Habitat Loss Shapes Isotopic Niche Responses of a Didelphid Opossum to Fragmentation in Neotropical Semideciduous Dry Forests of Central Brazil

ABSTRACT Habitat loss and fragmentation have notable effects on species' trophic ecology, often most pronounced in landscapes with intermediate levels of remaining habitat, where patch configuration can vary significantly. We assessed how habitat fragmentation influences the carbon‐ and nitrogen‐based isotopic niche space of the agile opossum ( Gracilinanus agilis ) across landscapes with varying habitat loss in semideciduous dry forests in central Brazil. We found that δ 13 C values did not vary with patch size or habitat loss, suggesting a consistent reliance on forest resources. The opossum exhibited a niche shift only in intermediate and more conserved landscapes, transitioning from insectivory to frugivory in small and large patches, respectively, with a stronger effect in intermediate landscapes. In the most degraded landscape, niche width expanded in smaller patches, likely due to the inclusion of less valuable dietary items in a context of limited food availability and high forager density. Conversely, there was a niche expansion towards larger patches as one moved from intermediate to more conserved landscapes. This shift was attributed to higher resource availability and diversity in areas with better habitat quality and increased forest complexity. There is clear evidence that fragmentation and habitat loss modify the trophic niche of G. agilis , potentially hampering its ecological role as a seed disperser, especially in more degraded landscapes. Although the opossum exhibits high adaptability to landscape alterations through trophic plasticity, even small patches might be crucial for their populations in highly fragmented landscapes due to their reliance on forest resources.