Relative effects of time for speciationand tropical niche conservatism on the latitudinal diversity gradient of phyllostomid bats

Determinants of contemporary patterns of diversity, particularly those spanning extensive latitudinal gradients,are some of the most intensely debated issues in ecology. Recently, focus has shifted from acontemporary environmental perspective to a historical one in an attempt to better understand the constructionof latitudinal gradients. Although the vast majority of research on historical mechanisms hasfocused on tropical niche conservatism (TNC), other historical scenarios could produce similar latitudinalgradients. Herein, I formalize predictions to distinguish between two such historical processes-namely time for speciation (TFS) and TNC-and test relative support based on diversity gradients ofNewWorld bats. TFS and TNC are distinctly spatial and environmental mechanisms, respectively. Nonetheless,because of the way that environmental characteristics vary spatially, these two mechanisms arehard to distinguish. Evidence provided herein suggests that TNC has had a more important effectthan TFS in determining diversity gradients of New World bats. Indeed, relative effects of different historicalmechanisms, as well as relative effects of historical and contemporary environmental determinants,are probably context-dependent. Future research should move away from attempting to identify themechanism with primacy and instead attempt to understand the particular contexts in which differentmechanisms have greater influence on diversity gradients.