Environmental granularity, rivers and climate history as shaping factors for species' distribution and diversity patterns

Abstract

Species distributions are composed by those places in which the environmental conditions are suitable for the species to survive and maintain populations; where the interactions with other species are adequate; that have been accessible given species' dispersal capabilities. Biodiversity patterns have been explained by: environmental heterogeneity, latitudinal gradients, system energy, and biogeographic history among others. Several attempts have been made to replicate biodiversity using spatially and environmentally explicit null models with different degrees of success, but they do not analyze individual effects of factors involved in the production of such patterns. Here, I use artificial species that mimic environmental granularity in combination with three other variables involved in shaping species' distributions (physical barriers, seasonality, and climatic history), to study: (1) environmental granularity, physical barriers (i.e., rivers), and seasonality as shaping factors for species' distributions (2) Janzen's ideas about the role of seasonality for the creation of biodiversity in South America; and (3) the effect of recent climatic history (135,000 years ago) in shaping present day patterns of biodiversity via the analysis of environmental stability through time. I analyzed the patterns obtained through scatter plots that relate the distribution ranges of the species and the richness of the sites of the study area (range-diversity plots). Results from this analysis show that: (1) only when seasonality was included, it was possible to replicate general patterns of biodiversity; (2) predictions derived from Janzen's ideas were amply supported; (3) changes in climate since the last interglacial period had been more drastic in Africa than in South America; therefore (4) more environmentally stable areas were found in South America which could have facilitated the persistence of species during this period of time; (5) general support for the existence refugia during the Last Glacial Maximum; and (6) each of the analyzed factors have different effects on the patterns of biodiversity. The study of the factors included in this work helped the understanding of their particular role in shaping biodiversity patterns and species distributions; however, many other factors are left to be studied in more detail.