Ancient events are still impacting mammals worldwide

In the first study of its kind, researchers have discovered that events from 20,000 years ago or more are still impacting the diversity and distribution of mammal species worldwide.

"Our study shows that mammal biodiversity in the tropics and subtropics today is still being shaped by ancient human events and climate changes," said study lead author John Rowan of the University of Massachusetts Amherst. "In some cases, we found that ancient climate or human events were more important than their present-day counterparts in explaining present patterns of biodiversity."

The research is available online this week in the Proceedings of the National Academy of Sciences. The authors spent more than five years compiling and analyzing data about the diets, body sizes and variety of species in 515 mammal communities - each with multiple species - in the tropical and subtropical regions of the Americas, Africa and Asia. Separate statistical analyses were conducted for each community to determine how well recent and ancient events - both climatic and human - could account for present-day diets, body sizes and species variation.

Study co-author Lydia Beaudrot of Rice University said the study findings are especially important given the increasing questions ecologists face about how anthropogenic climate change and other human impacts will affect biodiversity this century.

"If current climate is what's most important for where you see species, then as climate changes, we might expect species to track climate to the best of their abilities," she said. "This study suggests things are more complex, and that we will need to take legacy effects into consideration when making predictions about how climate change will affect species distributions."

Beaudrot, an assistant professor of biosciences at Rice, said the study stemmed from discussions that began in 2013 when she was a graduate student at the University of California, Davis, working on research and grant applications with senior co-author Jason Kamilar, now an associate professor of anthropology at UMass Amherst, and with co-author Kaye Reed, a president's professor and the director of the School of Human Evolution and Social Change at Arizona State University (ASU). Rowan, who was then a graduate student of Reed's, is now a postdoctoral fellow working with Kamilar.

As an ecologist, Beaudrot said it was particularly surprising to see that historic climate does a better job than current climate of explaining the communities that are present today.

"As an ecologist, I'm typically focused on the present day, but this study demonstrates the importance of interdisciplinary research for advancing science," she said. "When ecologists, paleoecologists and anthropologists combine forces, we can generate and test more complex and interesting questions that generate surprising new findings."

The study also found that ancient human events were also still reflected in mammal biodiversity patterns. For example, most large-bodied mammals in South America went extinct when humans first appeared on the continent about 12,000 years ago.

"When you're looking at what explain mammal communities today in the Neotropics, these historical human impacts are a better predictor than current or past climate," she said.

Beaudrot said the reason it took so many years to complete the study was that the team had to create the database that would allow them to make comparisons across mammal communities worldwide. Most of the profiled communities are in national parks, places where conservationists have worked for years observing mammals.

"One reason the NSF (National Science Foundation) funded us was to bring all of that together and create this database," Beaudrot said. "It was a huge effort, especially on John's part, and going forward there is so much that can be done to add to what we already have. For example, the mammal communities that are most affected by climate change today are near the poles. We started in the tropics and subtropics because that's where you find most national parks, but we want to continue adding to this, for as many communities in as many places as we can."

The data can give scientists a clearer idea of what happened in the past and how it affected the present, but it doesn't paint a clear picture for the future, she said.

"Predicting how species will respond to climate change is very hard," Beaudrot said. "We already knew that, and this work suggests that it's perhaps even more complex than we thought."

Connecting the prehistoric past to the global future
Tempe AZ (SPX) Dec 18 - Research on global biodiversity has long assumed that present-day biodiversity patterns reflect present-day factors, namely contemporary climate and human activities. A new study shows that climate changes and human impacts over the last 100,000 years continue to shape patterns of tropical and subtropical mammal biodiversity today - a surprising finding.

The new research - coauthored by Kaye E. Reed and Irene Smail, Arizona State University; Lydia Beaudrot, Rice University; Janet Franklin, University of California Riverside; and John Rowan, Andrew Zamora, and Jason M. Kamilar, University of Massachusetts Amherst - will be published in the Proceedings of the National Academy of Sciences.

Understanding the factors that structure global biodiversity patterns - the distribution and diversity of life on Earth - has been of long-standing scientific interest. To date, much of this research has focused on present-day climate, such as average temperature or rainfall, because climate is well-known to influence species geographic distributions and because human-caused climate change is a major threat. Likewise, other recent human impacts are well-known to influence biodiversity and are well-studied, such as deforestation and urbanization of wild lands that destroy habitats for many species.

What many of these studies overlook, however, is that present-day biodiversity patterns are the outcome of thousands of years of changes in Earth's climate and, more recently, prehistoric human activity. Thus, present-day biodiversity patterns need not be primarily driven by recent climate or human impacts. A small but growing body of studies suggest that legacies of the ancient past continue to structure patterns of life on Earth today. Indeed, though this may be the case, global-scale analyses on this issue remained elusive until now.

To tackle this issue, the researchers analyzed a database of 515 mammal communities across the globe. For each community (i.e., an assemblage of mammal species occupying the same area), they collected data on the species present, their ecological characteristics (body size, diet, etc.) and their evolutionary relationships to one another.

They used this information to measure the ecological and evolutionary structure of each community and then asked whether it was best explained by present-day climate (current temperature and rainfall), Quaternary paleoclimate changes (changes in temperature and rainfall from around 22,000 years ago and 6,000 years ago to the present), recent human activity (land-use change since the Industrial Revolution) or prehistoric human activity (human-driven mammal extinctions that happened over the last 100,000 years as humans spread across the globe).

The research 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, but specific effects vary by region.

"We have long been interested in finding overarching explanations for what drives mammal diversity across the globe," said John Rowan. "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."

In the Neotropics (South and Central America), for example, mammal communities are strongly influenced by prehistoric human-driven extinctions over the last 100,000 years. When humans arrived in the Neotropics, they caused massive extinctions of the region's mammals, the effects of which linger today in the surviving communities. Conversely, Africa was lightly impacted by these extinctions, and the region's present-day communities are mainly shaped by current and prehistoric climates. Southeast Asia and Madagascar also have their own suite of past and present climatic and human factors that shape them.

These global differences highlight an important finding of the study - there is no one-size-fits-all explanation for what structures mammal biodiversity across the world. 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.

"Now that we have a global study of the similarities and differences of the overarching effects on mammal communities," said Kaye Reed, "we will continue to explore each region in depth to examine other factors that affected these communities in the past and what that might mean for the future."

The climatic and human-impact legacies of the ancient past can be, and often are, as or more important than their present-day counterparts. As scientists continue to understand global patterns of biodiversity, the researchers 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.

Research Report: "Geographically divergent evolutionary and ecological legacies shape mammal biodiversity in the global tropics and subtropics"

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