Stochasticity in Structural and Functional Characteristics of an Indiana Stream Fish Assemblage: A Test of Community Theory

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Abstract
In general, ecological assemblages and communities appear to be regulated primarily by either deterministic or stochastic processes. To quantify the relative frequencies of these 2 types of assemblages is currently important since most ecological theory is applicable only to deterministic systems. To distinguish the mechanism regulating species abundances and trophic structure in an Indiana stream fish assemblage, samples were collected over a 12-yr period and separated by season (spring, summer and autumn) and species were assigned to a trophic group based on published dietary data. Analyses showed a total lack of persistence for the ranks of species abundances and the ranks of trophic groups for all seasons. This assemblage is probably regulated by stochastic factors. This finding is concordant with many other studies which have documented the substantial effects of environmental unpredictability (i.e., floods and droughts) on other stream taxocenes.