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  • 51. 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.

  • 52.
    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.

  • 53.
    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.

  • 54.
    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 study.2010In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 88, p. 1077-1085Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to identify the use of marine versus terrestrial food items by terrestrial arthropod predators on Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g., chironomids). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis in a two source mixing model. The results suggest that spiders are the terrestrial predators mainly utilizing nutrients and energy of marine origin on Baltic Sea shores, whereas insect predators such as beetles and heteropterans mainly utilize nutrients and energy derived from terrestrial sources, possibly owing to differences in hunting behaviour. That spiders are the predators which 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.

  • 55.
    Mellbrand, Kajsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lavery, Paul
    Edith Cowan University, Perth, Australia.
    Hyndes, Glenn
    Edith Cowan University, Perth, Australia.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Linking land and sea: Arthropod vectors for marine subsidiesManuscript (Other academic)
    Abstract [en]

    Several studies have shown nutrients and energy derived from marine plants and algae to subsidize shore ecosystems, increasing productivity and affecting food web dynamics and structure. In this study we have examined how the inland reach of such inflow effects depends on vectors carrying the marine inflow inland and on landscape structure. We examined the roles of arthropod vectors in carrying marine derived carbon inland in two very different shore ecosystems: shore meadows in Sweden with marine inflows of algae and emerging chironomid midges, and sandy beaches and shore dunes in Western Australia with marine inflows of algae and seagrass. In both systems we found a larger inland reach of the marine subsidy than could be accounted for by deposited material on shores alone, and that dipterans and spiders functioned as vectors for the inflow. Our results indicate that marine inflows are important for near-shore terrestrial ecosystems well above the water’s edge, and that this effect is largely due to arthropod vectors (mainly dipterans and spiders) in both low productivity sandy beach ecosystems at the Indian Ocean coast of Australia, and more productive shore meadows on the Baltic Sea coast of Sweden.

  • 56.
    Mellbrand, Kajsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Östman, Örjan
    Uppsala Universitet.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Effect of subsidized predators on coastal food webs in the Baltic Sea areaManuscript (Other academic)
    Abstract [en]

    The aim of this study was to examine top-down effects of spiders in subsidized coastal food webs. This was done through a large-scale removal experiment, where spiders were removed from small islands using pitfall traps. Arthropods were sampled using a vacuum sampling device at three occasions each summer 2004-2007. The uniqueness of the study lies in its scale: these types of experiments are typically made using small (one or a few m2) enclosures, in which the food web is manipulated, but this study use islands (20-2000 m2) as natural enclosures. Though the use of islands allows a lesser degree of control of the study system than enclosures, large-scale studies include a large realism by allowing for more natural dynamics. The results suggest that the high spider densities on shores have negative effects on insect predator densities, probably through a combination of competition and intraguild predation. No treatment effects were found on herbivore or detritivore densities, and we suggest that the negative effect of spiders on herbivore and detritivore densities on control islands may be at least partly balanced by an increased effect of insect predators utilizing mainly terrestrial prey on treatment (removal) islands. Our study does not exclude the possibility of top-down effects in the system from spiders on herbivores, but in case they do exist, they are likely behaviour mediated rather than a result of direct spider predation.

  • 57.
    Mellbrand, Kajsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Östman, Örjan
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of subsidized spiders on coastal food webs in the Baltic Sea area2010In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 11, no 5, p. 450-458Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to examine top-down effects of cursorial spiders in subsidized coastal food webs. Top-down effects were examined by selectively removing cursorial spiders, mainly wolf spiders, from small islands (26-1834 m(2)) during 2004-2007. The removal success varied among islands and years, and spider densities were reduced by 30-65%. To examine treatment effects, arthropods were sampled using a vacuum sampling device at three occasions each summer. The densities of other arthropod predators, especially web spiders and carabids, were higher on islands where cursorial spiders had been removed compared to control islands. This treatment effect probably occurred through a combination of competitive release and reduced intraguild predation from cursorial spiders. No treatment effects were found on herbivore or detritivore densities and plant biomass. This lack of effect may either be because spiders indeed have fairly weak effects on herbivore and detritivore densities on Baltic shorelines or that the removal success of spiders was insufficient for observing such effects. Treatment effects may also be weak because negative effects exerted by spiders on herbivore and detritivore populations were balanced by increased predation by insect predators.

  • 58.
    Nylin, Sören
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Agosta, Salvatore
    Bensch, Staffan
    Boeger, Walter A.
    P. Braga, Mariana
    Stockholm University, Faculty of Science, Department of Zoology.
    Brooks, Daniel R.
    Forister, Matthew L.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hoberg, Eric P.
    Nyman, Tommi
    Schäpers, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Stigall, Alycia L.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology.
    Österling, Martin
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Embracing Colonizations: A New Paradigm for Species Association Dynamics2018In: Trends in Ecology & Evolution, ISSN 0169-5347, E-ISSN 1872-8383, Vol. 33, no 1, p. 4-14Article, review/survey (Refereed)
    Abstract [en]

    Parasitehost and insectplant research have divergent traditions despite the fact that most phytophagous insects live parasitically on their host plants. In parasitology it is a traditional assumption that parasites are typically highly specialized; cospeciation between parasites and hosts is a frequently expressed default expectation. Insectplant theory has been more concerned with host shifts than with cospeciation, and more with hierarchies among hosts than with extreme specialization. We suggest that the divergent assumptions in the respective fields have hidden a fundamental similarity with an important role for potential as well as actual hosts, and hence for host colonizations via ecological fitting. A common research program is proposed which better prepares us for the challenges from introduced species and global change.

