Erosion of primate functional diversity in small and isolated forest patches within movement-resistant landscapes

Habitat disturbance is disrupting ecological processes globally. The Atlantic Forest is particularly affected by land-use intensification and defaunation, where primates play a key role in seed dispersal. Here, we evaluate how primate assemblages in the Atlantic Forest change according to landscape modification and the ecological consequences on seed dispersal. For this, we used 38 primate assemblages in the state of Sao Paulo, Brazil. We assessed the effects of patch size, mean inter-patch distance, functional connectivity and matrix permeability on primate species richness, functional evenness and functional dispersion, distinguishing response traits (sensitivity to habitat disturbance) from effect traits (effect on seed dispersal). We further investigated which primate functional response-effect traits were retained in forest patches of different sizes. Increased inter-patch distance reduced primate species richness. Decreased patch size led to a more uneven and less divergent distribution of response trait values within the functional space indicating the filtering of primates with similar strategies to cope with habitat loss. However, the increased divergence of effect traits in smaller patches indicates that those primates present distinct traits as seed dispersers. Finally, less permeable landscapes retained an uneven distribution of primate effect traits. Our findings indicate that reduced patch size results in primates with similar response traits, living in small groups and travelling short distances daily, but with contrasting traits as seed dispersers, which is positive for the persistence of non-redundant services in disturbed landscapes. However, the reduced species richness in such isolated patches and the resistance to movement among them may compromise the long-term viability of primate ecosystem services. Therefore, we encourage that further conservation planning should increase landscape connectivity, ensure the effective protection of native forests and increase anthropogenic matrix quality to develop biodiversity-friendly landscapes that protect not only species but also the ecosystem services they provide.