Loss Of Large Fruit-Eating Animals Could Accelerate Climate Change

Tropical rainforests could suffer if large fruit-eating animals such as primates, tapirs and even toucans were to go extinct, simply because trees can't disperse their seeds without the help of these animals. This could drastically accelerate the impacts of climate change since tropical forests are natural carbon sinks, according to researchers at the University of East Anglia (UEA).

"Large birds and mammals provide almost all the seed dispersal services for large-seeded plants. Several large vertebrates are threatened by hunting, illegal trade and habitat loss. But the steep decline of the megafauna in overhunted tropical forest ecosystems can bring about large unforeseen impacts," Professor Carlos Peres, one of the study researchers from UEA's School of Environmental Sciences, explained in a news release. "We show that the decline and extinction of large animals will over time induce a decline in large hardwood trees. This in turn negatively affects the capacity of tropical forests to store carbon and therefore their potential to counter climate change."

Comparatively, large trees in highly dense tropical rainforests are more effective at capturing and storing carbon dioxide from the atmosphere than smaller trees, researchers say. Large frugivores -- any animal that is either a herbivore or omnivore, but prefers fruit -- essentially promote the growth of new trees by ingesting seeded fruits and depositing the seeds throughout the forest in their feces.

For their study, researchers analyzed data collected from more than 2,000 tree species in Brazil's Atlantic Forest, along with nearly 800 animal species. Their findings revealed small frugivores -- birds, bats and marsupials -- are not specifically targeted by hunters, but can only able to disperse small seeds that grow small trees. On the other hand, large heavy-wooded trees, which can capture and store greater amounts of carbon, are associated with larger seeds. However, these seeds are only dispersed by large animals that are more regularly hunted. 

"The big frugivores, such as large primates, the tapir, the toucans, among other large animals, are the only ones able to effectively disperse plants that have large seeds," Professor Mauro Galetti São Paulo State University added in the release. "Usually, the trees that have large seeds are also big trees with dense wood that store more carbon." 

It follows then that the removal of large animals would trigger a subsequent trees loss, which would then lead to less carbon being locked away. This could ultimately escalate the impacts of climate change. 

"When we lose large frugivores we are losing dispersal and recruitment functions of large seeded trees and therefore, the composition of tropical forests changes. The result is a forest dominated by smaller trees with milder woods which stock less carbon," Carolina Bello, a Ph.D. student from the São Paulo State University, concluded in UEA's news release. 

Researchers suggest that government policies should broaden their efforts to protect vital populations of large vertebrates, rather than focusing solely on deforestation. 

"We hope that our findings will encourage United Nations programs on Reducing Emissions from Deforestation and Forest Degradation (REDD+) to consider faunally intact forests and their full functionality as a critical precondition of maintaining forest carbon stocks," Bello said. "The effectiveness of these programs will be improved if the preservation of ecological processes that sustain the ecosystem service of carbon storage over time is guaranteed."

Their findings were recently published in the journal Science Advances. 

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