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  • 59. Ohgushi, Takayuki
    et al.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Toward a spatial perspective of plant-based indirect interaction webs: Scaling up trait-mediated indirect interactions2015In: Perspectives in plant ecology, evolution and systematics, ISSN 1433-8319, E-ISSN 1618-0437, Vol. 17, no 6, p. 500-509Article, review/survey (Refereed)
    Abstract [en]

    Phenotypic plasticity of plants following herbivory is ubiquitous in a wide range of terrestrial systems. Importantly, it can largely determine community properties of arthropods associated with induced plants. Effects of herbivore-induced plant phenotypes on species diversity, abundance, and community composition of higher trophic levels would depend on spatial variations in the altered phenotypes. To understand how arthropod communities are organized by plant phenotypic plasticity, we should focus on neighbor effects, as well as how these effects scale up to influence community structure and biodiversity within and between plant populations. Here, we encourage ecologists to meet the challenge of this novel issue by addressing the scaling up of trait-mediated indirect effects of the prevalent herbivory via plant phenotypic plasticity in a spatial context. We first examine how herbivore-induced phenotypic plasticity in terrestrial plants affects arthropod communities. Specifically, we review how different types of induced plant traits alter species diversity, overall abundance, and community composition of associated arthropods. Second, we provide a conceptual framework addressing how the combinations of induced and constitutive (i.e., non-induced) traits in a plant population result in resource heterogeneity available to herbivores in a more explicit spatial context. In particular, we pay special attention to the contrasting responses of specialist and generalist herbivores to induced plant phenotypes. Last, we highlight how induced resource heterogeneity affects distribution and diversity of arthropods through movements onto and away from plant individuals in a plant patch.

  • 60. Oksanen, Lauri
    et al.
    Oksanen, Tarja
    Dahlgren, Johan
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Ekerholm, Per
    Lindgren, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Olofsson, Johan
    Islands as tests of the green world hypothesis.2010In: Trophic Cascades – Predators, Prey, and the changing dynamics of Nature, Washihgton DC: Island Press , 2010, p. 163-178Chapter in book (Other academic)
  • 61.
    Samnegård, Ulrika
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Alins, Georgina
    Boreux, Virginie
    Bosch, Jordi
    García, Daniel
    Happe, Anne-Kathrin
    Klein, Alexandra-Maria
    Miñarro, Marcos
    Mody, Karsten
    Porcel, Mario
    Rodrigo, Anselm
    Roquer-Beni, Laura
    Tasin, Marco
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Management trade-offs on ecosystem services in apple orchards across Europe: Direct and indirect effects of organic production2019In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 56, no 4, p. 802-811Article in journal (Refereed)
    Abstract [en]

    Apple is considered the most important fruit crop in temperate areas and profitable production depends on multiple ecosystem services, including the reduction of pest damage and the provision of sufficient pollination levels. Management approaches present an inherent trade-off as each affects species differently. We quantified the direct and indirect effects of management (organic vs. integrated pest management, IPM) on species richness, ecosystem services, and fruit production in 85 apple orchards in three European countries. We also quantified how habit composition influenced these effects at three spatial scales: within orchards, adjacent to orchards, and in the surrounding landscape. Organic management resulted in 48% lower yield than IPM, and also that the variation between orchards was large with some organic orchards having a higher yield than the average yield of IPM orchards. The lower yield in organic orchards resulted directly from management practices, and from higher pest damage in organic orchards. These negative yield effects were partly offset by indirect positive effects from more natural enemies and higher flower visitation rates in organic orchards. Two factors other than management affected species richness and ecosystem services. Higher cover of flowering plants within and adjacent to the apple trees increased flower visitation rates by pollinating insects and a higher cover of apple orchards in the landscape decreased species richness of beneficial arthropods. The species richness of beneficial arthropods in orchards was uncorrelated with fruit production, suggesting that diversity can be increased without large yield loss. At the same time, organic orchards had 38% higher species richness than IPM orchards, an effect that is likely due to differences in pest management.Synthesis and applications. Our results indicate that organic management is more efficient than integrated pest management in developing environmentally friendly apple orchards with higher species richness. We also demonstrate that there is no inherent trade-off between species richness and yield. Development of more environmentally friendly means for pest control, which do not negatively affect pollination services, needs to be a priority for sustainable apple production. Our results indicate that organic management is more efficient than integrated pest management in developing environmentally friendly apple orchards with higher species richness. We also demonstrate that there is no inherent trade-off between species richness and yield. Development of more environmentally friendly means for pest control, which do not negatively affect pollination services, needs to be a priority for sustainable apple production. Editor's Choice

  • 62.
    Samnegård, Ulrika
    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.
    Eardley, Connal
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Turnover in bee species composition and functional trait distributions between seasons in a tropical agricultural landscape2015In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 211, p. 185-194Article in journal (Refereed)
    Abstract [en]

    A comprehensive understanding of how spatial variation across landscapes regulates local abundances and species richness also needs to consider possible temporal changes in such relationships. In many tropical areas, the contrast between dry and rainy season is pronounced and the types and distributions of the main floral resources differ (herbs vs trees). This shift in resources could result in different pollinator abundances, species richness and trait compositions between seasons, as well as in how these components are spatially distributed. We compared the bee species composition between dry and rainy season in an agricultural mosaic landscape in southwestern Ethiopia, and analyzed it in relation to forest cover. We sampled bees for 67 days in the dry season and 86 days in the rainy season with pan and vane traps in 28 homegardens covering a gradient from low to high tree cover in the surrounding area. We found a clear shift in species composition between seasons, with more small bee species and more below-ground nesting bees in the rainy season compared to the dry season. The distribution of height at which the bees were foraging shifted between seasons with a higher proportion of the bees foraging at tree level in the dry season. Bee abundance and richness were generally positively affected by higher forest cover surrounding the homegardens, but there were no clear interaction effects between seasons, in contrast to our hypothesis. The clear turnover in species composition between seasons and the positive effect of forest cover show that mechanisms acting both at spatial and temporal scales are important in regulating local bee communities.

