, body N content was not consistently lower for all species with low N resources, as species feeding on plant material were indistinguishable in stoichiometry from predators with high N diets. We suggest that these results emerge because larval resource exploitation is poorly understood in herbivorous Diptera species. Body P content for Swedish Diptera decreased with body size for all trophic modes, and the only difference among trophic modes was that blood feeders had higher P content than other groups. The regional comparison further showed that the allometry of body P content is a labile trait that may vary at regional scales, as there was no allometric scaling of body P content in the Arizona data set, in contrast to the Swedish data set. These results are not easily explained by existing theoretical frameworks, but instead point to a general context-dependence of P stoichiometry, which should now be a focus for future work.

  • 31.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Summerville, Keith
    Steffen-Dewenter, Ingolf
    Krauss, Jochen
    Englund, Göran
    Crist, Thomas
    Habitat specialisation, body-size and family identity explain Lepidopteran density-area relationships in a cross-continental comparison.2007In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 104, p. 8368-8373Article in journal (Refereed)
    Abstract [en]

    Habitat fragmentation may strongly affect species density, species interactions and the rate of ecosystem processes. It is therefore important to understand the observed variability among species responses to fragmentation, and the underlying mechanisms. In this study, we compare density-area relationships (DAR) for 344 lepidopteran species belonging to 22 families (butterflies and moths). This analysis suggested that the DARslope is generally positive for moths and negative for butterflies. The differences are suggested to occur because moths are largely olfactory searchers, whereas most butterflies are visual searchers. The analysis also suggests that DARs vary as a function of habitat specialisation and body size. In butterflies, generalist species had a more negative DARslope than specialist species because of a lower patch size threshold. In moths, the differences in DARslope between forest and open habitat species were large for small species but absent for large species. This is argued to occur because the DARslope in large species mainly reflect their search mode, which does not necessarily vary between moth groups, whereas the slope in small species reflect population growth rates.

  • 32.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Vogt, MajBritt
    Tscharntke, Teja
    Thies, Carsten
    Englund, Göran
    Top-down and bottom-up effects on the spatiotemporal dynamics of cereal aphids: testing scaling theory for local density2007In: Oikos, Vol. 116, p. 1995-2006Article in journal (Refereed)
    Abstract [en]

    The relationship between density and area depends on local growth rates and the area-dependence of migration rates. These rates vary among taxa due to dispersal behaviour, plot productivity and natural enemy impact. Previous studies in aphids suggest that aphid densities are highest in patches of intermediate sizes, and lower in small and large patches. The suggested mechanism causing these patterns is that the dispersal behaviour in aphids creates a mixture of area- and perimeter-dependent migration rates. In this paper, we used these predictions to examine the additional consequences of nutrient availability and natural enemies on the densityarea

    relationship. The derived predictions were compared to data from a system with three aphid species, a set of aphid parasitoids and generalist natural enemies, and at two levels of plant nutrient availability. We find that predictions from the model based only on dispersal and local growth agree with the temporal dynamics of

    density-area relationships for aphids in high nutrient patches. In patches with low nutrients, high parasitism rates appeared to cause a negative density-area relationship for aphids, thereby deviating from predictions driven by the aphids’ dispersal behavior. Hence, the dispersal model with scale-dependent migration rates can provide a useful tool for understanding insect distribution in patch size gradients, but the relative importance of top-down effects can completely change with plot productivity.

  • 33.
    Hansson, Christer
    et al.
    Dept Biol, Zool Museum, Lund, Sweden.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Three cryptic species in Asecodes (Forster) (Hymenoptera, Eulophidae) parasitizing larvae of Galerucella spp. (Coleoptera, Chrysomelidae), including a new species2013In: JOURNAL OF HYMENOPTERA RESEARCH, ISSN 1070-9428, Vol. 30, p. 51-64Article in journal (Refereed)
    Abstract [en]

