Effects of Habitat Loss and Fragmentation on the Occurrence of Alouatta guariba in Brazil

Habitat loss is considered a major global threat to biodiversity. Yet, the effects of fragmentation are strongly debated, with studies showing positive, negative, or null effects on species. Understanding the effects of fragmentation has key conservation implications as negative effects prioritize large, contiguous habitats; null or weak effects highlight the protection of all habitat patches, regardless of their size; and positive effects support the preservation of small patches. This information is particularly important for highly threatened species with declining populations, such as primates. In this study, we assessed the independent effects of habitat amount (forest cover) and fragmentation (patch density) on the patch occurrence of the brown howler monkey ( Alouatta guariba ) across 956 forest patches in Brazil, using data from 53 studies. We found that both forest cover and patch density positively, but non-significantly, affect the occurrence of the brown howler monkey in forest patches. Weak effects of forest cover on patch occurrence are likely due to the ability of howlers to cope with habitat loss, although the long-term consequences of habitat destruction are considered negative for the species. Weak effects of fragmentation underscore the importance of maintaining both small and large forest patches for the conservation of the brown howler monkey.