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Abstract
In 1975 E. H. Rapoport described a pattern of increasing latitudinal range sizes for organisms with increasing latitude, a pattern that is now known as Rapoport's rule. The universal applicability of Rapoport's rule has been long contested, making it one of the more controversial biogeographic “rules.” This study aims to reassess the applicability of Rapoport's rule to U.S. tree species. Data presented here suggest that Rapoport's rule does indeed apply to most tree taxa within the United States, but may be taxon specific. In addition, data presented here suggest that tree range patterns consistent with Rapoport's rule in the United States are not restricted to high latitudes and are not the result of a “boundedness effect” but may be intimately linked with the glacial history and physical geography of North America. The analyses conducted here are intended to emphasize the utility of such biogeographic rules even if they are not universally applicable and should, in turn, only be considered biogeographic patterns.
Notes
aThe number of tree species in each latitudinal grouping; species were grouped based on the latitudinal midpoint of their range.
bCalculated r values for the linear regression analysis.
*Result is statistically significant at the 0.05 level.
**Despite the high r value, the sample size is too small for this regression analysis to be significant.
*I wish to thank Dr. Daniel Simberloff and Dr. Sandy Echternacht for their comments, advice, and support regarding this project. I also wish to thank Kyle J. Schlachter for his assistance with data collection and analysis. Finally, I thank four anonymous reviewers for their detailed comments and suggestions, which improved this manuscript considerably.