Edge effects and vertical stratification of aerial insectivorous bats across the interface of primary-secondary Amazonian rainforest

Abstract

Edge effects, abiotic and biotic changes associated with habitat boundaries, are key drivers of community change in fragmented landscapes. Their influence is heavily modulated by matrix composition. With over half of the world’s tropical forests predicted to become forest edge by the end of the century, it is paramount that conservationists gain a better understanding of how tropical biota is impacted by edge gradients. Bats comprise a large fraction of tropical mammalian fauna and are demonstrably sensitive to habitat modification. Yet, knowledge about how bat assemblages are affected by edge effects remains scarce. Capitalizing on a whole-ecosystem manipulation in the Central Amazon, the aims of this study were to i) assess the consequences of edge effects for twelve aerial insectivorous bat species across the interface of primary and secondary forest, and ii) investigate if the activity levels of these species differed between the understory and canopy and if they were modulated by distance from the edge. Acoustic surveys were conducted along four 2-km transects, each traversing equal parts of primary and ca. 30-year-old secondary forest. Five models were used to assess the changes in the relative activity of forest specialists (three species), flexible forest foragers (three species), and edge foragers (six species). Modelling results revealed limited evidence of edge effects, except for forest specialists in the understory. No significant differences in activity were found between the secondary or primary forest but almost all species exhibited pronounced vertical stratification. Previously defined bat guilds appear to hold here as our study highlights that forest bats are more edge-sensitive than edge foraging bats. The absence of pronounced edge effects and the comparable activity levels between primary and old secondary forests indicates that old secondary forest can help ameliorate the consequences of fragmentation on tropical aerial insectivorous bats.

Secondary forest buffers the effects of fragmentation on aerial insectivorous bat species following 30 years of passive forest restoration

“…This resulted in the selection of 272,201 calls from nine species and one sonotype; Centronycteris maximiliani , Cormura brevirostris , Saccopteryx bilineata , S. leptura , Furipterus horrens , Molossus sonotype (including currentium / rufus calls), Pteronotus alitonus , P. rubiginosus , Eptesicus brasiliensis , and Myotis riparius (Table S1). Following Yoh et al (2022), we assigned species/sonotypes to guilds based on ecological requirements and foraging strategies: EF— C. brevirostris , C. maximiliani , S. bilineata , S. leptura ; FS— E. brasiliensis , F. horrens , M. riparius ; FF—both Pteronotus species; OS— Molossus sonotype (included in the guild analysis for comparison only as represented by a single sonotype).…”

“…Farneda et al 2018Farneda et al , 2022Rocha et al 2018), recent research has also targeted the ensemble of aerial insectivorous bats (e.g. Appel et al 2021b;Yoh et al 2022), which comprises a considerable fraction of the BDFFP bat fauna. Multi-dimensional (taxonomic, functional, and phylogenetic) diversity responses of the aerial insectivorous bat ensemble to vegetation and landscape structure indicated subtle scalesensitive associations for functional diversity only .…”

“…Farneda et al 2018, 2022; Rocha et al 2018), recent research has also targeted the ensemble of aerial insectivorous bats (e.g. Appel et al 2021 b ; López‐Baucells et al 2022; Yoh et al 2022), which comprises a considerable fraction of the BDFFP bat fauna.…”

“…In contrast, forest edges generally harbored higher taxonomic, functional, and phylogenetic diversity compared to continuous forest interiors. Recent research investigating species‐specific responses of aerial insectivores to edge effects across the interface of continuous and secondary forest suggested that the regenerating secondary forest might have recovered enough that edge effects are no longer evident for most common species (Yoh et al 2022). In contrast, Appel et al (2021 b ) found lower activity in the regenerating secondary forest suggesting that even after 30 years it remains less attractive as a foraging habitat.…”

“…Here, we build on our previous multi‐dimensional diversity analysis (López‐Baucells et al 2022) and investigated (1) how species‐specific occupancy and activity differ across the four main habitats (continuous forest [CF], forest fragment interiors [I], fragment edges [E], and secondary forest matrix sites [M]), considering both the disturbance interior‐edge‐matrix [IEM]) and fragment‐size gradients; and (2) whether local vegetation structure and landscape metrics influence activity across multiple spatial scales. These comparisons were conducted for a selection of common species/sonotypes and four functional guilds (edge foragers [EF], forest specialists [FS], flexible forest foragers [FF] and open space specialists [OS] sensu Yoh et al 2022).…”