Events from 20,000 years ago, or more -such as ancient climate and human events -are still impacting the diversity and distribution of mammals worldwide, according to a first-of-its-kind study that offers insights into how similar factors may impact species in the remainder of this century.
The study, published in the journal PNAS, noted that modern-day mammal biodiversity in the tropical and subtropical regions is still being shaped by these ancient factors in a way that is more important than present-day human and climate events.
The researchers, including those from Rice University in the US, spent more than five years compiling and analysing 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.
They separately conducted statistical analyses for each community to determine how well recent and ancient events -- both climatic and human -- could account for the present-day diets, body sizes, and species variation in these animals.
"If the 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," said study co-author Lydia Beaudrot of Rice University.
According to the researchers, these ancient factors have "legacy effects" which span for millennia after they came into existence.
They said historic climate does a better job than the current climate of explaining the mammal communities that are present today.
"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 said.
The findings of the study also revealed that ancient human events were still reflected in mammal biodiversity patterns.
Citing an example, the researchers said, the 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 explains mammal communities today in the Neotropics, these historical human impacts are a better predictor than current or past climate," Beaudrot said.
To conduct the study, the researchers had to create a database that would allow them to make comparisons across mammal communities worldwide.
Using this database, they profiled mammal communities that are in national parks - places where conservationists have worked for years observing mammals.
"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," Beaudrot said.
The researchers said the data they have gathered can give scientists a clearer idea of what happened in the past, and how it affected the present.
However, they said it doesn't paint a clear picture of the future.
"Predicting how species will respond to climate change is very hard. We already knew that, and this work suggests that it's perhaps even more complex than we thought," Beaudrot added.
According to Beaudrot, the current study demonstrates the importance of interdisciplinary research for advancing science.
"When ecologists, paleoecologists, and anthropologists combine forces, we can generate and test more complex and interesting questions that generate surprising new findings," she said.