about half of plant species depend on animals to disperse its seeds. In this mutualistic relationship, known as zoochory, the animals receive a nutritional reward and the seeds are transferred to the fruit.

Study shows for the first time that the loss of bird and mammal biodiversity causes a 60% decrease in seed propagation globally

In this way, several functions are fulfilled for plants: on the one hand, they regenerate and, on the other hand, their populations spread geographically. But what happens when birds and mammals, some of the main seed-dispersing vertebrates, disappear?

A new study, magazine cover Science this week demonstrates for the first time that the loss of bird and mammal biodiversity causes a 60% decrease in seed propagation globally. The research focused on fleshy plant species and the frugivorous animals that spread them.

“When we lose mammals and birds from ecosystems, we don’t just lose species. Extinction and habitat loss damage complex ecological networks. This study shows that declining animals can disrupt ecological networks in ways that jeopardize the climate resilience of entire ecosystems that people depend on.” Evan C Fricke, first author of the work and researcher at the rice university, In the United States.

A blackbird (Turdus migratorius) eats a winter berry. Small birds such as thrushes often disperse seeds over relatively short distances. / Paul D. Vitucci

Plants most vulnerable to climate emergency

Because it doesn’t spread out enough, the impact directly to plant species is that they will have greater difficulty in adapting to the climate crisis. “To maintain adequate environmental conditions in a changing climate, many plant species need to ‘migrate’, changing their geographic distribution to overcome climate change”, explains Fricke to SINC.

According to the expert, as many plant species depend on animals to spread their seeds, the ability of many of them to adapt to climate change through migration depends on adequate dispersion.

By not spreading far enough, the direct impact for plant species is that they will have a harder time adapting to the climate crisis.

As a consequence, scientists believe that if these plant species cannot cope with temperature changes, plant biodiversity and the ecosystem services they provide will decline.

Fricke and his colleagues gathered data in the scientific literature from more than 400 seed dispersal networks around the world and developed machine learning models to predict changes in seed dispersal due to declines in seed-scattering animals.

“Based on the species of birds and mammals present at each location, we estimated how many seeds would be dispersed over the distances necessary to adapt to climate change”, adds the scientist. They then compared current seed dispersal maps with those showing what dispersal would look like without human-caused extinctions or species restrictions.

black bear

A black bear eats hawthorn berries. Large animals can disperse seeds over long distances, but many of the large seed dispersers are extinct or in decline. / Paul D. Vitucci

Temperate regions, where dispersion is most lost

The results revealed that the current seed dispersal function has declined dramatically from its natural level, with an especially widespread decline outside the tropics.

“At temperate regions show some of the largest declines in seed dispersal function. These are areas where the large seed dispersers that can transport many seeds over great distances have already disappeared or now exist in very restricted distribution areas”, specifies the ecologist.

The current seed dispersal function has drastically decreased from its natural level

in many tropical regions, the currently endangered seed dispersers perform much of the remaining dispersal function. This also threatens the ecological functions (such as propagating seeds) that these species perform.

This research shows the clear links between the biodiversity crisis and the climate crisis. Scientists propose to improve habitat connectivity to ensure that existing seed dispersers can circulate freely. “Another way is the recovery of important seed dispersers in their historical distribution areas”, says Fricke to SINC.

In this sense, the work highlights the need to restore fauna to ensure effective diffusion in the face of rapid climate change. For this, farm animals are especially relevant. Big size to increase the resistance of plant communities against these circumstances.

“Large mammals and birds are especially important as long-distance seed dispersers, but they have largely been lost from natural ecosystems,” he concludes. Christian Svenning, lead author of the study and professor and director of the Center for Biodiversity Dynamics in a Changing World at Aarhus University in Denmark.


Rights: Creative Commons.



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