Diversity in constant and fluctuating environments

Abstract

IT has been suggested that environmental fluctuations will limit the degree to which species may be packed; the closeness of the packing increasing with increasing environmental stability¹. This theory has been challenged by the suggestion that although there is a limit to the degree of niche overlap in the real world, the limit is only sensitive to severe environmental fluctuations². The fluctuations are regarded as severe when their variance to mean ratio is greater than or equal to 0.3 (ref. 2). We report here our studies on populations of ciliate protozoa of a freshwater community maintained in temperature-controlled microcosms. Comparisons were made between the changes in diversity of the ciliates in a microcosm maintained in a fluctuating temperature and the changes taking place in a control maintained at a constant temperature. The results suggest that the diversity of the ciliates is significantly greater in the fluctuating-temperature system than in the constant-temperature system.