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  • 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 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.

  • 3.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Mountain Hare Populations on Islands - Effects of Predation by Red Fox1989In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 81, no 3, p. 335-340Article in journal (Refereed)
    Abstract [en]

    On islands off the west coast of Sweden the density of mountain hares (Lepus timidus L.) is very high. One of the main predators on hares, the red fox (Vulpes vulpes L.), is only present during short periods. Data on hare density and predation by red fox and eagle owl (Bubo bubo (L.)) has been analyzed from five islands over several years. Winter mortality in years with low predation pressure was independent of hare density. But when red fox or eagle owl were present on islands (i.e., high predation pressure) winter mortality became density dependent. Thus, at low density, winter mortality did not increase through red fox predation. But at densities up to two hares/ha, predation pressure was increasing and could be limiting for these populations. At still higher hare density predation pressure became less intensive. The functional response for foxes preying on hares showed a type II or a sigmoid type III response pattern. In normal summers, the population increase due to reproduction was at least two-fold. When a fox was present there was instead a sharp decrease in hare numbers. Fox predation had a stronger effect in summer than in winter. By switching between islands and mainland areas from winter to summer, a fox can stabilize fluctuations in hare numbers on the islands. This is dependent on how often the ice permits a fox to reach an island and the lack of numerical response by predators.

  • 4.
    Auffret, Alistair G.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Plue, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Scale-dependent diversity effects of seed dispersal by a wild herbivore in fragmented grasslands2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, no 1, p. 305-313Article in journal (Refereed)
    Abstract [en]

    Dispersal limitation between habitat fragments is a known driver of landscape-scale biodiversity loss. In Europe, agricultural intensification during the twentieth century resulted in losses of both grassland habitat and traditional grassland seed dispersal vectors such as livestock. During the same period, populations of large wild herbivores have increased in the landscape. Usually studied in woodland ecosystems, these animals are found to disperse seeds from grasslands and other open habitats. We studied endozoochorous seed dispersal by roe deer (Capreolus capreolus) in fragmented grasslands and grassland remnants, comparing dispersed subcommunities of plant species to those in the established vegetation and the seed bank. A total of 652 seedlings of 67 species emerged from 219 samples of roe deer dung. This included many grassland species, and several local grassland specialists. Dispersal had potentially different effects on diversity at different spatial scales. Almost all sites received seeds of species not observed in the vegetation or seed bank at that site, suggesting that local diversity might not be dispersal limited. This pattern was less evident at the landscape scale, where fewer new species were introduced. Nonetheless, long-distance dispersal by large wild herbivores might still provide connectivity between fragmented habitats within a landscape in the areas in which they are active. Finally, as only a subset of the available species were found to disperse in space as well as time, the danger of future biodiversity loss might still exist in many isolated grassland habitats.

  • 5. Bonnot, Nadège C.
    et al.
    Bergvall, Ulrika A.
    Stockholm University, Faculty of Science, Department of Zoology. Swedish University of Agricultural Sciences, Sweden.
    Jarnemo, Anders
    Kjellander, Petter
    Who's afraid of the big bad wolf? Variation in the stress response among personalities and populations in a large wild herbivore2018In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 188, no 1, p. 85-95Article in journal (Refereed)
    Abstract [en]

    Faced with rapid environmental changes, individuals may express different magnitude and plasticity in their response to a given stressor. However, little is known about the causes of variation in phenotypic plasticity of the stress response in wild populations. In the present study, we repeatedly captured individual roe deer (Capreolus capreolus) from two wild populations in Sweden exposed to differing levels of predation pressure and measured plasma concentrations of stress-induced cortisol and behavioral docility. While controlling for the marked effects of habituation, we found clear between-population differences in the stress-induced cortisol response. Roe deer living in the area that was recently recolonized by lynx (Lynx lynx) and wolves (Canis lupus) expressed cortisol levels that were around 30% higher than roe deer in the human-dominated landscape free of large carnivores. In addition, for the first time to our knowledge, we investigated the stress-induced cortisol response in free-ranging newborn fawns and found no evidence for hypo-responsiveness during early life in this species. Indeed, stress-induced cortisol levels were of similar magnitude and differed between populations to a similar extent in both neonates and adults. Finally, at an individual level, we found that both cortisol and docility levels were strongly repeatable, and weakly negatively inter-correlated, suggesting that individuals differed consistently in how they respond to a stressor, and supporting the existence of a stress-management syndrome in roe deer.

  • 6.
    Dahlgren, Johan P.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Southern Denmark, Denmark.
    Östergård, Hannah
    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.
    Local environment and density-dependent feedbacks determine population growth in a forest herb2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 176, no 4, p. 1023-1032Article in journal (Refereed)
    Abstract [en]

    Linking spatial variation in environmental factors to variation in demographic rates is essential for a mechanistic understanding of the dynamics of populations. However, we still know relatively little about such links, partly because feedbacks via intraspecific density make them difficult to observe in natural populations. We conducted a detailed field study and investigated simultaneous effects of environmental factors and the intraspecific density of individuals on the demography of the herb Lathyrus vernus. In regression models of vital rates we identified effects associated with spring shade on survival and growth, while density was negatively correlated with these vital rates. Density was also negatively correlated with average individual size in the study plots, which is consistent with self-thinning. In addition, average plant sizes were larger than predicted by density in plots that were less shaded by the tree canopy, indicating an environmentally determined carrying capacity. A size-structured integral projection model based on the vital rate regressions revealed that the identified effects of shade and density were strong enough to produce differences in stable population sizes similar to those observed in the field. The results illustrate how the local environment can determine dynamics of populations and that intraspecific density may have to be more carefully considered in studies of plant demography and population viability analyses of threatened species. We conclude that demographic approaches incorporating information about both density and key environmental factors are powerful tools for understanding the processes that interact to determine population dynamics and abundances.

