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It is true that species can become extinct (and in fact have done so in the past) naturally, without human influence on the process. But today, human activities disrupt nature and ecosystems so much that the extinction process accelerates exponentially because of the human species. Processes such as deforestation, in which humans are solely responsible, lead species to extinction about a hundred times faster than natural evolutionary processes. This is what researchers say in an article published in the journal Science. An example is the disappearance of the large fruits on which the birds of the tropical forests of Brazil feed. Forest palms in the region produce smaller seeds, which are less successful in survival. In Green Ecologist, we are going to show why humans are largely responsible for the extinction of species.
The role of humans in the extinction of species
The team led by Mauro Galetti, from the Universidade Estadual Paulista in Sao Paulo, Brazil, has studied the forest used for coffee and cane sugar plantations. Almost ten thousand seeds were collected from 22 different populations of palm trees of the species Euterpe edulis. Later, analyzing statistics, genetics and evolutionary models, they have determined that the absence of large birds, which are the ones that disperse the seeds, has been the main reason for the decrease in the size of the seed.
This process occurs in other parts of the world. The disappearance of large vertebrates from their natural habitats will produce unprecedented changes in the evolutionary trajectories of many tropical species. Scientists estimate a extinction at a speed one hundred times faster by the action of man than by natural evolution.
The palms produced minor seeds in the parts of the forest that had been used for coffee and sugar cane plantations. Large open-mouthed birds or those whose beaks are more than twelve millimeters wide, such as toucans and large cotingas, did not disperse them. On the other hand, in forests where man has not laid his hand, palm trees continue to produce large seeds, which can be successfully dispersed by birds. In addition, small seeds are less resistant to desiccation and are less resistant to climate change.
Climate change also influences
The researchers took into account several factors, such as climate, soil fertility or forest cover. The conversion of tropical forests for agriculture, begun in 1800, which caused many large birds to flee the region, led to a rapid evolution of forest palms that produced smaller seeds.
To this must be added that, according to climate projections, in the coming decades there will be longer dry spells and warmer weather, which will harm tropical trees that depend on animals to disperse their seeds. According to the research, 80% of the biomass of the Atlantic Forest, one of the most threatened types of tropical forest on the planet, is in danger.
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