Studying primate behavior to avoid primate extinction

More than half of all the primates scattered across the globe, a group that includes our own species along with the rest of the great apes, gibbons, monkeys, lemurs, lorises, galagos, and tarsiers, are threatened with extinction. When considering any group of animals that risks disappearing from the face of the earth, researchers focus on both the inherent properties that make them vulnerable to extinction as well as external, often anthropogenic, factors. The external ones are usually obvious: habitat loss, climate change, invasive species, pollution, and so on. These risks aren’t distributed evenly across the globe, so animals in some spots will suffer more from them than those elsewhere.

But even in a single geographic location or ecosystem, different species can have a greater or lesser risk of extinction, and that’s because of intrinsic factors. Species with longer gestation periods, for example, can have a higher risk because they produce fewer offspring over time. While researchers have long known how these sorts of life-history variables can influence extinction risk, fewer have paid much attention to animal behavior.

That’s why graduate student Amélie Christelle Lootvoet from University Paris-Sud and her colleagues decided to see whether there were social behavioral variables that could help explain why some primates risk extinction while others don’t, even in the same parts of the world. In addition to collecting data on the external pressures that each species faces, Lootvoet also focused on behavioral factors that she thought could play a role in extinction risk.

The first was social and mating systems, which were combined into a single variable because they’re so tightly correlated. For example, primates that live in pairs tend to be monogamous, while solitary species are always polygynous. They also looked at average group size. Third, they rated the species according to their level of sexual dimorphism as a proxy for sexual selection.

The researchers also accounted for life-history traits, like gestation period and body size, as well as ecological factors, like average territory size and the type of food that the animals eat.

In all, they had data available for 93 primate species, ranging from the diminutive Mohol bushbaby to the massive western gorilla. Using a series of mathematical models, Lootvoet was able to work out which factors were most predictive of a species’ IUCN classification, which ranged from “least concern” to “critically endangered.” Unsurprisingly, the human footprint on their habitat ranked important, as did home range size. In a world of increasing habitat loss, animals that require large territories are at a disadvantage. Frugivorous animals were also more likely to be threatened with extinction than those with other diets, perhaps because fruits are more patchily distributed than are leaves.

When it came to the behavioral variables, group size stood out. Primates that live in larger groups are less likely to be threatened with extinction than those that live in smaller groups. The researchers say this could be explained by an “Allee effect”: individuals living in larger groups are more fit than those that live in smaller groups. It makes intuitive sense. Animals that live in bigger groups will find it easier to find sexual partners than solitary animals, meaning that they might be able to produce enough offspring to offset the stresses imposed by other factors.

The researchers say that theirs is the first study to identify a behavioral factor – social grouping – that contributes to extinction risk among primates. They argue that identifying the risk factors for extinction is necessary for mitigating those risks and stemming the tide of the rapidly advancing “sixth extinction.” Indeed, more nuanced conservation plans can be designed if they’re informed by more specific information about any particular species and the threats they face. “By doing so,” they say, “the preservation of populations threatened by extinction should be more efficient” – and more cost-effective. – Jason G. Goldman | 16 October 2015

Source: Lootvoet, A. C., Philippon, J., & Bessa-Gomes, C. (2015). Behavioral Correlates of Primates Conservation Status: Intrinsic Vulnerability to Anthropogenic Threats. PLoS ONE, 10(10): e0135585. DOI: 10.1371/journal.pone.0135585.

Header image: Male gorilla via