When Resources Become Limited: Trophic Niches Shift From Generalism to Specialization in Dung Beetles (Coleoptera: Scarabaeinae)

Abstract

Resource availability and predictability can shape trophic organization in ecological communities. In livestock pastures, cattle dung represents a highly abundant and predictable trophic subsidy for dung beetles, potentially promoting generalist foraging strategies. Here, we test how cattle exclusion affects trophic organization in dung beetle assemblages in the Brazilian Pantanal. We compared dung beetle richness, abundance, assemblage composition, and trophic classification between cattle-grazed and ungrazed pastures (< 20 years of cattle exclusion) using carrion and cattle dung as bait resources. Species richness and abundance did not differ between bait types in either system. However, dung beetle assemblages differed significantly between carrion and dung baits only in ungrazed pastures. In grazed pastures, assemblages were dominated by trophic generalists, whereas ungrazed pastures showed increased trophic specialization, including shifts of four species from generalist to specialist classifications following cattle exclusion. These findings indicate that predictable trophic subsidies homogenize trophic structure by promoting broad resource use, whereas resource limitation restores trophic differentiation and niche partitioning. Our results demonstrate how changes in resource availability can reorganize trophic interactions in decomposer communities and potentially alter patterns of functional complementarity in ecosystems.