How complex are the effects of habitat complexity in trophic interactions?
Aquatic habitats vary in the amount and type of habitat complexity provided by submerged macrophytes, tree trunks and branches or (artificial) coral reefs. These structures are regularly modified in habitat management as obstacles are removed or added for the sake of convenience, flood management, or restoration purposes. These changes can profoundly affect the diversity and composition of local communities through multiple mechanisms including changes in trophic interactions.
Figure: Larva of Aeshna waiting for prey among submerged vegetation (Photo: Vojtěch Kolář)
A new study published in Journal of Animal Ecology shows that the effects of habitat complexity on trophic interactions can be surprisingly complex. The research lead by Julien Mocq from the Laboratory of biodiversity and ecology of aquatic insects at the Institute of Entomology combined two different experimental approaches to understand how the functional response – the relationship between prey density and the number of prey eaten by a predator – changes along an artificial gradient of habitat complexity mimicking entirely barren to densely vegetated habitats. They used larvae of the dragonfly Aesha cyanea as predators and the phantom midge larvae (Chaoborus obscuripes) as prey. While they observed the largest change in functional response as the habitat transitioned from no structure (without any submerged macrophytes) to sparse vegetation, they detected other, more subtle nonlinear changes along the entire gradient of habitat complexity.
Their paper showed that the commonly used single-experiment approach comparing the presence/absence scale of habitat complexity may lead to incomplete or incorrect results. This can have important implications in more applied efforts trying to forecast the responses of trophic interactions and community structures to habitat alterations. A comparison to previous studies also revealed a striking difference in the effects of habitat complexity on trophic interactions in 2D and 3D environments.
Mocq J. H., Soukup P., Näslund J., Boukal D. (2021) Disentangling the nonlinear effects of habitat complexity on functional responses. Journal of Animal Ecology in press: DOI: 10.1111/1365-2656.13473