Food webs: From the response to environmental conditions to effects on ecosystem functions and species coexistence
Food webs depict the trophic interactions between species within communities. Consequently, they represent a set of ecological constraints related to the access of species to energy that underlie ecosystem functioning and species coexistence. Therefore, the organisation of these trophic interactions among species (i.e., food web structure or topology) can be viewed as both an effect variable and a response variable: changes in food web structure are associated with alterations in environmental conditions that will thereafter affect ecological processes at the community and ecosystem level. Therefore, the body of methods and theories centred on trophic interactions defines a framework able to link mechanistically modifications of environmental conditions and perturbations to species coexistence and ecosystem functions. This will be illustrated with examples based on two different approaches. First, models of population dynamics can be used to integrate biological scales -from physiology to communities- and predict the response of local communities to temperature increase. Second, the calculation of energy fluxes in food webs can be used to assess how ecological gradients will affect ecosystem functions, making connections between food webs and functional ecology.