Four closely related civet species, small nocturnal mammals found in Africa and Asia, have decided to coexist in the rainforests of Borneo. Generally, species that are closely related face challenges when living together due to competition for the same resources. However, in this case, binturongs, small-toothed palm civets, masked palm civets, and common palm civets all consume the same figs yet are able to share their habitat. To delve deeper into how they manage this coexistence, researchers conducted a study examining their levels of faunivory, which is the consumption of animal matter. The findings were published in Progress in Earth and Planetary Science on October 2, 2024.
Using observational techniques alone to study the behaviors of civets did not yield sufficient insights. This limitation arises from their behavioral traits—being nocturnal and semi-arboreal (capable of climbing trees 30 to 60 meters tall)—which make them hard to observe. Moreover, relying solely on fecal sampling proved inadequate for collecting dietary information about these civets.
“The hidden nature of these nocturnal and solitary forest animals complicates our understanding of how these four closely related species manage to coexist. While studies based on observations show that fruits are the primary component of their diet, we suspected that faunivory—the consumption of other animals and insects—could be more significant. Therefore, we applied stable carbon and nitrogen isotopic analyses to investigate this,” shared Miyabi Nakabayashi, an associate professor at Hiroshima University’s Graduate School of Integrated Sciences for Life in Japan.
One effective strategy for species with similar behavioral patterns to cohabit in the same area is to utilize different food sources. Given the typically low and variable abundance of fruits in the tropical forests of Borneo in comparison to those in Sumatra, it is likely that fruits alone cannot fulfill the dietary needs of all four civet species.
The research team used stable isotope analysis on the samples from each civet species to determine the nitrogen isotope ratios present in their fur, which helps indicate the amount of animal protein in their diets.
The civets were captured using box traps, and fur samples were collected for bulk stable isotope analysis as well as compound-specific nitrogen isotope analysis of their amino acids. Local insects and fruits were also gathered based on their proximity to where the civets live and the observed dietary habits. This analysis was performed on hair samples from two individuals of each civet species alongside insect and plant samples. The researchers determined the trophic positions (TP) or food web standings of the civets based on stable nitrogen isotope ratios from the amino acids glutamic acid and phenylalanine.
The findings revealed that faunivory was more prevalent among three of the civet species than previously thought.
“Among the four civet species, the bulk stable isotope analysis showed notably low nitrogen isotope ratios in binturongs, indicating that they are the least reliant on animal protein. Their trophic position is nearly akin to that of species that primarily consume plants, as shown by the nitrogen isotope ratios of their amino acids. Following binturongs are the small-toothed palm civets, masked palm civets, and common palm civets, which have trophic levels that align more with omnivorous species. These findings imply that the varying degrees to which these species consume animal-based sources—such as insects—play a crucial role in how they partition their ecological niches in Borneo,” explained Takumi Tsutaya, an assistant professor at the Graduate University for Advanced Studies (SOKENDAI) in Japan.
Going forward, the researchers aim to broaden their investigations into tropical rainforests to better understand how ecologically similar species can coexist in close proximity.
“Tropical rainforests boast the highest biodiversity compared to other forest types. This study shed light on one mechanism that allows different animal species to coexist in these environments. We hope to uncover other factors enabling the coexistence of numerous closely related species, not only among civets but also other animal groups,” Nakabayashi added.
Other contributors to this research include Yoko Sasaki, Nanako O. Ogawa, Naoto F. Ishikawa, and Naohiko Ohkouchi from the Japan Agency for Marine-Earth Science and Technology, along with Abdul Hamid Ahmad from Universiti Malaysia Sabah in Malaysia.
This study was supported by various organizations including the Inui Memorial Trust for Research on Animal Science, the Shikata Memorial Trust for Nature Conservation, the Fujiwara Natural History Foundation, the JSPS Core-to-Core Program, A. Advanced Research Networks, the “Evolutionary Studies of Complex Adaptive Systems” Research Grant, and Grants-in-Aid for Scientific Research from JSPS.
