Considering Extinction’s Bigger Picture

By Kardelen Koldas ’15Photography by Ben Wheeler
April 14, 2021

Giant pandas have become an international symbol for species at risk of extinction. They are cultural icons, bringing ecotourism dollars to local economies. With extensive conservation efforts, panda populations have increased significantly, but is that enough to prevent their demise? If their main food source, bamboo, went extinct, would they survive? Would ecotourism?

Maybe not, predicts a recent Nature Communications paper coauthored by Allison Barner, the Clare Boothe Luce Assistant Professor of Biology.  

“It’s not enough to just focus on our charismatic species that provide services [to humans],” said Barner. “We could have all these protections in place, and they could still go locally extinct because we’re not protecting their resources or the things that they need”—like bamboo.

This might sound intuitive. However, the impact of losing species that neither directly face extinction nor are primary providers of benefits to humans—think food, clean air, and shoreline protection, all what in science terminology are called ecosystem services—has implications up the food chain.

The importance of those services has been an understudied topic in biology literature. But Barner and her colleagues Aislyn Keyes, John McLaughlin, and Laura Dee looked at the role of supporting species and how their extinctions affect their contributions to our well-being. They found that supporting species play essential roles in ecosystems by maintaining diverse food webs as well as supplying services that humans care about. Consequently, the paper calls for conservation efforts to extend beyond species most visibly and directly at risk in ecosystems.

In other words, we have to think about more than the panda.

In ecosystems, species don’t live in isolation, Barner and her colleagues say. Species interact with one another, as prey, predator, or protector. They also contribute to the welfare of humans by yielding various benefits. Yet human activities have been altering ecosystems and wiping out some species, which causes further extinction, called secondary extinction. 

In such an interconnected system, how does losing one species influence other species and what they offer to humans?

For answers, the scientists used data sets from three different salt marshes, which detailed each species’ place in the marshes’ food webs and their benefits, or services, to humans. Next, they simulated a dozen extinction scenarios through modelling. When they artificially removed a species from the ecosystem, they saw that the loss similarly affected both food webs and services. “It’s very striking how correlated these two ways of approaching ecosystems are,” Barner said.

“We could have all these protections in place, and they [species] could still go locally extinct because we’re not protecting their resources or the things that they need.”

Allison Barner, Clare Boothe Luce Assistant Professor of Biology

To explain why this was so striking, Barner used the analogy of Jenga, a game with stacked wooden blocks. Food webs and species’ benefits to humans are like two separate Jenga towers, with each block representing a kind of species. When one block—or species—was removed, both towers, though independent structures, collapsed at the same rate. “That’s the piece that no one had ever understood before,” she said. 

Now scholars can use information from one system to predict how the other system might react to the disappearance of a species even in the absence of data.  

Another finding revealed that species producing direct benefits to humans—like pandas—don’t play a key role in food webs. Supporting species that aid them, on the other hand, are essential to both food webs and services. “These supporting species are … disproportionately important for providing services that humans care about,” Barner said. But they “might be easily overlooked because it’s not the panda, it’s the bamboo.” 

This piece of information also indicated that in their study, every species played a part in services contributing to the well-being of humans. “That’s not something that we necessarily fully understood before,” she noted. 

Soon, these results will be tested in real life. 

Barner and coauthor Dee, assistant professor of ecology and evolutionary biology at the University of Colorado at Boulder, will expand on this research through a three-year National Science Foundation grant. Starting this summer, they’ll conduct a follow-up study to put the paper’s model-based findings to a test in nature in Colby’s backyard, Allen Island in the Gulf of Maine.

While Dee’s team will work on modeling in their Boulder lab, Barner’s team, including Colby students, will collect data on Allen Island to see how simulated extinction scenarios from their paper unfold in the field and a new ecosystem. They’ll put together a food web for the island’s marine species and carry out onsite experiments to observe how these species respond to each other’s absence and how those impact services to humans. 

“I think we’ll learn a lot from that,” said Barner. “If our models pretty much predict what happens in nature, that’s going to be fascinating; and if they don’t, I think we’re going to learn a lot about how to improve these types of models.”