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  • 1.
    Bergström, Ulf
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Englund, Göran
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Spatial scale, heterogeneity and functional responses2004In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 73, no 3, p. 487-493Article in journal (Refereed)
    Abstract [en]

    1. In a laboratory experiment, we studied the effect of arena size on the functional response of the mysid shrimp Neomysis integer preying on the cladoceran Polyphemus pediculus. The aim of the study was to examine mechanisms that cause the functional response to be scale-dependent, by documenting the spatial distribution and the movement behaviour of predator and prey.

    2. The attack rate was significantly higher in large arenas, while the handling time did not differ between arena sizes. The difference in attack rate could be explained by differences in aggregative behaviour of predator and prey and in swimming activity of the predator. It is suggested that distributions of animals are often affected by the walls of the experimental arenas and that this spatial heterogeneity is scale-dependent, which may have a considerable impact on estimates of ecological process rates.

    3. A method of correcting attack rate estimates for artefacts caused by such spatial heterogeneity is presented.

  • 2. Cote, Julien
    et al.
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fogarty, Sean
    Sih, Andrew
    Non-random dispersal mediates invader impacts on the invertebrate community2017In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 86, no 6, p. 1298-1307Article in journal (Refereed)
    Abstract [en]

    Dispersers are often not a random draw from a population, dispersal propensity being conditional on individual phenotypic traits and local contexts. This non-randomness consequently results in phenotypic differences between dispersers and non-dispersers and, in the context of biological invasions, in an invasion front made of individuals with a biased phenotype. This bias of phenotypes at the front may subsequently modulate the strength of ecological effects of an invasive species on invaded communities. We recently demonstrated that more asocial mosquitofish (Gambusia affinis), one of the 100 worst invasive species, disperse further, suggesting a sociability-biased invasion front. As behavioural types are related to the strength of interspecific interactions, an invasion by a biased subset of individuals should have important ecological implications for native communities. Here, we tested the impact of phenotypic biases in dispersing individuals (relative to non-dispersers) on prey communities in experimental mesocosms. We show that dispersers reduce prey abundance more than do non-dispersers during the first 4 weeks after introduction, and that the disperser's social types are likely drivers of these differences. These differences in prey communities disappeared after 8 weeks suggesting prey community resilience against predation in these mesocosm ecosystems. Consequently, we call for the integration of non-random dispersal, dispersal syndromes and more generally intraspecific variation into studies predicting the impacts of invasions.

  • 3.
    Despres, Laurence
    et al.
    Laboratoire d’Ecologie Alpine, CNRS-UMR 5553, Université J. Fourier.
    Cherif, Mehdi
    Biogéochimie et Ecologie des Milieux Continentaux Laboratory, Unité Mixte de Recherche 7618 Ecole Normale Supe´rieure.
    The role of competition in adaptive radiation: a field study on sequentially ovipositing host-specific seed predators2004In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 73, no 1, p. 109-116Article in journal (Refereed)
    Abstract [en]

    1. We propose an alternative model to the host-shifting model of sympatric speciation in plant-insect systems. The role of competition in driving ecological adaptive radiation was evaluated in a seed predator exploiting a single host-plant species. Sympatric speciation may occur through disruptive selection on oviposition timing if this shift decreases competition among larvae feeding on seeds. 2. The globeflower fly Chiastocheta presents a unique case of adaptive radiation, with at least six sister species co-developing in fruits of Trollius europaeus. These species all feed on seeds, and differ in their oviposition timing, one species ovipositing in 1-day-old flowers (early species), while all the other species sequentially oviposit throughout the flower life span (late species). We evaluated the impact of conspecific and heterospecific larvae on larval installation success, and on larval fresh mass and area, for early and late species, in natural conditions. 3. None of the three larval traits measured was correlated with fruit size, and no fruit lost all seeds to predation, suggesting that seed availability was not a limiting factor for larval development. 4. Our results show strong intraspecific competition among early larvae for larval installation, and among late larvae for larval mass. By contrast, larval competition between species was weak. These results are consistent with the hypothesis that shifts in oviposition promoted rapid radiation in globeflower flies by lowering competition among larvae.

