Birds involved in more seed dispersal have evolutionary stability

A study from the University of São Paulo has found that the evolutionary stability of a bird species depends on its role in seed dispersal networks. The experts report that the stability of each species increases with the more types of seeds that it disperses.

More than 70 percent of all flowering plants depend on birds to disperse their seeds. The research suggests that birds which feed on fruit from a wide variety of plants have better evolutionary chances.

“The bird species that occupy more central positions in a network, that have more connections, tend to be more stable in macroevolutionary terms,” said study first author Gustavo Burin.

According to Burin, establishing this correlation between species interactions and their evolutionary dynamics was a huge challenge because it required an analysis of two processes – seed dispersal and evolution – that occur on entirely different time scales. While evolution plays out over millions of years, seed dispersal is an annual process.

“We worked on this for four years, integrating data on 468 bird species belonging to 29 seed dispersal networks,” said Burin. “We demonstrated that the more links a bird species establishes with plant species, the greater its evolutionary chances.”

“More precisely, the greater the evolutionary stability of a bird species, the more chances we have of observing its relative importance in a seed dispersal network, measured by the number and pattern of interactions established by the bird species.”

Burin explained that bird species which occupy central positions in a seed dispersal network have two important traits – “either they live longer or they belong to groups that accumulate many species in a relatively short time, so that if a species disappears it’s replaced by many other similar ones.”

In Brazil, examples of long-lived species include the Rufous-bellied thrush and the Sayaca tanager.

“Here we’re emphasizing the importance of interaction with plants to the evolutionary success of bird species, but the reverse may also be true in the sense that plants that can rely on more bird species to disperse their seeds are more likely to propagate and survive. When a dispersing vertebrate exists, the seeds can be carried dozens of miles away from the plant,” said Burin.

The effects are the strongest in tropical areas that are warm and wet with less seasonal variability. This helps to explain why biodiversity hotspots persist in Colombia’s Amazon region and in Southeast Asia, explained the researchers.

The study was funded by São Paulo Research Foundation, FAPESP,  and is published in the journal Science.

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By Chrissy Sexton, Earth.com Staff Writer