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Jonathan B Shurin - One of the best experts on this subject based on the ideXlab platform.
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niche evolution trophic structure and species turnover in model food webs
The American Naturalist, 2009Co-Authors: Travis Ingram, Luke J. Harmon, Jonathan B ShurinAbstract:The features that govern the stability and persistence of species interaction networks, such as food webs, remain elusive, but recent work suggests that the distribution and strength of trophic links play an important role. Potential Omnivory-stability relation- ships have been investigated and debated extensively, but we still have a relatively poor understanding of how levels of Omnivory relate to the stability of diverse food webs. Here, we use an evolutionary assembly model to investigate how different trade-offs in resource use influence both food web structure and dynamic stability during the assembly process. We build on a previous model by allowing speciation along with the evolution of two traits: body size and feed- ing-niche width. Across a wide range of conditions, the level of Omnivory in a food web is positively related to its dynamic instability (variability and species turnover). Parameter values favoring omni- vory also allow a wider range of phenotypes to invade, often dis- placing existing species. This high species turnover leaves signatures in reconstructed phylogenies, with shorter branches connecting ex- tant species in more omnivorous food webs. Our findings suggest that features of the environment may influence both trophic structure and dynamic stability, leading to emergent Omnivory-stability
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the ubiquity of Omnivory
Internationale Vereinigung für theoretische und angewandte Limnologie: Verhandlungen, 2009Co-Authors: Ross M Thompson, Martin Hemberg, Brian M. Starzomski, Jonathan B ShurinAbstract:Summary attributes of the 3food webs from each pond.2a 2b 2c 13a 13b 13c#taxaintrophiclevel1 17 18 19 19 19 19# taxa in trophic level 2 22 25 26 17 17 20#taxaintrophiclevel3 421886#omnivoroustaxa 311222Total no. of trophic links 76 77 73 73 92 83Proportion trophic links via omnivorous food chains 0.07 0.04 0.05 0.11 0.10 0.10Total trophic interaction score (TIS) 159 163 155 134 161 150Proportion TISvia omnivorous food chains 0.09 0.02 0.03 0.10 0.09 0.09Average TIS 2.09 2.12 2.12 1.84 1.75 1.81Average omnivore TIS 1.56 1.00 1.25 1.75 1.67 1.75Average TISfrom omnivores to least connected trophiclevel111111 food webs, with 94% (Pond 2) and 93% (Pond 13) oftaxa attributable to an integer trophic position (Table 1).Considering only animal taxa, this represents 12% and14% of animal taxa being considered omnivorous(Table 1). Between 4 and 11% of the total trophic linksand between 2 and 10% of the total TISoccurred in foodchains with omnivores. Average link strengths to omni-vores were lower than the average for the whole foodweb, and the link score from omnivores to the least fre-quently occurring trophic level in their guts were weak(an average score of 1).The majority of Omnivory was due to small amountsof organic matter being ingested by predators (e.g., thedragonfly
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Niche Evolution, Trophic Structure, and Species Turnover in Model Food Webs
The American naturalist, 2009Co-Authors: Travis Ingram, Luke J. Harmon, Jonathan B ShurinAbstract:The features that govern the stability and persistence of species interaction networks, such as food webs, remain elusive, but recent work suggests that the distribution and strength of trophic links play an important role. Potential Omnivory-stability relationships have been investigated and debated extensively, but we still have a relatively poor understanding of how levels of Omnivory relate to the stability of diverse food webs. Here, we use an evolutionary assembly model to investigate how different trade-offs in resource use influence both food web structure and dynamic stability during the assembly process. We build on a previous model by allowing speciation along with the evolution of two traits: body size and feeding-niche width. Across a wide range of conditions, the level of Omnivory in a food web is positively related to its dynamic instability (variability and species turnover). Parameter values favoring Omnivory also allow a wider range of phenotypes to invade, often displacing existing species. This high species turnover leaves signatures in reconstructed phylogenies, with shorter branches connecting extant species in more omnivorous food webs. Our findings suggest that features of the environment may influence both trophic structure and dynamic stability, leading to emergent Omnivory-stability relationships.
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trophic levels and trophic tangles the prevalence of Omnivory in real food webs
Ecology, 2007Co-Authors: Ross M Thompson, Martin Hemberg, Brian M. Starzomski, Jonathan B ShurinAbstract:The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top-down control within food webs, but it has been criticized for ignoring Omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4%) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic-level-based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.
Kevin S Mccann - One of the best experts on this subject based on the ideXlab platform.
