Spatial heterogeneity and functional response: An experiment in microcosms with varying obstacle densities

UMR7625 Ecologie et Evolution, Université Pierre et Marie Curie, Paris, France.
Oecologia (Impact Factor: 3.09). 03/2010; 163(3):625-36. DOI: 10.1007/s00442-010-1585-5
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Spatial heterogeneity of the environment has long been recognized as a major factor in ecological dynamics. Its role in predator-prey systems has been of particular interest, where it can affect interactions in two qualitatively different ways: by providing (1) refuges for the prey or (2) obstacles that interfere with the movements of both prey and predators. There have been relatively fewer studies of obstacles than refuges, especially studies on their effect on functional responses. By analogy with reaction-diffusion models for chemical systems in heterogeneous environments, we predict that obstacles are likely to reduce the encounter rate between individuals, leading to a lower attack rate (predator-prey encounters) and a lower interference rate (predator-predator encounters). Here, we test these predictions under controlled conditions using collembolans (springtails) as prey and mites as predators in microcosms. The effect of obstacle density on the functional response was investigated at the scales of individual behavior and of the population. As expected, we found that increasing obstacle density reduces the attack rate and predator interference. Our results show that obstacles, like refuges, can reduce the predation rate because obstacles decrease the attack rate. However, while refuges can increase predator dependence, we suggest that obstacles can decrease it by reducing the rate of encounters between predators. Because of their opposite effect on predator dependence, obstacles and refuges could modify in different ways the stability of predator-prey communities.

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    • "Moreover, the number of laboratory studies of invertebrate functional responses outnumbers field studies enormously while laboratory set-ups including complex habitat structure are found in lesser numbers than studies in simplified unstructured systems. Fortunately, however, there are now certain studies where the effects on feeding rates were directly compared between simplified and complex structured habitats for different terrestrial invertebrates (e.g., Munyaneza and Obrycki 1997, Hohberg and Traunspurger 2005, Hauzy et al. 2010, Vucic-Pestic et al. 2010a, Kalinkat et al. 2013a). But there is still a need to define improved standards to measure functional responses such as including habitat structure, a sufficient large arena size and extended prey-density ranges to avoid artificially biased results. "
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    ABSTRACT: All biological rates depend on temperature, as they are based on biochemical reactions. Hence, the same holds for feeding rates and their functional components. From a ‘biologically relevant’ scope, feeding rates increase exponentially with temperature. Recent studies suggest that this increase of feeding rates with warming is shallower than the increase in metabolism. Theoretically, this mismatch should lead to a lower numerical response of biological control agents, presumably resulting in a higher probability of insect pest outbreaks. While depending on temperature, the more complex, non-linear nature of feeding rates further implies that they are also critically dependent on prey densities (i.e. the functional response). The fundamental elements of the functional response are the capture rate and the handling time. Basically, the capture rate determines the feeding success at low densities, whereas the handling time determines the maximum amount a predator is able to consume in a given time window. Moreover, capture rates themselves can also depend on prey density, turning a hyperbolic type II into a sigmoid type III functional response. This shift in the shape of the response is introduced by refuges for the prey, among other mechanisms. Contrasting the type II functional response, type III functional responses are well known to promote stable population dynamics and community structure. Therefore, changes in habitat complexity driven by climate change might also affect feeding interactions and insect pest control. Here, we review how climate change influences the functional responses of predator–prey and parasitoid–host pairs directly via increased temperature and indirectly via changes in habitat structure. We complement our review by exploring the potential consequences of feeding relations that are altered by climate change-induced mechanisms, through the application of model simulations of such consumer–resource population dynamics.
    Climate Change and Insect Pests, Edited by Christer Björkman, Pekka Niemelä, 10/2015: chapter 5: pages 74-91; CABI., ISBN: 9781780643786
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    • "). Indeed, spatial structure increases consumerresource persistence by creating permanent or temporary refuges for the resource (Huffaker 1958; Ellner et al. 2001; Neubert et al. 2002; Brockhust et al 2006; Hauzy et al. 2010b). Local extinctions can also be prevented by dispersal from other patches (Holyoak and Lawler 1996), and populations in unfavorable ecosystems (sinks) can be maintained by immigration from more favorable source ecosystems (Amezcua and Holyoak 2000; Casini et al. 2012). "
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    ABSTRACT: The paradox of enrichment has been studied almost exclusively within communities or metacommunities, without ex- plicit nutrient dynamics. Yet local recycling of materials from en- riched ecosystems may affect the stability of connected ecosystems. Here we study the effect of nutrient, detritus, producer, andconsumer spatial flows—combined with changes in regional enrichment—on the stability of a metaecosystem model.We considered both spatially homogeneous and heterogeneous enrichment. We found that nutri- ent and detritus spatial flows are destabilizing, whereas producer or consumer spatial flows are either neutral or stabilizing. We noticed that detritus spatial flows have only a weak impact on stability. Our study reveals that heterogeneity no longer stabilizes well-connected systems when accounting for explicit representation of nutrient dy- namics. We also found that intermediate consumer diffusion could lead to multiple equilibria in strongly enriched metaecosystems. Sta- bility can emerge from a top-down control allowing the storage of materials into inorganic form, a mechanism never documented be- fore. In conclusion, local enrichment can be stabilized if spatial flows are strong enough to efficiently redistribute the local excess of en- richment to unfertile ecosystems. However, high regional enrichment can be dampened only by intermediate consumer diffusion rates.
    The American Naturalist 12/2014; 184(6):752-763. · 3.83 Impact Factor
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    • "Manipulations of these metrics may necessitate a move away from the use of analogues of natural structures, such as macrophytes (Warfe & Barmuta 2004), towards artificial structures, which provide means to continuously vary specific facets of complexity. Although some have adopted such an approach (Huffaker 1958; Bartholomew, Diaz & Cicchetti 2000; Hauzy et al. 2010), it has also attracted criticism (Beck 2000). In practice, however, these approaches are complementary, with highly abstracted "
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    ABSTRACT: Predator-prey interactions are mediated by the structural complexity of habitats, but disentangling the many facets of structure that contribute to this mediation remains elusive. In a world replete with altered landscapes and biological invasions, determining how structure mediates the interactions between predators and novel prey will contribute to our understanding of invasions and predator-prey dynamics in general.Here, using simplified experimental arenas, we manipulate predator-free space, whilst holding surface area and volume constant, to quantify the effects on predator-prey interactions between two resident gammarid predators and an invasive prey, the Ponto-Caspian corophiid Chelicorophium curvispinum.Systematically increasing predator-free space alters the functional responses (the relationship between prey density and consumption rate) of the amphipod predators by reducing attack rates and lengthening handling times. Crucially, functional response shape also changes subtly from destabilising Type II towards stabilising Type III, such that small increases in predator-free space to result in significant reductions in prey consumption at low prey densities.Habitats with superficially similar structural complexity can have considerably divergent consequences for prey population stability in general and, particularly, for invasive prey establishing at low densities in novel habitats.This article is protected by copyright. All rights reserved.
    Functional Ecology 09/2014; 29(3):377-384. DOI:10.1111/1365-2435.12347 · 4.83 Impact Factor
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