HIGHLY STRUCTURED FISH COMMUNITIES IN AUSTRALIAN DESERT SPRINGS

To assess the pattern and causes of community structure, we sampled 38 isolated springs in the Dalhousie Basin of South Australia to determine the distributions of five taxa of native fishes. We visited each spring on at least two consecutive days, used several collecting methods to determine the presence or absence of each taxon, and took standardized measurements of abiotic environmental variables. Community organization was highly predictable: (1) number of species increased with spring size, (2) each species occurred in nearly all springs larger than a certain size, and (3) species composition exhibited nearly perfect nestedness. These results suggest that much of the variation in the composition of other communities may not be stochastic. When the influence of historical and environmental factors can be assessed, the colonization-extinction processes and ecological relationships that determine community structure may be highly deterministic.