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Food Chains and Omnivory
Food Webs (MPB-50), 2011Co-Authors: Kevin S MccannAbstract:This chapter extends the consumer–resource theory to include simple but common three-species modules behind the construction of whole food webs, with particular emphasis on food chains and Omnivory. It first considers some common simple modular food web structures and whether the dynamics of subsystems can be seen using the framework laid out in previous chapters. Specifically, it asks when common food web structure increases or weakens the relative interaction strengths and/or when a food web structure modifies flux between consumers and resources in a density-dependent manner such that the food web tends to increase flux rates in some situations and decrease the coupling in other situations. The chapter also explores how stage structure can influence food chain stability before concluding with a review of empirical evidence on the dynamical implications of Omnivory for food webs.
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Reconciling the Omnivory-Stability Debate
The American naturalist, 2011Co-Authors: Gabriel Gellner, Kevin S MccannAbstract:Abstract Despite attempts at reconciliation, the role of Omnivory in food web stability remains unclear. Here we develop a novel community matrix approach that is analogous to the bifurcation method of modular food web theory to show that the stability of omnivorous food chains depends critically on interaction strength. We find that there are only six possible ways that omnivorous interaction strengths can influence the stability of linear food chains. The results from these six cases suggest that: (1) strong Omnivory is always destabilizing, (2) stabilization by weak to intermediate omnivorous interaction strengths dominates the set of possible stability responses, and, (3) Omnivory can be occasionally strictly destabilizing or intermittently destabilizing. We then revisit the classical results of Pimm and Lawton to show that although their parameterization tends to produce a low percentage of stable omnivorous webs, the same parameterization shows strong theoretical support for the weak interaction eff...
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Food web stability: the influence of trophic flows across habitats.
The American naturalist, 1998Co-Authors: Gary R. Huxel, Kevin S MccannAbstract:In nature, fluxes across habitats often bring both nu- ory, which plays a central role in consumer-resource in- trient and energetic resources into areas of low productivity from areas of higher productivity. These inputs can alter consumption teractions and food web dynamics. They further rates of consumer and predator species in the recipient food webs, suggested that multichannel Omnivory can dampen or fa- thereby influencing food web stability. Starting from a well-studied cilitate trophic cascades. McCann and Hastings (1997) tritrophic food chain model, we investigated the impact of alloch- recently found that food web dynamics were stabilized by thonous inputs on the stability of a simple food web model. We weak to moderate amounts of trophic Omnivory, one considered the effects of allochthonous inputs on stability of the component of multichannel Omnivory. They did not, model using four sets of biologically plausible parameters that rep- however, examine the influence of other types of multi- resent different dynamical outcomes. We found that low levels of allochthonous inputs stabilize food web dynamics when species channel Omnivory on food web dynamics. In this article, preferentially feed on the autochthonous sources, while either in- we address this problem by extending a simple food creasing the input level or changing the feeding preference to favor chain to include a different component of multichannel allochthonous inputs, or both, led to a decoupling of the food Omnivory: allochthonous inputs (inputs entering from chain that could result in the loss of one or all species. We argue another habitat). We demonstrate that allochthonous that allochthonous inputs are important sources of productivity in sources can also stabilize food web dynamics, further many food webs and their influence needs to be studied further. suggesting that donor control may be an important fac- This is especially important in the various systems, such as caves, headwater streams, and some small marine islands, in which more tor in community dynamics and that trophic cascades energy enters the food web from allochthonous inputs than from may be weakened in systems that have relatively large al- autochthonous inputs. lochthonous inputs. The movement of resources across habitat boundaries
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re evaluating the Omnivory stability relationship in food webs
Proceedings of The Royal Society B: Biological Sciences, 1997Co-Authors: Kevin S Mccann, Alan HastingsAbstract:Under equilibrium conditions, previous theory has shown that the presence of Omnivory destabilizes food webs. Correspondingly, Omnivory ought to be rare in real food webs. Although, early food web ...
Travis Ingram - One of the best experts on this subject based on the ideXlab platform.
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stability and persistence of food webs with Omnivory is there a general pattern
Ecosphere, 2012Co-Authors: Pavel Kratina, Travis Ingram, Robin M Lecraw, Bradley R AnholtAbstract:The relationship between Omnivory and stability has been the subject of a longstanding debate in ecology. Early theory predicted that Omnivory would decrease the probability of food webs being stable. While early empirical data appeared to support the prediction that Omnivory should be rare, detailed study of food webs later revealed that Omnivory is ubiquitous across ecosystems and taxa. Recent years have seen renewed interest in the Omnivory-stability debate, and advances in mechanistic non-equilibrium models demonstrated that Omnivory can both increase and decrease stability. Current efforts have therefore focused on identifying biological mechanisms that promote the persistence of food webs with Omnivory. We synthesize recent evidence that Omnivory often stabilizes food webs when it occurs as life-history Omnivory, when prey experience reduced predation rates due to refuges or adaptive antipredator defences, and when omnivores interfere with each other or feed adaptively. Empirical research has lagged behind theory and there remains a shortage of studies directly measuring the stability of diverse natural communities that vary in the number and strength of omnivorous interactions. Early microcosm experiments indicated a narrow range of conditions for the persistence of simple omnivorous modules, while studies of Omnivory embedded within larger natural networks have demonstrated its stabilizing effects. These new findings alter our view of food web dynamics and show that rather than looking for a simple and general Omnivory-stability relationship, we should focus on identifying conditions under which Omnivory is a stabilizing feature of more complex natural systems.
