The Influence of Taxonomic Level on Biogeographic Patterns

Studies of extinctions are usually conducted at the family or genus level due to the volatile nature of species and the systematic difficulties in comparing species from distant geographic areas. In contrast, community analyses are typically performed at the genus or species level because these studies generally sample a small geographic area over a short temporal duration. In order to bridge the gap between large-scale and local-scale studies, it is necessary to understand how the taxonomic level of identification can influence the observed biogeographic patterns and relationships between sample sites. Does the taxonomic level used in biogeographic studies greatly affect the observed pattern of relationship among sample sites, when comparing communities that are biogeographically isolated from one another?

Modern biogeographic patterns based on the presence/absence of modern terrestrial vertebrate or vascular plant taxa from 16 U.S. National Parks were characterized using Nonmetric Multidimensional Scaling. Results of these analyses at species, genus, and family level are compared to determine if major patterns change with taxonomic level.

Results show that taxonomic level does not substantially influence the major patterns shown in biogeographic studies. The robustness of the ordination patterns is even more evident with the removal of avian taxa (56-69%) or rare taxa (20 to 70%). While the results of this study have direct applications to modern biogeographic studies, these results are especially exciting when applied to the fossil record. Many fossil taxa can only be identified to the family level due to poor preservation or a poor understanding of a group's systematics. The results of this study suggest that even such limited data can provide useful information on biogeography in Earth's past and how it has changed through time.