Hosted by

Stanislav Pekár

About the lecture

It is well recognized that predators can enhance plant growth by reducing herbivore abundance.

Yet the strength of such trophic cascades has been found to be quite variable both within and between communities. Moreover, effects of various taxa were usually summed within the effect of “predators” thus it remains unclear which predators and where might control trophic cascades. Even less know is the indirect effect of presence of predators on the changes in feeding behaviour of herbivores and its impact on plants. We hypothesise that birds, bats and ants are important predators of arthropods, which further affect plant growth directly and indirectly. However, their relative importance may differ along large (latitudinal) gradients due to changes in their richness and abundance and productivity of the environment. For similar reasons, we also expect that the importance of predators differs in forest canopies and understories, as productivity and trophic levels are predicted to be higher in the canopies.

To find out where top-down forces control food webs, we run predator exclosure experiments along latitudinal and vertical gradient(s). We exclude ants, birds, and/or bats separately and in combinations from saplings and from branches in forest canopies and run smaller experiments in laboratories to identify the direct and indirect effect of predators on lower trophic levels. We further investigate various plant defences, which are inevitably shaping the interactions via bottom up control and we fit our findings into a big picture of a global meta-analysis of similar studies during which predators were excluded. We discuss that stable arthropod populations are maintained by natural enemies of various importance along gradients and that disruption of communities of natural enemies often, but not always, result into significantly increased abundances of insect, increased herbivorous damage and into changes in leaf traits.