- Many species will have to relocate as the climate warms. Half of the world’s plants are dispersed by animals, but as animals are lost from ecosystems, plants are not moving as far.
- According to new research, the ability of animal-dispersed plant to track climate changes has been reduced by 60% due to the loss of birds and mammals.
- When animals die off in an ecosystem, we’re often losing the large ones first — those that are the best at long-distance dispersal. So, just a small decline in the number of animal species leads to a massive decline in plants’ ability to track climate change.
- This first global analysis of the loss of seed-dispersers demonstrates the interconnectedness of the climate change and biodiversity crises — two of the nine planetary boundaries identified by scientists. Human interference could lead the destruction or overshoot of some of these boundaries and cause the failure of critical Earth operational systems.
Animals that eat fruit and spread seeds in their droppings offer a complete transportation service. half the world’s flora. New research shows that some of these plant species may lose their ability shift their positions to cope with the increasing climate change as more seed-dispersing animals and mammals die.
“When you hear the headlines about the biodiversity crisis, some call it the sixth mass extinction, that decline of birds and mammals also means the decline of seed dispersers,” Evan Fricke, lead author of the new Study, recently published in ScienceMongabay, told.
Fricke and colleagues found that 60% of animals-dispersed plants are less able to track climate change because of the loss of birds, mammals, and other species.
This number “is somewhere in the alarm bell territory,” Fricke told Mongabay. “I hope [this finding] focuses people’s attention on the importance of seed-disperser biodiversity for plant adaptation to climate change.”
“If there are no animals available to eat their fruits or carry away their nuts,” Fricke said in a Press release “animal-dispersed plants aren’t moving very far.”
Many species will need to move to maintain a comfortable temperature range as the climate warms. This could mean that they move upslope by a few to tens per year on a mountain. To keep up with climate change, organisms must move towards the poles on flatter terrain. This can be hundreds of kilometers. Plants can track the speed at which climate zones are moving across the landscape, also known as the climate velocity, but it is more difficult to track flat land.
Plants cannot pick up or move, unlike animals that can fly, crawl, swim, swim, or fly to new places. So the question, Fricke said, becomes: “How many seeds disperse at least that distance that the climate has shifted during the year? How many seeds are dispersed far enough to keep pace with that climate change?”
In the past, scientists have studied what the loss of seed-dispersing animals means for plants in ecosystems, and they’ve also studied how plant populations respond to climate change. But combining those two catastrophes — climate change and mass extinction — on a global scale has been a tougher nut to crack.
Researchers used data from hundreds upon hundreds of studies to train a machine-learning algorithm to make estimates and draw conclusions about the potential loss of seed-dispersal service. These data sets included IUCN data from all over the world, which showed which animals disperse seeds; where and how far they travel; and how long it takes for seeds to travel through the digestive systems of their dispersers.
They found that seed-dispersal loss is most severe in the temperate areas of North America, Europe South America, South America, and Australia. Extinction of the world’s current endangered species would most impact dispersal in tropical regions in South America, Africa and Southeast Asia.
“This paper is an elegant analysis of how the loss of animals will affect plants under climate change scenarios,” Mauro Galetti a seed-dispersal researcher from the University of Miami who was not involved in the study, told Mongabay. “The results are worrisome because most natural ecosystems’ large fruit-eating animals are vanishing.”
The scientists also found that even just a small decline in the number of animal species leads to a massive decline in plants’ ability to track climate change. “One might expect that if a location loses 10% of its seed-dispersing animals, we would see a 10% decline in dispersal,” Fricke said, “but this is not the case.” When animals die off in an ecosystem, we’re often first losing the large ones — those that are the best at long-distance dispersal.
“We found regions where climate-tracking seed dispersal declined by 95%, even though they’d lost only a few percent of their mammal and bird species,” Fricke said.
“From elephants and gorillas in Africa, to toucans and tapirs in South America, large seed dispersers are vanishing rapidly and their dismissal will have strong consequences on seed dispersal,” Galetti said. “Many plants will be trapped in space without seed dispersers.”
This first global analysis of the loss of seed-dispersers, according to Fricke, demonstrates the critical interconnectedness of the climate change and biodiversity crises — two of the Nine planetary boundariesScientists have identified them. The failure of critical Earth operating systems could be caused by human interference or the destabilization of some of these boundaries.
“Biodiversity of seed-dispersing animals is key for the climate resilience of plants, which includes their ability to continue storing carbon and feeding people,” Fricke . “Extinction and habitat loss damage complex ecological networks. This study shows animal declines can disrupt ecological networks in ways that threaten the climate resilience of entire ecosystems that people rely upon.”
Fricke, E. C., Ordonez, A., Rogers, H. S., & Svenning, J. (2022). The effects of defaunation on plants’ capacity to track climate change. Science, 375(6577), 210-214. doi:10.1126/science.abk3510
Banner imageChristine Johnson captures a bohemian wing taking off with a piece of fruit in its bill.
Liz Kimbrough Mongabay staff writer. Find her on Twitter @lizkimbrough
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