The critical role of natural forest as refugium for generalist species in oil palm-dominated landscapes

Abstract

In Borneo, oil palm plantations have replaced much of natural resources, where generalist species tend to be the principal beneficiaries, due to the abundant food provided by oil palm plantations. Here, we analyse the distribution of the Asian water monitor lizard (Varanus salvator) population within an oil palm-dominated landscape in the Kinabatangan floodplain, Malaysian Borneo. By using mark-recapture methods we estimated its population size, survival, and growth in forest and plantation habitats. We compared body measurements (i.e. body weight and body length) of individuals living in forest and oil palm habitats as proxy for the population’s health status, and used general least squares estimation models to evaluate its response to highly fragmented landscapes in the absence of intensive hunting pressures. Contrary to previous studies, the abundance of lizards was higher in the forest than in oil palm plantations. Recruitment rates were also higher in the forest, suggesting that these areas may function as a source of new individuals into the landscape. While there were no morphometric differences among plantation sites, we found significant differences among forested areas, where larger lizards were found inhabiting forest adjacent to oil palm plantations. Although abundant in food resources, the limited availability of refugia in oil palm plantations may intensify intra-specific encounters and competition, altering the body size distribution in plantation populations, contrary to what happens in the forest. We conclude that large patches of forest, around and within oil palm plantations, are essential for the dynamics of the monitor lizard population in the Kinabatangan floodplain, as well as a potential source of individuals to the landscape. We recommend assessing this effect in other generalist species, as well as the impact on the prey communities, especially to reinforce the establishment of buffer zones and corridors as a conservation strategy within plantations.

The effect of oil palm‐dominated landscapes on the home range and distribution of a generalist species, the Asian water monitor

“…Nonetheless, these conditions may not remain favorable for them in the long run. The reduced and clustered distribution of suitable habitat in oil palm plantations might not be a problem for large individuals, but it may have negative impact on the survival of juveniles and hatchlings, because of predation and competition, as well as microclimatic conditions (Guerrero‐Sanchez et al, 2021).…”

“…However, a closer examination reveals that the resulting impacts of oil palm development on monitor lizard home ranges may influence the drastic shift in the population distribution, described by Guerrero-Sanchez et al (2021). Such impact is based not only on the altered prey community found in developed areas but also on the limited availability of suitable habitat, with potential consequences on both the population health and the prey community composition.…”

“…In order to minimize the effect of territoriality, lizards tagged within the same period of time were trapped with a minimum distance of 2 km from each other. All the lizards tagged were trapped using wired-mesh cage traps (L = 90 cm, W = 40 cm, H = 40 cm), and baited with chicken entrails (Guerrero-Sanchez et al, 2021). GPS-Tags were slightly modified from the VHF-tags described by Ciofi et al (2007) and Harlow et al (2010) for Komodo dragons.…”

“…The extremely broad diet of the species is associated with a spatially large foraging area, where solitary individuals roam actively searching for live prey or carcasses for large portions of the day (Fitzsimons & Thomas, 2016; Karunarathna et al, 2017; Traeholt, 1994). However, in the Kinabatangan floodplain, a previous study suggests that the forest surrounding large extensions of oil palm plantations plays an important role on the stability of the population (Guerrero‐Sanchez et al, 2021), raising fundamental questions on the spatial ecology of the species.…”

The fast-food effect: costs of being a generalist in a human-dominated landscape

“…In Asia, one of the largest beneficiaries of anthropogenic food is the Asian water monitor lizard ( Varanus salvator ), one of the largest predators in the region’s wetlands ( Traeholt, 1994 ; Guerrero-Sanchez et al, 2021 ). The species natural habitat is linked to lowland freshwater, such as mangroves, swamps and wetlands under 1000 m above the sea level (m.a.s.l.…”