  • 7.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Resolving temporal variation in vertebrate diets using naturally occurring stable isotopes2005In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Oecologia, Vol. 144, no 4, p. 647-658Article in journal (Refereed)
    Abstract [en]

    Assessments of temporal variation in diets are important for our understanding of the ecology of many vertebrates. Ratios of naturally occurring stable isotopes in animal tissues are a combination of the source elements and tissue specific fractionation processes, and can thus reveal dietary information. We review three different approaches that have been used to resolve temporal diet variation through analysis of stable isotopes. The most straightforward approach is to compare samples from the same type of tissue that has been sampled over time. This approach is suited to address either long or short-term dietary variation, depending on sample regime and which tissue that is sampled. Second, one can compare tissues with different metabolic rates. Since the elements in a given tissue have been assimilating during time spans specific to its metabolic rate, tissues with different metabolic rates will reflect dietary records over different periods. Third, comparisons of sections from tissues with progressive growth, such as hair, feathers, claws and teeth, will reveal temporal variation since these tissues will retain isotopic values in a chronological order. These latter two approaches are mainly suited to address questions regarding intermediate and short-term dietary variation. Knowledge of tissue specific metabolic rates, which determine the molecular turnover for a specific tissue, is of central importance for all these comparisons. Estimates of isotopic fractionation between source and measured target are important if specific hypotheses regarding the source elements are addressed. Estimates of isotopic fractionation, or at least of differences in fractionation between tissues, are necessary if different tissues are compared. We urge for more laboratory experiments aimed at improving our understanding of differential assimilation of dietary components, isotopic fractionation and metabolic routing. We further encourage more studies on reptiles and amphibians, and generally more studies utilizing multiple tissues with different turnover rates.

  • 8.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Oviedo, Spain; University of Pretoria, South Africa.
    Hellström, Peter
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Miranda, M.
    Nyström, Jesper
    Stockholm University, Faculty of Science, Department of Zoology.
    Ekenstedt, Johan
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Network topology of stable isotope interactions in a sub-arctic raptor guild2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 182, no 2, p. 511-518Article in journal (Refereed)
    Abstract [en]

    Predation is an ecologically important process, and intra-guild interactions may substantially influence the ecological effects of predator species. Despite a rapid expansion in the use of mathematical graph theory to describe trophic relations, network approaches have rarely been used to study interactions within predator assemblages. Assemblages of diurnal raptors are subject to substantial intra- and interspecific competition. Here we used the novel approach of applying analyzes based on network topology to species-specific data on the stable isotopes C-13 and N-15 in feathers to evaluate patterns of relative resource utilization within a guild of diurnal raptors in northern Sweden. Our guild consisted of the golden eagle (Aquila chrysaetos), the gyrfalcon (Falco rusticolus), the peregrine falcon (Falco peregrinus) and the rough-legged buzzard (Buteo lagopus). We found a modular trophic interaction structure within the guild, but the interactions were less nested than expected by chance. These results suggest low redundancy and hence a strong ecological importance of individual species. Our data also suggested that species were less connected through intra-guild interactions than expected by chance. We interpret our results as a convergence on specific isotope niches, and that body size and different hunting behaviour may mediate competition within these niches. We finally highlight that generalist predators could be ecologically important by linking specialist predator species with disparate dietary niches.

  • 9.
    Forslund, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia A.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Pavia, Henrik
    Higher resistance to herbivory in introduced compared to native populations of a seaweed2010In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 164, no 3, p. 833-840Article in journal (Refereed)
    Abstract [en]

    Non-indigenous species (NIS) are important components of global change, and in order to manage such species it is important to understand which factors affect their success. Interactions with enemies in the new range have been shown to be important for the outcome of introductions, but thus far most studies on NIS-enemy interactions have considered only specialist herbivores in terrestrial systems. Here we present the results from the first biogeographic study that compares herbivore resistance between populations in the native and new region of a non-indigenous seaweed. We show that low consumption of the non-indigenous seaweed by a generalist herbivore is caused by higher chemical defence levels and herbivore resistance in the new range-and not by the failure of the herbivore to recognise the non-indigenous seaweed as a suitable host. Since most seaweed-herbivore interactions are dominated by generalist herbivores, this pattern could be common in marine communities. Our results also reveal that traits used to predict the invasive potential of species, such as their resistance to enemies, can change during the invasion process, but not always in the way predicted by dominant theories.

  • 10. Friberg, M.
    et al.
    Posledovich, Diana
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Decoupling of female host plant preference and offspring performance in relative specialist and generalist butterflies2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 178, no 4, p. 1181-1192Article in journal (Refereed)
    Abstract [en]

    The preference-performance hypothesis posits that the host plant range of plant-feeding insects is ultimately limited by larval costs associated with feeding on multiple resources, and that female egg-laying preferences evolve in response to these costs. The trade-off of either using few host plant species and being a strong competitor on them due to effective utilization or using a wide host plant range but being a poor competitor is further predicted to result in host plant specialization. This follows under the hypothesis that both females and offspring are ultimately favoured by utilizing only the most suitable host(s). We develop an experimental approach to identify such trade-offs, i.e. larval costs associated with being a host generalist, and apply a suite of experiments to two sympatric and syntopic populations of the closely related butterflies Pieris napi and Pieris rapae. These butterflies show variation in their level of host specialization, which allowed comparisons between more and less specialized species and between families within species. Our results show that, first, the link between female host preference and offspring performance was not significantly stronger in the specialist compared to the generalist species. Second, the offspring of the host plant specialist did not outperform the offspring of the generalist on the former's most preferred host plant species. Finally, the more generalized species, or families within species, did not show higher survival or consistently higher growth rates than the specialists on the less preferred plants. Thus, the preference and performance traits appear to evolve as largely separated units.

  • 11.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Aalberg Haugen, Inger M.
    Stockholm University, Faculty of Science, Department of Zoology.
    Dahlerus, Josefin
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Asymmetric life-history decision-making in butterfly larvae2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 165, no 2, p. 301-310Article in journal (Refereed)
    Abstract [en]

    In temperate environments, insects appearing in several generations in the growth season typically have to decide during the larval period whether to develop into adulthood, or to postpone adult emergence until next season by entering a species-specific diapause stage. This decision is typically guided by environmental cues experienced during development. An early decision makes it possible to adjust growth rate, which would allow the growing larva to respond to time stress involved in direct development, whereas a last-minute decision would instead allow the larva to use up-to-date information about which developmental pathway is the most favourable under the current circumstances. We study the timing of the larval pathway decision-making between entering pupal winter diapause and direct development in three distantly related butterflies (Pieris napi, Araschnia levana and Pararge aegeria). We pinpoint the timing of the larval diapause decision by transferring larvae from first to last instars from long daylength (inducing direct development) to short daylength conditions (inducing diapause), and vice versa. Results show that the pathway decision is typically made in the late instars in all three species, and that the ability to switch developmental pathway late in juvenile life is conditional; larvae more freely switched from diapause to direct development than in the opposite direction. We contend that this asymmetry is influenced by the additional physiological preparations needed to survive the long and cold winter period, and that the reluctance to make a late decision to enter diapause has the potential to be a general trait among temperate insects.

