Human activities such as deforestation practice, leads to species extinction around a hundred times faster than natural evolutionary processes, explain researchers in an article in the journal Science. As an example, note that the disappearance of the large fruit-eating birds of tropical forests in Brazil has caused the region's forest palm trees produce seeds smaller, with less success in the last century.
Mauro Galetti, of the Universidade Estadual Paulista in Sao Paulo, Brazil, along with an international team of colleagues, used parts of the forest that had been fragmented by coffee plantations and sugar cane during the 1800s to establish its natural experiment. More than 9,000 were collected seeds of 22 different populations of Euterpe edulis palm trees and with a combination of statistics, genetics and evolutionary models to determine that the absence of large birds that disperse seeds in the area was the main reason for the decrease in size seed.
"Unfortunately, the effect we document our work is probably not an isolated case - said Galetti -. Widespread removal at a rapid rate of large vertebrates in their natural habitat is very likely to cause unprecedented changes in developmental trajectories many tropical species. " Thus, these scientists estimate extinction a hundred times faster by human activity than by natural evolution, something that few studies have documented.
Galetti and his colleagues found that the palms produced seeds significantly lower in forest patches that had been fragmented by coffee plantations and sugar cane, and were no longer able to support large-billed birds stunned or those whose peaks are more 12 mm wide, such as toucans and large cotingas. In undisturbed forest areas, on the other hand, these large birds still make their nests and palm trees still produce large seeds successfully dispersed by birds, they say.
"The small seeds are more vulnerable to desiccation and can not withstand projected climate change," warned Galetti, adding that small, such as thrushes, that inhabit fragmented forest patches are unable to swallow and disperse large seeds. As a result of this alteration of the dispersion, the regeneration of the palm is less successful in the area, with less vigorous seedlings that germinate from the smallest seeds.
The researchers took into account the influence of a wide range of environmental factors such as climate, soil fertility and forest cover, but can not explain the change in the size of the palm seed in recent years in the woods fragmented. Genetic analyzes were performed to determine the contraction of forest palm seeds in the region could have taken place a hundred years the initial disturbance.
This time scale suggests that the conversion of tropical forests for agriculture, which began in 1800 and many large bird populations displaced in the region, led to a rapid evolution of the forest palms leading to small seeds, with less success thrive.
Long periods of drought and increasingly warm weather (as predicted by climate model projections for South America) may be especially detrimental to the populations of tropical trees rely on animals to disperse their seeds. About 80 percent of the entire Atlantic Forest biome remains in small fragments, the researchers, and the successful restoration of these habitats depends fundamentally on the preservation of the mutual interactions between animals and plants.
"Habitat loss and species extinction is causing drastic changes in the composition and structure of ecosystems, essential ecological interactions that are missing," says Galetti. "This implies that the loss of key ecosystem functions can determine the evolutionary changes much faster than we expected. Our work highlights the importance of identifying these key functions for the rapid diagnosis of functional collapse of ecosystems" , concluded the expert
