The karst ecology of the Bakwena Cave (Gauteng)

Abstract

The Bakwena Cave houses a variety of organisms that form an intricate and interdependent food web. This cave is utilised as a permanent roost by a colony of Natal clinging bats. The bat guano and allochthonous plant material that fall into the cave from outside, form the basis of the ecology inside the cave which may be considered a typical example of a detritus ecosystem. Decomposers such as bacteria and fungi are responsible for the decay of the guano and plant detritus which, in turn, are utilised by several organisms, including nematodes and mites, as food source. These animals form the next trophic level which is utilised by predatory arthropods as food source. The Bakwena Cave is one of the few dolomitic caves in South Africa that provide access to the water table. The groundwater houses several types of organisms, including bacteria, fungi and animals – primarily nematodes and crustaceans. The Bakwena Cave is also the type locality for freshwater amphipods in Southern Africa. This unique and sensitive ecosystem is primarily dependent on bat guano. The grassland surrounding the cave is utilised by the bats as foraging area and is currently threatened by urban development and the resulting habitat fragmentation and destruction. A cascade of extinctions of the cave-dwelling organisms will follow if the bats abandon the cave.