  • 63.
    Samnegård, Ulrika
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Lund University, Sweden.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lemessa, Debissa
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    A heterogeneous landscape does not guarantee high crop pollination2016In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 283, no 1838, article id 20161472Article in journal (Refereed)
    Abstract [en]

    The expansion of pollinator-dependent crops, especially in the developing world, together with reports of worldwide pollinator declines, raises concern of possible yield gaps. Farmers directly reliant on pollination services for food supply often live in regions where our knowledge of pollination services is poor. In a manipulative experiment replicated at 23 sites across an Ethiopian agricultural landscape, we found poor pollination services and severe pollen limitation in a common oil crop. With supplementary pollination, the yield increased on average by 91%. Despite the heterogeneous agricultural matrix, we found a low bee abundance, which may explain poor pollination services. The variation in pollen limitation was unrelated to surrounding forest cover, local bee richness and bee abundance. While practices that commonly increase pollinators (restricted pesticide use, flower strips) are an integral part of the landscape, these elements are apparently insufficient. Management to increase pollination services is therefore in need of urgent investigation.

  • 64.
    Samnegård, Ulrika
    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.
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dominance of the semi-wild honeybee as coffee pollinator across a gradient of shade-tree structure in Ethiopia2014In: Journal of Tropical Ecology, ISSN 0266-4674, E-ISSN 1469-7831, Vol. 30, p. 401-408Article in journal (Refereed)
    Abstract [en]

    Mass-flowering plant species are often pollinated by social bees that are able to use the abundant resource by recruiting workers from their colonies. In this study we surveyed pollinators on the mass-flowering perennial crop coffee (Coffea arabica) in its native range in Ethiopia. Previous studies in areas where coffee is introduced often find the social honeybee, Apis mellifera, to be the dominant pollinator. In those areas, the bee-species composition visiting coffee varies with a higher bee diversity closer to forest or in less modified habitats. We surveyed pollinators of coffee under different shade-tree structures, by collecting hoverflies and bees landing on coffee flowers in 19 sites in south-west Ethiopia. We found the native honeybee (A. mellifera) to be the dominant visitor of coffee flowers in all sites. Honeybee abundance was not affected by the local shade-tree structure, but was positively affected by the amount of coffee flower resources. Other pollinators were positively affected by complex shade-tree structures. To conclude, the honeybee is clearly the dominant pollinator of coffee in Ethiopia along the whole shade-tree structure gradient. Its high abundance could be a consequence of the provision of traditional bee hives in the landscape, which are colonized by wild swarming honeybees.

  • 65.
    Samnegård, Ulrika
    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.
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Local and Regional Variation in Local Frequency of Multiple Coffee Pests Across a Mosaic Landscape in Coffea arabica's Native Range2014In: Biotropica, ISSN 0006-3606, E-ISSN 1744-7429, Vol. 46, no 3, p. 276-284Article in journal (Refereed)
    Abstract [en]

    Shaded coffee has been highlighted for its potential to conserve biodiversity, and thus perhaps also a diversity of natural enemies that could control pest organisms. In southwestern Ethiopia, coffee is grown in shade both in contiguous forests and in forest patches with native trees surrounded by open fields. We hypothesized that coffee grown in contiguous forests, which is the natural habitat for coffee (Coffea arabica) and its interacting organisms, would have less pest damage due to high protection by natural enemies. We surveyed pests on coffee plants in plots within contiguous forests (10 sites) and in forest patches (21 sites). In general, the variation in number of damaged or attacked leaves by individual insect or fungal pests was larger between plants than between plots, which suggests that very local conditions or processes are important. The spatial signals were generally weak. Coffee rust and coffee blotch miner tended to have lower infestation rates in accordance with our hypothesis, while fruit flies in ripe berries were more abundant in forest patches closer to contiguous forest. Based on interviews, olive baboons showed a clear dependency on contiguous forest habitat and were regarded as a problem only in contiguous forests and forest patches close to contiguous forests. In conclusion, we found no support for a generally stronger top-down control on coffee pests in sites within, or with connectivity to, contiguous moist afromontane forests in the native range of coffee.

  • 66. Samnegård, Ulrika
    et al.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Smith, Henrik G.
    Pollination treatment affects fruit set and modifies marketable and storable fruit quality of commercial apples2019In: Royal Society Open Science, E-ISSN 2054-5703, Vol. 6, no 12, article id 190326Article in journal (Refereed)
    Abstract [en]

    Insect-mediated pollination increases yields of many crop species and some evidence suggests that it also influences crop quality. However, the mechanistic linkages between insect-mediated pollination and crop quality are poorly known. In this study, we explored how different pollination treatments affected fruit set, dry matter content (DMC), mineral content and storability of apples. Apple flowers supplementary pollinated with compatible pollen resulted in higher initial fruit set rates, higher fruit DMC and a tendency for lower fruit potassium (K) : calcium (Ca) ratio than flowers that received natural or no pollination. These variables are related to desirable quality aspects, because higher DMC is connected to higher consumer preference and lower K : Ca ratio is related to lower incidence of postharvest disorders during storage. Using structural equation modelling, we showed an indirect effect of pollination treatment on storability, however mediated by complex interactions between fruit set, fruit weight and K : Ca ratio. The concentrations of several elements in apples (K, zinc, magnesium) were affected by the interaction between pollination treatment and apple weight, indicating that pollination affects element allocation into fruits. In conclusion, our study shows that pollination and the availability of compatible pollen needs to be considered in the management of orchard systems, not only to increase fruit set, but also to increase the quality and potentially the storability of apples.