  • 4. Effenberger, Michael
    et al.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gerth, Maximilian
    Matthaei, Christoph D
    Patchy bed disturbance and fish predation independently influence the distribution of stream invertebrates and algae2011In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 80, no 3, p. 603-14Article in journal (Refereed)
    Abstract [en]

    1. The identification of factors determining the patchy distribution of organisms in space and time is a central concern of ecology. Predation and abiotic disturbance are both well-known drivers of this patchiness, but their interplay is still poorly understood, especially for communities dominated by mobile organisms in frequently disturbed ecosystems. 2. We investigated the separate and interactive influences of bed disturbance by floods and predation by fish on the benthic community in a flood-prone stream. Electric fields excluded fish predators from half of 48 stream bed patches (area 0·49 m(2) ) with contrasting disturbance treatments. Three types of bed disturbance were created by either scouring or filling patches to a depth of 15-20 cm or by leaving the patches undisturbed, thus mimicking the mosaic of scour and fill caused by a moderate flood. Benthic invertebrates and algae were sampled repeatedly until 57 days after the disturbance. 3. Disturbance influenced all ten investigated biological response variables, whereas predation affected four variables. Averaged across time, invertebrate taxon richness and total abundance were highest in stable patches. Algal biomass and densities of five of the seven most common invertebrate taxa (most of which were highly mobile) were higher in fill than in scour patches, whereas two taxa were more abundant in scour and stable than in fill patches. Furthermore, two common invertebrate grazers were more abundant and algal biomass tended to be reduced in fish exclusion patches, suggesting a patch-scale trophic cascade from fish to algae. 4. Our results highlight the importance of patchy physical disturbance for the microdistribution of mobile stream organisms and indicate a notable, but less prevalent, influence of fish predation at the patch scale in this frequently disturbed environment. Disturbance and predation treatments interacted only once, suggesting that the observed predation effects were largely independent of local bed disturbance patterns.

  • 5.
    Englund, Göran
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Hambäck, Peter A.
    Top-down and bottom-up effects on the spatiotemporal dynamics of cereal aphids: Testing scaling theory for local density2007In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 76, no 1, p. 30-35Article in journal (Refereed)
    Abstract [en]
    • 1.We examine the relationship between immigration rate and patch area for different types of movement behaviours and detection modes. Theoretical models suggest that the scale dependence of the immigration rate per unit area (I/A) can be described by a power model I/A = i*Areaζ, where ζ describes the strength of the scale dependence.
    • 2.Three types of scaling were identified. Area scaling (ζ = 0) is expected for passively dispersed organisms that have the same probability of landing anywhere in the patch. Perimeter scaling (−0·30 > ζ > −0·45) is expected when patches are detected from a very short distance and immigrants arrive over the patch boundary, whereas diameter scaling (ζ = −0·5) is expected if patches are detected from a long distance or if search is approximately linear.
    • 3.A meta-analysis of published empirical studies of the scale dependence of immigration rates in terrestrial insects suggests that butterflies show diameter scaling, aphids show area scaling, and the scaling of beetle immigration is highly variable. We conclude that the scaling of immigration rates in many cases can be predicted from search behaviour and the mode of patch detection.
  • 6. Fors, Lisa
    et al.
    Markus, Robert
    Theopold, Ulrich
    Ericson, Lars
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hambäck, Peter A.
    Geographic variation and trade-offs in parasitoid virulence2016In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 85, no 6, p. 1595-1604Article in journal (Refereed)
    Abstract [en]

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

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

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

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

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

  • 7.
    Frainer, André
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    McKie, Brendan
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Malmqvist, Björn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    When does diversity matter?: Species functional diversity and ecosystem functioning across habitats and seasons in a field experiment2014In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 83, no 2, p. 460-469Article in journal (Refereed)
    Abstract [en]

