Patch size, isolation and forest cover variably shape the beta diversity of dung beetle assemblages in the eastern Amazon

Deforestation is a growing issue in the Amazon because it leads to loss of biodiversity and ecosystem services. Dung beetles (Scarabaeidae: Scarabaeinae) are vital to forest ecosystem dynamics, and thus understanding the effects of habitat loss and fragmentation on dung beetle distribution is crucial to evaluate the consequences of anthropogenic impacts on tropical forests. However, the outcomes and mechanisms through which deforestation reshapes the biodiversity of many Amazon taxa remain poorly understood, and few studies addressed the roles (and extent) that landscape structure attributes play in shaping dung beetle distribution in the Amazon. We assessed β-diversity patterns and assemblage structure of dung beetles in forest patches of different sizes and with surrounding land uses in a fragmented landscape in the eastern Amazon. We specifically investigated the extent to which dung beetle β-diversity replacement and nestedness vary in relation to patch size, isolation, forest cover and matrix composition. Beetles were collected using pitfall traps in Maranhão state (northern Brazil). Dung beetle β-diversity decreased in pasture-dominated matrices and more isolated patches, and was structured by a gradient of taxa turnover from forest- to pasture-dominated matrices (and by nestedness from smaller- to larger-sized patches). Our findings show that forest loss and landscape encroachment lead to homogenization of dung beetle assemblages, while forest loss at the patch level induce environmental changes which eventually modify dung beetle diversity in the eastern Amazon. This study helps untangle the mechanisms structuring dung beetle distribution along gradients of forest loss and fragmentation. Our findings can inform conservation strategies and land management practices aimed at preserving tropical forest biodiversity and ecosystem functions.