COMMUNITY STRUCTURE: GLOBAL EVALUATION AND THE ROLE OF WITHIN COMMUNITY BETA-DIVERSITY

Abstract

Community structure is defined as the mathematical statistical distribution of the relative species abundance vector. Consideration of the decomposition equation for species richness, S, evenness, E, and the Shannon estimate of entropy or information, H, plus their respective regressions on the accumulation of the number of individuals, N, in a sample leads to the establishment of three structural types. Each type is defined by the slope, β 1H , of the regression H versus lnN and depends on the accumulation rate of species between samples (beta-diversity) in a community. These types are designated as 1) Type 0, where H is constant with the accumulation of lnN denoting equilibrium or stability (Log series is a special case); 2) Type 1, where the slope of H is positive with the accumulation of lnN denoting growth or expansion (Log normal is a special case); and 3) Type −1, where the slope of H is negative with the accumulation of lnN denoting decline, instability or stress. In this study, 72 communities were analyzed from environments ranging from marginal marine to the abyss. Only 10 communities are identified as type −1 with the majority of these at lower bathyal and abyssal depths. At abyssal depths the average β 1H is −0.057 and data from fossil communities in the Arctic indicate that this unstable, stressed situation has persisted for at least 50 ka. In the Gulf of Mexico at shelf depths, low values for β 1H are registered near the Mississippi delta. In contrast, the open-ocean east of New Zealand has an average β 1H of 0.227, the highest recorded. Among marginal marine environments an average β 1H of −0.030 was recorded in Long Island Sound before the collapse of that community. In contrast, the Indian River Lagoon, Florida had the highest β 1H for a marginal marine environment with an average value of 0.195. No simple invariant pattern between type 0 and type 1 communities is prevalent in any environment. Overall 31 communities are type 0 and 31 are type 1. In marginal marine environments (22 communities) the average value of β 1H is 0.092. In the open-ocean (50 communities) the average value of β 1H is 0.093. Evidently, for any group to remain highly successful on the average a slightly positive value of β 1H is required.