    Despite ample experimental evidence indicating that biodiversity might be an important driver of ecosystem processes, its role in the functioning of real ecosystems remains unclear. In particular, the understanding of which aspects of biodiversity are most important for ecosystem functioning, their importance relative to other biotic and abiotic drivers, and the circumstances under which biodiversity is most likely to influence functioning in nature, is limited. We conducted a field study that focussed on a guild of insect detritivores in streams, in which we quantified variation in the process of leaf decomposition across two habitats (riffles and pools) and two seasons (autumn and spring). The study was conducted in six streams, and the same locations were sampled in the two seasons. With the aid of structural equations modelling, we assessed spatiotemporal variation in the roles of three key biotic drivers in this process: functional diversity, quantified based on a spe- cies trait matrix, consumer density and biomass. Our models also accounted for variability related to different litter resources, and other sources of biotic and abiotic variability among streams. All three of our focal biotic drivers influenced leaf decomposition, but none was important in all habitats and seasons. Functional diversity had contrasting effects on decomposition between habitats and seasons. A positive relationship was observed in pool habitats in spring, associated with high trait dispersion, whereas a negative relationship was observed in riffle habitats during autumn. Our results demonstrate that functional biodiversity can be as significant for functioning in natural ecosystems as other important biotic drivers. In particular, variation in the role of functional diversity between seasons highlights the importance of fluctuations in the relative abundances of traits for ecosystem process rates in real ecosystems.

  • 8.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Karin A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Experimental evidence for emergent facilitation: promoting the existence of an invertebrate predator by killing its prey2011In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 80, no 3, p. 615-621Article in journal (Refereed)
    Abstract [en]

    1. Recent theoretical insights have shown that predator species may help each other to persist by size-selective foraging on a shared prey. By feeding on a certain prey stage, a predator may induce a compensatory response in another stage of the same prey species, thereby favouring other predators; a phenomenon referred to as emergent facilitation.

    2. To test whether emergent facilitation may occur in a natural system, we performed an enclosure experiment where we mimicked fish predation by selectively removing large zooplankton and subsequently following the response of the invertebrate predator Bythotrephes longimanus.

    3. Positive responses to harvest were observed in the biomass of juvenile individuals of the dominant zooplankton Holopedium gibberum and in Bythotrephes densities. Hence, by removing large prey, we increased the biomass of small prey, i.e. stage-specific biomass overcompensation was present in the juvenile stage of Holopedium. This favoured Bythotrephes, which preferentially feed on small Holopedium.

    4. We argue that the stage-specific overcompensation occurred as a result of increased per capita fecundity of adult Holopedium and as a result of competitive release following harvest. If shown to be common, emergent facilitation may be a major mechanism behind observed predator extinctions and patterns of predator invasions.

  • 9.
    Johansson, Frank
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Jens
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Scared fish get lazy, and lazy fish get fat2009In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 78, no 4, p. 772-777Article in journal (Refereed)
    Abstract [en]

    Many biological textbooks present predator-induced morphological changes in prey species as an example of an adaptive response, because the morphological change is associated with lower predation risk. Here we show that the adaptive morphological response observed in many systems may actually be an indirect effect of decreased activity which reduces the predation risk rather than a direct adaptive response. One of the classical examples comes from crucian carp, where the presence of pike leads to a deeper body. We manipulated pike cues (presence and absence) and water current (standing and running water) and found that both standing water and pike cues similarly and independently induced a deeper body. Since the presence of pike cues as well as standing water might be associated with low swimming activity, we suggest that the presence of pike causes a reduction in activity (antipredator behaviour). Reduced activity subsequently induces a deeper body, possibly because the energy saved is allocated to a higher growth rate. Our result suggests that even if morphological change is adaptive, it might be induced indirectly via activity. This important conceptual difference may be similar in many other systems.

