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

Abstract

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 a contemporary environmental perspective to a historical one in an attempt to better understand the construction of latitudinal gradients. Although the vast majority of research on historical mechanisms has focused on tropical niche conservatism (TNC), other historical scenarios could produce similar latitudinal gradients. Herein, I formalize predictions to distinguish between two such historical processesnamely time for speciation (TFS) and TNC-and test relative support based on diversity gradients of New World bats. TFS and TNC are distinctly spatial and environmental mechanisms, respectively. Nonetheless, because of the way that environmental characteristics vary spatially, these two mechanisms are hard to distinguish. Evidence provided herein suggests that TNC has had a more important effect than TFS in determining diversity gradients of New World bats. Indeed, relative effects of different historical mechanisms, as well as relative effects of historical and contemporary environmental determinants, are probably context-dependent. Future research should move away from attempting to identify the mechanism with primacy and instead attempt to understand the particular contexts in which different mechanisms have greater influence on diversity gradients.

Phylogenetic fields of species: cross-species patterns of phylogenetic structure and geographical coexistence

“…geographical speciation, range dynamics, range size inheritance or traits related to it [42,43]) and niche conservatism (e.g. higher speciation rates at region of origin and shared environmental preferences among species [5][6][7]), as well as other potential processes (e.g. niche evolution and convergence) determine phylogenetic field patterns and their geographical arrangement in phyllostomids.…”

“…Geographical patterns of phyllostomid biodiversity are thought to result in part from historical processes [5], among which those related to tropical niche conservatism (TNC; e.g. shared environmental preferences among related species and higher speciation at region of origin [6]) have gained recent support [7]. Studies supporting historical processes as major determinants of phyllostomid assemblage patterns have been based on species coexisting at particular assemblages or sites (i.e.…”

“…According to TNC, we could expect species to coexist with a high number of related species, especially towards the equator, whereas at subtropical/ temperate latitudes, we may expect coexistence among less related species [5,7]. Thus, we make two specific predictions about the phylogenetic fields of phyllostomid bats: (i) a positive relationship between species richness and clustering of phylogenetic fields, in which species with richer diversity fields and negatively skewed SRFDs will show clustered phylogenetic fields; and (ii) a geographical gradient from clustered to overdispersed phylogenetic fields as we move away from the equator.…”

“…Based on previous studies that suggest an important role of historical processes in the origin and maintenance of phyllostomid assemblages previously discussed [5,[7][8][9][10], we expect that phylogenetic fields of phyllostomid bats should also reveal the effect of such historical processes. According to TNC, we could expect species to coexist with a high number of related species, especially towards the equator, whereas at subtropical/ temperate latitudes, we may expect coexistence among less related species [5,7].…”

“…Accordingly, genealogical relationships among species inhabiting an assemblage (i.e. its phylogenetic structure) are interpreted as a product of either ecological processes such as biotic interactions and habitat filters acting at local spatial scales [13], or historical processes like in situ speciation [15][16][17] and niche conservatism [6,7,18] acting at larger spatial and temporal scales [15,19]. The community phylogenetics approach has concentrated mainly on local to regional spatial scales and focusing on sites, whether single, multiple sites or entire regions [12,15,19]).…”