Geographic Aggregation of Regional Biodiversity Patterns at Multiple Scales

The amount of biodiversity contained within a region is strongly influenced by the range of environments represented within it. Each distinct environment exhibits a faunal assemblage made up of a few dominant and many rare taxa, some of which are endemic to the community in which it occurs. This mosaic of paleocommunities, contained within a variety of environments, arrayed through space within a region makes up the total picture of biodiversity, and incompletely sampling one portion of the mosaic can change perceptions of overall biodiversity.

This study illustrates how perceptions of regional biodiversity represented in the type Cincinnatian Kope Formation of Ohio, Indiana and Kentucky vary through space as a function of geographic scale and environmental heterogeneity. This research employs a series of sampling schemes derived from approximately equal-area grid cells across a regional ecological gradient to investigate how properties of biodiversity such as richness, rarity and the proportion of endemic taxa vary directly with the aggregation of geographic area. Richness varied as a function of geographic area, depicting a clear species-area effect, while rare genera (defined here as genera that occur only once among all samples within a geographic bin) exhibited relatively constant proportions among all geographic areas, provided that samples are compared to one another at sufficient sample size (n ≧300). The proportion of endemic taxa (defined here as genera that occur in only one geographic bin) increased with geographic area, in response to the inclusion of a wider range of depositional environments. While the geographic gridding scheme used here does not relate directly to traditional hierarchical definitions of alpha, beta and gamma diversity, the differentiation in diversity between geographic bins of different size can reveal how the geographic scale at which locality-level properties of biodiversity become amalgamated into regional biodiversity patterns.