Without animals to disperse seeds, some plants may not survive climate change

While birds and mammals that eat the fruit and seeds of plants -- an American robin is pictured eating winterberries -- can migrate to more hospital environs when needed, plants need these animals' help to do the same. Photo courtesy of Paul D. Vitucci/Rice University
While birds and mammals that eat the fruit and seeds of plants -- an American robin is pictured eating winterberries -- can migrate to more hospital environs when needed, plants need these animals' help to do the same. Photo courtesy of Paul D. Vitucci/Rice University

Jan. 13 (UPI) -- As ecosystems warm or dry out because of climate change, plants and animals are being forced to move in search of friendly conditions. Animals can swim, scamper and fly, but plants are rooted in place -- they rely on seed dispersal to migrate.

That's a problem, according to a study published Thursday in the journal Science, because the global loss of seed dispersers -- animals that spread plant seeds -- could inhibit the ability of plants to adapt to climate change.


Like animals, each plant species has evolved to thrive within a range of ideal conditions. While some species may be more adaptable than others, all plants have specific habitats for which they are best suited.

"Those habitat characteristics are going to be somewhere other than where they are now as a result of climate change," Rice University ecologist Evan Fricke, the study's first author, told UPI. "Our study focuses on how plants will get to those new places."


Plants need help to migrate

Trees don't have legs or wings, so they rely on other forces to colonize new territory. Natural forces like wind and flowing water can disperse seeds, but flowering species mostly rely on animals to scatter their progeny.

Until now, seed dispersal studies mostly were limited in scale, focused on a distinct location, a particular forest or an island.

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"Like most researchers, I had studied declines of seed dispersal on a pretty small scale, like on the island of Guam," Fricke said. "But seed dispersal is also important for this global phenomenon that is climate change, and seed dispersers are declining on a global scale."

To understand the global nature of the phenomenon, Fricke and his research partners -- including scientists from the University of Maryland, Iowa State University and Aarhus University in Denmark -- used data from several hundred seed dispersal studies to train a machine-learning algorithm to make connections between an animal's traits and its seed dispersal abilities.

"For example, the model can learn to realize that a small bird or bat won't disperse seeds as far as a large mammal like an elephant," Fricke said.

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But the model can make much more sophisticated inferences, too, Fricke said, like identifying the different dispersal patterns produced by a bird species that spends most of its time foraging on the ground and another that prefers to hang out in the tree canopy.


The model allowed researchers to more precisely estimate the seed dispersal capabilities of birds and mammals, for which there is little published research.

"We can infer what the seed dispersal would have been for now-extinct birds," Fricke said. "The same thing goes for a super rare monkey species that lives in a faraway isolated location."

Characterizing seed dispersal decline

Using the model, researchers characterized the global decline in seed-dispersing bird and mammal species. Fricke and associates estimate declines in seed disperser biodiversity has reduced the geographic mobility of plants by 60% globally.

Beyond identifying the scale of seed dispersal declines, the new analysis advances the quest to make sense of ecological complexity.

Inspired by what's called Ecological Network Theory, more and more scientists are paying closer attention to the mutualistic interactions that make ecosystems the diverse, dynamic places that they are.

"In short, networks are formed by sets of species, or nodes, connected by their interactions, or links, with each other in a certain location," ecologist Jeferson Vizentin-Bugoni told UPI in an email.

"Such interactions are often very complex and hard to study," said Vizentin-Bugoni, a postdoctoral researcher at the University of Illinois at Urbana-Champaign who was not involved in the study.


In a given ecosystem, for example, there may be 50 seed dispersing species and 100 plant species, forming as many as 5,000 unique links -- the kind of models developed by Fricke and others are essential to making sense of this complexity.

Though the algorithm developed by Fricke and company works to compensate for blind spots in the available data, Vizentin-Bugoni suggests the acquisition of more and better data remains the best way to make sense of network complexities, whether it's a forest or coral reef.

"The quality of the answers and solutions scientists provide to society depends on funding for better data to be collected and analyzed," Vizentin-Bugoni said. "This cannot be downplayed if society wants to understand and mitigate properly the impacts of climate change and species extinctions."

But data acquisition takes time, and the authors of the latest study suggest their findings have important implications for policy decisions being made right now.

Seeing the forest for the trees

Just as researchers have come to look at habitats and ecosystems more holistically, so too should conservationists and policy makers.

Too often, authors of the new study claim, conservation efforts focus on a single species instead of a community of connected plants and animals.


Efforts to preserve ecosystems and bolster the resiliency of plants and animals to climate change, they argue, must focus on protecting and re-establishing vital ecological relations -- between predator and prey, seed disperser and plant, pollinator and flower.

"While reforestation has been heralded as an important nature-based solution for mitigating climate change, this study underscores the importance of wildlife conservation and rewilding as a nature-based strategy for reducing the impacts of climate change on biodiversity," Haldre Rogers, co-author of the new study, told UPI in an email.

"Assisted migration is not feasible on a global scale. Therefore, conservation measures that protect and restore large-bodied seed dispersers are critical for facilitating movement of plant species to suitable habitat," said Rogers, an ecologist and associate professor at Iowa State University.

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