  • 67.
    Samnegård, Ulrika
    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.
    Lemessa, Debissa
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    A heterogeneous landscape does not guarantee high crop pollinationManuscript (preprint) (Other academic)
    Abstract [en]

    The expansion of pollinator-dependent crops, especially in the developing world, together with reports of world-wide pollinator declines, raises concern of possible yield gaps. Farmers directly reliant on pollination services for food supply often live in regions where our knowledge of pollination services is poor. In a manipulative experiment replicated at 23 sites across an Ethiopian agricultural landscape, we found poor pollination services and severe pollen limitation in a common oil crop. With supplementary pollination, the yield increased on average by 91%. Despite the heterogeneous agricultural matrix, we found a low bee abundance, which may explain poor pollination services. The variation in pollen limitation was unrelated to surrounding forest cover, local bee richness and bee abundance. While practices that commonly increase pollinators (e.g. organic farming, flower strips) are an integral part of the landscape, these elements are apparently insufficient. Management to increase pollination services is therefore in need of urgent investigation.

  • 68. Sirén, Anders H.
    et al.
    Cardenas, Juan-Camilo
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Parvinen, Kalle
    Distance Friction and the Cost of Hunting in Tropical Forest2013In: Land Economics, ISSN 0023-7639, E-ISSN 1543-8325, Vol. 89, no 3, p. 558-574Article in journal (Refereed)
    Abstract [en]

    Empirical studies of tropical forest hunting have shown the existence of marked spatial gradients of hunting effort, game harvest, and animal abundance, as hunters mostly hunt near villages, roads, and rivers. The mechanisms underlying these patterns have, however, hitherto been poorly known. This article presents a spatial bioeconomic model based on the concept of distance friction, that is, an increasing marginal cost of distance. The model is validated by comparison with an economic field experiment with Amazonian hunters and with previous empirical data on hunting.

  • 69. Stenberg, J. A.
    et al.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Host species critical for offspring fitness and sex ratio for an oligophagous parasitoid: implications for host coexistence2010In: Bulletin of entomological research, ISSN 0007-4853, E-ISSN 1475-2670, Vol. 100, no 6, p. 735-740Article in journal (Refereed)
    Abstract [en]

    In theory, inferior apparent competitors sharing a natural enemy with superior apparent competitors should be excluded in the absence of stabilising factors. Nevertheless, plentiful examples of coexisting apparent competitors exist. In this paper, we show that parasitoid resource competition within hosts affects both parasitoid sex ratio and female body size, with implication for population growth and apparent competition between the two closely related hosts experiencing a strong asymmetry in their interaction. While the superior competitor delivers parasitoids with higher fitness to the shared parasitoid pool, the inferior competitor delivers a higher proportion of female parasitoids. Hence, the inferior host experience an inflow of fit parasitoids from the superior competitor, which should increase the risk of exclusion, but also an outflow of parasitoid females, which should reduce the risk of exclusion and increase stability. We conclude that differential outcomes of parasitoid resource competition in different host species may have profound effects on shared parasitoid populations and should be included in future studies of apparent competition between hosts.

  • 70. Stenberg, Johan
    et al.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Ericson, Lars
    Herbivore-induced “rent-rise” in the host plant may drive a diet breadth enlargement in the tenant.2008In: Ecology, Vol. 89, p. 126-133Article in journal (Refereed)
    Abstract [en]

    Inter- and intra-species variations in host-plant traits are presumably involved in many host-shifts by insect herbivores, and elucidating the mechanisms involved in such shifts has been a crucial goal in insect-plant research for several decades. Here we propose that herbivore-induced evolutionary increases in host plant resistance may cause oligophagous insect herbivores to shift to other sympatric plants as currently preferred host plants become increasingly unpalatable. We tested this hypothesis in a system based on the perennial herb Filipendula ulmaria (Rosaceae), whose herbivory defense has become gradually stronger due to prolonged selection by Galerucella tenella (Coleoptera: Chrysomelidae) herbivory in a boreal archipelago. We show that Galerucella gradually increases its’ use of the alternative host plant Rubus arcticus (Rosaceae) in parallel to gradually increased resistance in Filipendula. Our results imply that by driving the evolutionary increase in Filipendula resistance, Galerucella is also gradually making the original host species more unpalatable and thereby driving its own host-breadth enlargement. We argue that such self-inflicted ‘rent rises’ may be an important mechanism behind host-plant shifts, which in turn are believed to have preceded speciation of many phytophagous insects.

  • 71.
    Strandmark, Alma
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Aggemyr, Elsa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Department of Physical Geography.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Drivers behind local and regional arhropod diversity in naturally fragmented landscapesManuscript (preprint) (Other academic)
  • 72.
    Strandmark, Alma
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bring, Arvid
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kautsky, Hans
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kolb, Gundula
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    de la Torre-Castro, Maricela
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Climate change effects on the Baltic Sea borderland between land and sea2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, p. s28-S38Article in journal (Refereed)
    Abstract [en]

    Coastal habitats are situated on the border between land and sea, and ecosystem structure and functioning is influenced by both marine and terrestrial processes. Despite this, most scientific studies and monitoring are conducted either with a terrestrial or an aquatic focus. To address issues concerning climate change impacts in coastal areas, a cross-ecosystem approach is necessary. Since habitats along the Baltic coastlines vary in hydrology, natural geography, and ecology, climate change projections for Baltic shore ecosystems are bound to be highly speculative. Societal responses to climate change in the Baltic coastal ecosystems should have an ecosystem approach and match the biophysical realities of the Baltic Sea area. Knowledge about ecosystem processes and their responses to a changing climate should be integrated within the decision process, both locally and nationally, in order to increase the awareness of, and to prepare for climate change impacts in coastal areas of the Baltic Sea.

