When people see a skunk, the reaction usually is “Eww,” but when they see a group of meerkats peering around, they often think “Aww.”
Why some animals use noxious scents while others live in social groups to defend themselves against predators is the question that biologists Theodore Stankowich of California State University, Long Beach (CSULB) and Tim Caro of UC Davis sought to answer through a comprehensive analysis of predator-prey interactions among carnivorous mammals and birds of prey.
Their results, “Ecological Drivers of Antipredator Defenses in Carnivores,” appears in the online edition of the journal Evolution.
“The idea is that we’re trying to explain why certain antipredator traits evolved in some species but not others,” said Stankowich, an assistant professor of biological sciences who noted that this study not only explains why skunks are stinky and why banded mongooses live in groups but also breaks new ground in the methodology of estimating predation risks.
The researchers collected data on 181 species of carnivores, a group in which many species are small and under threat from other members of their guild. They ran a comparison of every possible predator-prey combination, correcting for a variety of natural history factors, to create a potential risk value that estimates the strength of natural selection due to predation from birds and other mammals. Paul Haverkamp, a geographer who recently completed his Ph.D. at UC Davis, plus other organizations, assisted with the project.
“The goal here was to explain why both noxious spray behaviors and social groups evolve in the same order of mammals but never together in the same species. Our hypothesis was based around the idea that species that are under proportionately greater potential predation risk from a particular type of threat should have defenses tailored to specifically deal with that threat,” Stankowich said.
They hypothesized that carnivores at risk from other mammal predators, especially at night, would use spray defenses. He said, “Spraying is a good close-range defense in case you get surprised by a predator, so at night when you can’t detect things far away, you might be more likely to stumble upon a predator.”
Conversely, small carnivores like mongooses and meerkats usually are active during the day which puts them at risk from birds of prey would be more likely to rely on friends to thwart attack, so “Living in large social groups provides you with benefits of collective vigilance. More eyes on the sky mean you get an earlier warning. The benefits of doing that are enhanced during the daytime because you can see things from farther away,” Stankowich said. “With birds of prey, you have to monitor the sky in three dimensions as opposed to simply a two dimensional line on the horizon with mammalian predators.”
The social animals also use other defenses such as calling out a warning to other members of their group or even mobbing together to bite and scratch an intruder to drive it away.
The project was a major information technology undertaking involving plotting geographic range overlap of hundreds of mammal and bird species but will have long-term benefits for ongoing studies, as Stankowich expects to make the predator-prey database, which he calls the “Geography of Fear,” available to other researchers in the future.
For more information, see Theodore Stankowich, Paul J. Haverkamp and Tim Caro, “Ecological Drivers of Antipredator Defenses in Carnivores,” http://onlinelibrary.wiley.com/doi/10.1111/evo.12356/abstract or www.csulb.edu/~tstankow.