  • 12.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Dahlerus, Josefin
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Strategic larval decision-making in a bivoltine butterfly2012In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 169, no 3, p. 623-635Article in journal (Refereed)
    Abstract [en]

    In temperate areas, insect larvae must decide between entering winter diapause or developing directly and reproducing in the same season. Long daylength and high temperature promote direct development, which is generally associated with a higher growth rate. In this work, we investigated whether the larval pathway decision precedes the adjustment of growth rate (state-independent), or whether the pathway decision is conditional on the individual's growth rate (state-dependent), in the butterfly Pieris napi. This species typically makes the pathway decision in the penultimate instar. We measured growth rate throughout larval development under two daylengths: slightly shorter and slightly longer than the critical daylength. Results indicate that the pathway decision can be both state-independent and state-dependent; under the shorter daylength condition, most larvae entered diapause, and direct development was chosen exclusively by a small subset of larvae showing the highest growth rates already in the early instars; under the longer daylength condition, most larvae developed directly, and the diapause pathway was chosen exclusively by a small subset of slow-growing individuals. Among the remainder, the choice of pathway was independent of the early growth rate; larvae entering diapause under the short daylength grew as fast as or faster than the direct developers under the longer daylength in the early instars, whereas the direct developers grew faster than the diapausers only in the ultimate instar. Hence, the pathway decision was state-dependent in a subset with a very high or very low growth rate, whereas the decision was state-independent in the majority of the larvae, which made the growth rate adjustment downstream from the pathway decision.

  • 13.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Höglander, Helena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Andersen, Christian Marc
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Stable isotopes show food web changes after invasion by the predatory cladoceran Cercopagis pengoi in a Baltic Sea bay2005In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 143, no 2, p. 251-259Article in journal (Refereed)
    Abstract [en]

    Cercopagis pengoi, a recent invader to the Baltic Sea and the Laurentian Great Lakes, is a potential competitor with fish for zooplankton prey. We used stable C and N isotope ratios to elucidate trophic relationships between C. pengoi, zooplankton (microzooplankton, 90–200 m, mostly copepod nauplii and rotifers; mesozooplankton, >200 m, mostly copepods), and zooplanktivorous fish (herring, size range 5–15 cm and sprat, 9–11 cm) in a coastal area of the northern Baltic Sea. The isotope ratios in C. pengoi and fish were much higher than those of zooplankton, showing general trends of enrichment with trophic level. Young-of-the-year (YOY) herring had a significantly higher 15N/14N ratio than C. pengoi, suggesting of a trophic linkage between the two species. To evaluate the possible relative importance of different food sources for C. pengoi and YOY herring, two-source isotope-mixing models for N were used, with micro- and mesozooplankton as prey for C. pengoi and mesozooplankton and C. pengoi as prey for YOY herring. These models indicate that mesozooplankton was the major food source of both species. However, microzooplankton may be important prey for young stages of C. pengoi. Comparative analyses of the herring trophic position before and after the invasion by C. pengoi showed a trophic level shift from 2.6 to 3.4, indicating substantial alterations in the food web structure. Our findings contribute to a growing body of evidence, showing that C. pengoi can modify food webs and trophic interactions in invaded ecosystems.

  • 14.
    Haage, Marianne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Maran, Tiit
    Alm Bergvall, Ulrika
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Evolutionary maintenance of personality – a field experiment on survival and personalityIn: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939Article in journal (Refereed)
  • 15.
    Haage, Marianne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Maran, Tiit
    Alm Bergvall, Ulrika
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    The influence of spatiotemporal conditions and personality on survival in reintroductions-evolutionary implications2017In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 183, no 1, p. 45-56Article in journal (Refereed)
    Abstract [en]

    Personality exists in non-human animals and can impact fitness. There is, however, a shortage of empirical studies in certain areas within the field, and fundamental evolutionary theory on personality remains largely untested. For example, little is known on how variation in personality is maintained over evolutionary time. Theory suggests that fluctuating selection pressures due to spatiotemporal variation in conditions, e.g. food availability, is a possible mechanism and a few studies have shown that the success of different personality types varies with spatiotemporal conditions. However, it remains unknown whether different mechanisms can maintain personality within a species. Here we use a reintroduction programme for the critically endangered European mink (Mustela lutreola) to test whether multiple personality trait domains (boldness, exploration and sociability) affected survival in two different years and islands. This was done through pre-release personality tests and post-release radio-tracking monitoring. Survival was positively correlated with boldness, whereas the relationship with exploration was either negative or positive depending on year/island. The results show a complex relationship between personality and survival and suggest that exploration can be maintained over evolutionary time via spatiotemporal variation in conditions. However, in contrast to exploration, boldness did not vary spatiotemporally and sociability had no impact on survival. This indicates that different personality trait domains might be maintained by different mechanisms. To date, personality has been studied primarily within behavioural sciences, but through empirical findings we highlight the importance of personality also in ecology and conservation biology.