  • 73.
    Strandmark, Alma
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Verschut, Vasiliki
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Esparza Salas, Rodrigo
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Seasonally varying marine influences on the coastal ecosystem detected through molecular gut content analysis but not through stable isotope analyisManuscript (preprint) (Other academic)
  • 74.
    Strandmark, Alma
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Vicente, Raul
    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 structure of marine deposits affectes arthropod communities in southern Baltic shore ecosystemsManuscript (preprint) (Other academic)
  • 75.
    Underwood, Nora
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Florida State University, USA.
    Hambäck, Peter A.
    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, USA.
    Pollinators, Herbivores, and Plant Neighborhood Effects2020In: The Quarterly review of biology, ISSN 0033-5770, E-ISSN 1539-7718, Vol. 95, no 1, p. 37-57Article, review/survey (Refereed)
    Abstract [en]

    Pollinator and herbivore interactions with individual plants can be strongly influenced by the densities and frequencies of other plants in local neighborhoods. The importance of these neighborhood effects is not yet clear, due in part to a profound disconnect between studies of pollinator and herbivore neighborhood effects. Considering these effects jointly is critical for understanding the role of plant spatial heterogeneity because plant fitness is often affected by pollinators, herbivores, and their interactions. We bring together these two types of neighborhood effects, describing the pathways through which these insects mediate neighborhood effects, and comparing their implementation in mathematical models. We find that ideas from each field can improve work in the other. For example, pollinator theory should broaden consideration of how pollinator traits influence responses to plant neighborhoods, while herbivore theory should consider adaptive foraging and connect herbivore neighborhood effects to plant fitness. We discuss approaches to theory that integrate pollinator and herbivore effects, particularly considering the nested spatial and temporal scales of these insects' responses to neighborhoods. Ultimately, models will need to combine neighborhood effects from the diverse species that affect plants with direct plant interactions to determine the importance of spatial structure for plant performance and evolution.

  • 76. Underwood, Nora
    et al.
    Inouye, Brian D.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    A CONCEPTUAL FRAMEWORK FOR ASSOCIATIONAL EFFECTS: WHEN DO NEIGHBORS MATTER AND HOW WOULD WE KNOW?2014In: The Quarterly review of biology, ISSN 0033-5770, E-ISSN 1539-7718, Vol. 89, no 1, p. 1-19Article, review/survey (Refereed)
    Abstract [en]

    Interactions between individual consumer and resource organisms can be modified by neighbors, e.g., when herbivory depends on the identity or diversity of neighboring plants. Effects of neighbors on consumer-resource interactions (associational effects) occur in many systems, including plant-herbivore interactions, predator-prey interactions (mimicry), and plant-pollinator interactions. Unfortunately, we know little about how ecologically or evolutionarily important these effects are because we lack appropriate models and data to determine how neighbor effects on individuals contribute to net interactions at population and community levels. Here we supply a general definition of associational effects, review relevant theory, and suggest strategies for future theoretical and empirical work. We find that mathematical models from a variety of fields suggest that individual-level associational effects will influence population and community dynamics when associational effects create local frequency dependence. However, there is little data on how local frequency dependence in associational effects is generated, or on the form or spatial scale of that frequency dependence. Similarly, existing theory lacks consideration of nonlinear and spatially explicit frequency dependence. We outline an experimental approach for producing data that can be related to models to advance our understanding of how associational effects contribute to population and community processes.

  • 77.
    Verschut, Thomas A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Becher, Paul G.
    Anderson, Peter
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Disentangling associational effects: both resource density and resource frequency affect search behaviour in complex environments2016In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 30, no 11, p. 1826-1833Article in journal (Refereed)
    Abstract [en]

    Neighbouring resources have been found to either decrease or increase the likelihood that a consumer organism attacks a focal resource. These phenomena are referred to as associational resistance (AR) and associational susceptibility (AS), respectively. While associational effects have been observed in various field studies, little is known on how resource heterogeneity can cause associational effects. We used a laboratory approach in which we studied the effects of resource density and frequency in the search behaviour of Drosophila melanogaster as a model organism for olfactory-guided behaviour in insects. We first determined whether D.melanogaster could discriminate between odour sources that differ quantitatively. Secondly, we determined what the effect of resource density and frequency was on the search behaviour of D.melanogaster by combining these resources into various patch arrangements. Finally, we used the outcome of our experiments to disentangle the role of resource density and frequency in associational effects. We found that D.melanogaster has the ability to discriminate between quantitatively different resources, but that the attraction to resource density is constrained by an optimum after which attraction decreases. Furthermore, in heterogeneous environments, flies showed a strong preference towards the more apparent resource, leading to AS for the more apparent resources and AR for the less apparent resource. The strength of this interaction increased with a decreasing frequency of the more apparent resource. These results imply that D.melanogaster mainly selects patches at the level of individual resources. Consequently, when a patch contains qualitatively different resources, the more apparent resource will attract a higher number of flies than the less apparent resource irrespective of the frequency of the apparent resource within the patch. Our study shows that associational effects can be explained by determining the hierarchical level at which a consumer selects its resources. When a consumer selects resources at the individual level rather than at the patch level, our results can be used to explain the population dynamics of host plants and their associated consumers under field conditions.

