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Behavioural responses to predation may explain shifts in community structure

Hammill, Edd, Atwood, Trisha B., Corvalan, Paloma, Srivastava, Diane S.
Freshwater biology 2015 v.60 no.1 pp. 125-135
Culex, geographical distribution, Bromeliaceae, interspecific variation, risk, community structure, aquatic food webs, evolution, landscapes, tropics, Wyeomyia, predators, habitats, predation, ecosystems, insect larvae, surface water, Zygoptera, biogeography
Predators exert a strong selective force on the ecosystems in which they exist, thereby altering the structure of ecological communities and leading to the evolution of prey defences. However, how interspecific differences in defence ability affect habitat partitioning amongst competing prey species remains unresolved. We examined how prey defences affect species distribution in a natural ecosystem: the aquatic food web within Neotropical bromeliads. We first related differences in prey (mosquito) density to the presence and absence of predatory damselfly larvae. We then quantified behavioural responses to predators in the two most abundant mosquito species, and the effects of these behaviours on predator consumption rates. In the absence of damselflies, Wyeomyia was the most abundant mosquito genus in natural bromeliads. However, Wyeomyia numbers were reduced in the presence of damselflies. Numbers of the genus Culex increased with bromeliad size irrespective of the presence of damselflies. As a result of the differing effects of plant size and damselflies on the two genera of mosquito larvae, Culex were more numerous in large bromeliads containing damselflies. The most abundant Culex species, Culex jenningsi, had two kinds of behavioural defences: reduced movement and increased time at the water surface. These defences reduced damselfly attack rate on C. jenningsi, but not handling time. Consequently, consumption rate was reduced at all but the highest prey densities, altering the damselfly's functional response. Inducible defences were not seen in the most abundant Wyeomyia species, Wyeomyia abebela, and pre‐exposure to predation risk did not reduce predation on this species. Inducible behavioural defences, and the associated reductions in predation rate, evidently allow C. jenningsi to coexist with predators at a higher density than W. abebela. As predation risk is non‐randomly distributed amongst bromeliads, divergence between mosquito species in their response to predation may contribute to the coexistence of a number of mosquito species across the landscape.