‘Social Lives' of Animals Stabilize Ecosystem: Study
International research team overturns ideas about groups of prey, predators
BY LORI BONA HUNT
The secret to a sustainable ecosystem may be ensuring that animals are able to form social structures and groups, says Prof. John Fryxell, Integrative Biology.
In a paper published last month in Nature, Fryxell and a group of international scientists say that grouping stabilizes interactions between predators and prey, and that social groups rather than individuals are the basic building blocks for interactions in the animal kingdom.
The study may help explain the rise of humans — the most social predators — and suggest the need to curb activities that break up animals' social structure.
“The greater the tendency to form groups, the higher the stability of numbers of both species over time,” says Fryxell, lead author on the study. “Before now, people hadn't appreciated the degree to which group formation has implications.”
The findings break with 80 years of ecological theory. Biologists have long modelled interactions between predators and prey by taking head counts of each species and assuming that individuals are evenly dispersed over a landscape, ignoring the fact that many predators and their prey both form social groups.
But the number and distribution of groups, rather than individuals, are most important in determining how often — and for how much longer — the two species will interact, the researchers found.
“We're saying it's vital to study social dynamics if you want to fully understand the ecology of predators and their prey and to manage these systems adequately,” says Fryxell, whose research was funded by the Natural Sciences and Engineering Research Council.
The researchers based their findings on data on lions and wildebeest in Africa's Serengeti Plain, drawing on four decades of observations of lions' general behaviour, their hunting behaviour and censuses, as well as censuses of wildebeest and other herbivore herds in the same area.
They found social grouping by both wildebeest and lions was more strongly correlated with the long-term stability of the ecosystem than no grouping or grouping of either species alone.
This implies that even if an ecosystem has lots of carnivores and herbivores, the two populations may be in trouble if the animals are social but cannot readily form groups.
“This result is remarkable in light of the intense scrutiny that predator-prey relationships have received in ecology,” says Saran Twombly, program director in the division of environmental biology at the U.S. National Science Foundation, which also supported the research. “The finding is likely to have broad implications for diverse types of interactions and their effects on community or ecosystem stability.”
Fryxell adds that the results also have implications for managing large ecosystems. For example, managers of national parks sometimes bore holes to create watering spots for animals, an activity that spreads wildlife out and may keep them from grouping. Road building and disruptions by tourists may do the same.
“Anything that tends to fragment aggregates of animals could work against the protection that group formation provides, threatening the stability of the whole food web,” he says.
Fryxell worked on the study with Craig Packer and Anna Mosser of the University of Minnesota and Tony Sinclair of the University of British Columbia.