  • 10. KORPIMÄKI, ERKKI
    et al.
    OKSANEN, LAURI
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    OKSANEN, TARJA
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    KLEMOLA, TERO
    NORRDAHL, KAI
    BANKS, PETER B.
    Vole cycles and predation in temperate and boreal zones of Europe2005In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 74, no 6, p. 1150 -1159Article in journal (Refereed)
    Abstract [en]
    • 1.Graham & Lambin (2002) have reported on a weasel-reduction experiment, concluding that the impact of weasel predation on field vole survival was neither sufficient nor necessary to initiate and drive the cyclic decline of field vole populations in Kielder Forest, northern England. They also stated that their findings contradict conclusively the specialist predator hypothesis put forward to explain population cycles of voles in North Europe.
    • 2.Straightforward inferences from Kielder Forest to the northern boreal zone are misleading, because the population cycles of voles in Kielder Forest differ essentially from North European vole cycles. The low amplitude of the vole cycles in Kielder Forest, their restricted spatial synchrony in comparison to northern Europe and the virtual lack of interspecific synchrony in Kielder Forest suggest that there are essential differences between the mechanisms responsible for the two types of cyclic fluctuations of voles.
    • 3.The weasel-reduction experiment may provide a misleading picture on the role of predators, even in the Kielder Forest cycle. The experimental reduction of weasels alone may not stop the population decline of voles, because competing larger predators are expected to increase their hunting in the weasel-reduction areas. The small spatial scale of the experiment, which produced only slight, short-term differences in weasel densities between reduction and control areas, also suggests that other predators could have compensated easily for the weasels that were removed.
    • 4.We propose a new version of the predation hypothesis to explain low-amplitude population cycles of voles in temperate Europe, including the Kielder Forest. The interaction between generalist predators and vole populations might account for these cycles because generalists can have a functional response that is destabilizing in the neighbourhood of the equilibrium point. As most generalists are orders of magnitude larger than weasels, and thus need much more food for survival, generalist-driven cycles should be characterized by high prey minima, as observed in Kielder Forest.
  • 11.
    Liess, Antonia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Martin I.
    Rowe, Owen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Cool tadpoles from Arctic environments waste fewer nutrients - high gross growth efficiencies lead to low consumer-mediated nutrient recycling in the North2015In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 84, no 6, p. 1744-1756Article in journal (Refereed)
    Abstract [en]

    Endothermic organisms can adapt to short growing seasons, low temperatures and nutrient limitation by developing high growth rates and high gross growth efficiencies (GGEs). Animals with high GGEs are better at assimilating limiting nutrients and thus should recycle (or lose) fewer nutrients. Longer guts in relation to body mass may facilitate higher GGE under resource limitation. Within the context of ecological stoichiometry theory, this study combines ecology with evolution by relating latitudinal life-history adaptations in GGE, mediated by gut length, to its ecosystem consequences, such as consumer-mediated nutrient recycling. In common garden experiments, we raised Rana temporaria tadpoles from two regions (Arctic/Boreal) under two temperature regimes (18/23 degrees C) crossed with two food quality treatments (high/low-nitrogen content). We measured tadpole GGEs, total nutrient loss (excretion+egestion) rates and gut length during ontogeny. In order to maintain their elemental balance, tadpoles fed low-nitrogen (N) food had lower N excretion rates and higher total phosphorous (P) loss rates than tadpoles fed high-quality food. In accordance with expectations, Arctic tadpoles had higher GGEs and lower N loss rates than their low-latitude conspecifics, especially when fed low-N food, but only in ambient temperature treatments. Arctic tadpoles also had relatively longer guts than Boreal tadpoles during early development. That temperature and food quality interacted with tadpole region of origin in affecting tadpole GGEs, nutrient loss rates and relative gut length, suggests evolved adaptation to temperature and resource differences. With future climate change, mean annual temperatures will increase. Additionally, species and genotypes will migrate north. This will change the functioning of Boreal and Arctic ecosystems by affecting consumer-mediated nutrient recycling and thus affect nutrient dynamics in general. Our study shows that evolved latitudinal adaption can change key ecosystem functions.

