Analysis of Simple Cave Communities. III. Control of Abundance

Abstract

In several cave-stream populations of Stygonectes spinatus and Gammarus minus, but not Asellus holsingeri, there was a large drop in abundance during spring high water. A long-lasting rather than short-term distributional change, this drop in abundance occurred despite the fact that the amount of food available is greatest during spring high water. Stygonectes species are less abundant than G. minus, largely because of the former's higher washout rate. This explains the rather difficult-to-grasp fact that the older cave species are less common. Experiments in an artificial stream indicate that washout rate is density- dependent, at least in G. minus, with some density-independent washout occurring under extreme environmental conditions. Washout is increased by increasing current velocity, increasing density, decreasing the size of the animals, or reducing the amount of available food.