  • 16.
    Hellström, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Nyström, Jesper
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Functional responses of rough-legged buzzards in a multi-prey system2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 174, no 4, p. 1241-1254Article in journal (Refereed)
    Abstract [en]

    The functional response is a key element of predator–prey interactions. Basic functional response theory explains foraging behavior of individual predators, but many empirical studies of free-ranging predators have estimated functional responses by using population-averaged data. We used a novel approach to investigate functional responses of an avian predator (the rough legged-buzzard Buteo lagopus Pontoppidan, 1763) to intra-annual spatial variation in rodent density in subarctic sweden, using breeding pairs as the sampling unit. the rough-legged buzzards responded functionally to norwegian lemmings (Lemmus lemmus l. 1758), grey-sided voles (Myodes rufocanus Sundevall, 1846) and field voles (Microtus agrestis L. 1761), but different rodent prey were not utilised according to relative abundance. the functional response to norwegian lemmings was a steep type II curve and a more shallow type III response to grey-sided voles. the different shapes of these two functional responses were likely due to combined effects of differences between lemmings and grey-sided voles in habitat utilisation, anti-predator behaviour and size-dependent vulnerability to predation. Diet composition changed less than changes in relative prey abundance, indicating negative switching, with high disproportional use of especially lemmings at low relative densities. Our results suggest that lemmings and voles should be treated separately in future empirical and theoretical studies in order to better understand the role of predation in this study system.

  • 17.
    Johansson, Veronika A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mikusinska, Anna
    Ekblad, Alf
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Partial mycoheterotrophy in Pyroleae: nitrogen and carbon stable isotope signatures during development from seedling to adult2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, no 1, p. 203-211Article in journal (Refereed)
    Abstract [en]

    Mycoheterotrophic plants (MHP) are divided into non-photosynthesizing full MHP and green-leaved partial or initial MHP. We investigated 13C and 15N isotope enrichment in five putatively partial MHP species in the tribe Pyroleae (Ericaceae): Chimaphila umbellata, Moneses uniflora, Orthilia secunda, Pyrola chlorantha and Pyrola minor, sampled from forest sites on Öland, Sweden. For M. uniflora and P. chlorantha, we investigated isotope signatures of subterranean seedlings (which are mycoheterotrophic), to examine how the use of seedlings instead of full MHP species (Hypopitys monotropa) as reference species affects the assessment of partial mycoheterotrophy. Our main findings were as follows: (1) All investigated Pyroleae species were enriched in 15N compared to autotrophic reference plants. (2) significant fungal-derived C among the Pyroleae species was found for O. secunda and P. chlorantha. For the remaining species of C. umbellata, M. uniflora and P. minor, isotope signatures suggested adult autotrophy. (3) C and N gains, calculated using seedlings as a full MHP reference, yielded qualitatively similar results as when using H. monotropa as a reference. However, the estimated differences in C and N gains became larger when using seedlings as an MHP reference. (4) A previously unknown interspecific variation in isotope signature occurs during early ontogeny, from seed production to developing seedlings. Our findings suggest that there is a variation among Pyroleae species concerning partial mycoheterotrophy in adults. Adult autotrophy may be most common in Pyroleae species, and these species may not be as dependent on fungal-derived nutrients as some green orchids.

  • 18. Jormalainen, Veijo
    et al.
    Wikström, Sowa A.
    Stockholm University, Faculty of Science, Department of Botany.
    Honkanen, Tuija
    Fouling mediates grazing: intertwining of resistances to multiple enemies in the brown alga Fucus vesiculosus2008In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 155, no 3, p. 559-569Article in journal (Refereed)
    Abstract [en]

    Macroalgae have to cope with multiple natural enemies, such as herbivores and epibionts. As these are harmful for the host, the host is expected to show resistance to them. Evolution of resistance is complicated by the interactions among the enemies and the genetic correlations among resistances to different enemies. Here, we explored genetic variation in resistance to epibiosis and herbivory in the brown alga Fucus vesiculosus, both under conditions where the enemies coexisted and where they were isolated. F. vesiculosus showed substantial genetic variation in the resistance to both epibiosis and grazing. Grazing pressure on the alga was generally lower in the presence than in the absence of epibiota. Furthermore, epibiosis modified the susceptibility of different algal genotypes to grazing. Resistances to epibiosis and grazing were independent when measured separately for both enemies but positively correlated when both these enemies coexisted. Thus, when the enemies coexisted, the fate of genotypes with respect to these enemies was intertwined. Genotypic correlation between phlorotannins, brown-algal phenolic secondary metabolites, and the amount of epibiota was negative, indicating that these compounds contribute to resistance to epibiosis. In addition, phlorotannins correlated also with the resistance to grazing, but this correlation disappeared when grazing occurred in the absence of epibiota. This indicates that the patterns of selection for the type of the resistance as well as for the resistance traits vary with the occurrence patterns of the enemies.

  • 19.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ryden, Sara Blomgren
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Polychaete invader enhances resource utilization in a species-poor system2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, no 4, p. 1055-1065Article in journal (Refereed)
    Abstract [en]

    Ecosystem consequences of biodiversity change are often studied from a species loss perspective, while the effects of invasive species on ecosystem functions are rarely quantified. In this experimental study, we used isotope tracers to measure the incorporation and burial of carbon and nitrogen from a simulated spring phytoplankton bloom by communities of one to four species of deposit-feeding macrofauna found in the species-poor Baltic Sea. The recently invading polychaete Marenzelleria arctia, which has spread throughout the Baltic Sea, grows more rapidly than the native species Monoporeia affinis, Pontoporeia femorata (both amphipods) and Macoma balthica (a bivalve), resulting in higher biomass increase (biomass production) in treatments including the polychaete. Marenzelleria incorporated and buried bloom material at rates similar to the native species. Multi-species treatments generally had higher isotope incorporation, indicative of utilization of bloom material, than expected from monoculture yields of the respective species. The mechanism behind this observed over-yielding was mainly niche complementarity in utilization of the bloom input, and was more evident in communities including the invader. In contrast, multi-species treatments had generally lower biomass increase than expected. This contrasting pattern suggests that there is little overlap in resource use of freshly deposited bloom material between Marenzelleria and the native species but it is likely that interference competition acts to dampen resulting community biomass. In conclusion, an invasive species can enhance incorporation and burial of organic matter from settled phytoplankton blooms, two processes fundamental for marine productivity.

