February 11, 2014
Is It Better To Be Social Or Stinky In Thwarting A Predatory Attack?
Lawrence LeBlond for redOrbit.com - Your Universe Online
Skunks do it best when halting a predator in its tracks, unleashing a noxious stream of urine that can send the most lethal of hunters in the opposite direction. Other animals of the same group tend to rely on strong social bonds to thwart impending attacks.But why do some animals use noxious scents while others use strong social groups to defend against predation?
To better answer this question, Theodore Stankowich, of California State University, Long Beach (CSULB), and Tim Caro, of UC Davis, conducted a comprehensive analysis of the predator-prey interactions that exist between carnivorous mammals and birds of prey. The results of their study have been published 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,” Stankowich, a CSULB assistant professor of biological sciences, said in a statement.
Stankowich noted that the study not only explains why skunks use a noxious scent gland and why banded mongooses live in social groups but it also “breaks new ground in the methodology of estimating predation risks.”
For the study, the team collected data on 181 species of carnivores, a group in which many species are small and under constant threat from other animals, including those from their own group. Once the data were in hand, the team ran a comparison of every possible predator-prey combination to create a potential risk value that estimates the risk of natural selection due to predation from other animals.
“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.
The team theorized that carnivores that are most active at night, such as skunks, would benefit more from having a noxious scent gland that packs a powerful punch to any would-be predator.
“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,” said Stankowich in a statement.
For small carnivorous mammals that are more active during the daytime, such as mongooses and meerkats, having a strong social group may be more fitting to thwart attacks from birds of prey and other hungry animals.
“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.”
Animals living in social groups also have other defenses that are not typically found in those that rely on their noxious stench. Social carnivores use calls to warn other members of the group and sometimes form large mobs to launch a defensive attack against a predator 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,” wrote the authors.
Stankowich noted that he plans to make the predator-prey database, which he calls the “Geography of Fear,” available to other researchers in the future.
Paul Haverkamp, a geographer who recently completed his PhD at UC Davis, assisted with the study.