UC study: Losing species means losing community

Many animals at risk of extinction today are among the biggest: whales, elephants, rhinos, giraffes.

And their loss could have a more profound impact than we realize, according to new research by the University of Cincinnati.

UC paleontologist Joshua Miller said the loss of so-called megafauna during the ice age mass extinction resulted in North American species being organized in ways that are less structured by biological interactions compared with periods when megafauna roamed the continent. 

Losing the biggest animals had a ripple effect that changed the rules dictating where species are found and with which other animals. The study was published in the journal Science.

The study demonstrates UC's commitment to research as described in its strategic direction called Next Lives Here.

“Anywhere you have lots of species, you have lots of opportunities for interactions. And if you have an ecosystem with a lot of interactions, that increases the resilience of that community,” Miller said. “Our study suggests that we not only lost large numbers of species at the end of the ice age but that those losses fundamentally changed how species organize themselves. It also suggests that the resilience of today’s ecosystems may be in something of an 11,000-year deficit.”

Miller, an assistant professor in UC’s McMicken College of Arts and Sciences, has co-authored several papers on the interaction of animal communities. He also uses isotopic analysis and accumulations of bones to identify historical calving grounds for elk and arctic caribou, among other projects.

Researchers found that after the biggest animals went extinct, surviving species became increasingly widespread across North America while their associations with other species became increasingly limited as species became less likely to share the same spaces together.

Surviving species largely were generalists, or species able to thrive under a wide variety of conditions or resources, compared to megafauna that tended toward specialized diets.

“The loss of large mammals can result in big changes, leading to new risks and challenges for surviving species,” said Anikó Tóth, the study’s lead author and a postdoctoral fellow at Australia's Macquarie University.

Tóth said the study found that modern North American ecosystems are structured differently than those from 11,000 years ago that included megafauna.

“During the ice age, biology and biological interactions with other species were a big driver of where species where found across North America,” she said. “Those patterns were dramatically reshaped following megafaunal extinction.”

Today, the relationships among species of mammals seem to be far less important to their survival compared to other drivers such as climate, the environment and geography, she said.

Many larger animals of the Pleistocene probably served as keystone species upon which other animals depended for their livelihoods.

“When a keystone species goes extinct or is drastically reduced in numbers, it can lead to major ecosystem changes,” Tóth said. “When elephants are removed from an area, woodlands often replace grassland savannas, changing the environment for a host of other species and potentially causing them to decline or move away.”

UC’s Miller said mammoths and mastodons likely served a similar keystone role during the Pleistocene.

“Mammoths likely behaved similarly to modern elephants in some ways, creating and maintaining open grasslands that can have downstream effects for carnivores and other herbivores,” Miller said. 

“Losing megafauna has a disproportionate effect on remaining species,” Tóth said.

Think of iconic scenes of African lions, giraffes, zebras and antelope at a waterhole sharing the same space. During the worst droughts, elephants dig for water, helping other animals.

“If we lose the rest of the African megafauna, Africa could come to resemble the drastically reduced assemblages of species we see in North America today,” she said.

Smaller animals such as jackals, baboons and warthogs, which already have proven adaptable around people, could become more common, while the great menageries of animals could disappear. Human impacts and climate will determine where species are found, not the location of the species’ natural interaction partners as predators, prey, competitors or facilitators.

“We have a planet losing species. Every time we lose one, we lose all the cryptic interactions that are important to the functioning of an ecosystem,” Miller said. “It’s becoming increasingly important to preserve what we’ve got left.”

Featured image at top: University of Cincinnati assistant professor Joshua Miller and graduate student Abby Kelly look at a prehistoric speciment in his lab. Photo/Andrew Higley/UC Creative Services