Species Diversity Patterns in Woody Flora on Three North American Peninsulas

Abstract

Species richness gradients along the Florida, Aleutian and Seward peninsulas were observed for woody flora by dividing each peninsula into quadrats of equal width and tabulating the total number of woody species found within each quadrat. In contrast to the pattern exhibited by several vertebrate groups of decreasing species density from the base to the tip of a peninsula, the woody flora of Florida does not show a decrease in overall species density. However, there is a marked change in species composition from the base to the tip of the Florida peninsula; fewer species were found to range throughout the Florida peninsula than on nine continental transects of similar size. Palynological records for Florida suggest that the steep gradient between temperate and tropical species pools is a result of climatic differences and habitat shifts over the length of the peninsula and not a result of historical disequilibrium. Two Alaskan peninsulas, the Aleutian and Seward peninsulas, exhibit relatively small changes in climate and topography and show little difference in species density from base to tip. While the peninsula effect has been attributed to a number of different phenomena for the varied taxonomic groups in which it has been observed, the floral evidence from three North American peninsulas suggests that changes in peninsular species density are a result of abiotic changes along these peninsulas.