  • 20.
    Khalil, Hussein
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Pasanen Mortensen, Marianne
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    The relationship between wolverine and larger predators, lynx and wolf, in a historical ecosystem context2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, no 2, p. 625-637Article in journal (Refereed)
    Abstract [en]

    Apex predators play an important role in shaping ecosystem structure. They may suppress smaller predators (mesopredators) but also subsidize scavengers via carrion provisioning. However, the importance of these interactions can change with ecosystem context. The wolverine (Gulo gulo) is a cold-adapted carnivore and facultative scavenger. It has a circumboreal distribution, where it could be either suppressed or subsidized by larger predators. In Scandinavia, the wolverine might interact with two larger predators, wolf (Canis lupus) and lynx (Lynx lynx), but human persecution decimated the populations in the nineteenth and early twentieth century. We investigated potential relationships between wolverine and the larger predators using hunting bag statistics from 15 Norwegian and Swedish counties in 1846-1922. Our best models showed a positive association between wolverine and lynx trends, taking ecological and human factors into account. There was also a positive association between year-to-year fluctuations in wolverine and wolf in the latter part of the study period. We suggest these associations could result from positive lynx-wolverine interactions through carrion provisioning, while wolves might both suppress wolverine and provide carrion with the net effect becoming positive when wolf density drops below a threshold. Wolverines could thus benefit from lynx presence and low-to-intermediate wolf densities.

  • 21.
    König, Malin A. E.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Context-dependent resistance against butterfly herbivory in a polyploid herb2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 174, no 4, p. 1265-1272Article in journal (Refereed)
    Abstract [en]

    Spatial variation in biotic interactions and natural selection are fundamental parts of natural systems, and can be driven by differences in both trait distributions and the local environmental context of the interaction. Most studies of plant–animal interactions have been performed only in natural settings, making it difficult to disentangle the effects of traits and context. To assess the relative importance of trait differences and environmental context for among-population variation in plant resistance to herbivory, we compared oviposition by the butterfly Anthocharis cardamines on two ploidy types of the herb Cardamine pratensis under experimentally controlled conditions with oviposition in natural populations. Under controlled conditions, plants from octoploid populations were significantly more preferred than plants from tetraploid populations. This difference was largely mediated by differences in flower size. Among natural populations, there was no difference in oviposition rates between the two ploidy types. Our results suggest that differences in oviposition rates among populations of the two cytotypes in the field are caused mainly by differences in environmental context, and that the higher attractiveness of octoploids to herbivores observed under common environmental conditions is balanced by the fact that they occur in habitats which harbor lower densities of butterflies. This illustrates that spatial variation in biotic interactions is the net result of differences in trait distributions of the interacting organisms and differences in environmental context, and that variation in both traits and context are important in understanding species interactions.

  • 22. 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.

  • 23. Lehtilä, Kari
    et al.
    Dahlgren, Johan P.
    Garcia, Maria Begona
    Leimu, Roosa
    Syrjänen, Kimmo
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Forest succession and population viability of grassland plants: long repayment of extinction debt in Primula veris2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 181, no 1, p. 125-135Article in journal (Refereed)
    Abstract [en]

    Time lags in responses of organisms to deteriorating environmental conditions delay population declines and extinctions. We examined how local processes at the population level contribute to extinction debt, and how cycles of habitat deterioration and recovery may delay extinction. We carried out a demographic analysis of the fate of the grassland perennial Primula veris after the cessation of grassland management, where we used either a unidirectional succession model for forest habitat or a rotation model with a period of forest growth followed by a clear-cut and a new successional cycle. The simulations indicated that P. veris populations may have an extinction time of decades to centuries after a detrimental management change. A survey of the current incidence and abundance of P. veris in sites with different histories of afforestation confirmed the simulation results of low extinction rates. P. veris had reduced incidence and abundance only at sites with at least 100 years of forest cover. Time to extinction in simulations was dependent on the duration of the periods with favourable and unfavourable conditions after management cessation, and the population sizes and growth rates in these periods. Our results thus suggest that the ability of a species to survive is a complex function of disturbance regimes, rates of successional change, and the demographic response to environmental changes. Detailed demographic studies over entire successional cycles are therefore essential to identify the environmental conditions that enable long-term persistence and to design management for species experiencing extinction debts.

  • 24.
    Meijer, Tomas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Eide, Nina E.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Life history traits in a cyclic ecosystem: a field experiment on the arctic fox2013In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 173, no 2, p. 439-447Article in journal (Refereed)
    Abstract [en]

    The reproduction of many species depends strongly on variation in food availability. The main prey of the arctic fox in Fennoscandia are cyclic small rodents, and its number of litters and litter size vary depending on the phase of the rodent cycle. In this experiment, we studied if the arctic fox adjusts its reproduction as a direct response to food abundance, in accordance with the food limitation hypothesis, or if there are additional phase-dependent trade-offs that influence its reproduction. We analysed the weaning success, i.e. proportion of arctic fox pairs established during mating that wean a litter in summer, of 422 pairs of which 361 were supplementary winter fed, as well as the weaned litter size of 203 litters of which 115 were supplementary winter fed. Females without supplementary winter food over-produced cubs in relation to food abundance in the small rodent increase phase, i.e. the litter size was equal to that in the peak phase when food was more abundant. The litter size for unfed females was 6.38 in the increase phase, 7.11 in the peak phase and 3.84 in the decrease phase. The litter size for supplementary winter-fed litters was 7.95 in the increase phase, 10.61 in the peak phase and 7.86 in the decrease phase. Thus, feeding had a positive effect on litter size, but it did not diminish the strong impact of the small rodent phase, supporting phase-dependent trade-offs in addition to food determining arctic fox reproduction.

  • 25. Moura, Nárgila G.
    et al.
    Lees, Alexander C.
    Aleixo, Alexandre
    Barlow, Jos
    Berenguer, Erika
    Ferreira, Joice
    Mac Nally, Ralph
    Thomson, James R.
    Gardner, Toby A.
    Stockholm University, Stockholm Environment Institute. International Institute for Sustainability, Rio De Janeiro, Brazil.
    Idiosyncratic responses of Amazonian birds to primary forest disturbance2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 3, p. 903-916Article in journal (Refereed)
    Abstract [en]

    As humans continue to alter tropical landscapes across the world, it is important to understand what environmental factors help determine the persistence of biodiversity in modified ecosystems. Studies on well-known taxonomic groups can offer critical insights as to the fate of biodiversity in these modified systems. Here we investigated species-specific responses of 44 forest-associated bird species with different behavioural traits to forest disturbance in 171 transects distributed across 31 landscapes in two regions of the eastern Brazilian Amazon. We investigated patterns of species occurrence in primary forests varyingly disturbed by selective-logging and fire and examined the relative importance of local, landscape and historical environmental variables in determining species occurrences. Within undisturbed and disturbed primary forest transects, we found that distance to forest edge and the biomass of large trees were the most important predictors driving the occurrence of individual species. However, we also found considerable variation in species responses to different environmental variables as well as inter-regional variation in the responses of the same species to the same environmental variables. We advocate the utility of using species-level analyses to complement community-wide responses in order to uncover highly variable and species-specific responses to environmental change that remain so poorly understood.

