Bornean monitor lizards seek refuge in forest patches next to plantations
On the Asian island of Borneo, divided between Brunei, Malaysia and Indonesia, agricultural expansion has replaced much of the natural resources. In some areas, such as the state of Sabah, more than 70% of the wild forest has been converted into some type of cultivation, especially in oil palm plantations (Elaeis guineensis). For some animal species, this change in land use is a major setback.
In the state of Sabah, in Borneo, more than 70% of the wild forest has been converted into some type of cultivation, especially oil palm plantations
Reduction of individuals, limitation and alteration of movements, conflicts with humans, among other impacts, is what they suffer orangutans, nebulous panthers, asian elephants, malay bears or the wild cattle. But they are not the only threats stemming from loss of habitat.
There is also “an increase in poaching and the extraction of animals for the illegal trafficking of species, such as the pangolin or the Malayan bear, which are in great demand in traditional oriental medicine,” he tells SINC. Sergio Guerrero-Sánchez, former doctoral student at the Cardiff University (United Kingdom), and current associate researcher at the Borneo Studies Institute of the University College Sabah Foundation (Malaysia).
Another consequence is the appearance of diseases due to the constant interaction of wild species with humans and domestic animals, “causing epidemic outbreaks with great local and global impact,” adds Guerrero-Sánchez.
For specialist species, which only depend on forest resources, such as panthers or gibbons, this fragmentation of their habitat affects their reproductive potential, and therefore reduces the number of individuals over time.
More food, worse conditions
However, for many animals, especially the most generalistsCapable of adapting and developing in various types of environment and feeding on a variety of resources, such as wild pigs or macaques, these plantations represent a new source of food, favoring the increase in populations.
The environmental conditions of the plantations are not entirely favorable for the lizard population, at least in the Kinabatangan plain.
This is also the case with the aquatic monitor (Varanus salvator), whose status, population growth and survival have been analyzed for four years as part of a collaborative project between the University of Cardiff, the Danau Girang Field Center biological station, and the Sabah Wildlife Department, Malaysia, with support from the Council of Science and Technology (CONACYT) of the Government of Mexico, through its doctoral scholarship program abroad.
“These plantations offer an abundant amount of food, which has altered the diet of these reptiles,” Guerrero-Sánchez informs SINC. Previously, the scientists had determined that their diet in the plantations consisted of more than 80% of rats, while in the natural forest, this proportion dropped to less than 20%.
Now the new work, published in the magazine PLoS ONE, reveals, however, that the environmental conditions of the plantations are not entirely favorable for the lizard population, at least in the Kinabatangan plain, where the investigation was carried out. To reach these conclusions, more than 700 individuals were captured (and released), of which 400 of them were marked, being one of the most robust studies on the species, in terms of sampling.
“The lack of shelter or sites with an adequate microclimate makes the surrounding forest play an important role both in reproduction and in the protection of young individuals, which sooner or later will migrate to the plantations”, explains the wildlife veterinarian. .
Distribution of the aquatic monitor capture sites and areas covered during the study in the Lower Kinabatangan Wildlife Sanctuary and surrounding plantations. / Sergio Guerrero-Sánchez et al.
Thus, the abundance of rodents in the plantations and the lack of shelter make these animals concentrate in small areas. This territorial limitation may cause an overconsumption of resources, and as a consequence, a imbalance in the ecosystem.
In addition, despite the fact that this generalist species has benefited from the abundance of food in the oil palm plantations, “without the protection of the forest, it is very possible that their populations will be seriously affected,” warns Guerrero-Sánchez.
This reptile has a state of minor concern and its populations are for the moment stable, according to the Red List of the International Union for Conservation of Nature (IUCN, for its acronym in English). “In Borneo, the species is considered a super predator, only after the saltwater crocodile, and the clouded panther”, indicates the researcher.
The lack of shelter or sites with an adequate microclimate means that the surrounding forest plays an important role both in reproduction and in the protection of young individuals.
However, the monitor lizard becomes a good indicator of what can happen to other species that lose their habitat with which it may be more difficult to work because their numbers are very small or because their study requires a greater amount of resources, he points out. the expert.
The ecosystem loses out
Despite providing nutrients, plantations have serious consequences on the dynamics of the forest, in the case of seed dispersers who see their movements altered, and the community of small animals, in the case of predators such as the aquatic monitor.
We hope this information helps us understand what may be happening in other species, which are also being affected by agricultural expansion in Borneo.
“The large amount of succulent food that exists in palm plantations has caused the migrations of bearded pigs, excellent seed dispersers, to stop occurring, and that maintenance of the forest does not occur, altering its natural dynamics,” he stresses. the scientist. Other animals, such as bats, bears, and pangolins, lose their habitats and become easy prey for animals. poachers and illegal traders.
The work thus shows the importance of maintaining the surrounding forest, as well as building and strengthening more forest within the plantations, in the form of corridors or contiguous patches that allow animals to move more freely.
In addition, the research opens the door to other questions about the distribution of the lizard in the landscape, its habitat preference, the impact of forest loss on genetic diversity or the health of populations. “We hope that this information helps us understand what may be happening in other species, which are also being affected by agricultural expansion in Borneo and in other regions that suffer from the same problem,” concludes Sergio Guerrero-Sánchez.
Sergio Guerrero-Sánchez et al. “The critical role of natural forest as refugium for generalist species in oil palm-dominated landscapes” PLoS ONE