Caves as Oligotrophic Ecosystems

Abstract

Oligotrophic caves are characterized by very limited sources of organic material and simplified trophic structure due to their predominant isolation from surface ecosystems. Trophic structure of caves depends on their connectivity and interactions with the epigean environment. The food base for biota in nutrient poor caves is mostly confined to organic substances encompassed in percolating water, which also mediates transport of microbes and microfauna into subterranean habitats. Many of the cave microbes are genetically divergent from surface microbes and adapted to the aphotic and oligotrophic cave environment. In nutrient-poor caves heterotrophic bacteria dominate accompanied by a number of chemoautotrophs that gain energy from inorganic chemicals through chemosynthesis and fix inorganic carbon. Chemoautotrophs may thus impact many geological or geochemical processes in subterranean systems and serve as the food source for microbivorous and omnivorous subterranean animals. In caves, food scarcity acts as a selective force and requires evolutionary adaptations in animals related to their morphological and biological traits. In warmer regions of the globe, oligotrophic habitats are characterized by high proportions of the community being troglobiotic or stygobiotic. The amount and nature of the food supply control the presence of troglo- and stygobionts and the overall composition of animal assemblages.