  • 26.
    Nascimento, Francisco J. A.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Diversity of larger consumers enhances interference competition effects on smaller competitors2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, no 2, p. 337-347Article in journal (Refereed)
    Abstract [en]

    Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0-3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods' incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

  • 27.
    Nielsen, Jens M.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Popp, Brian N.
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 178, no 3, p. 631-642Article in journal (Refereed)
    Abstract [en]

    Estimating trophic structures is a common approach used to retrieve information regarding energy pathways, predation, and competition in complex ecosystems. The application of amino acid (AA) compound-specific nitrogen (N) isotope analysis (CSIA) is a relatively new method used to estimate trophic position (TP) and feeding relationships in diverse organisms. Here, we conducted the first meta-analysis of delta N-15 AA values from measurements of 359 marine species covering four trophic levels, and compared TP estimates from AA-CSIA to literature values derived from food items, gut or stomach content analysis. We tested whether the AA trophic enrichment factor (TEF), or the N-15 enrichment among different individual AAs is constant across trophic levels and whether inclusion of delta N-15 values from multiple AAs improves TP estimation. For the TEF of glutamic acid relative to phenylalanine (Phe) we found an average value of 6.6 aEuro degrees across all taxa, which is significantly lower than the commonly applied 7.6 aEuro degrees. We found that organism feeding ecology influences TEF values of several trophic AAs relative to Phe, with significantly higher TEF values for herbivores compared to omnivores and carnivores, while TEF values were also significantly lower for animals excreting urea compared to ammonium. Based on the comparison of multiple model structures using the metadata of delta N-15 AA values we show that increasing the number of AAs in principle improves precision in TP estimation. This meta-analysis clarifies the advantages and limitations of using individual delta N-15 AA values as tools in trophic ecology and provides a guideline for the future application of AA-CSIA to food web studies.

  • 28.
    Norén, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Carmichael, Lindsey
    Fuglei, Eva
    Eide, Nina
    Hersteinsson, Pall
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Pulses of movement across the sea ice: population connectivity and temporal genetic structure in the arctic fox2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, no 4, p. 973-984Article in journal (Refereed)
    Abstract [en]

    Lemmings are involved in several important functions in the Arctic ecosystem. The Arctic fox (Vulpes lagopus) can be divided into two discrete ecotypes: “lemming foxes” and “coastal foxes”. Crashes in lemming abundance can result in pulses of “lemming fox” movement across the Arctic sea ice and immigration into coastal habitats in search for food. These pulses can influence the genetic structure of the receiving population. We have tested the impact of immigration on the genetic structure of the “coastal fox” population in Svalbard by recording microsatellite variation in seven loci for 162 Arctic foxes sampled during the summer and winter over a 5-year period. Genetic heterogeneity and temporal genetic shifts, as inferred by STRUCTURE simulations and deviations from Hardy–Weinberg proportions, respectively, were recorded. Maximum likelihood estimates of movement as well as STRUCTURE simulations suggested that both immigration and genetic mixture are higher in Svalbard than in the neighbouring “lemming fox” populations. The STRUCTURE simulations and AMOVA revealed there are differences in genetic composition of the population between summer and winter seasons, indicating that immigrants are not present in the reproductive portion of the Svalbard population. Based on these results, we conclude that Arctic fox population structure varies with time and is influenced by immigration from neighbouring populations. The lemming cycle is likely an important factor shaping Arctic fox movement across sea ice and the subsequent population genetic structure, but is also likely to influence local adaptation to the coastal habitat and the prevalence of diseases.

  • 29.
    Posledovich, Diana
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Toftegaard, Tenna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Latitudinal variation in diapause duration and post-winter development in two pierid butterflies in relation to phenological specialization2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, no 1, p. 181-190Article in journal (Refereed)
    Abstract [en]

    Diapause plays a central role in insect life cycles by allowing survival during adverse seasonal conditions as well as synchronizing life cycles with the period of mate and food availability. Seasonal timing is expected to be particularly important for species that are dependent on resources available during a short time window-so-called phenological specialists-and latitudinal clines in seasonality are expected to favor local adaptation in phenological timing. However, to what degree latitudinal variation in diapause dynamics and post-winter development due to such local adaptation is influenced by the degree of phenological specialization is not well known. We experimentally studied two pierid butterfly species and found that the phenological specialist Anthocharis cardamines had shorter diapause duration than the phenological generalist Pieris napi along a latitudinal gradient in Sweden. Moreover, diapause duration increased with latitude in P. napi but not in A. cardamines. Sensitivity of the two species to winter thermal conditions also differed; additional cold temperature during the winter period shortened diapause duration for P. napi pupae but not for A. cardamines pupae. In both species, post-winter pupal development was faster after longer periods of cold conditions, and more southern populations developed faster than northern populations. Post-winter development was also invariably faster at higher temperatures in both species. We argue that the observed differences in diapause dynamics between the two species might be explained by the difference in phenological specialization that influences the costs of breaking diapause too early in the season.

