Fish modulate how connectivity and local factors shape food webs of permanent ponds

The propagation of metacommunity processes through local trophic interactions has seldom been explored, particularly in empirical studies. This study examines how local environmental conditions and metacommunity connectivity influence community assembly and food web structure in pondscapes. We survey taxonomic richness, abundance and isotopic niches across multiple assemblage, including zooplankton, macroinvertebrates, tadpoles, turtles and fish. A gradient in the composition of the pond community representing the dominance of fish or other taxa and another gradient associated with macroinvertebrate diversity were evidenced. Pond size and connectivity promoted fish richness and abundance, representing the main path through which metacommunity processes cascade down within communities, determining the assembly of the whole system. The dominance of fish was associated with large food chains, a reduction in both the food web width and the trophic spacing. Local conditions such as macrophyte coverage and pond size modulate the strength of these fish effects, determining the representation of macroinvertebrates and amphibians. Consequently, the effects of pond connectivity on community assembly may result as a consequence of isolation's influence on top predators' performance, rather than by the direct effect of dispersal on different species, as is usually assumed. Metacommunity theory has highlighted the direct effect of dispersal on species performance and diversity. Our study highlights the indirect influence of landscape mediated by keystone species, which connect metacommunity dispersal with local community processes more than previously thought.