Functional trait space overlaps reveal ecological resilience of bird communities in Atlantic Forest fragments

Abstract

While fragmentation is known to affect species diversity, the degree to which functional structure is retained relative to primary forests and the factors driving this retention remain poorly understood. Here, we applied the concept of ecological resilience to forest fragmentation by examining the extent to which bird communities in 20 forest fragments (27-926 ha) retain the functional trait space observed in a large, protected area of primary forest used as a reference, Iguaçu National Park (INP), within the Seasonal Semideciduous Atlantic Forest of southern Brazil. We used retention of the functional trait space of the reference forest as an indicator of potential ecological resilience and, consequently, conservation value. Functional trait spaces were estimated using kernel hypervolumes, and three metrics were calculated: (1) the percentage overlap between the trait spaces of INP and each fragment; (2) the fraction of trait space unique to INP; and (3) the fraction unique to each fragment. Functional overlap ranged from 63 to 77%, the fraction unique to INP ranged from 5 to 29%, and the fraction unique to fragments ranged from 14 to 24%. Although observed functional overlap was substantial, it did not differ significantly from null expectations based on species richness and abundance structure. Landscape diversity is associated with a higher percentage of trait space unique to fragments, whereas larger fragment area was associated with greater overlap in trait space between INP and fragments. Assessing trait space overlap between continuous forest and fragments provides a novel perspective on functional responses to fragmentation and can help identify patterns potentially relevant to ecosystem functioning.