  • 12.
    Liess, Antonia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rowe, Owen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Thomsson, Gustaf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Martin I.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. University of Sheffield, UK and Uppsala University, Sweden.
    Hot tadpoles from cold environments need more nutrients - life history and stoichiometry reflects latitudinal adaptation2013In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 82, no 6, p. 1316-1325Article in journal (Refereed)
    Abstract [en]

    1. High-latitude species (and populations within species) are adapted to short and cold summers. They often have high growth and development rates to fully use the short growing season and mature before the onset of winter. Within the context of ecological stoichiometry theory, this study combines ecology with evolution by relating latitudinal life-history adaptations to their molecular consequences in body nutrient composition in Rana temporaria tadpoles. Temperature and food quality were manipulated during the development of tadpoles from Arctic and Boreal origins. We determined tadpole growth rate, development rate, body size and nutrient content, to test whether (i) Arctic tadpoles could realize higher growth rates and development rates with the help of higher-quality food even when food quantity was unchanged, (ii) Arctic and Boreal tadpoles differed in their stoichiometric (and life history) response to temperature changes, (iii) higher growth rates lead to higher tadpole P content (growth rate hypothesis) and (iv) allometric scaling affects tadpole nutrient allocation. We found that especially Arctic tadpoles grew and developed faster with the help of higher-quality food and that tadpoles differed in their stoichiometric (and life history) response to temperature changes depending on region of origin (probably due to different temperature optima). There was no evidence that higher growth rates mediated the positive effect of temperature on tadpole P content. On the contrary, the covariate growth rate was negatively connected with tadpole P content (refuting the growth rate hypothesis). Lastly, tadpole P content was not related to body size, but tadpole C content was higher in larger tadpoles, probably due to increased fat storage. We conclude that temperature had a strong effect on tadpole life history, nutrient demand and stoichiometry and that this effect depended on the evolved life history.

  • 13.
    Nilsson, Karin A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    van Kooten, Tobias
    Wageningen IMARES, PO Box 68, 1970 AB IJmuiden, the Netherlands.
    Complete compensation in Daphnia fecundity and stage-specific biomass in response to size-independent mortality2010In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 79, no 4, p. 871-878Article in journal (Refereed)
    Abstract [en]

    1. Recent theory suggests that compensation or even overcompensation in stage-specific biomass can arise in response to increased mortality. Which stage that will show compensation depends on whether maturation or reproduction is the more limiting process in the population. Size-structured theory also provides a strong link between the type of regulation and the expected population dynamics as both depend on size/stage specific competitive ability.

    2. We imposed a size-independent mortality on a consumer-resource system with Daphnia pulex feeding on Scenedesmus obtusiusculus to asses the compensatory responses in Daphnia populations. We also extended an existing stage-structured biomass model by including several juvenile stages to test whether this extension affected the qualitative results of the existing model.

    3. We found complete compensation in juvenile biomass and total population fecundity in response to harvesting. The compensation in fecundity was caused by both a higher proportion of fecund females and a larger clutch size under increased mortality. We did not detect any difference in resource levels between treatments.

    4. The model results showed that both stages of juveniles have to be superior to adults in terms of resource competition for the compensatory response to take place in juvenile biomass.

    5. The results are all in correspondence with that the regulating process within the population was reproduction. From this we also conclude that juveniles were superior competitors to adults, which has implications for population dynamics and the kind of cohort cycles seen in Daphnia populations.

    6. The compensatory responses demonstrated in this experiment have major implications for community dynamics and are potentially present in any organisms with food-dependent growth or development.

  • 14.
    Persson, Lennart
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, Andre M.
    Mixed competition-predation: potential vs. realized interactions2012In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 81, no 2, p. 483-493Article in journal (Refereed)
    Abstract [en]

    1. Life-history omnivory or size-induced mixed competitionpredation systems have under many conditions theoretically been shown to be fragile, whereas at the same time existing empirical data suggest such systems to be common in nature. 2. In a whole lake experiment covering 17 years, we analysed the effects of the introduction of the intraguild prey roach (Rutilus rutilus) on the population size and individual performance of the intraguild predator perch (Perca fluviatilis) and on resource levels in two low productivity systems. 3. A strong long-term effect of roach on the zooplankton resource but not on the macroinvertebrate resource was present. Competitive effects of roach on perch were observed in one of the lakes the first years after the introduction, but at the end of the study no competitive effect of roach on either size class of perch was observed in any of the two lakes. In contrast, a positive predatory effect reflected in improved growth rates of older perch was present. 4. The lack of a support for a competitive effect of roach on small perch raises the question of the importance of mixed competition-predation interactions in life-history omnivorous systems and the problem of comparing descriptive data on feeding relationships with theoretical predictions based on interaction modules.