    Three morphologically very similar species of Asecodes Forster (Hymenoptera: Eulophidae) are reviewed. Asecodes parviclava (Thomson) is removed from synonymy under A. lucens stat. rev., and differentiated from A. lucens (Nees) and A. lineophagum sp. n. All three species develop as gregarious endoparasitoids in larvae of Galerucella spp. (Coleoptera: Chrysomelidae), but each species has its own unique host range. Asecodes lineophagum attacks only Galerucella lineola (Fabr.) and A. lucens only G. sagittariae (Gyllenhal), whereas A. parviclava parasitizes G. tenella (L.), G. calmariensis (L.) and G. pusilla (Duftschmid). The Asecodes species are similar but display small though distinct morphological differences, and are distinguished also through molecular differences. The genetic distance in mitochondrial CO1 ranged from 2.3% to 7.3% between the species. Five names, one valid and four synonyms, were available for this group of species, but none of them was linked to a primary type. To promote stability of nomenclature, primary types are designated for all five names, neotypes for Eulophus lucens Nees, Entedon mento Walker and Derostenus parviclava Thomson, and lectotypes for Entedon chthonia Walker and Entedon metagenes Walker. Entedon mento, E. chthonia and E. metagenes remain synonymized under A. lucens.

  • 34.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ekholm, Janna
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of seabird nesting colonies on algae and aquatic invertebrates in coastal watersIn: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599Article in journal (Refereed)
    Abstract [en]

    Seabirds concentrate marine nutrients, from large marine areas, on their nesting islands. The high nutrient load may cause runoff into surrounding waters and affect marine communities in similar ways as reported from marine fertilization experiments. In order to test if cormorant colonies affect algae and invertebrates in surrounding coastal waters, we collected Fucus vesiculosus fronds, its epiphytic algae and associated invertebrate fauna near abandoned and active cormorant nesting islands and reference islands without nesting cormorants in the Stockholm archipelago in the northern Baltic Proper, Sweden. First, we showed, with δ15N analyses, that ornithogenic nitrogen provided a significant nitrogen source for algae and invertebrate consumers near islands with high nest density. Second, the nitrogen and phosphorus content of algae near active cormorant islands with high nest density was elevated and epiphytic algae increased relative to Fucus. Third, 3 of 5 invertebrate taxa (Jaera albifrons, Gammarus spp. and Chironomidae) showed increased biomasses near islands with high nest density, but contrary to earlier fertilization studies only J. albifrons increased in abundance compared to reference islands. We conclude that runoff from seabird colonies has a profound effect on primary producers and some consumers in the surrounding water, but only if the colonies exceed a certain nest density. Thus, seabirds not only affect marine communities via top-town forces as commonly assumed, but also via bottom-up forces by concentrating nutrients around their nesting islands. Consequently, seabird islands can be seen as natural fertilization experiments and give important insights in the effects of eutrophication of marine systems.

  • 35.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ekholm, Janna
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of seabird nesting colonies on algae and aquatic invertebrates in coastal waters2010In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 417, p. 287-300Article in journal (Refereed)
    Abstract [en]

    Seabirds concentrate nutrients from large marine areas on their nesting islands. The high nutrient load may cause runoff into surrounding waters and affect marine communities in similar ways to those reported from marine fertilization experiments. In order to test if cormorant colonies affect algae and invertebrates in surrounding coastal waters, we collected Fucus vesiculosus fronds, its epiphytic algae, and associated invertebrate fauna near abandoned and active cormorant nesting islands as well as reference islands without nesting cormorants in the Stockholm archipelago in the northern Baltic Sea, Sweden. First, we showed, with delta N-15 analyses, that ornithogenic nitrogen provided a significant nitrogen source for algae and invertebrate consumers near islands with high nest density. Second, the nitrogen and phosphorus content of algae near active cormorant islands with high nest density was elevated, and epiphytic algae increased relative to F. vesiculosus. Third, 3 of 5 invertebrate taxa (Jaera albifrons, Gammarus spp., and Chironomidae) showed increased biomasses near islands with high nest density; but, contrary to former fertilization studies, only J. albifrons increased in abundance compared to reference islands. We conclude that runoff from seabird colonies has a profound effect on primary producers and some consumers in the surrounding water, but only if the colonies exceed a certain nest density. Thus, seabirds not only affect marine communities via top-town forces as commonly assumed, but also via bottom-up forces by concentrating nutrients around their nesting islands. Consequently, seabird islands can be seen as natural fertilization experiments and give important insights to the effects of eutrophication of marine systems.