  • 78.
    Verschut, Thomas A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Blažytė-Čereškienė, Laima
    Apšegaitė, Violeta
    Mozūraitis, Raimondas
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Institute of Ecology, Nature Research Centre, Lithuania.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Natal origin affects host preference and larval performance relationships in a tritrophic system2017In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 7, p. 2079-2090Article in journal (Refereed)
    Abstract [en]

    Many insects face the challenge to select oviposition sites in heterogeneous environments where biotic and abiotic factors can change over time. One way to deal with this complexity is to use sensory experiences made during developmental stages to locate similar habitats or hosts in which larval development can be maximized. While various studies have investigated oviposition preference and larval performance relationships in insects, they have largely overlooked that sensory experiences made during the larval stage can affect such relationships. We addressed this issue by determining the role of natal experience on oviposition preference and larval performance relationships in a tritrophic system consisting of Galerucella sagittariae, feeding on the two host plants Potentilla palustris and Lysimachia thyrsiflora, and its larval parasitoid Asecodes lucens. We firstly determined whether differences in host-derived olfactory information could lead to divergent host selection, and secondly, whether host preference could result in higher larval performance based on the natal origin of the insects. Our results showed that the natal origin and the quality of the current host are both important aspects in oviposition preference and larval performance relationships. While we found a positive relationship between preference and performance of natal Lysimachia beetles, natal Potentilla larvae showed no such relationship and developed better on L. thyrsiflora. Additionally, the host selection by the parasitoid was mainly affected by the natal origin, while its performance was higher on Lysimachia larvae. With this study we showed that the relationship between oviposition preference and larval performance depends on the interplay between the natal origin of the female and the quality of the current host. However, without incorporating the full tritrophic context of these interactions, their implication in insect fitness and potential adaptation cannot be fully understood.

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  • 79.
    Verschut, Thomas A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology.
    Anderson, Peter
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sensory mutations in Drosophila melanogaster influence associational effects between resources during oviposition2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 9352Article in journal (Refereed)
    Abstract [en]

    Neighboring resources can affect insect oviposition behavior when the complexity of sensory information obscures information about host resource availability in heterogeneous resource patches. These effects are referred to as associational effects and are hypothesized to occur through constraints in the sensory processing of the insect during host search, resulting into suboptimal resource use. Because the possibilities to study these constraints on naturally occurring animals are limited, we instead used sensory mutants of Drosophila melanogaster to determine the importance of sensory information in the occurrence of associational effects. We found that oviposition was mainly governed by non-volatile chemical cues and less by volatile cues. Moreover, the loss of gustatory sensilla resulted in random resource selection and eliminated associational effects. In conclusion, our study shows that associational effects do not necessarily depend on constraints in the sensory evaluation of resource quality, but may instead be a direct consequence of distinctive selection behavior between different resources at small scales.

  • 80.
    Verschut, Thomas A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Department of Zoology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Scaling the interactive effects of attractive and repellent odours for insect search behaviour2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 15309Article in journal (Refereed)
    Abstract [en]

    Insects searching for resources are exposed to a complexity of mixed odours, often involving both attractant and repellent substances. Understanding how insects respond to this complexity of cues is crucial for understanding consumer-resource interactions, but also to develop novel tools to control harmful pests. To advance our understanding of insect responses to combinations of attractive and repellent odours, we formulated three qualitative hypotheses; the response-ratio hypothesis, the repellent-threshold hypothesis and the odour-modulation hypothesis. The hypotheses were tested by exposing Drosophila melanogaster in a wind tunnel to combinations of vinegar as attractant and four known repellents; benzaldehyde, 1-octen-3-ol, geosmin and phenol. The responses to benzaldehyde, 1-octen-3-ol and geosmin provided support for the response-ratio hypothesis, which assumes that the behavioural response depends on the ratio between attractants and repellents. The response to phenol, rather supported the repellent-threshold hypothesis, where aversion only occurs above a threshold concentration of the repellent due to overshadowing of the attractant. We hypothesize that the different responses may be connected to the localization of receptors, as receptors detecting phenol are located on the maxillary palps whereas receptors detecting the other odorants are located on the antennae.

  • 81.
    Verschut, Thomas A.
    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.
    A random survival forest illustrates the importance of natural enemies compared to host plant quality on leaf beetle survival rates2018In: BMC Ecology, ISSN 1472-6785, E-ISSN 1472-6785, Vol. 18, article id 33Article in journal (Refereed)
    Abstract [en]

    Background: Wetlands are habitats where variation in soil moisture content and associated environmental conditions can strongly affect the survival of herbivorous insects by changing host plant quality and natural enemy densities. In this study, we combined natural enemy exclusion experiments with random survival forest analyses to study the importance of local variation in host plant quality and predation by natural enemies on the egg and larval survival of the leaf beetle Galerucella sagittariae along a soil moisture gradient.

    Results: Our results showed that the exclusion of natural enemies substantially increased the survival probability of G. sagittariae eggs and larvae. Interestingly, the egg survival probability decreased with soil moisture content, while the larval survival probability instead increased with soil moisture content. For both the egg and larval survival, we found that host plant height, the number of eggs or larvae, and vegetation height explained more of the variation than the soil moisture gradient by itself. Moreover, host plant quality related variables, such as leaf nitrogen, carbon and phosphorus content did not influence the survival of G. sagittariae eggs and larvae.

