Temporal changes and the effects of disturbance on the partitioning of biodiversity of terrestrial gastropods at various spatial scales

Christopher L. Higgins, Christopher P. Bloch, and Michael R. Willig

The additive partitioning of total biodiversity (γ) into within (α) and among (β) components is an increasingly important topic in ecology because estimates of each spatial component are directly comparable and scaled in a hierarchical fashion.  Nonetheless, little is known regarding temporal changes in the contribution of each component to total biodiversity, especially in systems that experience periodic disturbances.  We examined temporal changes in patterns of spatial partitioning of biodiversity of terrestrial gastropods in the Luquillo Experimental Forest of Puerto Rico, where effects of historic land use are still evident despite two major hurricanes (Hurricane Hugo in 1989 and Hurricane Georges in 1998).  We analyzed long-term data (1991-2007) on the distribution and abundance of terrestrial gastropods to quantify biodiversity at five scales: within sites (α_sites), among sites (β_sites), within landuse categories (α_landuse), among landuse categories (β_landuse), and total (γ).  Our main objectives were to determine if different measures of biodiversity (i.e., species richness, Shannon diversity, Camargo evenness, Berger-Parker dominance, and rarity) changed through time in a scale-dependent manner and if these effects differed between hurricanes.  Species richness, regardless of spatial scale, was not different between Hurricanes Hugo and Georges, and no post-disturbance trend was discernable.  Diversity, evenness, dominance, and rarity each decreased over time, but at different spatial scales.  These scale-dependent reductions in biodiversity are attributable to the disproportionate increase in abundance of Nenia tridens during secondary succession.  Shannon diversity and Berger-Parker dominance were each significantly different between hurricanes, at least at the local scale (within sites).  Spatial configuration of biodiversity differs among indices, and the relative contributions of additive components vary during secondary succession in a hurricane-specific manner.