Who's Afraid of the Big Bad Wolf? Fear and Loathing in YNP
The presence of predators has wide-ranging impacts on animals and ecosystems.
Posted June 5, 2013
"Fear and intimidation are far more common in nature than we realised, with surprising consequences not just for animals but for the entire landscape"
A recent essay by Ed Yong in New Scientist magazine called "Scared to death: How intimidation changes ecosystems" challenges many deeply rooted assumptions about the significance of the presence of predators on the lives of prey species and on landscapes. Currently, the essay is only available to subscribers, so here I highlight some of the major discoveries in studies of what's called the landscape or cartography of fear because I find them both surprising and incredibly fascinating. The lead quotation and those below are from the essay in New Scientist.
Fear and loathing in Yellowstone
It's not an overstatement to say that many animals live in constant fear. Consider the reintroduction of grey wolves into Yellowstone National Park (YNP) that began in 1995. While most of the attention focused on these magnificent animals, biologist John Laundré was more interested in the elk who had been living in the park without wolves and causing serious damage to trees in the park. To quote Dr. Laundré: "'It was a scene out of a Disney film,'" says Laundré, an ecologist at the State University of New York at Oswego. But in areas the wolves had colonised, things were very different. The calves were pinned to the sides of their ever-wary mothers. 'It was like looking at two different countries, one at war and one at peace' ...For Laundré, it was a light-bulb moment. He realised that wolves don't just kill elk, they also change the deer's behaviour without even lifting a claw. Their mere presence – perhaps their scent on the wind and tracks in the dirt – creates a perpetual state of apprehension in their prey. Seen through the eyes of an elk, the physical terrain is overlaid with a mental map of risk, complete with 'mountains' where the odds of being eaten are high and they must be constantly vigilant, and 'valleys' of relative safety where they can lower their guard. To describe this psychological environment, Laundré coined the term 'landscape of fear'". (For the record, I-Fu Tan published a book called Landscapes of Fear in 1980 and world renowned field biologist Joel Berger also published a book in 2008 on the same topic called The Better to Eat You With: Fear in the Animal World.)
Intimidation, not, slaughter, is responsible for many different animals to live in perpetual fear. Predators "can influence how successfully their potential victims feed, breed and raise their young, all without a single kill. And it doesn't end there: these effects trickle through entire ecosystems, shaping the make-up of the local flora and even influencing the flow of nutrients through the soil. The implications are huge. Through the landscape of fear, predators can unwittingly remodel the physical landscape – just by being scary."
The bioenergetics of fear and chronic stress
Scott Creel, who works out of Montana State University in Bozeman, has conducted detailed research into the relationship between fear and lifestyle in the Yellowstone elk discovered "when wolves were around, elk more than doubled the time they spent on watch. They also moved away from the grassy fields they prefer into wooded areas that offer more protection but less food. These changes slashed the amount of energy they were getting by around a quarter – with dire consequences. When Creel saw a dramatic decline in calf numbers, he knew the wolves were not directly responsible because they rarely kill young elk. Measuring levels of progesterone – a hormone that spikes during pregnancy – in stool samples from 1500 female elk, he found that they were far lower in areas where wolves lived. Many elk were in such poor condition they didn't have enough energy to reproduce." The abstract for "Glucocorticoid stress hormones and the effect of predation risk on elk reproduction" by Scott Creel and his colleagues can be seen here.
Ecological cascades and webs of nature: The effects of fear and stress are ubiquitous
The reintroduction of wolves has had many diverse effects on the ecology of YNP. Elk numbers are down from about 19,000 to 6,000 and aspen, willows, and cottonwoods are increasing. There are more saplings because the stressed out elk don't nibble on their lower branches and older trees have greatly increased in height (see "Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction" by William J. Ripple and Robert L. Beschta). There are more beavers and by damming rivers there is more habitat for birds, fish, amphibians, and other species. The effects of fear and stress are truly ubiquitous. And it is not predation, but rather the landscapes of fear and stress, that are responsible for changing the ecology of YNP.
There are other fascinating changes. For example, "Sparrows that regularly heard predator sounds raised 40 per cent fewer chicks each year than those that heard the noises of harmless animals. They laid fewer eggs. Those that were laid were lighter and more frequently failed to hatch, partly because the skittish mothers spent less time incubating them. And the chicks that did hatch were more likely to die of starvation, because their fearful parents brought less food to the nest" (see "Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year"). According to Liana Zanette of the University of Western Ontario in Canada, "It was the first study to unambiguously show that fear can affect populations."
Even grasshoppers get into the act. In the presence of spiders stressed grasshoppers show an increase of 40% in their metabolic rate when compared to unstressed grasshoppers. In Israel's Ein Avdat National Park Nubian ibex eat less in the presence of tourists (see "Impact of tourism on Nubian Ibex (Capra nubiana) revealed through assessment of behavioral indicators") because they are "particularly spooked by the appearance of tourists on slopes above them, cutting off their lines of escape."
Animals want to live in peace and safety and understanding and further studies and more detailed data about landscapes of fear can be used to further our understanding of Earth's abundant magnificent webs of nature. These data will be very useful for conservation projects whose goal is to protect vulnerable and endangered species. For example, "conservation groups trying to return bighorn sheep to parts of the south-western US. In the bighorn's former range, vegetation has grown significantly and now easily conceals stalking predators. 'They bring the sheep in, and mountain lions kill them, to the point where they think they need to control the lions,' says Laundré. He suspects that simply trimming the shrubs along corridors connecting mountain ridges would make a big difference, allowing the sheep to let down their guard and move freely."
The last paragraph of the New Scientist essay sums up the importance of understanding the pervasive role of fear. "Landscapes of fear may be psychological, but for prey they are as real as their physical counterparts. 'Every step an animal takes out there happens in a changing risk environment,' says [Joel] Brown. 'That topography exists in the mind of the animal.' This realisation has big implications for how we understand ecology. Indeed, Laundré believes the future of conservation lies in managing these metaphysical landscapes – keeping just the right levels of risky and safe habitats to maintain stable populations of both predator and prey. 'This could be one of the most valuable tools we have in conservation ecology,' he says." I think he's right on the mark.
Just when we think we know it all ...