    Conclusion: Our results suggest that the soil moisture content is not an overarching factor that determines the interplay between factors related to host plant quality and factors relating to natural enemies on the survival of G. sagittariae in different microhabitats. Moreover, the natural enemy exclusion experiments and the random survival forest analysis suggest that natural enemies have a stronger indirect impact on the survival of G. sagittariae offspring than host plant quality.

  • 82.
    Verschut, Thomas A.
    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.
    Anderson, Peter
    Mating affects resource selection and modulates associational effects between neighbouring resourcesIn: Oikos, ISSN 0030-1299, E-ISSN 1600-0706Article in journal (Refereed)
  • 83.
    Verschut, Thomas A.
    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.
    Anderson, Peter
    Mating affects resource selection and modulates associational effects between neighbouring resources2017In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 126, no 12, p. 1708-1716Article in journal (Refereed)
    Abstract [en]

    Associational effects occur when the attack rate on a resource depends on neighbouring resources in the environment. These effects are predicted to result from mismatches experienced by the consumer organism in resource selection along hierarchical search levels. As resource selection depends on sensory information used during search behaviour, we expected that different physiological states of an insect might modulate the outcome of associational effects due to differences in resource selection. We used Drosophila melanogaster, as a model organism for olfactory-guided behaviour in insects, to study the effects of mating induced behavioural changes on associational effects between two alternative resources. We found that mating has no effect on the ability of D. melanogaster to locate resource patches, but rather affects the perception of the resources within the patch. Consequently, we only found associational effects in the experiments with unmated females and not in the experiments with mated females. Our results suggest that the lack of associational effects for mated females resulted from changes in the use of short-range olfactory cues, leading to random selection among the resources. In conclusion, our results suggest that the physiological state of an insect modulates associational effects by affecting resource selection rates within the patch.

  • 84.
    Verschut, Thomas A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Inouye, Brian D.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sensory deficiencies affect resource selection and associational effects at two spatial scales2018In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 8, no 21, p. 10569-10577Article in journal (Refereed)
    Abstract [en]

    Many insect species have limited sensory abilities and may not be able to perceive the quality of different resource types while approaching patchily distributed resources. These restrictions may lead to differences in selection rates between separate patches and between different resource types within a patch, which may have consequences for associational effects between resources. In this study, we used an oviposition assay containing different frequencies of apple and banana substrates divided over two patches to compare resource selection rates of wild-type Drosophila melanogaster at the between- and within-patch scales. Next, we compared the wild-type behavior with that of the olfactory-deficient strain Orco(2) and the gustatory-deficient strain Poxn(Delta M22-B5) and found comparable responses to patch heterogeneity and similarly strong selection rates for apple at both scales for the wild-type and olfactory-deficient flies. Their oviposition behavior translated into associational susceptibility for apple and associational resistance for banana. The gustatory-deficient flies, on the other hand, no longer had a strong selection rate for apple, strongly differed in between- and within-patch selection rates from the wild-type flies, and caused no associational effects between the resources. Our study suggests that differences in sensory capabilities can affect resource selection at different search behavior scales in different ways and in turn underlie associational effects between resources at different spatial scales.

  • 85.
    Verschut, Vasiliki
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Strandmark, Alma
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Esparza-Salas, Rodrigo
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Seasonally varying marine influences on the coastal ecosystem detected through molecular gut analysis2019In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 28, no 2, p. 307-317Article in journal (Refereed)
    Abstract [en]

    Terrestrial predators on marine shores benefit from the inflow of organisms and matter from the marine ecosystem, often causing very high predator densities and indirectly affecting the abundance of other prey species on shores. This indirect effect may be particularly strong if predators shift diets between seasons. We therefore quantified the seasonal variation in diet of two wolf spider species that dominate the shoreline predator community, using molecular gut content analyses with general primers to detect the full prey range. Across the season, spider diets changed, with predominantly terrestrial prey from May until July and predominantly marine prey (mainly chironomids) from August until October. This pattern coincided with a change in the spider age and size structure, and prey abundance data and resource selection analyses suggest that the higher consumption of chironomids during autumn is due to an ontogenetic diet shift rather than to variation in prey abundance. The analyses suggested that small dipterans with a weak flight capacity, such as Chironomidae, Sphaeroceridae, Scatopsidae and Ephydridae, were overrepresented in the gut of small juvenile spiders during autumn, whereas larger, more robust prey, such as Lepidoptera, Anthomyidae and Dolichopodidae, were overrepresented in the diet of adult spiders during spring. The effect of the inflow may be that the survival and growth of juvenile spiders is higher in areas with high chironomid abundances, leading to higher densities of adult spiders and higher predation rates on the terrestrial prey next spring.