  • 30.
    Sagerman, Josefin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Enge, Swantje
    Pavia, Henrik
    Wikström, Sofia A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. AquaBiota Water Research, Sweden.
    Divergent ecological strategies determine different impacts on community production by two successful non-native seaweeds2014In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, no 3, p. 937-946Article in journal (Refereed)
    Abstract [en]

    The consequences of plant introductions into ecosystems are frequently reported from terrestrial environments, but little is known about the effects on ecosystem functioning caused by non-native primary producers in marine systems. In this study we explored the effects of the invasion by the two filamentous red algae Heterosiphonia japonica and Bonnemaisonia hamifera on the primary production of seaweed communities by using single and mixed cultures of non-native and native red algae. The experiments were conducted both in the presence and absence of herbivores. Biomass production of the invaded community increased more than four times in mixed cultures with H. japonica, while introduction by B. hamifera had no significant effect. The different impact on community production could be explained by differences in life history strategies between the invaders; H. japonica grew considerably faster than the native seaweeds which directly increased the community production, while B. hamifera showed a relatively slow growth rate and therefore had no effect. From previous studies it is known that B. hamifera produces a highly deterrent, but also costly, chemical defence. The assessment of survival and growth of a native generalist herbivore further corroborated that the biomass produced by B. hamifera constitutes a very low-quality food, whereas the performance of herbivores on a diet of H. japonica was comparable to that on native algal diets. In summary, this study demonstrates that successful invaders belonging to the same functional group (filamentous red algae) may have distinctly different impacts on productivity in the recipient community, depending on their specific life history traits.

  • 31.
    Schmalholz, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    Boulders increase resistance to clear-cut logging but not subsequent recolonization rates of boreal bryophytes2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 167, no 4, p. 1093-1101Article in journal (Refereed)
    Abstract [en]

    The extent to which a plant assemblage might recolonize a disturbed system is in general related to the availability of propagule sources and sites with appropriate conditions for establishment. Both these factors might be sensitive to aspects of spatial heterogeneity. Microtopographic variation may enhance initial resistance by reducing the impact of the disturbance and facilitating establishment of incoming propagules by providing shaded safe-sites. This study explores the influence of microtopographic heterogeneity (caused by variation in surface boulder cover) on the recolonization of closed-canopy forest floor bryophytes using a chronosequence of 75 spruce-dominated forests in south-central Sweden (2-163 years after clear-cutting). We found that high boulder cover did increase survival and subsequent persistence in young forests at both investigated scales (i.e. 1,000 and 100 m(2)), although this pattern became less evident on the smaller spatial scale. Species accumulation in boulder-poor subplots was not different when surrounded by boulder-rich compared with boulder-poor subplots suggesting short-distance recolonization from boulder-created refugia to be of little importance during recolonization. To conclude, it seems that boulders increase initial resistance to clear-cutting for this bryophyte guild, but that the subsequent recolonization process is more likely to depend on external propagule sources and factors affecting establishment such as the microclimate in the developing stand.

  • 32.
    Schäpers, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Specialist and generalist oviposition strategies in butterflies: maternal care or precocious young?2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 2, p. 335-343Article in journal (Refereed)
    Abstract [en]

    Herbivorous insects specialized on a narrow set of plants are believed to be better adapted to their specific hosts. This hypothesis is supported by observations of herbivorous insect species with a broader diet breadth which seemingly pay a cost through decreased oviposition accuracy. Despite many studies investigating female oviposition behavior, there is a lack of knowledge on how larvae cope behaviorally with their mothers' egg-laying strategies. We have examined a unique system of five nymphalid butterfly species with different host plant ranges that all feed on the same host plant. The study of this system allowed us to compare at the species level how oviposition preference is related to neonate larval responses in several disadvantageous situations. We found a general co-adaptation between female and larval abilities, where species with more discriminating females had larvae that were less able to deal with a suboptimal initial feeding site. Conversely, relatively indiscriminate females had more precocious larvae with better abilities to cope with suboptimal sites. Despite similarities between the tested species with similar host ranges, there were also striking differences. Generalist and specialist species can be found side by side in many clades, with each clade having a specific evolutionary history. Such clade-specific, phylogenetically determined preconditions apparently have affected how precisely a broad or narrow diet breadth can be realized.

  • 33.
    Tannerfeldt, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Exclusion by interference competition? The relationship between red and arctic foxes2002In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 132, no 2, p. 213-220Article in journal (Refereed)
    Abstract [en]

    The distribution of many predators may be limited by interactions with larger predator species. The arctic fox in mainland Europe is endangered, while the red fox is increasing its range in the north. It has been suggested that the southern distribution limit of the arctic fox is determined by interspecific competition with the red fox. This has been criticised, on the basis that the species co-exist on a regional scale. However, if the larger red fox is superior and interspecific competition important, the arctic fox should avoid close contact, especially during the breeding season. Consequently, the distribution of breeding dens for the two species would be segregated on a much smaller spatial and temporal scale, in areas where they are sympatric. We tested this hypothesis by analysing den use of reproducing arctic and red foxes over 9 years in Sweden. High quality dens were inhabited by reproducing arctic foxes more often when no red foxes bred in the vicinity. Furthermore, in two out of three cases when arctic foxes did reproduce near red foxes, juveniles were killed by red foxes. We also found that breeding arctic foxes occupied dens at higher altitudes than red foxes did. in a large-scale field experiment, red foxes were removed, but the results were not conclusive. However, we conclude that on the scale of individual territories, arctic foxes avoid areas with red foxes. Through interspecific interference competition, the red fox might thus be excluding the arctic fox from breeding in low altitude habitat, which is most important in years when food abundance is limited and competition is most fierce. With high altitude refuges being less suitable, even small-scale behavioural effects could scale up to significant effects at the population level.

  • 34.
    Tegelaar, Karolina
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Glinwood, Robert
    Pettersson, Jan
    Leimar, Olof
    Stockholm University, Faculty of Science, Department of Zoology. Wissenschaftskolleg zu Berlin, Germany.
    Transgenerational effects and the cost of ant tending in aphids2013In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 173, no 3, p. 779-790Article in journal (Refereed)
    Abstract [en]

    In mutualistic interactions, partners obtain a net benefit, but there may also be costs associated with the provision of benefits for a partner. The question of whether aphids suffer such costs when attended by ants has been raised in previous work. Transgenerational effects, where offspring phenotypes are adjusted based on maternal influences, could be important in the mutualistic interaction between aphids and ants, in particular because aphids have telescoping generations where two offspring generations can be present in a mature aphid. We investigated the immediate and transgenerational influence of ant tending on aphid life history and reproduction by observing the interaction between the facultative myrmecophile Aphis fabae and the ant Lasius niger over 13 aphid generations in the laboratory. We found that the effect of ant tending changes dynamically over successive aphid generations after the start of tending. Initially, total aphid colony weight, aphid adult weight and aphid embryo size decreased compared with untended aphids, consistent with a cost of ant association, but these differences disappeared within four generations of interaction. We conclude that transgenerational effects are important in the aphid-ant interactions and that the costs for aphids of being tended by ants can vary over generations.

