Abstract

Structural complexity of habitats modifies trophic interactions by providing refuges and altering predator and prey behaviour. Nonlinear effects on trophic interaction strengths driven by these mechanisms may alter food web dynamics and community structure in response to habitat modifications. However, changes in functional response, the relationship between prey density and feeding rate, along habitat complexity (HC) gradients are little understood.We quantified functional responses along a HC gradient from an entirely unstructured to highly structured habitat in a freshwater system, using dragonfly larvae (Aeshna cyanea) preying on Chaoborus obscuripes larvae. To disentangle mechanisms by which changes in HC affect functional responses, we used two different approaches-a population-level and a behavioural experiment-applied an information theoretic approach to identify plausible links between HC and functional response parameters, and compared our results to previous studies.Functional response shape did not change, but we found strong evidence for nonlinear dependence of attack rate and handling time on HC in our study. Combined results from both experiments imply that attack rate increased stepwise between the unstructured and structured habitats in line with the threshold hypothesis, because the predators gained better access to the prey. Handling time was lowest at an intermediate HC level in the population-level experiment while the direct estimate of handling time did not vary with HC in the behavioural experiment. These differences point towards HC-driven changes in foraging activity and other predator and prey behaviour.Most previous studies reported stepwise decrease in attack rate in line with the threshold hypothesis or no change with increasing HC. Moreover, changes in the handling time parameter with HC appear to be relatively common but not conforming to the threshold hypothesis. Overall, increased HC appears to, respectively, weaken and strengthen trophic links in 2D and 3D predator-prey interactions.We conclude that detailed understanding of HC effects on food webs requires complementary experimental approaches across HC gradients that consider predator foraging strategies and predator and prey behaviour. Such studies can also help guide conservation efforts as addition of structural elements is frequently used for restoration of degraded aquatic habitats.

Keywords

Aeshna; attack rate; Chaoborus; dimensionality of predator–prey interactions; habitat domain; handling time; refuge; threshold hypothesis

Published in

Journal of Animal Ecology
2021, Volume: 90, number: 6, pages: 1525-1537
Publisher: WILEY

SLU Authors

• Näslund, Joacim

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    
  • University of South Bohemia in České Budějovice

UKÄ Subject classification

Ecology


Publication identifier

DOI: https://doi.org/10.1111/1365-2656.13473

Permanent link to this page (URI)

https://res.slu.se/id/publ/111484