Global patterns of tree species richness in moist forests: distinguishing ecological influences and historical contingency

Latham and Ricklefs observed statistically significant continent (region) e ffects in global comparisons of the species richness of forest trees. They argued that ecologists should entertain diversity hypotheses that include r egion-specific effects of history and geography on biological diversity. Fr ancis and Currie rejected this approach, claiming that alternative hypothes es based on variation in local ecological conditions are more parsimonious. In response, we point out that the diversity of the earth's biota, whether examined at the local, regional, or global level, does have a history and is responsive to large-scale events and processes that have region-specific expression and influence the net rate of diversification, Francis and Curr ie state that historical explanations may not be proper hypotheses because they make no predictions about contemporary patterns. However, historical i nsights into the accumulation of diversity within regions do invite the dev elopment of testable, mechanistic hypotheses about how geography and climat e influence rates of speciation and extinction. Diversification at the inte rsection of ecology and evolution presents biologists with both a formidabl e challenge and an exciting, but largely unexploited opportunity to further their understanding of biological communities at many stales of analysis.