Colonization alters community structure by modulating food web interactions
It has been demonstrated that food web interactions and colonization can each influence community structure. However, these mechanisms may not be independent as species faced with diet choice may alter foraging strategies depending on the supply of different resources, which is determined in large part by colonization processes. Here we combine mathematical models with laboratory and field mesocosm experiments to show that interactions between omnivores, animal consumers, and plant resources in aquatic food webs are modulated by colonization rates. This has consistent effects on community structure.
We experimentally manipulated consumer colonization rate and the presence of omnivores in a field array of aquatic mesocosms. Higher colonization rates led to stronger omnivore effects on consumer biomass than in communities experiencing low colonization rates. In turn, there was strong depression of algae biomass by omnivores when colonization rate was low, and neutral or positive effects on algae biomass when colonization rate was high. Models and laboratory experiments suggest an underlying mechanism: increasing consumer colonization rate shifts omnivore foraging effort increasingly away from resources. These changes can occur on timescales that are relevant to real ecological systems, and affect the distribution of biomass among trophic levels.