Article

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
Source: PubMed

ABSTRACT

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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    • "However, the physical environment (e.g., the landscape) can also significantly influence foraging behavior, and may have a positive or a negative effect on self-sustainability (e.g., Klecka and Boukal 2014; King and With 2002). For instance, predator–prey dynamics in microcosms can be affected if obstacles are considered, as they can reduce the encounter rate between individuals, and thus reduce the predation rate (Hauzy et al. 2010; Salvador et al. 2009). "
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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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