  • 36.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Ecological stoichiometry and homeostasis of plants and invertebrates on and nearby heavily fertilized cormorant nesting islandsManuscript (preprint) (Other academic)
    Abstract [en]

    Ecological stoichiometry has generalized the fundamental role of individual nutrient demand in all ecological processes and interactions. It implies that the elemental composition (C:N:P) of a consumer relative to the C:N:P of its resource determines its growth rate and thus secondary productivity. A central, but recently questioned, principle of ecological stoichiometry is the assumption that heterotrophs, in contrast to autotrophs, keep their elemental composition strongly homeostatic. Since neither the relationship between consumer C:N:P and its numeric response to changes in resource C:N:P nor the C:N:P homeostasis of arthropods have been extensively studied for arthropods, we used a natural gradient of N and P loads, in form of seabird and non-seabird islands, to investigate the stoichiometry and homeostasis of primary producers and invertebrates, both on and around islands. We then looked for causal relationships between stoichiometry and the level of homeostasis of a taxonomic group, respectively, and observed numerical responses to seabird fertilization. We found in accordance to principal theories that invertebrates, generally, strongly regulated their stoichiometry while autotrophs were stoichiometrically plastic. Thus, we found no causal relationship between consumer homeostasis and displayed numeric responses. Furthermore, we found only weak support for the hypothesis that the C:N:P of a taxa determines its numeric response to increased resource nutrient content (lepidopteran larvae had high P:C and high abundance on P-rich cormorant islands). We conclude that other species traits than nutrient content mainly determine the success of a taxa in a certain environment. Additionally, due to the strong effects of different level of homeostasis on ecological interactions, food web dynamics and nutrient cycles, we underline the need of further studies on the homeostasis of arthropods.

  • 37.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Jerling, Lenn
    Stockholm University, Faculty of Science, Department of Botany.
    Essenberg, Carolina
    Stockholm University, Faculty of Science, Department of Botany.
    Palmborg, Cecilia
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    The impact of nesting cormorants on plant and arthropod diversity2012In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 35, no 8, p. 726-740Article in journal (Refereed)
    Abstract [en]

    Seabirds can strongly affect several major factors correlated with species diversity by concentrating marine nutrients on their nesting islands and by physically disturbing island vegetation. In this study, we investigated the effects of nesting cormorants on the abundance, species richness, and composition of plants and arthropods (Coleoptera, Heteroptera, Araneae, and Chironomidae) on islands in Stockholm archipelago, Sweden. Nesting cormorants negatively affected plant species richness and vegetation cover and that changed plant species composition. The effect of nesting cormorants on island arthropods varied between feeding groups and sampling methods. Most orders did not change in abundance or species richness but some, such as coleopterans and spiders changed in species composition. Herbivorous coleopterans were generally negatively affected by cormorants whereas fungivorous species and scavengers were generally positively affected. In structural equation modeling we found that the effect of cormorants was sometimes direct, such as on scavengers, but many effects on island consumers were mediated by changes in vegetation caused by cormorant presence. Overall, arthropod communities were highly dissimilar between cormorant and reference islands, and we therefore conclude that nesting cormorants not only affect the diversity of their nesting islands but also of the archipelago as a whole. The total diversity in the archipelago may increase through regional increased habitat heterogeneity and by adding species which are favored by seabirds (e.g. scavenging and fungivorous coleopterans).

  • 38.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Jerling, Lenn
    Stockholm University, Faculty of Science, Department of Botany.
    Essenberg, Caroline
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    The impact of nesting cormorants on plant and arthropod diversityArticle in journal (Refereed)
    Abstract [en]

    Seabirds can strongly affect major factors correlated with species diversity – primary productivity, heterogeneity, and disturbance – on their nesting islands through the concentration of marine nutrients and physical disturbing island vegetation. In this study, we investigated the effects of nesting cormorants on the abundance, species richness, and composition of plants and arthropods (Coleoptera, Heteroptera, Araneae, and Chironomidae) on islands in Stockholm archipelago, Sweden. We found that cormorants had a negative effect on plant species richness and vegetation cover and that they changed plant species composition. Plant biomass showed no linear correlation with nest density when considering all islands studied, but was negatively correlated with nest density when considering only cormorant islands. The effect of nesting cormorants on island arthropods varied across feeding groups and sampling methods. Coleopterans and cursorial spiders responded with shifts in species richness and composition, and several coleopteran feeding groups and chironomids also changed in abundance. The abundance and species richness of saprophagous and fungivorous coleopterans were higher on active cormorant islands than on reference islands, while the abundance and species richness of herbivorous coleopterans and the species richness of cursorial spiders were negatively correlated with nest density. In structural equation modeling we found that some feeding groups were directly affected by nest density, but that many of the effects of seabirds on island consumers were mediated by changes in vegetation. We conclude that nesting cormorants affect the diversity of their nesting islands and the archipelago as a whole. Although cormorant colonies can decrease the species diversity of plants and some invertebrate groups on their nesting islands, the total diversity in the archipelago may increase through regional increased habitat heterogeneity and by adding species which are favored by seabirds (e.g., saprophagous and fungivorous coleopterans).

