Abstract
ABSTRACTFood web studies commonly ignore individual variation within a population and variation in the environment and assume these factors have insignificant effects on community dynamics relative to interspecific interactions. However, variation in body sizes within a population (size structure) and the physical structure of habitats (habitat complexity) can both affect interspecific interactions independently, with possible interactive effects. Using experimental mesocosms, we examined effects of predator size structure and habitat complexity on predation by two common predators in fishless ponds: larval aquatic beetles (Cybister fimbriolatus) and larval dragonflies (Anax junius). Cannibalism, intraguild predation, and predation on shared prey were measured at two levels of habitat complexity crossed with six size-structured pairs of predators. We found that highly complex habitats sustain a higher prey density because prey can take refuge from predators. Additionally, size structure had direct (size better predicted predation rate than did species identity) and indirect (IGP and cannibalism lowered predation rates) effects on consumptive interactions, which changed the composition and density of the predator guild. The identified size- and habitat-mediated mechanisms can change the frequencies of intraguild vs. interguild predation (a balance important in determining top–down control of predators), and therefore we argue that these sources of heterogeneity should be included in community ecology studies where possible.
Highlights
A perennial challenge in ecology is to develop models that are detailed enough to describe complex systems but general enough to apply to multiple systems
Models typically consider the average individual of a population and average environmental conditions, but natural populations and ecosystems have heterogeneity that is critical for understanding complex community dynamics (Bolnick et al 2011; Gibert and Brassil 2014)
Realistic models must consider how each is affected because the relative frequencies of cannibalism, intraguild predation (IGP), and predation have important implications for the coexistence of functionally similar species and the degree of top–down control in ecosystems (Finke and Denno 2002; Persson et al 2003; Rudolf 2007a). Our research addresses this gap through the following questions: (1) How do size structure and habitat complexity independently and interactively influence relative frequencies of IGP, cannibalism, and predation? (2) Do predators’ tendencies toward cannibalism or IGP differ, and could these differences clarify seemingly unstable models of coexistence?
Summary
A perennial challenge in ecology is to develop models that are detailed enough to describe complex systems but general enough to apply to multiple systems. Two sources of heterogeneity known to influence predator–prey interactions are variation in individual body size within a population (size structure) (Crumrine 2005; Petchey et al 2008) and variation in vegetation density (a component of habitat complexity) (Finke and Denno 2006; Reichstein et al 2013). This picture is further complicated when effects of
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