Understanding the factors that structure global biodiversity patterns has been of long-standing scientific interest. To date, much of the research has focused on present-day climate, such as average temperature or rainfall, and recent human impacts, such as deforestation and urbanization of wild lands that destroy habitats for many species.
In fact, the present-day biodiversity patterns are the outcome of thousands of years of changes in Earth's climate and, more recently, prehistoric human activity, according to the study, which will be published in the Proceedings of the National Academy of Sciences.
The researchers analyzed a database of 515 mammal communities across the globe. For each community, they collected data on the species present, their ecological characteristics and their evolutionary relationships to one another.
They used this information to measure the ecological and evolutionary structure of each community, trying to find out whether it was best explained by present-day climate, Quaternary paleoclimate changes, recent human activity or prehistoric human activity.
Their findings show, for the first time, that current patterns of mammal diversity across the world's tropical and subtropical regions are structured by both past and present climate and human impacts.
"We have long been interested in finding overarching explanations for what drives mammal diversity across the globe," said John Rowan, researcher at the University of Massachusetts Amherst. "For our research group, this study made us realize that there probably isn't one -- every region of the world has its own distinct history, and that history matters today."
Global differences highlight an important finding of the study. Each of world's major regions has a unique ecological and evolutionary history, and these histories continue to strongly influence the distribution and diversity of mammalian life on Earth, according to the study.
As scientists continue to understand global patterns of biodiversity, they suggest that past climate and human impact factors should be incorporated into future studies.
They propose that this will result in a more holistic understanding of what drives biodiversity and how it may respond to ongoing and future human-caused changes in the 21st century.