  • 39.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Jerling, Lenn
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    The impact of cormorants on plant–arthropod food webs on their nesting islands2010In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 13, no 3, p. 353-366Article in journal (Refereed)
    Abstract [en]

    This study investigated the effects of cormorant colonies on plant–arthropod island food webs, the consequences of nutrient-rich runoff on marine communities, and feedback loops from marine to terrestrial ecosystems. Terrestrial plant responses were as expected, with the highest plant biomass on islands with low nest density and the highest nitrogen (N) content on islands with high nest density. In contrast to our hypothesis, we found no uniform density response across guilds. Among herbivores, the variable responses may depend on the relative importance of plant quality or quantity. As expected, nutrient-rich runoff entered water bodies surrounding cormorant nesting islands, but only at high nest density, and increased the density of emerging insects. This created a potential feed-back loop to spiders (major terrestrial predators), where stable isotope analyses suggested great use of chironomids. Contrary to our expectation, this potential feed-back did not result in the highest spider density on islands with a high cormorant nest density. Web spiders showed no changes in density on active cormorant islands, and lycosids were actually less abundant on active cormorant islands compared to reference islands. The variable response of spiders despite increased dipteran densities, and also in other consumer groups, may be due to direct negative effects of cormorants on soil chemistry, vegetation cover, and other density regulating forces (for example, top–down forces) not studied here. This study highlights the importance of including processes in the surrounding marine ecosystem to understand the impacts of seabirds on the food web structures of their nesting islands. 

  • 40.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Palmborg, Cecilia
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ecological Stoichiometry and Density Responses of Plant-Arthropod Communities on Cormorant Nesting Islands2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 4, p. e61772-Article in journal (Refereed)
    Abstract [en]

    Seabirds deposit large amounts of nutrient rich guano on their nesting islands. The increased nutrient availability strongly affects plants and consumers. Consumer response differs among taxonomic groups, but mechanisms causing these differences are poorly understood. Ecological stoichiometry might provide tools to understand these mechanisms. ES suggests that nutrient rich taxa are more likely to be nutrient limited than nutrient poorer taxa and are more favored under nutrient enrichment. Here, we quantified differences in the elemental composition of soil, plants, and consumers between islands with and without nesting cormorant colonies and tested predictions made based on ES by relating the elemental composition and the eventual mismatch between consumer and resource stoichiometry to observed density differences among the island categories. We found that nesting cormorants radically changed the soil nutrient content and thereby indirectly plant nutrient content and resource quality to herbivores. In contrast, consumers showed only small differences in their elemental composition among the island categories. While we cannot evaluate the cause of the apparent homeostasis of invertebrates without additional data, we can conclude that from the perspective of the next trophic level, there is no difference in diet quality (in terms of N and P content) between island categories. Thus, bottom-up effects seemed mainly be mediated via changes in resource quantity not quality. Despite a large potential trophic mismatch we were unable to observe any relation between the invertebrate stoichiometry and their density response to nesting cormorant colonies. We conclude that in our system stoichiometry is not a useful predictor of arthropod responses to variation in resource nutrient content. Furthermore, we found no strong evidence that resource quality was a prime determinant of invertebrate densities. Other factors like resource quantity, habitat structure and species interactions might be more important or masked stoichiometric effects.

