With the planet’s changing climate, insects, birds, and other animals are moving to more suitable environments. However, 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.
According to a new study published January 13 in the journal Science, half of all plant species rely on animals to disperse their seeds. U.S. and Danish researchers showed the ability of animal-dispersed plants to keep pace with climate change has been reduced by 60 percent due to the loss of mammals and birds that help such plants adapt to environmental change.
From honey bees and other flying insects that distribute pollen of flowering plants to animals that eat fruits and defecate the seeds elsewhere, much of the Earth’s flora is dependent on the dispersal of seeds and pollen.
But deforestation, poaching, and other human pressures are causing population declines in some crucial mammalian and avian seed-spreading species.
“The study’s really exciting,” says Alexa Fredston, a quantitative ecologist at Rutgers University, who was not involved with the new research. She adds that it is surprising “how substantially plants have already lost their ability to track climate change.”
This also underscores how deeply intertwined biodiversity loss is with the climate crisis now facing the planet, she adds.
Scientific American quotes Evan Fricke, an ecologist at Rice University and a co-author of the new study who says, “We’re trying to understand, when we lose biodiversity, what does that mean for the ecosystems that those species are lost from?”
“Some plants live hundreds of years, and their only chance to move is during the short period when they’re a seed moving across the landscape,” Fricke adds.
Tracking the seed-dispersing birds and animals
Researchers from Rice University, the University of Maryland, Iowa State University, and Aarhus University used machine learning and data from thousands of field studies to map the contributions of seed-dispersing birds and mammals worldwide.
The researchers were able to compare maps of seed-dispersal today with maps showing what dispersal would look like without human-caused extinctions or species range restrictions. This helped in bringing into focus the severity of the declines.
“If there are no animals available to eat their fruits or carry away their nuts, animal-dispersed plants aren’t moving very far,” Fricke said, reports Science Daily.
Fricke said the study is the first to quantify the scale of the seed-dispersal problem globally and to identify the regions most affected. He said developing estimates of seed-dispersal losses required two significant technical advances.
“First, we needed a way to predict seed-dispersal interactions occurring between plants and animals at any location around the world,” Fricke said. They used over 400 field studies to accurately predict interactions between plants and seed dispersed.
“Second, we needed to model how each plant-animal interaction actually affected seed dispersal,” he said. “For example, when an animal eats a fruit, it might destroy the seeds or it might disperse them a few meters away or several kilometers away.”
To accomplish this the researchers used data from thousands of studies that addressed how many seeds specific species of birds and mammals disperse, how far they disperse them, and how well those seeds germinate.
The study’s conclusions are important
The study showed seed-dispersal losses were especially severe in temperate regions across North America, Europe, South America, and Australia. If endangered species go extinct, tropical regions in South America, Africa, and Southeast Asia would be most affected.
“We found regions where climate-tracking seed dispersal declined by 95 percent, even though they’d lost only a few percent of their mammal and bird species,” Fricke said.
Fricke said seed-disperser declines highlight an important intersection of the climate and biodiversity crises. “This study shows animal declines can disrupt ecological networks in ways that threaten the climate resilience of entire ecosystems that people rely upon.”
