Hunting threatens to leave the jungles in silence | Science

There are already jungles where the largest animals have disappeared due to hunting. Practiced by humans from its origin to survive, human expansion has been cornering other species. Now, a study shows that hunters are reaching the last refuges: Half of the tropical forests and savannas have already lost a good part of their populations of mammals, especially the largest ones. It will become increasingly common to hear about the concept and the word defaunation.

The felling, the advance of agriculture, the urban expansion and infrastructures have reduced the extension of the jungles, they have quartered and isolated. Thanks to new satellite technologies and modern remote sensing techniques, you can almost count the remaining trees. But with animals, things get complicated. You have to be on the ground to count them and do it periodically. And there are many jungles to control. Determining the impact of hunters on life is even more complicated. In tropical regions, hunting is still a necessity, it is scarcely regulated, poorly controlled and the demand does not stop feeding poaching.

The most hunted mammals are large herbivores and large carnivores

"The satellites tell you what deforestation there is, but the impact of hunting is very difficult to quantify," recalls the researcher at the Doñana Biological Station (CSIC) and the study's lead author at the Radboud University in Nijmegen (Countries). Bajos), Ana Benítez. In 2017, the researcher published another work in which she showed that, where the hunters arrived, the abundance of animal life had been reduced by up to 90%. Now they have extended the study to the almost 4.00 species of mammals that inhabit the 14 million square kilometers of tropical forests and savannas that remain.

The work, published in PLoS Biology, estimates that 13% of the species included in the analysis, have reduced their populations due to hunting. "But most small mammals either do not hunt or reproduce so fast that it barely affects them, which distorts the average," says Benítez. In fact, if mammals are classified by size, the results are dramatically different: animals of medium size (between one kilogram and 20 kg) have seen their populations depleted by up to 27%. Meanwhile, in those with the highest body mass (above 20 kg), the percentage rises to 40%. "In addition to being the most profitable for hunters, they have longer breeding times and less breeding per reproductive event", explains the researcher.

The factors that most affect hunting pressure are, in this order, the distance to the nearest town or human infrastructure (roads, for example), the body mass of the species or the density of human population in the region. As the study shows, 60% of tropical forests are less than 10 kilometers from a human settlement, a percentage that increases to 80% if the distance to 20 km is increased. Perhaps for a hunter in Europe or the United States they are great distances, but they are the habitual ones for a hunter who does it to feed himself or to sell the meat of the animal.

By area, approximately 47% of what remains of tropical forest is being defaunada to a greater or lesser extent. Where losses are greater, more than 70% of animal life, is in West Africa (the jungles of Cameroon, Gambia or Ghana) and large regions of Southeast Asia (Thailand, Bangladesh, Indonesia …). The areas least affected by hunting are the region of the Guianas and the most hidden Amazon jungles. "These are areas where you can only get there with a helicopter or with very low population densities," recalls Benítez.

The consequences are still to be determined, although they are already glimpsing. When preying on larger animals, especially carnivores and herbivores, hunters are disrupting entire ecosystems. "90% of plant species need animals for the dispersal of their seeds and only large herbivores can disperse the larger fruits and seeds," recalls Benítez. In the long term, the absence of these animals will modify the plant composition of the forest itself. On the other hand, the drastic reduction of large carnivores could favor an explosion of herbivores and, therefore, extra pressure on plant resources.

The study has the following question in its title: Jungle intact, but empty? And that is the main conclusion of this work. There is a real risk that many forests lose most of their large and medium mammals, with the cascade effect that this can initiate. And with the increasingly empty tropical forests, "the soundscape of the jungle will become impoverished," Benítez laments.

60% of the remaining forests are less than 10 kilometers from a human settlement

The researcher Gerardo Ceballos, of the Institute of Ecology of the National Autonomous University of Mexico, does not believe positive to demonize hunting as a category. "Legal hunting is an economic activity that has had a huge positive impact in maintaining species in many regions of the world, with success stories in the United States, Spain, Mexico or various countries in Africa," he says. He gives as an example the many species of ducks and geese that, being on the verge of extinction, ended up recovering thanks to the regulated hunting in the USA. "The same happens with deer and bighorn sheep in Mexico and species such as the elephant in many countries in Africa.The unilateral prohibition of legal hunting generally causes deterioration and incites illegal hunting," adds this ecologist not related to the study.

However, it coincides with the results of the work and points to hunting and illegal trafficking as "one of the causes of the sixth mass extinction". Ceballos, who has spent years researching and warning that this global event is already happening, also points to subsistence hunting and commercialization in local wildlife markets as part of this sixth extinction.

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