Indirect Effects of Habitat Amount Mediated by Habitat Configuration Determine Bat Diversity in Peninsular Malaysia

As habitat loss is the primary cause of habitat fragmentation, understanding the inter-related effects of these processes is key to minimize biodiversity loss. Despite this, only a few studies have considered such inter-relationships. To help fill this gap, we assessed how habitat amount and configuration influence insectivorous bat assemblages, considering both their direct effects, as well as the indirect effects of habitat amount mediated through configuration. Bats were acoustically surveyed along a range of habitat amount (forest cover) and configuration (number of patches and edge density) across 28 insular landscapes embedded within a Malaysian hydroelectric reservoir. Using Structural Equation Modeling, the direct and indirect effects of habitat amount were examined considering bat sonotype richness, total, and guild-specific activity (i.e., forest, edge and open-space foragers). The relationship between edge density and forest cover depended on the forest amount remaining in the landscape: below 30% of forest cover, forest cover had a positive effect on the edge density; and, above 30%, the opposite relationship was observed. Forest cover had a direct positive effect on sonotype richness and forest forager activity. Owing to the overall low habitat amount in our landscapes and negative effects of edge density, the indirect effects of forest cover, mediated through edge density, were therefore negative on sonotype richness. Our results highlight that any alteration of habitat amount influences habitat configuration, thereby preventing independent management of these threats. Minimizing habitat loss is therefore essential to balance the associated negative effects of fragmentation on insectivorous bats across tropical forests.