  • 15.
    Reichstein, Birte
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Schröder, Arne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, A. M.
    Habitat complexity does not promote coexistence in a size-structured intraguild predation system2013In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 82, no 1, p. 55-63Article in journal (Refereed)
    Abstract [en]

    Size-dependent interactions and habitat complexity have been identified as important factors affecting the persistence of intraguild predation (IGP) systems. Habitat complexity has been suggested to promote intraguild (IG) prey and intraguild predator coexistence through weakening trophic interactions particularly the predation link. Here, we experimentally investigate the effects of habitat complexity on coexistence and invasion success of differently sized IG-predators in a size-structured IGP system consisting of the IG-predator Poecilia reticulata and a resident Heterandria formosa IG-prey population. The experiments included medium-long and long-term invasion experiments, predator-prey experiments and competition experiments to elucidate the mechanisms underlying the effect of prey refuges. Habitat complexity did not promote the coexistence of IG-predator and IG-prey, although the predation link was substantially weakened. However, the presence of habitat structure affected the invasion success of large IG-predators negatively and the invasion success of small IG-predators positively. The effect of refuges on size-dependent invasion success could be related to a major decrease in the IG-predator's capture rate and a shift in the size distribution of IG-predator juveniles. In summary, habitat complexity had two main effects: (i) the predation link was diminished, resulting in a more competition driven system and (ii) the overall competitive abilities of the two species were equalized, but coexistence was not promoted. Our results suggest that in a size-structured IGP system, individual level mechanisms may gain in importance over species level mechanisms in the presence of habitat complexity.

  • 16.
    Schröder, Arne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Karin A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    van Kooten, Tobias
    Wageningen IMARES, PO Box 68, 1970 AB Ijmuiden, The Netherlands.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Invasion success depends on invader body size in a size-structured mixed predation-competition system2009In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 78, no 6, p. 1152-1162Article in journal (Refereed)
    Abstract [en]

    1. The size of an individual is an important determinant of its trophic position and the type of interactions it engages in with other heterospecific and conspecific individuals. Consequently an individual's ecological role in a community changes with its body size over ontogeny, leading to that trophic interactions between individuals are a size-dependent and ontogenetically variable mixture of competition and predation.

    2. Because differently sized individuals thus experience different biotic environments, invasion success may be determined by the body size of the invaders. Invasion outcome may also depend on the productivity of the system as productivity influences the biotic environment.

    3. In a laboratory experiment with two poeciliid fishes the body size of the invading individuals and the daily amount of food supplied were manipulated.

    4. Large invaders established persistent populations and drove the resident population to extinction in 10 out of 12 cases, while small invaders failed in 10 out of 12 trials. Stable coexistence was virtually absent. Invasion outcome was independent of productivity.

    5. Further analyses suggest that small invaders experienced a competitive recruitment bottleneck imposed on them by the resident population. In contrast, large invaders preyed on the juveniles of the resident population. This predation allowed the large invaders to establish successfully by decreasing the resident population densities and thus breaking the bottleneck.

    6. The results strongly suggest that the size distribution of invaders affects their ability to invade, an implication so far neglected in life-history omnivory systems. The findings are further in agreement with predictions of life-history omnivory theory, that size-structured interactions demote coexistence along a productivity gradient.

  • 17.
    Svanbäck, Richard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Individual diet specialization, niche width and population dynamics: implications for trophic polymorphisms2004In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 73, no 5, p. 973-982Article in journal (Refereed)
    Abstract [en]

    1. We studied a perch Perca fluviatilis L. population that during a 9-year period switched between a phase of dominance of adult perch and a phase dominated by juvenile perch driven by cannibalism and intercohort competition. We investigated the effects of these population fluctuations on individual diet specialization and the mechanisms behind this specialization.

    2. Due to cannibalism, the survival of young-of-the-year (YOY) perch was much lower when adult perch density was high than when adult perch density was low.