  • 86. Wirta, Helena K.
    et al.
    Vesterinen, Eero J.
    Hambäck, Peter A.
    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.
    Rasmussen, Claus
    Reneerkens, Jeroen
    Schmidt, Niels M.
    Gilg, Olivier
    Roslin, Tomas
    Exposing the structure of an Arctic food web2015In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 5, no 17, p. 3842-3856Article in journal (Refereed)
    Abstract [en]

    How food webs are structured has major implications for their stability and dynamics. While poorly studied to date, arctic food webs are commonly assumed to be simple in structure, with few links per species. If this is the case, then different parts of the web may be weakly connected to each other, with populations and species united by only a low number of links. We provide the first highly resolved description of trophic link structure for a large part of a high-arctic food web. For this purpose, we apply a combination of recent techniques to describing the links between three predator guilds (insectivorous birds, spiders, and lepidopteran parasitoids) and their two dominant prey orders (Diptera and Lepidoptera). The resultant web shows a dense link structure and no compartmentalization or modularity across the three predator guilds. Thus, both individual predators and predator guilds tap heavily into the prey community of each other, offering versatile scope for indirect interactions across different parts of the web. The current description of a first but single arctic web may serve as a benchmark toward which to gauge future webs resolved by similar techniques. Targeting an unusual breadth of predator guilds, and relying on techniques with a high resolution, it suggests that species in this web are closely connected. Thus, our findings call for similar explorations of link structure across multiple guilds in both arctic and other webs. From an applied perspective, our description of an arctic web suggests new avenues for understanding how arctic food webs are built and function and of how they respond to current climate change. It suggests that to comprehend the community-level consequences of rapid arctic warming, we should turn from analyses of populations, population pairs, and isolated predator-prey interactions to considering the full set of interacting species.

  • 87. Wirta, Helena K.
    et al.
    Weingartner, Elisabeth
    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.
    Roslin, Tomas
    Extensive niche overlap among the dominant arthropod predators of the High Arctic2015In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 16, no 1, p. 86-92Article in journal (Refereed)
    Abstract [en]

    In the High Arctic, the species richness of spiders is typically low, but abundances can be very high. Thus, how the few spider species occurring in the region choose their prey, and what prey taxa they focus on, may significantly affect the community structure of arctic arthropods. Here we estimate the ecological imprint of adult spiders of three large-bodied species coexisting in Northeast Greenland: the morphologically similar crab spiders Xysticus deichmanni and X. labradorensis (Thomisidae) and the wolf spider Pardosa glacialis (Lycosidae). To describe an important part of these spiders' diet in detail, we amplified and sequenced DNA from prey remains in their guts, selectively focusing on two of the most abundant prey orders in the area (Diptera and Lepidoptera). By comparing the resultant sequences to a reference library including most taxa encountered in the region, we assigned the prey to species. Among the spider taxa occurring in the region, the wolf spider Pardosa glacialis is dominant in terms of both biomass and density. All three spider species proved to be wide generalists, with no detectable differences in prey choice among either the two crab spiders, or among these crab spiders and the wolf spider. This lack of dietary differentiation among species may be caused by the limited prey availability in the Arctic, forcing the predators to both generalism and opportunism. Given the substantial abundance of spiders and the lack of other predatory arthropods in the region, the opportunistic prey choice observed implies that these High-Arctic spider species have the potential for inflicting a strong influence on their prey community.

  • 88.
    Åhlén, Imenne
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Thorslund, Josefin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Frampton, Andrew
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Wetlandscape size thresholds for ecosystem service delivery: Evidence from the Norrström drainage basin, Sweden2020In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 704, article id 135452Article in journal (Refereed)
    Abstract [en]

    Wetlands are interconnected with the larger surrounding landscape through the hydrological cycling of water and waterborne substances. Therefore, the borders of individual wetlands may not be appropriate landscape system boundaries for understanding large-scale functions and ecosystem services of wetlandscapes (wetland network - landscape systems), and how these can be impacted by climate and land-use changes. Recognizing that such large-scale behaviours may not be easily predicted by simple extrapolation of individual wetland behaviours, we here investigate properties of 15 Swedish wetlandscapes in the extensive (22 650 km(2)) Norrstrom drainage basin (NDB) comprising as many as 1699 wetlands. Results based on wetland survey data in combination with GIS-based ecohydrological analyses showed that wetlands located in wetlandscapes above a certain size (in the NDB: similar to 250 km(2)) consistently formed networks with characteristics required to support key ecosystem services such as nutrient/pollutant retention and biodiversity support. This was in contrast to smaller wetlandscapes (<250 km(2)), which had smaller and less diverse wetlands with insufficient throughflow to significantly impact large-scale flows of water and nutrients/pollutants. The existence of such wetlandscape-size thresholds is consistent with scale-dependent flow accumulation patterns in catchments, suggesting likely transferability of this result also to other regions.

  • 89.
    Östergård, Hannah
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Pre-dispersal seed predation: the role of fruit abortion and selective oviposition2007In: Ecology, Vol. 88, no 12, p. 2959-2965Article in journal (Refereed)
  • 90.
    Östman, Örjan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Mellbrand, Kajsa
    Stockholm University, Faculty of Science, Department of Botany.
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Edge or dispersal effects - Their relative importance on arthropod densities on small islands2009In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 10, p. 475-484Article in journal (Refereed)
    Abstract [en]

    Abstract Dispersal behaviour and edge effects are two potential factors determining population densities, and both effects are likely to vary with patch size. However, the relative importance of these two effects may be hard to separate because they may produce similar patterns. Here, we separate these two effects on population densities of seven groups of arthropods on small islands. To separate dispersal behaviour and edge effects, we use the fact that the slope of the density–area relationships (DAR-slope) should change with the absolute rates of dispersal, as would occur in response to island isolation, whereas the edge effect is expected not to be dependent on island isolation. For lycosid spiders, parasitic wasps and possibly herbivorous Homoptera DAR-slopes changed between isolated and non-isolated islands, suggesting dispersal behaviour to berelatively more important for explaining variation in their densities. Other arthropods (ants and Collembola), typically those with a predicted low dispersal among islands, showed similar DAR-slopes between isolated and non-isolated islands consistent with dominant edge effects. For two groups (web spider sand Diptera) the results were inconclusive. We conclude that both migratory processes and edge effects should be considered in the evaluation of patch size and isolation on density–area relationships.

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