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Are monocultures enemies of birds?

Are monocultures enemies of birds?

Human activity is a threat to the rest of the species. Among all, agriculture is one of the actions of man that can have the most negative effect on ecosystems. As we clear large fields to grow our food, we destroy the habitat of so many living things.

Although we cannot give up eating, there are ways to obtain our food in a more friendly way. Scientists from Stanford University and the University of California, Berkeley, carried out an investigation that shows that monocultures have a great impact on the bird species in their surroundings, while in agricultural areas where there is more diversity of plants they are manages to maintain a population similar in variety to that which can be observed in a forest.

The study is based on bird watching for 12 years in four different places in Costa Rica, including humid Sarapiquí and the more arid Guanacaste. An article about this work was recently published in the magazineScience.

An investigation of this type was urgent because “humanity is leading to the extinction of half of the known species, mainly through agricultural activities to sustain our diet rich in meat. So how are we restructuring the tree of life? What are the implications for people? What can we do to harmonize agriculture with nature? ”Justified Gretchen Daily, a Stanford professor and author of the study.

What did you do?

As explained in the article, the scientists developed a data model on the sightings of 120,000 birds of 500 species recorded during a dozen years in Costa Rica.

The objective was to show the impacts of human activity on phylogenetic diversity, that is, how evolutionarily close or distant some species were from others.

When two evolutionarily very different species are found in a site, such as the Tinamus and the Blackbirds (which separated about 100 million years ago) then the site has a much greater phylogenetic diversity than a place where there are only Blackbirds or only Tinamus or else species close to each of them.

Preserving phylogenetic diversity is critical for the health of forests, but also for farms. Different species specialize, some in keeping different insect pests under control, some in pollinating flowers, and some in dispersing seeds.

The results

With the information in hand, they were able to see how the intensification of agriculture is most notably affecting evolutionarily distinct species while tending to favor a group of species with few evolutionary lineages, such as blackbirds (genus Turdus) and gleaners (also known as espigueros, genus Sporophila).

The data also showed that, while monocultures support an average of 900 million years of evolutionary history less than forests, diversified agricultural areas support an average of 300 million years of evolutionary history less; in other words, they are much closer to what an ecosystem untouched by man can sustain.


The collared trogon (Trogon collaris) is difficult to find in cultivated areas, but it is seen in tropical forests.Daniel Karp / Science

“The loss of habitats due to agriculture is the main factor in the global loss of diversity, but we did not know until now how it affected agriculture in the evolutionary context. We found that forests perform better than agricultural fields in supporting a large number of species, which are more distantly related, ”he explained toScientific American study co-author Luke Frishkoff.

The differences in what was observed in a monoculture with a mixed agricultural area or with a forest also showed that some species seem to have their evolutionary history in their favor in the current situation.

“While sparrows are adapted to seek refuge in agricultural areas and eat a wide variety of seeds in these areas, tinamus and other evolutionarily distinct species are highly dependent on the forest and have specific needs in their diet that can only be met in those areas. environments, ”explained Frishkoff.

Friendly agriculture

For Frishkoff, the conclusions of the study allow us to affirm that public policies that increase the number of trees in agricultural areas seem to be a way to ensure that humans will have enough food in the future but also that forest animals will be able to sustain themselves. at the same time.

"The data show that even small increases in available forest cover in an area can create relatively large differences in the total number of bird species that can survive in the area," explained the scientist.

Now, he added, there are two issues they want to follow up on. The first is to know if birds have something special that makes them relate as they do with monocultures and the most diverse agricultural areas, or if amphibians, reptiles or mammals also respond in the same way.

"Second, what is it about certain bird species that allow them to be successful in agricultural habitats?" Frishkoff asked.

For now, what they have observed is that natural savannas share some characteristics of diversified agriculture and have found evidence indicating that birds that evolved in that type of habitat, such as sparrows (family Passeridae), do well in those sites .

Cover photo: The Ruffed Jacamara (Galbula ruficauda) inhabits a great variety of dry or humid forests, it is not common to see it near agricultural areas.Daniel Karp / Science

Scientific American


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