By Fernanda Wenzel
How do wild animals manage to continue hunting and reproducing in areas occupied by houses, roads, domestic animals and crops? Scientists increasingly point out that the only solution for most species is to drastically change their habits, in a forced adaptation process whose consequences for the surroundings are still uncertain.
An article published in early February in the journal Global Ecology and Conservation shows that many animals end up becoming more nocturnal as a way of avoiding human presence.
The study, which gathered researchers from the University of Manchester in the U.K. and the Ecology and Conservation Laboratory (Laec) at the University of São Paulo in Ribeirão Preto, Brazil, is part of a broad project started in 2013-14, when camera traps were installed in different parts of northeast São Paulo.
The area, originally covered by the Cerrado biome, has undergone changes caused by different crops for more than 200 years. It started with coffee in the 18th and 19th centuries, followed by livestock farming, and it has recently been taken over by sugar cane plantations as well as planted forests of pine and eucalyptus. “These animals have been in contact with people for a long time,” says Adriano Chiarello from Laec, who is the head of the study.
Researchers used camera traps to monitor circulation times and areas of five species of mammals in northeast São Paulo. Image courtesy of the USP Ecology and Conservation Laboratory.
Camera traps — small devices that capture images every time someone or something crosses in front of them — were installed in areas with different levels of preservation, including private properties and protected areas such as the Jataí Ecological Station.
“We have a very interesting design. A landscape with a large block of protected area, another one with a sea of forestry where there is only a sliver of forest, and a third landscape with a mixture of the other two, where you have forestry, sugar cane and protected areas,” Chiarello describes.
The photos taken years ago resulted in a series of scientific articles identifying the areas occupied by animals and the characteristics that made them more or less attractive to wildlife. In the most recent study, however, the aim was to understand how human presence affects animals’ habits.
“Because sometimes the animal continues to live in a space where there is anthropic [human] disturbance such as a dirt road or a sugar cane plantation, but it will not be active during the hours when it is most exposed to the possibility of human contact,” the researcher explains.
The aim was to compare the active hours of animals that belong to the same species but live in places with different levels of preservation and are more or less distant from the presence of humans, dogs and homes.
Of the six mammal species observed — jaguar (Puma concolor), ocelot (Leopardus pardalis), giant anteater (Myrmecophaga tridactyla), brown brocket deer (Subulo gouazoubira), agouti (Dasyprocta azarae) and crab-eating fox (Cerdocyon thous) — five presented changes in their behavior in areas that are unprotected and/or close to human occupation. Four of these species living in areas under more human pressure responded by becoming significantly more nocturnal.
The puma, which is usually active 24 hours a day, has become a nocturnal animal to avoid contact with people. Image courtesy of the USP Ecology and Conservation Laboratory.
In their natural habitat, pumas are active 24 hours a day, but they began to restrict their circulation in areas of human occupation to evening, night and early morning hours, between 6 p.m. and 6 a.m. The agouti, a rodent that is active throughout the day under normal conditions, now only circulates during the early hours of the morning.
“They have to be active early in the day because after that there will be people and cars there, and they don’t feel good about it. So it’s a time restriction with consequences for their ecological role,” explains Chiarello, referring to agoutis.
Giant anteaters, which feed on termites and ants and may have already become extinct in vast areas of Central and South America, are forced by dogs to adopt more nocturnal habits. In rural areas, many dogs roam free and end up chasing or even hunting wild animals during the day, when they are more active.
The article’s first author, Heather Ewart, explains that changing behavior or migrating to other regions are the only options for these animals as their habitats are being destroyed at a fast pace.
“Because we can’t see this evolutionary change in the timescales that we need, animals are either left with two options. And if they can’t do either of those two options, you’re seeing large-scale population decline,” says Ewart, who is finishing her Ph.D. studies at the University of Manchester.
Chain reaction
The study’s findings support what was observed by other researchers, such as the group headed by professor Maria João Ramos Pereira from the Department of Zoology at the Federal University of Rio Grande do Sul. Originally from Portugal and currently based in Brazil, she and her colleagues have been studying how human presence is related to the behavior of mammals in what remains of the Atlantic Forest in the state of Rio Grande do Sul and, more recently, in the Pampa biome.
“Unfortunately, we have been finding these [behavioral] changes, which are often specific to each species. Not all wildlife responds in the same way,” Pereira says.
Dogs, which usually roam free in rural areas, are the main stress factor for the giant anteater, which is endangered. Image courtesy of Adriano Chiarello.
Some species may even benefit from human presence. This is the case of the crab-eating fox, which, according to the article in Global Ecology and Conservation, is found more frequently in areas occupied by humans than in preserved areas. One of the reasons, researchers believe, is the fact that they eat virtually everything and find a greater variety of foods in these places.
In the case of other species, what happens is behavioral fine-tuning. Pereira and her colleagues studied how a group of pampas fox (Lycalopex gymnocercus) avoided being attacked by dogs. The researchers found that the animals continued to occupy the same spaces but not all at the same time. “It’s like if we both used the same apartment and we were both active during the day, except I’m active today and you’re active tomorrow,” she compares.
In most cases, destruction of native vegetation and proximity of human presence end up restricting animals’ circulation area and hours, with consequences that are still unknown.
“It’s like reducing a family’s budget; they will struggle to survive. Animals have to find a way. For example, I can no longer go out all day, only in the evenings. Life becomes more difficult, and in these situations of stress they will reproduce less, live less,” Chiarello explains. “There are mechanisms that allow some resilience, but after a certain level, species become extinct, and that’s what is already happening,” Pereira says.
This imposed adaptation not only impacts the species, forced to change their habits, but also the entire environment. “Most species have key roles in their ecosystem. The agouti, for example, is a seed disperser, and that will then translate into plants being grown,” explains Ewart.
“What is happening is a chain reaction that may have consequences not only for those species but also for the system as a whole. Ecosystems are these very complex and interconnected networks,” Pereira agrees.
For the researchers, the study’s findings stress the importance of creating protected areas and complying with the Forest Code on private properties, regarding permanent preservation areas — on river banks, for example — and legal reserves. “Because this little bit of forest is a stronghold for these animals,” Chiarello explains. “These protected areas do protect the species, their natural behavior and their natural populations,” Ewart says.
Banner image: The ocelot (Leopardus pardalis), one of the species whose altered behavior was found by the study. Image by Instituto Últimos Refúgios via Wikimedia Commons (CC BY-SA 4.0).
Citations:
Ewart, H. E., Pasqualotto, N., Paolino, R. M., Jensen, K., & Chiarello, A. G. (2024). Effects of anthropogenic disturbance and land cover protection on the behavioural patterns and abundance of Brazilian mammals. Global Ecology and Conservation, 50, e02839. doi:10.1016/j.gecco.2024.e02839
This article was originally published on Mongabay
