Responding To Predators
The changing climate is the most familiar symbol of the Anthropocene, the geological era in which humans are the dominant force shaping our planet. Images of polar bears on shrinking ice floes, for instance, remind us how our actions affect other animals. This paper explores a less familiar instance of human impact on the world around us. We alter the evolutionary pressures that nonhuman animals face, over time causing changes in their traits. In this case, the researchers examine the change in how animals living in human spaces respond to predators.
Responding to predators takes time and energy away from other activities, such as foraging for food. This cost means that in an environment with few predators, animals who put less effort into antipredator responses will thrive. For example, cautious animals are more likely to survive when predators are lurking, but when predators are largely absent, their skittishness may harm their success at foraging. Therefore, over the course of generations, antipredator characteristics decrease in populations where predators are few.
Humans both actively and passively reduce predation, through protecting animals from predators and through our presence acting as a deterrent. Three groups of animals live most closely with humans: domesticated animals (e.g. companion animals like our dogs and cats), captive animals (e.g. zoo animals), and urban animals (e.g. squirrels and pigeons, who thrive in urban jungles).
Even from the first generation exposed to humans, the researchers found a rapid reduction in antipredator responses. Domestication caused the most rapid reduction in antipredator characteristics, bottoming out after only thirty generations, compared to ninety for urbanized animals.
In addition to examining antipredator responses among these three groups, researchers looked at the relationship between the rate of change and other aspects of the species’ life history. Results showed that diet and social behavior were the life history traits most closely related to changes in antipredator responses. For example, their data showed that domesticated herbivores lost antipredator characteristics particularly quickly, and that social species lost antipredator responses more slowly than solitary ones. The researchers suggest that this may be because certain antipredator responses serve a social function, too.
This study tells us more about how humans affect the animals who live alongside us, and emphasizes how quickly human-driven changes can take place. Human presence makes animals less well-equipped to cope with predators, and may thus harm their chances of survival in the long term.
This research is particularly relevant for conservation programs that hope to reintroduce animals into the wild, suggesting that we need to be proactive about preventing the loss of crucial antipredator responses. To animal advocates, intentionally exposing animals to predators may seem counterintuitive. After all, we strive to protect them, not to put them in harm’s way. But if we want species to return to nature, such actions may be necessary – leaving us with the question, how do we asses trade offs between a natural life and a protected life for nonhuman animals?