The ability of plants dispersed by animals to keep pace with climate change is reduced by 60%
In one of the first studies of its kind, researchers assessed the impact of biodiversity loss in birds and mammals on the chances of plants adapting to human-induced global warming.
More than half of plant species depend on animals to disperse their seeds. In a study featured on the cover of this week’s issue of ScienceAmerican and Danish researchers have shown that the ability of plants dispersed by animals to keep pace with climate change has been reduced by 60% due to the loss of mammals and birds that help these plants adapt to the changes environmental.
Researchers from Rice University, University of Maryland, Iowa State University and Aarhus University used machine learning and data from thousands of studies on the field to map the contributions of seed-dispersing birds and mammals around the world. To understand the severity of the declines, the researchers compared seed dispersal maps today with maps showing what dispersal would look like without human-caused extinctions or species range restrictions.
“Some plants live for hundreds of years, and their only chance to move is during the short period when they are a seed moving across the landscape,” said rice ecologist Evan Fricke, first author of the study.
As the climate changes, many plant species must move to a more suitable environment. Plants that rely on seed dispersers can face extinction if there are too few animals to move their seeds far enough to keep pace with changing conditions.
“If there are no animals available to eat their fruit or take away their nuts, plants dispersed by animals don’t travel very far,” he said.
And many plants that people rely on, both economically and ecologically, depend on seed-dispersing birds and mammals, said Fricke, who conducted the research while on a postdoctoral fellowship at the National Socio-Environmental Synthesis Center. (SESYNC) from the University of Maryland in collaboration with co-authors Alejandro Ordonez and Jens-Christian Svenning from Aarhus and Haldre Rogers from Iowa State.
Fricke said the study is the first to quantify the magnitude of the seed dispersal problem on a global scale and identify the regions most affected. The authors used data synthesized from field studies around the world to train a machine learning model for seed dispersal, then used the trained model to estimate the loss of dispersal from climate monitoring caused by the decline of animals.
He said that developing estimates of seed dispersal losses required two important technical advances.
“First, we needed a way to predict seed dispersal interactions occurring between plants and animals anywhere in the world,” Fricke said.
By modeling data on species interaction networks from more than 400 field studies, researchers found they could use data on plant and animal traits to accurately predict interactions between plants and seed dispersers.
“Second, we had to model how each plant-animal interaction actually affected seed dispersal,” he said. “For example, when an animal eats a fruit, it can destroy the seeds or scatter them a few meters or several kilometers away.”
The researchers used data from thousands of studies looking at how many seeds specific species of birds and mammals disperse, how far they disperse them, and how well those seeds germinate.
“In addition to sounding the alarm that the decline of animal species has dramatically limited the ability of plants to adapt to climate change, this study beautifully demonstrates the power of complex analyzes applied to huge publicly available data,” said said Doug Levey, of the National Science Foundation’s (NSF) Biological Sciences Branch Program Director, which partially funded the work.
The study showed that seed dispersal losses were particularly severe in temperate regions of North America, Europe, South America and Australia. If endangered species were to disappear, the tropical regions of South America, Africa and Southeast Asia would be the most affected.
“We found regions where climate-tracking seed dispersal decreased by 95%, even though they had lost only a few percent of their mammal and bird species,” Fricke said.
Fricke said the decline of seed dispersers highlights an important intersection of climate and biodiversity crises.
“The biodiversity of seed-dispersing animals is essential for the climate resilience of plants, which includes their ability to continue to store carbon and feed people,” he said.
Restoring ecosystems to improve the connectivity of natural habitats can counteract some declines in seed dispersal, Fricke said.
“Large mammals and birds are particularly important as long-distance seed dispersers and have been largely lost in natural ecosystems,” said Svenning, the study’s lead author, professor and director of the Center for Biodiversity Dynamics. in a Changing World from Aarhus University. “The research highlights the need to restore faunas to ensure effective dispersal in the face of rapid climate change.”
Fricke said: “When we lose mammals and birds from ecosystems, we don’t just lose species. Extinction and habitat loss damage complex ecological networks. This study shows that animal decline can disrupt ecological networks in a way that threatens the climate resilience of entire ecosystems that people rely on.”
NSF’s Levey said: “Through SESYNC and other NSF investments, we are enabling conservationists to predict what will happen to plants when their disperser ‘teammates’ disappear in the same way that we predict sports game outcomes. .”
The research was supported by the NSF (1639145), the Villum Foundation (16549), and the Aarhus University Research Foundation (AUFF-F-2018-7-8).