# Bat Colony and Cave Zone Shape Arthropod Assemblages in Levantine Caves

## TL;DR

Bats influence the types and numbers of arthropods in caves, with different bat diets and cave zones shaping biodiversity.

## Contribution

This study reveals how bat guano type and cave zones affect arthropod assemblages, emphasizing bats' role in cave ecosystems.

## Key findings

- Caves with bat colonies have more predators and decomposers than those without bats.
- Fruit-eating bat caves have fewer flies compared to insect-eating bat or no-bat caves.
- Arthropod diversity and composition differ between twilight and dark cave zones.

## Abstract

Caves are unique environments, markedly distinguished from above-ground habitats by the absence of light in their deeper regions. Life in most caves relies on external nutrient subsidies, since photosynthetic organisms, which form the basis of most food-webs, cannot grow in the absence of light. Bat droppings, or guano, constitute an important nutrient source that supports unique food-webs in caves. In this study, we explore how different types of bat guano (from fruit-eating vs. insect-eating bats) and different zones within a cave (twilight vs. deeper regions) affect the number and type of arthropods, such as insects, spiders, and woodlice, inhabiting the cave. Our results indicate that caves with bat colonies contain more predators and decomposers than caves without bats. Additionally, caves hosting fruit-eating bats contained fewer flies than those inhabited by insect-eating bats and those lacking bat colonies. Moreover, the microhabitat within the cave is of importance: certain areas, such as the cave walls, support fewer species. This research highlights the role that bats play in controlling key ecosystem processes in caves. By demonstrating the important role played by bats in supporting underground arthropod life, this study emphasizes the necessity of protecting both bats and caves in order to preserve the hidden biodiversity of caves.

Caves are characterized by unique abiotic conditions such as limited light, and they therefore support distinct faunal assemblages that often include endemic species. Due to light limitations, photoautotrophic organisms are absent from many subterranean food-webs, which therefore predominantly rely on allochthonous nutrient sources. For this reason, hypogean habitats are expected to display lower assemblage diversity than that seen in epigean ecosystems. Bat guano, a major source of allochthonous nutrients in caves, varies substantially in composition based on its origin—whether it is produced by frugivorous or by insectivorous bats—and on its deposition site within the cave. This study examines how allochthonous nutrient sources and zones within caves influence arthropod diversity and assemblage composition. We found that both the type of allochthonous nutrient source and cave characteristics strongly affect the composition of arthropod assemblages. Our results show that caves harboring frugivorous bat colonies have a lower abundance of flies than caves with either insectivorous bat colonies or no bat colonies. Moreover, caves without bat colonies were seen to have low species richness of both detritivores and predators compared to caves housing either frugivorous or insectivorous bats. Additionally, species diversity and assemblage composition differed substantially between the twilight and dark zones of the caves. These findings demonstrate that allochthonous nutrient sources, the ecological zone, and the microhabitat within the cave are key drivers of arthropod assemblage composition and diversity. This study advances our understanding of cave ecology and underscores the importance of conserving diverse cave types for protecting their unique arthropod diversity.