  • 41.
    Kolb, Gundula S.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Palmborg, Cecilia
    Taylor, Astrid R.
    Bååth, Erland
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of Nesting Cormorants (Phalacrocorax carbo) on Soil Chemistry, Microbial Communities and Soil Fauna2015In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 18, no 4, p. 643-657Article in journal (Refereed)
    Abstract [en]

    Seabirds act as vectors transporting marine nutrients to land by feeding on fish while nesting and roosting on islands. By depositing large amounts of nutrient-rich guano on their nesting islands they strongly affect island soils, vegetation and consumers. However, few studies have investigated how nesting seabirds affect soil communities. In this study, we investigated how cormorant nesting colonies affect soil chemistry, soil microbes and soil and litter fauna on their nesting islands in the Stockholm archipelago, Sweden. We found that cormorant colonies strongly increase organic soil N and P concentrations, and the effect is stronger close to cormorant nests. Microbial communities were studied by extracting phospholipid fatty acids (PLFA) from the soil. The total amounts of PLFA and the amount of PLFA indicating bacterial biomass were lower on active cormorant islands than on reference islands. Furthermore, PLFA structure and thus microbial community structure differed between cormorant and reference islands. Among ten investigated soil and litter arthropod groups three groups (Thysanoptera, Araneae and Oribatida) showed lower densities and one group (Astigmata) showed higher densities in soils on active cormorant than on reference islands. Some arthropod groups showed strong spatial variation on the cormorant islands. Astigmata, Mesostigmata and Diptera showed higher densities in soil samples close to cormorant nests, whereas Oribatida, Collembola and Hemiptera showed lower densities in litter samples close to cormorant nests than in samples taken 3-20 m away from nests. Overall, the cormorant colonies strongly affected soil ecosystems of their nesting islands, but causal correlations between arthropod densities and soil factors were difficult to reveal. One likely reason may be that nesting cormorant islands are very heterogeneous habitats showing large spatial variation in both soil properties as well as fauna densities.

  • 42. Lehndal, Lina
    et al.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ericson, Lars
    Ågren, Jon
    Herbivory strongly influences among-population variation in reproductive output of Lythrum salicaria in its native range2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 4, p. 1159-1171Article in journal (Refereed)
    Abstract [en]

    Herbivory can negatively affect several components of plant reproduction. Yet, because of a lack of experimental studies involving multiple populations, the extent to which differences in herbivory contribute to among-population variation in plant reproductive success is poorly known. We experimentally determined the effects of insect herbivory on reproductive output in nine natural populations of the perennial herb Lythrum salicaria along a disturbance gradient in an archipelago in northern Sweden, and we quantified among-population differentiation in resistance to herbivory in a common-garden experiment in the same area. The intensity of leaf herbivory varied > 500-fold and mean female reproductive success > 400-fold among the study populations. The intensity of herbivory was lowest in populations subject to strong disturbance from ice and wave action. Experimental removal of insect herbivores showed that the effect of herbivory on female reproductive success was correlated with the intensity of herbivory and that differences in insect herbivory could explain much of the among-population variation in the proportion of plants flowering and seed production. Population differentiation in resistance to herbivory was limited. The results demonstrate that the intensity of herbivory is a major determinant of flowering and seed output in L. salicaria, but that differences in herbivory are not associated with differences in plant resistance at the spatial scale examined. They further suggest that the physical disturbance regime may strongly influence the performance and abundance of perennial herbs and patterns of selection not only because of its effect on interspecific competition, but also because of effects on interactions with specialized herbivores.

  • 43. Lemessa, Debissa
    et al.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Arthropod but Not Bird Predation in Ethiopian Homegardens Is Higher in Tree-Poor than in Tree-Rich Landscapes2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5, article id e0126639Article in journal (Refereed)
    Abstract [en]

    Bird and arthropod predation is often associated with natural pest control in agricultural landscapes, but the rates of predation may vary with the amount of tree cover or other environmental factors. We examined bird and arthropod predation in three tree-rich and three tree-poor landscapes across southwestern Ethiopia. Within each landscape we selected three tree-rich and three tree-poor homegardens in which we recorded the number of tree species and tree stems within 100 x 100 m surrounding the central house. To estimate predation rates, we attached plasticine caterpillars on leaves of two coffee and two avocado shrubs in each homegarden, and recorded the number of attacked caterpillars for 7-9 consecutive weeks. The overall mean daily predation rate was 1.45% for birds and 1.60% for arthropods. The rates of arthropod predation varied among landscapes and were higher in tree-poor landscapes. There was no such difference for birds. Within landscapes, predation rates from birds and arthropods did not vary between tree-rich and tree-poor homegardens in either tree-rich or tree-poor landscapes. The most surprising result was the lack of response by birds to tree cover at either spatial scale. Our results suggest that in tree-poor landscapes there are still enough non-crop habitats to support predatory arthropods and birds to deliver strong top-down effect on crop pests.