    3. Both the individual niche breadth (if weighed for resource encounter) and the population niche breadth were highest when adult population density was high and, consequently, individual specialization was highest at high adult perch densities.

    4. When adult perch density was low, the abundances of benthic invertebrate and YOY perch were high and dominated the diet of adult perch, whereas the density of zoo-plankton was low due to predation from YOY perch. At high perch densities, benthic invertebrate abundance was lower and zooplankton level was higher and some perch switched to feed on zooplankton.

    5. Our results show that individual specialization may fluctuate with population density through feedback mechanisms via resource levels. Such fluctuations may have profound implications on the evolution of resource polymorphisms.

  • 18.
    ten Brink, Hanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Amsterdam, The Netherlands.
    Mazumdar, Abul Kalam Azad
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huddart, Joseph
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Life Sciences, Imperial College London, Ascot, UK.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Cameron, Tom C.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. School of Biological Sciences, University of Essex, Colchester, UK.
    Do intraspecific or interspecific interactions determine responses to predators feeding on a shared size-structured prey community?2015In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 84, no 2, p. 414-426Article in journal (Refereed)
    Abstract [en]

    1. Coexistence of predators that share the same prey is common. This is still the case in size-structured predator communities where predators consume prey species of different sizes (interspecific prey responses) or consume different size classes of the same species of prey (intraspecific prey responses). A mechanism has recently been proposed to explain coexistence between predators that differ in size but share the same prey species, emergent facilitation, which is dependent on strong intraspecific responses from one or more prey species. Under emergent facilitation, predators can depend on each other for invasion, persistence or success in a size-structured prey community. Experimental evidence for intraspecific size-structured responses in prey populations remains rare, and further questions remain about direct interactions between predators that could prevent or limit any positive effects between predators [e.g. intraguild predation (IGP)]. Here, we provide a community-wide experiment on emergent facilitation including natural predators. We investigate both the direct interactions between two predators that differ in body size (fish vs. invertebrate predator), and the indirect interaction between them via their shared prey community (zooplankton). Our evidence supports the most likely expectation of interactions between differently sized predators that IGP rates are high, and interspecific interactions in the shared prey community dominate the response to predation (i.e. predator-mediated competition). The question of whether emergent facilitation occurs frequently in nature requires more empirical and theoretical attention, specifically to address the likelihood that its pre-conditions may co-occur with high rates of IGP.

  • 19.
    Tibblin, Petter
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Forsman, Anders
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Borger, Tobias
    Cty Adm Kalmar.
    Larsson, Per
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Causes and consequences of repeatability, flexibility and individual fine tuning of of migratory timing in pike2016In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 85, no 1, p. 136-145Article in journal (Refereed)
    Abstract [en]

    1. Many organisms undertake migrations between foraging and breeding habitats and while it is assumed that reproductive timing affects fitness, little is known about the degree of individual consistency, and about the causes and consequences of individual variation in migratory timing in organisms other than birds. 2. Here, we report on a 6-year mark-recapture study, including 2048 individuals, of breeding migration in anadromous pike (Esox lucius), an iteroparous top-predatory fish that displays homing behaviour. By repeated sampling across years at a breeding site, we first quantify individual variation both within and between breeding events and then investigate phenotypic correlates and fitness consequences of arrival timing to the breeding site. 3. Our data demonstrate that males arrive before females, that large males arrive later than small males, that the timing of breeding migration varies among years and that individuals are consistent in their timing across years relative to other individuals in the population. 4. Furthermore, data on return rates indicate that arrival time is under stabilizing viability selection, and that individuals who are more flexible in their timing of arrival during the first reproductive years survive longer compared with less flexible individuals. Finally, longitudinal data demonstrate that individuals consistently fine-tune their arrival timing across years, showing that the timing of arrival to breeding sites is influenced by experience. 5. These findings represent rare evidence of how between-and within-individual variations in migratory timing across breeding events are correlated with phenotypic and fitness traits in an ecologically important keystone species. Our results emphasize the importance of considering variation in migratory timing both between and within individuals in studies investigating the fitness consequences of migratory behaviour and have implications for future management.

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