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niche evolution trophic structure and species turnover in model food webs
The American Naturalist, 2009Co-Authors: Travis Ingram, Luke J. Harmon, Jonathan B ShurinAbstract:The features that govern the stability and persistence of species interaction networks, such as food webs, remain elusive, but recent work suggests that the distribution and strength of trophic links play an important role. Potential Omnivory-stability relation- ships have been investigated and debated extensively, but we still have a relatively poor understanding of how levels of Omnivory relate to the stability of diverse food webs. Here, we use an evolutionary assembly model to investigate how different trade-offs in resource use influence both food web structure and dynamic stability during the assembly process. We build on a previous model by allowing speciation along with the evolution of two traits: body size and feed- ing-niche width. Across a wide range of conditions, the level of Omnivory in a food web is positively related to its dynamic instability (variability and species turnover). Parameter values favoring omni- vory also allow a wider range of phenotypes to invade, often dis- placing existing species. This high species turnover leaves signatures in reconstructed phylogenies, with shorter branches connecting ex- tant species in more omnivorous food webs. Our findings suggest that features of the environment may influence both trophic structure and dynamic stability, leading to emergent Omnivory-stability
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Niche Evolution, Trophic Structure, and Species Turnover in Model Food Webs
The American naturalist, 2009Co-Authors: Travis Ingram, Luke J. Harmon, Jonathan B ShurinAbstract:The features that govern the stability and persistence of species interaction networks, such as food webs, remain elusive, but recent work suggests that the distribution and strength of trophic links play an important role. Potential Omnivory-stability relationships have been investigated and debated extensively, but we still have a relatively poor understanding of how levels of Omnivory relate to the stability of diverse food webs. Here, we use an evolutionary assembly model to investigate how different trade-offs in resource use influence both food web structure and dynamic stability during the assembly process. We build on a previous model by allowing speciation along with the evolution of two traits: body size and feeding-niche width. Across a wide range of conditions, the level of Omnivory in a food web is positively related to its dynamic instability (variability and species turnover). Parameter values favoring Omnivory also allow a wider range of phenotypes to invade, often displacing existing species. This high species turnover leaves signatures in reconstructed phylogenies, with shorter branches connecting extant species in more omnivorous food webs. Our findings suggest that features of the environment may influence both trophic structure and dynamic stability, leading to emergent Omnivory-stability relationships.
Sebastian Diehl - One of the best experts on this subject based on the ideXlab platform.
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adaptive Omnivory and species coexistence in tri trophic food webs
Theoretical Population Biology, 2005Co-Authors: Vlastimil Krivan, Sebastian DiehlAbstract:The commonness of Omnivory in natural communities is puzzling, because simple dynamic models of tri-trophic systems with Omnivory are prone to species extinction. In particular, the intermediate co ...
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Adaptive Omnivory and species coexistence in tri-trophic food webs.
Theoretical population biology, 2005Co-Authors: Vlastimil Krivan, Sebastian DiehlAbstract:The commonness of Omnivory in natural communities is puzzling, because simple dynamic models of tri-trophic systems with Omnivory are prone to species extinction. In particular, the intermediate consumer is frequently excluded by the omnivore at high levels of enrichment. It has been suggested that adaptive foraging by the omnivore may facilitate coexistence, because the intermediate consumer should persist more easily if it is occasionally dropped from the omnivore's diet. We explore theoretically how species permanence in tri-trophic systems is affected if the omnivore forages adaptively according to the "diet rule", i.e., feeds on the less profitable of its two prey species only if the more profitable one is sufficiently rare. We show that, compared to systems where Omnivory is fixed, adaptive Omnivory may indeed facilitate 3-species persistence. Counter to intuition, however, facilitation of 3-species coexistence requires that the intermediate consumer is a more profitable prey than the basal resource. Consequently, adaptive Omnivory does not facilitate persistence of the intermediate consumer but enlarges the persistence region of the omnivore towards parameter space where a fixed omnivore would be excluded by the intermediate consumer. Overall, the positive effect of adaptive Omnivory on 3-species persistence is, however, small. Generally, whether Omnivory is fixed or adaptive, 3-species permanence is most likely when profitability (=conversion efficiency into omnivores) is low for basal resources and high for intermediate consumers.
