Researchers have discovered that a population of chimpanzees in Uganda is three times larger than previously estimated. The findings, published in BMC Ecology this week, suggest that the apes may be adapting to fragmented habitats better than we thought.
Together, the protected Budongo and Bugoma Forest Reserves make up about a quarter of the total chimpanzee population in the country. Between the two reserves, there is an unprotected area with agricultural fields, natural grassland, and forested areas containing villages. From 2000 to 2010, at least 450 square kilometers (174 square miles) of forest were lost between the reserves, but this degraded, human-dominated habitat might be a potentially vital corridor for chimps migrating between them.
So, University of Southern California’s Maureen McCarthy and colleagues spent 15 months conducting what’s called “genetic censusing” to count chimpanzees in the corridor area. They collected 865 fecal samples and, using genetic analysis, identified the presence of 182 individual chimps. From this they estimated a total population size of either 256 or 319 chimpanzees (depending on the calculations used). The findings suggest the population comprises at least nine communities, each containing at least eight to 33 individuals. That’s more than three times the total indicated by a previous study based on small-scale nest count surveys.
A chimpanzee mother and infant cross through farmland Hoima District, Uganda. Jack Lester
The larger than expected population is “very surprising given the fragmentation of forests in this region and the high human population density,” McCarthy explained in a statement. According to the team, the higher estimate reflects the greater accuracy genetic censusing offers over other methods and not a significant population growth between studies, which is unlikely given the long interval between chimpanzee births and the fast rate of habitat loss in the area. “Chimpanzees,” she added, “appear surprisingly resilient and can survive even in degraded habitats if they are not hunted.”
These surprising levels of chimp survival might be partly thanks to their behavioral flexibility, which includes adding novel – and often human-cultivated – food resources to their diets. “Even unprotected and degraded habitats can have high conservation value,” McCarthy said. Though it’s unclear what future survival rates will be like if habitat loss continues.
A male chimpanzee on the forest edge. The tree he sits in was logged some days later. Jack Lester