  • 35. Torang, Per
    et al.
    Ehrlen, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Agren, Jon
    Linking environmental and demographic data to predict future population viability of a perennial herb2010In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 163, no 1, p. 99-109Article in journal (Refereed)
    Abstract [en]

    Recent advances in stochastic demography provide tools to examine the importance of random and periodic variation in vital rates for population dynamics. In this study, we explore with simulations the effect of disturbance regime on population dynamics and viability. We collected 7 years of demographic data in three populations of the perennial herb Primula farinosa, and used these data to examine how variation in vital rates affected population viability parameters (stochastic growth rate, lambda(S)), and how vital rates were related to weather conditions. Elasticity analysis indicated that the stochastic growth rate was very sensitive to changes in regeneration, quantified as the production, survival, and germination of seeds. In one of the study years, all seedlings and mature plants in the demography plots died. This extinction coincided with the driest summer during the study period. Simulations suggested that a future increase in the frequency of high-mortality years due to climate change would result in reduced population growth rate, and an increased importance of survival in the seed bank for population viability. The results illustrate how the limited demographic data typically available for many natural systems can be used in simulation models to assess how environmental change will affect population viability.

  • 36. Unnsteinsdottir, E. R.
    et al.
    Hersteinsson, P.
    Pálsson, S.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    The fall and rise of the Icelandic Arctic fox (Vulpes lagopus): a 50-year demographic study on a non-cyclic Arctic fox population2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 181, no 4, p. 1129-1138Article in journal (Refereed)
    Abstract [en]

    In territorial species, observed density dependence is often manifest in lowered reproductive output at high population density where individuals have fewer resources or are forced to inhabit low-quality territories. The Arctic fox (Vulpes lagopus) in Iceland is territorial throughout the year and feeds mostly on birds, since lemmings are absent from the country. Thus, the population does not exhibit short-term population cycles that are evident in most of the species' geographical range. The population has, however, gone through a major long-term fluctuation in population size. Because of the stability in hunting effort and reliable hunting records since 1958, the total number of adult foxes killed annually can be used as an index of population size (N (t) ). An index of carrying capacity (K) from population growth data for five separate time blocks during 1958-2007 revealed considerable variation in K and allowed a novel definition of population density in terms of K, or N (t) /K. Correlation analysis suggested that the reproductive rate was largely determined by the proportion of territorial foxes in the population. Variation in litter size and cub mortality was, on the other hand, related to climatic variation. Thus, Arctic foxes in Iceland engage in typical contest competition but can adapt their territory sizes in response to both temporal and spatial variation in carrying capacity, resulting in surprisingly little variation in litter size.

  • 37.
    Vanhoenacker, Didrik
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ågren, Jon
    Plant Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Villavägen 14, 752 36 Uppsala.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Spatial variability in seed predation in Primula farinosa:  local population legacy versus patch selection2009In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 160, no 1, p. 77-86Article in journal (Refereed)
    Abstract

    Spatio-temporal variation in seed predation may strongly influence both plant population dynamics and selection on plant traits. The intensity of seed predation may depend on a number of factors, but the relative importance of previous predator abundance (“local legacy”), spatial distribution of the host plant, environmental factors and plant characteristics has been explored in few species. We monitored seed predation in the perennial herb Primula farinosa, which is dimorphic for scape length, during 5 consecutive years, in a 10-km × 4-km area comprising 79 P. farinosa populations. A transplant experiment showed that the seed predator, the oligophagous tortricid moth Falseuncaria ruficiliana, was not dispersal limited at the spatial scale corresponding to typical distances between P. farinosa populations. Correlations between population characteristics and incidence and intensity of seed predation varied among years. The incidence of the seed predator was positively correlated with host population size and mean number of flowers, while intensity of seed predation in occupied patches was positively related to the frequency of the long-scaped morph in 2 years and negatively related to host population size in 1 year. In both scape morphs, predation tended to increase with increasing frequency of the long morph. There was no evidence of a local legacy; incidence and intensity of seed predation were not related to the abundance of the seed predator in the population in the previous year. Taken together, the results indicate that among-population variation in seed predation intensity is determined largely by patch selection and that the seed predator's preference for tall and many-flowered inflorescences may not only affect selection on plant traits within host plant populations, but also the overall intensity of seed predation.

  • 38.
    Vanhoenacker, Didrik
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ågren, Jon
    Toräng, Per
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Spatial variability in seed predation in Primula farinosa: local population legacy vs. patch selection2009In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 160, p. 77-86Article in journal (Refereed)
  • 39.
    Wikstrom, Sofia A.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hillebrand, Helmut
    Invasion by mobile aquatic consumers enhances secondary production and increases top-down control of lower trophic levels2012In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 168, no 1, p. 175-186Article in journal (Refereed)
    Abstract [en]

    Increased biological diversity due to invasion by non-indigenous species (NIS) is a global phenomenon with potential effects on trophic interactions and ecosystem processes in the invaded habitat. We assessed the effects of resource availability and invasion of three non-indigenous invertebrate grazers (two crustaceans and a snail) on secondary production, relative dominance of NIS grazers and resource depletion in experimental freshwater mesocosms. The relative dominance of NIS grazers increased with increasing initial resource availability, although the effect was largest for one of the three species. The effect was due to the fact that all the included non-indigenous grazers were able to expand their populations quickly in response to resource addition. For the most dominating species, the increased grazer diversity due to invasion in turn resulted in higher production of grazer biomass and a more efficient depletion of the periphyton resource. The effect was largest at high initial resource availability, where NIS dominance was most pronounced. Our results show that an invasion-induced increase in species diversity can increase resource depletion and consequently production, but that the effect depends on identity of the introduced species. The results also suggest that properties of the recipient system, such as resource availability, can modulate ecosystem effects of NIS by affecting invader success and dominance.

  • 40.
    Wikström, Sofia A.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Pavia, Henrik
    Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds2004In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 138, no 2, p. 223-230Article in journal (Refereed)
    Abstract [en]

    It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus.

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