Food web, taxonomy and functional level community response to large-scale biogeographical gradient

Abstract

Food webs are being increasingly used to predict ecosystem stability. The ultimate food web properties already account for the abiotic (environment) and biotic interactions (i.e. predator-prey interactions). While the importance of abiotic environment on a single taxonomical or functional diversity is being recognized, the role of environment in structuring trophic interactions is less explored. Additionally, food web complexity can often be difficult to interpret or link with specific predictors (i.e. increasing temperature). To fill this knowledge gap we studied trophic structure of freshwater pond communities together with its taxonomical and functional (body size and feeding traits) attributes across biogeographic gradient that ranged from semi-arid to alpine environments. We aimed to understand if taxonomical, functional and community trophic structure are uniformly driven by the biogeographical gradient of abiotic variables. We used stable isotopes and calculated isotopic metrics of trophic structure that can be easily comparable among sites and communities. The highest isotopic richness and nitrogen range was at the temperate climate sites and one mountainous. This pattern was also corroborated by the highest biomass of predators and omnivores at these sites. The simplest food webs were found at the arid climates where community was dominated by zooplankton and small herbivores that constituted the majority of the biomass. Regardless this obvious pattern, trophic metrics were highly variable within sites preventing to obtain clear signals with abiotic variables. Abiotic variables related to biogeographic gradient were more evident to shape taxonomical and functional community structure whereas food webs were rather reflecting smaller scale variability associated to pond characteristics.