A community-level analysis of spatial mortality patterns

Abstract

Spatial patterns of mortality often reflect ecological processes controlling sessile communities. An analysis combining indices of patchiness and species association that describes the effect of conspecifics and interspecifics on spatial patterns of mortality is introduced. This analysis may be especially suitable for community-level descriptions when low densities preclude ecologically meaningful examinations of population-level patterns. Because densities of individuals (expressed on a per quadrat basis) decrease with spatial scale (quadrat size), this analysis may be particularly appropriate for understanding the role of processes such as competition for substratum space whose intensities increase with increasing proximity among individuals. Alternatively, the usefulness of this analysis may be restricted to situations where all species are affected similarly by underlying causal processes. I used the analysis to examine small-scale ( 1 64 m 2 ) mortality patterns in two shallow-water gorgonian communities in Puerto Rico from 1983–1993. Analytical results, which were consistent with ‘random thinning’ Monte Carlo simulations, indicated that mortality is independent of abundances of conspecific and interspecific colonies. These results indicate that competition for substratum space among gorgonians does not play a major role in the dynamics of this community.