Fragmenting Forests And Primate Encounters
A chimpanzee emerges from the forest, eating her fill from a patch of maize grown by a farmer. A young man disappears into the trees, gathering firewood and other materials. Where human and nonhuman animals live in close proximity, such criss-crossings between spaces are inevitable. Yet they can pose problems: conflict and injury on both sides, for example, and the risk (especially potent in the context of the current pandemic) that diseases slip across.
In this study, researchers examined contact between humans and our fellow primates in rural Ugandan communities, to understand how characteristics of the landscape shape such encounters. Where farmland meets forest, interactions between humans and nonhumans are more frequent. As more land is needed for agriculture, forested areas (termed “core”) shrink and become increasingly fragmented, creating more “edges” and thus more frequent interactions.
The study took place between 2011 and 2015 in the area around Kibale National Park in western Uganda, a densely-populated region with mainly subsistence farmers. The researchers used data from self-reported surveys to understand human contact with other primates, and used satellite imagery to analyze the changing landscape. To quantify habitat fragmentation, they calculated the “edge density” of the landscape, where a higher edge density reflects a greater amount of fragmented forest habitat, and a lower density reflects less forest or a more intact forest habitat.
The survey was administered in 2015 and asked respondents how often they use forested areas (i.e., the core), and about what they do in the core and in areas settled by humans (termed “matrix”). Respondents were also asked about nonhuman primates they had encountered – e.g. how far away they were, and details of any physical contact.
Of a total of 364 survey respondents, just under a third (115) had experienced at least one encounter with a nonhuman primate within the past four years. As edge density increased (i.e. a more fragmented habitat), so too did the likelihood of contact with a nonhuman primate. Respondents who foraged or hunted in the forest were over twice as likely to have encountered a nonhuman primate. Analyzing the information provided about the location of encounters found that on average these took place about 30 meters (roughly 100ft) from the nearest patch of forest, and about 80 meters (about 260ft) from the respondent’s home.
In addition to helping researchers understand the relationship between landscape and primate encounters, satellite images provided insight into how the landscape changed over time. Comparing satellite images from 2011 to 2015 revealed the loss of 32km (about 20 miles) of forest, and a gain within Kibale of 1.6km (about one mile). The researchers note that such habitat loss will further harm local nonhuman primates, already considered threatened. It will also increase the frequency of encounters between human and nonhuman primates, and thus heighten the risk that economic and health-related problems arise.
Understanding how certain factors shape the likelihood of encounters between primates can help mitigate the potential harms to both sides. At a more granular level, this study suggests that we should prevent habitat fragmentation and decrease certain human activities in forested areas. But it also raises a broader question for animal advocates. Implicitly, it asks us to reflect on how we navigate our interspecies communities, so that we can foster relationships with other animals that are both respectful and safe for us all.