18% of vertebrate species could disappear by 2100

Research predicts that by 2100, co-extinctions, when the end of one species leads to the extinction of another, will become more frequent and this could lead to the disappearance of about a fifth (17.6%) of vertebrate categories.

The article was published this Friday (16) in the scientific journal Science Advances, from the Science group, and is a collaboration between Giovanni Strona, a researcher at the European Commission in Ispra (Italy), and Corey Bradshaw, from the University of Flinders, in Adelaide (Australia). ).

To calculate the rate of extinction, the study used computational modeling that considered how the disappearance of a species causes a direct or indirect impact on others, through the so-called ecological relationships between them (which can be prey and predator, parasites, hosts or commensalism, when one species depends on the other for survival).

Based on predictions of how species relate to each other —through food webs—, scientists simulated extinctions on a global scale, considering three climate scenarios: one in which greenhouse gas emissions will continue at the current rate, one of intermediate increase and one of accelerated increase of emissions.

In all three scenarios, climate change, rather than changes in land use, was the main factor that was associated with increased local extinctions, including co-extinctions, of the “virtual” species used in the study—the researchers chose to use species virtual, and not real, as local extinction data in different regions of the world are incomplete, which may lead to inconsistencies in the analysis.

Taking into account the effects of extinction of one species on the disappearance of other species, co-extinctions can have an effect of up to 184% more on top of primary extinctions.

This effect was even more deleterious in species classified as “vulnerable” in the ecological model, although it is difficult to calculate how much of the effect would be real in living species.

“We are not mapping the total disappearance of a particular species on the planet, but rather making a realistic projection, based on its behavior and relationship with other species, given the current pace of climate change and land use,” said Giovanni Strona, in an interview with Sheet🇧🇷

The author recalls that although they are models, they are very predictable and are close to what is observed today with some species. “What we demonstrated in the study is that when we leave a situation where some highly specialized groups are extinct, others that depend directly on them will suffer an impact, making ecological relationships less efficient”, he explains.

He cites a real-life example, that of the largest known fly from Africa, the species Gyrostigma rhinocerontis, which is a parasite of the African black rhinoceros. “This is a good example of a highly specialized species that has evolved over thousands of years to be parasitic on just one animal, the rhinoceros, and with overhunting it is declining because there are very few populations of the black rhinoceros in southern Africa.” , it says.

In this way, coextinction, although it may seem like a distant phenomenon, is much closer.

The herpetologist (who studies reptiles and amphibians) and professor at the Federal University of Bahia Luisa Diele-Viegas, who did not participate in the research, cites studies produced in Brazil that already show these population declines due to climate change and the effects on other species.

One example was a recently published study that shows that climate change has caused the savannization of areas in the Amazon due to changes in the rainfall regime, affecting the local fauna.

“What we observe is that as deforestation and climate change progress, forest loss increases and species that are more generalist [grosso modo, que possuem muitas outras fontes de alimento] enter the areas that were originally forested, and this means that the more specialized species, endemic to the forests, are gradually eliminated locally until they become extinct”, he explains.

In relation to Brazilian biomes, a difference that can already be observed, including in studies carried out by the researcher herself, is in relation to the increase in fires in areas of the caatinga. “The caatinga, unlike the cerrado, is not a fire-dependent biome [ou seja, que precisa do fogo constante para se manter em equilíbrio]so the frequent burnings end up harming the local fauna and flora and can lead to the disappearance of species”, he says.

These more intense fires are already a direct result of climate change, according to a report by the IPCC (UN climate panel) released this year, which says that extreme weather events are increasingly frequent and intense.

For the researcher, using predictive models is an essential tool precisely to identify those ecosystems at greater risk of suffering extinction due to changes in land use. “Using different scenarios, from the most pessimistic to the most optimistic, it is possible to identify areas called refuges, which will help maintain these species and help with preservation policies”, she says.

Strona and Bradshaw’s research had a result that was considered surprising by many scientists: the change in land use, mainly caused by deforestation, does not play such a significant role in the extinction of species.

“But this is a simplistic interpretation, because deforestation is a determining factor in climate change, as it also increases greenhouse gas emissions. What we saw is that, comparatively, the number of extinctions [medido pela taxa de perda de biodiversidade] is smaller than that caused by climate change”, he says.