Macroinvertebrate diversity patterns in a guano-rich temperate cave

Abstract

Most caves in temperate regions are energy-poor, leading to low richness and abundances of terrestrial macroinvertebrates. However, caves with abundant bat populations may represent a notable exception, as bat guano serves as a significant source of organic matter, supporting diverse specialized invertebrates. Yet, given the overall rarity of guano-rich caves in temperate region, their ecological dynamics are poorly understood. We conducted a year-long monthly standardized monitoring of the macroinvertebrates of the Buca dei Ladri cave, a guano-rich cavity in Tuscany, Italy. At each survey, we counted species within different sampling quadrats and collected environmental variables such as temperature, structural heterogeneity of the substrate, dominant substrate, and presence of bats. Over the year, we identified 31 macroinvertebrate species in the cave as both morphospecies and molecular lineages, based on mitochondrial COI and nuclear 18S genes. The latter approach hinted at the presence of cryptic diversity in some species. We observed an increase in species diversity with increasing structural complexity and the presence of bats, whereas a lower species diversity was found in guano-dominated substrates, probably due to the old age and subsequent low nutritional value of the historical guano deposits. Changes in the abundance of species within the cave were primarily explained by differences in structural complexity across sampling quadrats, whereas the distance from the cave entrance mostly explained species replacement. Our results underscore the importance of preserving healthy bat populations and a high habitat heterogeneity within the cave for the long-term conservation of the unique macroinvertebrate assemblages of the cave.