  • 44.
    Lemessa, Debissa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The effect of local and landscape level land-use composition on predatory arthropods in a tropical agricultural landscape2015In: Landscape Ecology, ISSN 0921-2973, E-ISSN 1572-9761, Vol. 30, no 1, p. 167-180Article in journal (Refereed)
    Abstract [en]

    It has been suggested that the composition of different non-crop land-use types along with tree density regulate local biodiversity in agricultural landscapes. However, specific data is limited, not least from tropical regions. We examined how different land-use types and forest cover at different scales influenced the abundance and species composition of predatory arthropods in 40 homegardens of southwest Ethiopia. We collected specimens using pitfall traps during two separate months and related sample composition to land-use in the vicinity (1 ha plot, local scale, field data) and tree cover within 200 and 500 m radius zones (landscape scale, satellite data). Spiders, beetles and ants were most common. A high abundance of ants was found in tree-rich homegardens while the variation in abundance of spiders was best explained by the interaction between tree cover at the local and landscape scales. The highest spider abundances were found when either the homegarden or the surroundings had high tree-cover and was lower in both the most tree-rich and tree-poor landscape-garden combinations. In addition, open non-crop cover (mostly grasslands) and ensete (a banana-like perennial crop) favored spiders. This pattern demonstrates that different land-use types at different scales can interact to create variations in biodiversity across an agricultural landscape. To enhance numbers of predatory arthropods in homegardens, which may be beneficial for natural pest control, our results suggest that different strategies are needed depending on the target group or species. Grasslands, ensete fields and tree-rich habitats seem to play important roles.

  • 45.
    Lemessa, Debissa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Birds and arthropod predation on plasticine caterpillars across tropical agricultural landscapesManuscript (preprint) (Other academic)
  • 46.
    Lemessa, Debissa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Composition of crops and land-use types in relation to crop raiding pattern at different distances from forests2013In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 167, p. 71-78Article in journal (Refereed)
    Abstract [en]

    Among the issues that farmers need to account for when planning their land-use and crop choice is yield loss from wild animals. The aim of this study was to examine both the distribution of land-use types and crops (in fields and homegardens) in relation to distance from forest edges and the possible impact of crop raiding mammals. Thirty transects of 1 km in length were laid out in a pair-wise design - 15 close to (<= 0.3 km) and 15 far from (1-3.5 km) forest edges. We measured the cover of the land-use types and field crops in each transect and assessed crop species composition in 4-6 homegardens along each transect. We also conducted a questionnaire survey for the occurrence of baboons and bush pigs in maize fields and in homegardens. Our results indicated that the distribution of land-use types and field crops was not significantly different between sites close to and far from forest edges. Similarly, the distributions of field and homegarden crop species composition were also similar between these locations. The occurrence pattern of baboons and bush pigs coming to the fields and homegardens was however strongly inclined toward transects close to forest edges according to the answers from the farmers. Although crops, such as maize, sorghum, tuber and root crops are frequently attacked by either baboons or pigs or both, farmers apparently did not stop growing these crops. The major reasons for this lack of response in growing practices between sites close to and far from forests could either be a perceived lack of alternative less susceptible crops or that farmers have adapted different protection mechanisms for the problem to be manageable. Both ecological and socio-economic studies are needed in order to understand the variation (and sometimes lack of variation) of ecosystem properties and corresponding management practices across landscapes.

  • 47. Lemessa, Debissa
    et al.
    Samnegård, Ulrika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Tree cover mediates the effect on rapeseed leaf damage of excluding predatory arthropods, but in an unexpected way2015In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 211, p. 57-64Article in journal (Refereed)
    Abstract [en]

