Abstract
Between-habitat distributions of prey shared by multiple predators depend on habitat use by the predators, whose own distributions may interact. We used a large-scale, whole-system natural experiment to examine distributions of anuran tadpoles and insect predators between pond microhabitats with contrasting complexity (open water vs emergent littoral vegetation) in drainable ponds that were either kept fishless or stocked with fish. Total relative densities of insect predators did not significantly differ with respect to the fish status of the ponds. Individual anuran taxa responded variously, but only fish-tolerant Bufo bufo densities were higher in the presence of fish. The densities of both insect predators and tadpoles showed positive interactions between fish presence and the use of complex littoral habitat. The habitat shift to littoral vegetation could be indirectly amplified by fish adverse impact on submerged macrophytes, the main structured microhabitat in open-water areas. Irrespective of mechanisms of fish effects (direct consumption, behavioral deterrence or alteration of habitat conditions), aggregation of both tadpoles and insect predators in littoral vegetation may put tadpoles at greater risk of predation by insects, a potentially important factor of amphibian mortality in waters containing fish.
Highlights
Distributions of predators and prey across space can have major community-level consequences (Krivan, 1997; Lima, 2002)
The relative densities of anuran taxa varied with respect to fish presence; B. bufo was clearly more abundant in ponds with fish, and the densities of P. fuscus and H. orientalis were significantly lower in fish-containing ponds than in fishless ponds, while Pelophylax and Rana frog densities did not differ between ponds with and without fish (Table 1)
The main effects of habitat complexity indicated that insect predators and Rana tadpoles were more numerous overall in the littoral habitat, while P. fuscus and Pelophylax tadpoles preferred open-water habitat
Summary
Distributions of predators and prey across space can have major community-level consequences (Krivan, 1997; Lima, 2002). Predation has been demonstrated to alter habitat use and distribution of prey organisms (e.g., Gonzalez & Tessier, 1997; Dupuch et al, 2009; Hanisch et al, 2012). Predators that typically forage actively in simple open habitats are hampered by vegetation, and complex-structured microhabitats may relax their predation pressure on prey populations (Crowder & Cooper, 1982; Heck & Crowder, 1991). Multiple predators interact with one another, including intraguild predation (IGP), as well as with habitat complexity (Gonzalez & Tessier, 1997; Swisher et al, 1998; Anderson & Semlitsch, 2016). Prey shared by multiple predators should choose among habitats according to their use by top predators and by mesopredators, whose own spatial distributions are dependent on the distribution of top predators
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