Study Examines Nocturnal Predator-Prey Relationship

A new Harvard study published in the Journal of Animal Ecology reveals that predator animals are less active on most moonlit nights, while prey animals that exhibit visual acuity and have more habitual cover, such as lemurs, are more active.

Many nocturnal prey animals perform activities under the cover of darkness to protect themselves from predators. Scientists traditionally suspected that these prey animals are less active on bright nights when increased moonlight enhances predators’ ability to detect them.

However, the new study conducted by Harvard research associate Christopher D. Golden ’05 and University of Alaska-Fairbanks professor Laura R. Prugh found that moonlight does not necessarily increase predation risk—the extra light also gives prey increased ability to detect predators.

“What we found was that if predators were benefited by moonlight, then the prey may also benefit,” Golden said.

The study examined the effects of moonlight on the activity of 59 nocturnal mammal species. The researchers investigated factors such as habitat cover preference, visual acuity, taxonomy and trophic level—an animal’s position on the food chain.

“Our results were unanticipated because we had thought that the effect of moonlight would be moderated by the influence of a species’ trophic level,” Golden said.

Golden and Prugh said that they were surprised to discover that trophic level did not play a huge role in predation risk in animals. Instead, the scientists found that prey species with vision as their primary sensory system were more active in the moonlight, whereas prey species with other primary senses were less active.

“The ways in which species find and detect each other was a primary determinant of the way in which moonlight influenced behavior where those who rely on sight were the most affected, Golden said. “Secondly, taxonomy was a major influence as well perhaps explaining that there are some evolutionary or adaptive roots to the role of moonlight in behavior.”

Thus, primates like lemurs increased their activity on moonlit nights while predator activity and  the activity of some prey animals with evolutionary predispositions away from moonlight  including rodents, rabbits, and bats fell.

Golden also suggests that human behavior may also have an effect on the predator-prey dynamic through the use of artificial lights during nighttime hours.

“With urbanization ever increasing and city lights pouring out into wild areas, it is possible that these artificial lights are having similar or stronger effects than moonlight on the behavior of organisms,” Golden said.

Golden believes his and Prugh’s study begs scientists to reconsider the popular expectation that predator behavior drives that of prey. He instead suggested that the prey’s reduced activity may reduce the activity of predators due to predators’ reduced ability to hunt successfully when the prey stays hidden.