Matching patterns with processes: Predicting the effect of size and mobility on the spatial distributions of the bivalves Macomona liliana and Austrovenus stutchburyi

Abstract

Descriptions of patterns of community or population variation in space can provide a stepping stone to inferring the relevant processes affecting spatial patterns. However, matching patterns to particular processes has proven difficult. In this study we make a priori predictions about the form and intensity of spatial patterns in abundance of the infaunal bivalves Macomona liliana and Austrovenus stutchburyi based on size, feeding mode and mobility. These predictions are tested by describing the spatial patterns found for a range of scales (5 to 33 cm and 33 cm to 6 m). In order to incorporate environmental variation, patterns were studied at 2 sites of different sediment grain size and hydrodynamic regime. Most of the spatial patterns found were the same in intensity and patch size at both sites, suggesting that biological rather than environmental processes were important. In particular, patch size appeared to be a function of mobility for all but M. liliana juveniles. Over the scales investigated in this study, individual mobility and inter-individual interactions appeared important processes influencing the observed spatial patterns of both juveniles and adults of these 2 functionally different species. This has important implications, as the ability to predict the relative importance of different processes through an understanding of an organism's natural history allows a much better appreciation of the effects of generalising results from small- scale studies.