Functional diversity and trait filtering of insectivorous bats on forest islands created by an Amazonian mega dam

1. Mega dams in lowland tropical forests often create large archipelagos,
leading to biodiversity decay and disruption of ecosystem functioning in
remnant habitat islands. 2. We investigated the functional diversity and
functional trait filtering of aerial insectivorous bats in both insular
forest patches created by a vast ~30-yr-old hydropower reservoir and the
adjacent mainland continuous forest in Central Amazonia. 3. Bats were
surveyed using passive bat recorders across 34 forest sites. Based on a
set of morphological traits derived for each species recorded, we
estimated both the bat functional richness, functional evenness and
functional dispersion at each surveyed site. We further assessed the
effects of local vegetation, patch and landscape features on patterns of
functional diversity. The interaction between functional traits,
environmental characteristics, and species distribution was investigated
using a combination of RLQ and fourth-corner analyses. 4. We found that
mainland sites retained higher functional richness and lower functional
evenness compared to forest islands, indicating a more complete functional
assemblage in the mainland. Additionally, species composition was affected
by local vegetation structure and forest area, with small isolated islands
exhibiting pervasive loss of functional traits. RLQ and fourth-corner
analyses showed that larger understorey foraging species with greater
dispersal capacity, constant frequency-frequency modulated calls, and
higher frequency of maximum energy were associated with more isolated
small islands. Conversely, forest subcanopy species, exhibiting
quasi-constant frequency calls and presenting low dispersal capacity were
associated with continuous forests and islands with greater forest area,
and were therefore more sensitive to habitat insularization. 5. Our study
calls attention to the pervasive impacts induced by large dams on the
functional diversity of tropical insectivorous bats. We recommend that
future assessments of the effects of habitat fragmentation on mammals
should include traits linked to ecosystem services. In designing and
licensing new dams, we suggest the creation of extensive protected areas
surrounding mainland forests to minimize the detrimental impacts of small
isolated islands and safeguard the full complement of key ecological
functions provided by insectivorous bats.