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effects of enrichment on three level food chains with Omnivory
The American Naturalist, 2000Co-Authors: Sebastian Diehl, Margit FeiselAbstract:abstract: Although Omnivory (the consumption of resources from more than one trophic level) is widespread, this fundamental limitation to the applicability of food chain theory to real communities has received only limited treatment. We investigated effects of enrichment (increasing carrying capacity, K, of the resource) on a system consisting of a resource (R), an intermediate consumer (N), and an omnivore (P) using a general mathematical model and tested the relevance of some of its predictions to a laboratory system of mixed bacteria (=R) and the ciliates Tetrahymena (=N) and Blepharisma (=P). The model produced six major predictions. First, N may facilitate or inhibit P. Enrichment may revert the net effect of N on P from facilitation to inhibition. Second, along a gradient of K, up to four regions of invasibility and stable coexistence of N and P may exist. At the lowest K, only R is present. At somewhat higher K, N can coexist with R. At intermediate K, either N and P coexist, or either consumer exc...
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Effects of enrichment on three-level food chains with Omnivory
The American naturalist, 2000Co-Authors: Sebastian Diehl, Margit FeißelAbstract:Although Omnivory (the consumption of resources from more than one trophic level) is widespread, this fundamental limitation to the applicability of food chain theory to real communities has received only limited treatment. We investigated effects of enrichment (increasing carrying capacity, K, of the resource) on a system consisting of a resource (R), an intermediate consumer (N), and an omnivore (P) using a general mathematical model and tested the relevance of some of its predictions to a laboratory system of mixed bacteria (=R) and the ciliates Tetrahymena (=N) and Blepharisma (=P). The model produced six major predictions. First, N may facilitate or inhibit P. Enrichment may revert the net effect of N on P from facilitation to inhibition. Second, along a gradient of K, up to four regions of invasibility and stable coexistence of N and P may exist. At the lowest K, only R is present. At somewhat higher K, N can coexist with R. At intermediate K, either N and P coexist, or either consumer excludes the other depending on initial conditions. At the highest K, N may be excluded through apparent competition and only R and P can coexist. The pattern of persistence of Tetrahymena and Blepharisma along an enrichment gradient conformed fairly well to the scenario allowing coexistence at intermediate K. Third, for stable equilibria of the Omnivory system, R always increases and N always decreases with K. The abundances of bacteria and Tetrahymena were suggestive of such a pattern but did not allow a strict test because coexistence occurred at only one level of enrichment. Fourth, an omnivore can invade an R-N system at a lower K than an otherwise identical specialist predator of N. Fifth, an omnivore can always invade a food chain with such a specialist predator. Sixth, over ranges of K where both Omnivory systems and otherwise identical three-level food chains are feasible, N is always less abundant in the Omnivory system, whereas the relative abundances of R and P in Omnivory systems compared to food chains may change with K. It is thus possible that total community biomass at a given K is lower in an Omnivory system than in a food chain. Both the model and the experimental results caution that patterns of trophic-level abundances in response to enrichment predicted by food chain theory are not to be expected in systems with significant Omnivory.
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direct and indirect effects of Omnivory in a littoral lake community
Ecology, 1995Co-Authors: Sebastian DiehlAbstract:In spite of the ubiquity of Omnivory in nature, its consequences for population dynamics have received little attention from theoretical and experimental ecologists. Having three direct consumer-re ...
Sambhav Sachdev - One of the best experts on this subject based on the ideXlab platform.
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Omnivory and the stability of simple food webs
Oecologia, 1998Co-Authors: Marcel Holyoak, Sambhav SachdevAbstract:Traditional ecological theory predicts that the stability of simple food webs will decline with an increasing number of trophic levels and increasing amounts of Omnivory. These ideas have been tested using protozoans in laboratory microcosms. However, the results are equivocal, and contrary to expectation, Omnivory is common in natural food webs. Two recent developments lead us to re-evaluate these predictions using food webs assembled from protists and bacteria. First, recent modelling work suggests that Omnivory is actually stabilizing, providing that interactions are not too strong. Second, it is difficult to evaluate the degree of Omnivory of some protozoan species without explicit experimental tests. This study used seven species of ciliated protozoa and a mixed bacterial flora to assemble four food webs with two trophic levels, and four webs with three trophic levels. Protist species were assigned a rank for their degree of Omnivory using information in the literature and the results of experiments that tested whether the starvation rate of predators was influenced by the amount of bacteria on which they may have fed and whether cannibalism (a form of Omnivory) occurred. Consistent with recent modelling work, both bacterivorous and predatory species with higher degrees of Omnivory showed more stable dynamics, measured using time until extinction and the temporal variability of population density. Systems with two protist species were less persistent than systems with one protist species, supporting the prediction that longer food chains will be less stable dynamically.
