An international study with the participation of the Doñana Biological Station (EBD-CSIC) reveals that the most of European forest communities are dispersed by birds that migrate to warmer latitudes to the south, while only a minority are dispersed by birds that migrate to the north, towards colder latitudes. This limits the adaptation of plant species in Europe to climate change since the climatic optimum (comfort conditions) for many species have moved to colder areas.  The study has been published in Nature and has the participation of 18 scientists belonging to 13 European research centers, including Pedro Jordano and Juan Miguel Arroyo, from the Doñana Biological Station (EBD-CSIC) and the first also from the University of Seville.

Global warming is causing the redistribution of life on Earth. Mobility allows animals to move to new areas with appropriate climates, however, plants do not have this ability. In processes of change in distribution and adaptation, they depend on animals for long-distance seed dispersal and the expansion of their distribution areas.

This new study shows that only one third (35%) of the plants are dispersed by birds that migrate north in spring, while most cases take place when the birds move towards warmer areas in autumn. “The climate change is so quick that many plants require much wider dispersal distances than those produced locally. Here is where migratory birds can play a decisive role, since they are capable of dispersing seeds over many kilometres. We proposed this research to know the potential of plant species for their dispersal by migratory birds towards future favorable areas ”, explains Juan Pedro González-Varo, first author of the study, who did his post-doctorate at the Doñana Biological Station (CSIC) and who is now a professor-researcher in the Department of Biology at the University of Cádiz.

“A large part of Mediterranean trees and shrubs persist thanks to animals (called frugivores) when they disperse their seeds, sometimes over very long distances. These animals are decisive, for example, in the colonization of islands by many plants”, points out Anna Traveset, a CSIC scientist at the Mediterranean Institute for Advanced Studies (IMEDEA-CSIC-UIB).

The research has been based on analyses and models of plant-bird interaction networks, that is, techniques that allow to describe the great diversity of interactions between communities of birds that consume the fruits and disperse the seeds of plant communities. For this, using the work of the infrastructure of the Molecular Laboratory of the ICTS-EBD, advanced DNA barcoding techniques have been used, this is a technique for molecular identification of species that consists of the use of a small region of a gene and allows to determine which species of bird has dispersed a sampled seed in the field. The scientists have incorporated information on the fruiting period of the plants and the migratory flows of the birds into these networks, in order to characterize the potential for long-distance seed dissemination, both north and south.

The study has been carried out in forest áreas located in Spain, Portugal, the United Kingdom, Germany, Italy and Poland, including a total of 46 species of birds and 81 of plants. 

Birds that winter in Europe is the only hope

Despite the fact that all migratory birds in Europe migrate in the same direction (from south to north in spring and from north to south in autumn), this study has shown that the birds with the greatest potential to disperse European plants towards colder latitudes are Palearctic species, that is, they do not cross the Sahara during their migration, but they winter in central and southern Europe or North Africa. These species are, in general, very common and abundant on the European continent, such as robins, blackcaps, blackbirds, and various species of thrushes. “Many common bird species are showing an alarming decline across Europe. These small migratory birds feed on the fruits of plants and are essential for the regeneration of our forests; they are the gardeners of the forest, and the plants in turn are essential for their migratory journey”, points out Jordano. 

“Although these are common species, the potential for seed dispersal to the north lies in few species, some of them heavily hunted in the Mediterranean area, both legally and illegally. We believe that our study gives added value to species considered vulgar, since they carry the burden of helping European plant communities in the face of climate change”, explains González-Varo.

The researchers also reveal that the plant species with the greatest potential for dispersal to colder latitudes belong to related species and are characterized by ripening their fruits when the birds are migrating north. “For the birds that migrate north to disperse the seeds of a plant species, it has to bear fruits between February and April. The species with fruits in this period are well characterized by having a very long fruiting, as occurs in junipers, mastic, myrtle, wild olive or holly, or by having a very late fruiting, as in the case of ivy ", says Juan Pedro González-Varo.

This study shows the ecological role that some bird species play in maintaining biodiversity. Therefore, "they must be protected at all costs,” Traveset emphasizes. "Our work shows how ecological interactions within ecosystems - not just species - are crucial for the conservation of biodiversity in the face of the accelerated global change that is taking place on the planet," explains Jordano. Scientists suggest that dispersal to new areas will have consequences for the composition of future forests, as different species may not equally colonize new territories. "This could lead to important changes in the functioning of the ecosystem, which we are still far from understanding," adds Traveset. 

Reference:

Juan P. González-Varo, Beatriz Rumeu, Jörg Albrecht, Juan M. Arroyo, Rafael S. Bueno, Tamara Burgos, Luís P. da Silva, Gema Escribano-Ávila, Nina Farwig, Daniel García, Ruben H. Heleno, Juan C. Illera, Pedro Jordano, Przemysław Kurek, Benno I. Simmons, Emilio Virgós, William J. Sutherland y Anna Traveset. Limited potential for bird migration to disperse plants to cooler latitudes. Nature. DOI: 10.1038/s41586-021-03665-2