Estimates of insect consumption and guano input in bat caves in Brazil

Abstract

Bat caves harbor exceptional populations of insectivorous bats. Those bats play an important role as insect suppressors and produce large quantities of guano, which is essential for maintaining cave ecosystems since entire highly specialized cave biotas may heavily rely on bat guano as their main energy input. Although ecologically relevant, few studies have estimated insect consumption and guano input in Neotropical bat caves. We provide estimates for five bat caves used by Pteronotus gymnonotus and P. personatus (Mormoopidae) in northeastern Brazil. Using a non-invasive automated system, we counted bats, then captured and weighted individuals to estimate insect consumption, and, with collectors and rulers, estimated the amount and speed of guano accumulation in cave sectors. Bat abundance varied between and within caves, up to 158,884 bats, indicating highly dynamic occupation patterns. Insect consumption varied from 0.6 to 2.5 g/bat for P. gymnonotus (~5 to 20% of their body weight) and 0.8 to 2.0 g/bat for P. personatus (~10 to 28% of their body weight). Guano deposition was spatially and temporally heterogeneous (from 0 to 738 g/m2/96h). Some caves showed a 15-cm increase in guano deposits on the cave floor in 7 months. Bulky guano deposits in those caves stressed the bat role as insect suppressors. The present study provides baseline quantitative data on the contributions of bats to cave ecosystems and valuable data for estimates of ecosystem services provided by bats.