Biodiversity Loss Hampers Climate Adaptation

 

• As the climate warms, many species will be forced to move to habitats with warmer temperatures. Half of the planet's plants are dispersed by animals, but while animals are disappearing from ecosystems, plants aren't moving very far.
• According to recent research, the loss of birds and mammals has reduced the ability of plants spread by animals to keep pace with climate change by 60%.
• When animals are lost within an ecosystem, the first to disappear are often the largest animals, those that spread their seeds best over long distances. Therefore, even a small decline in the number of animal species leads to a huge reduction in plants' ability to adapt to climate change.
• This first global analysis of the loss of disseminators demonstrates the interconnectedness of climate change and the biodiversity crisis, two of the nine planetary boundaries identified by scientists. If one or more of these boundaries is destabilized or crossed due to human action, the Earth's critical operating spaces could be compromised.

Animals that feed on fruits and spread seeds through their excrement provide a complete transport service for half of the planet's flora . However, as more and more mammals and disseminators of seeds disappear globally, according to recent research, some of these plant species will lose the ability to shift their habitats and keep pace with increasingly intense climate change.

“When the biodiversity crisis makes headlines, they often call it the sixth mass extinction and say that the decline of birds and mammals also means the decline of disseminators,” Evan Fricke, lead author of the new study ,  published in Science , told Mongabay.

Fricke and his colleagues report that the loss of birds and mammals has reduced the ability of plants disseminated by animals to keep pace with climate change by 60%.

"This number is a wake-up call," Fricke added. "I hope this discovery will draw public attention to the importance of disseminator-based biodiversity for plant adaptation to climate change."

“If there are no animals to eat their fruits or transport the nuts,” Fricke said in a press release, “zoochorous plants do not travel long distances.”

A black bear eats hawthorn berries. Large animals spread seeds long distances, but many of the large seed spreaders are extinct or in decline. Photo by Paul D. Vitucci.

As the climate warms, many species will be forced to move to live in environments where they can tolerate the temperature range. In the mountains, this could mean climbing the slope by just a few meters, up to ten meters per year. In flat lands, however, organisms must move poleward, sometimes hundreds of kilometers, to adapt to climate change. The speed at which suitable climate zones move across the landscape (known as the rate of climate change) is faster in flat lands, requiring plants to work harder to keep pace.

Animals can crawl, fly, swim, or walk to new territories, while plants cannot. Therefore, according to Fricke, the question is: "How many seeds are dispersed at least along the path of the shift that climate change has caused over the course of a year? How many seeds are dispersed far enough to keep pace with climate change?"

In the past, scientists have studied the consequences of the loss of animal disseminators for the plants of an ecosystem, and have also attempted to understand how plant populations respond to climate change. However, the combination of these two catastrophic global events—climate change and mass extinction—has proven an even more daunting task.

To achieve this goal, the researchers used data from hundreds of previous studies to implement a machine learning model capable of generating calculations and conclusions about the loss of dissemination services. The large-scale datasets analyzed and compared IUCN data for animal populations across the planet; which seeds are dispersed by which animals; where and how far these animals move; and how long it takes for seeds to pass through the digestive tracts of their disseminators.

A migratory American mockingbird eats berries of the evergreen hollyhock. Small birds like mockingbirds typically scatter seeds over relatively short distances. Photo by Paul Vitucci.

The research findings reveal that losses of disseminators are most significant in temperate regions of North America, Europe, South America, and Australia. The extinction of currently threatened species would have a significant impact on dissemination in tropical regions of South America, Africa, and Southeast Asia.

Mauro Galetti, a dissemination researcher at the University of Miami who was not involved in the study, told Mongabay that "this study is a sophisticated analysis of how, under climate change, the loss of animal species will affect plants. The results are concerning because most large fruit-eating animals are disappearing from natural ecosystems."

Scientists have also discovered that even a minimal decline in the number of animal species leads to a huge decline in plants' ability to keep pace with climate change. "In a habitat that loses 10 percent of its animal disseminators, you'd expect to see a 10 percent decrease in dissemination," Fricke said, "but that's not the case." When animals are lost within an ecosystem, the first to disappear are often the largest animals, those that disseminate best over long distances.

“We observed regions where dispersal, as a result of climate change, has decreased by 95% compared to a minimal loss of bird and mammal species,” Fricke explained.

A tapir and some of the seeds it sows. Photo by Mauro Galetti.

"From elephants and gorillas in Africa to toucans and tapirs in South America, large disseminators are rapidly disappearing, and this will have serious consequences for dissemination," Galetti argues. "Many plants will remain trapped in places devoid of disseminators."

The first global analysis of the loss of disseminators, according to Fricke, demonstrates the crucial interconnection between climate change and the biodiversity crisis, two of the nine planetary boundaries identified by scientists. If one or more of these boundaries is destabilized or crossed due to human action, the Earth's critical operating spaces could be compromised.

"The biodiversity of animal disseminators is key to plants' resilience to climate change, which also includes their ability to store carbon dioxide and feed humans," explains Fricke. "Extinction and habitat loss disrupt complex ecological networks. This study demonstrates that the decline of animal species can disrupt ecological networks, threatening the climate resilience of entire ecosystems on which the human population relies."