    Birds and predatory arthropods are often implicated in pest control, but their relative impact and how this is mediated by variation in tree cover requires elucidation. We excluded birds and ground predatory arthropods from rapeseed plants in 2.5 x 1 m plots in 26 homegardens in Ethiopia, leaving the same sized control plots. From six groups of plants in bird exclosure and control plots, respectively, three groups were excluded from ground predatory arthropods. Data on leaf damage were surveyed four times at weekly intervals. The tree cover and land-use composition within 100 x 100 m surrounding each plots were recorded in the field and from a satellite image within 200 and 500 m buffer zones. The results show that the mean leaf damage was higher on rapeseed plants from which predatory arthropods were excluded than on control plants. However, excluding birds had no or only a weak impact on leaf damage. The mean leaf damage within predatory arthropod exclosures decreased with increasing tree, forest and perennial cover but increased with increasing grazing land cover and annual crop cover, while on control plants it was low across the tree cover variation. This pattern may indicate the presence of a higher density of herbivores on rapeseed plants and also more predatory arthropods (i.e., to control them) in tree-poor homegardens compared to tree-rich homegardens. Hence, tree-poor homegardens in this landscape have sufficient habitat heterogeneity to support natural enemies to deliver significant pest control on rapeseed. Our results show that there was variation in the dynamics of pests and predatory arthropods across the tree cover variation, suggesting changes in landscape composition could affect the pest control services and the outcomes for local farmers.

  • 48. Martinson, Holly
    et al.
    Schneider, Katie
    Gilbert, James
    Hines, Jessica
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Fagan, William
    Detritivory: stoichiometry of a neglected trophic level.2008In: Ecological Research, Vol. 23, p. 487-491Article in journal (Refereed)
    Abstract [en]

    Previous syntheses have identified the key roles that phylogeny, body size, and trophic level play in determining arthropod stoichiometry. To date, however, detritivores have been largely omitted from such syntheses, despite their importance in nutrient cycling, biodiversity, and food web interactions. Here, we report on a compiled database of the allometry and nutritional stoichiometry (N and P) of detritivorous arthropods. Overall, both N and P content for detritivores varied among major phylogenetic lineages. Detritivore N content was similar to the N content of herbivores, but below that of predators. By contrast, detritivore P content was independent of trophic level. Contrary to previous reports, neither nutrient varied with body size. This analysis places detritivores in the context of related herbivores and predators, and as such, sets the stage for future investigations into the causes and consequences of elemental (mis)matches between detritivores and their detrital resources.

  • 49.
    Mellbrand, Kajsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Enskog, Maria
    Stockholm University, Faculty of Science, Department of Botany.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Individual variation between spiders on shores in the utilization of aquatic subsidiesManuscript (Other academic)
    Abstract [en]

    Intrapopulation variation is common in nature, and many generalist species actually consists of individual specialists. In food web ecology, stable isotope analysis is a common tool for examining energy and nutrient flows both between and within ecosystems, but large intrapopulation variation in isotopic values may lead to over- or underestimations of dietary variation between populations or species. Such large intraguild variation is common in spiders, which often are generalist predators. In this study we have used carbon and nitrogen stable isotope analysis to examine diets of shore-dwelling spiders, in relation to aquatic inflows to shore ecosystems. The study was carried out on shores inside and outside a eutrophicated bay in the Baltic Sea, using carbon and nitrogen stable isotope analysis. Aquatic subsidies consisted of inflows of algae (mainly green filamentous algae) and emerging insects (Chironomidae). We found that spiders inside the bay all utilized mainly terrestrial prey, while spiders outside the bay, in particular wolf spiders, were separated into individuals utilizing either terrestrial or aquatic prey. The total population niche width was therefore larger outside than inside the bay. This individual specialization may be related to differences in nutrient enrichment in the aquatic ecosystem and/or salinity between sites inside and outside the bay, and we suggest that eutrophication decreases total niche width by affecting prey availability and prey choice of individual predators. We also conclude that while stable isotope analysis remains a useful tool for examining flows across ecosystem boundaries, caution is needed in the interpretation of data with large intrapopulation variation.

  • 50.
    Mellbrand, Kajsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Coastal niches for terrestrial predators: a stable isotope studyManuscript (Other academic)
    Abstract [en]

    The purpose of this study was to identify if terrestrial arthropod predators on Baltic Sea shores vary in their use of marine versus terrestrial food items, and to construct a bottom-up food web for Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g. phantom midges, Chironomidae). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis, and a two source mixing model was used to examine proportions of marine carbon to diets. The results suggest that spiders are the terrestrial predators mainly utilizing nutrients and energy of marine origin on Baltic Sea shores, while insect predators such as beetles and hemipterans mainly utilize nutrients and energy derived from terrestrial sources, possibly due to differences in hunting behaviour. That spiders are the predators that benefit the most from the marine inflow suggest that eventual effects of marine subsidies for the coastal ecosystem as a whole are likely mediated by spiders.

12 1 - 50 of 79
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf