Some plants will not survive the loss of seed dispersing animals •

In the past, when climates changed, forests were distributed further north or south of their previous locations. This does not mean that the trees themselves have moved. On the contrary, the ranges of tree species have changed. For example, records of fossil plants and pollen show that the ranges of tree species have shifted north at a rate of 50 km per century as the climate warmed after the retreat of the ice cap. North American.

Migration of trees is facilitated by the movement of seeds. When the climate changes, the trees begin to form more seeds; these are propagated by dispersing agents and can germinate in areas more favorable to growth. Although wind and water can carry seeds, the vast majority of trees depend on animals to disperse them to new areas. But now many of these seed-dispersing animals are themselves under threat as climate change and habitats are lost.

In a study featured on the cover of this week’s issue of Science, American and Danish researchers are examining how the loss of bird and animal species will impact the ability of plants to adapt to human-induced climate change in the future. While animals can often fly, walk, run or swim to more suitable areas, trees cannot escape the heat. Tree species that need to keep their offspring away from warmer temperatures will only be able to do so through the activities of seed dispersers, such as mammals and birds.

“Some plants live for hundreds of years, and their only chance to move is during the short time they are a seed moving across the landscape,” said Evan Fricke, a Rice University ecologist and first author of the study. “If there are no animals available to eat their fruit or take away their nuts, the plants scattered by the animals do not move very far.”

Working with researchers at the University of Maryland, Iowa State University, and Aarhus University, the Rice team used machine learning and data from thousands of studies in the field to map the contributions of seed-dispersing birds and mammals around the world. They compared the seed dispersal maps today with maps showing what dispersal would look like if there were no human-caused extinctions or range restrictions of the species.

The experts also used data synthesized from field studies around the world to train a machine learning model for seed dispersal, and then used the trained model to estimate the climate tracking dispersal loss. caused by the decline of animals.

Fricke explained that developing estimates of seed dispersal losses due to animal and bird extinctions or changes in their ranges requires two important technical advances: world. “

To do this, they used data on species interactions from more than 400 field studies that detailed the number of seeds dispersed by particular species of birds and mammals, how far they are dispersed and how far away they are. how well these seeds germinate. Based on this data, the researchers were able to predict the interactions between plants and seed dispersers.

“Second, we had to model how each plant-animal interaction actually affects seed dispersal,” said Fricke. “For example, when an animal eats a fruit, it can destroy the seeds or scatter them a few meters or several kilometers away.

The results of the study showed that many mammals and seed dispersers have already been lost, especially in temperate regions of North America, Europe, South America and Australia. In addition, if currently threatened species were to become extinct, the tropics of South America, Africa and Southeast Asia would be severely affected.

“We found regions where the dispersal of climate tracking seeds declined by 95%, even though they had lost only a few percent of their mammal and bird species,” Fricke said.

The results showed that the ability of plants dispersed by animals to keep up with climate change was reduced by 60% due to the loss of mammals and birds that help these plants adapt to environmental changes.

“Along with the red flag that declining animal species have 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 Doug Levey, program director of the National Science Foundation (NSF) Biological Sciences Branch, which partially funded the work.

Fricke explained that the study is the first to quantify the extent of the seed dispersal problem on a global scale and identify the regions most affected. He pointed out that declines in seed disperser populations highlight an important intersection between climate and biodiversity crises impacting natural environments today.

“The biodiversity of seed-dispersing animals is essential for the climate resilience of plants, which includes their ability to continue to store carbon and nourish people,” he said, adding that restoring ecosystem connections in natural habitats may counter some declines in seed dispersal, but not all. People also depend, both economically and ecologically, on seed-dispersing birds and mammals for the supply of important resources.

“Large mammals and birds are particularly important as long-range seed dispersers and have been largely lost from natural ecosystems,” said Svenning, lead author of the study. “Research highlights the need to restore wildlife to ensure effective dispersal in the face of rapid climate change. ”

“When we lose mammals and birds from ecosystems, we don’t just lose species. Extinction and habitat loss damage complex ecological networks, ”said Fricke. “This study shows that the decline of animals can disrupt ecological networks in ways that threaten the climate resilience of entire ecosystems on which people depend.”

Through Alison bosman, Editor-in-chief

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