Last year two ecologists from Yale University released spiders into cages of grasshoppers. However, the spiders didn't eat even one grasshopper because their mouthparts had been glued shut. Still, the grasshoppers were terrified, and it was noted that their metabolism increased by at least 40 percent. This led to a significant change in their diet, as they ate more carb-heavy goldenrod plants and decreased their protein intake from grasses.
This change in animal behavior signals what might be called a paradigm shift in ecological thinking. Just the mere fear of predation can lead to remarkable changes in an animal's behavior. And this in turn has a big impact on the landscape. And of course, since ecosystems involve long routes of energy flow, the impact on the landscape then further impacts the lives of other animals.
John Laundre, an ecologist at the State University of New York at Oswego, noticed the impact of fear on animals' behavior after the re-introduction of grey wolves in Yellowstone National Park while he was studying elk. And he has found that the greatest impact predators can have over their prey is not by killing but rather by instilling fear in them. He coined the term for this: landscape of fear.
SmartPlanet spoke with Laundre about his observations in Yellowstone and how the idea of a landscape of fear can be used today to change and rebuild entire ecosystems.
SmartPlanet: In 1995 you observed an amazing change in elk behavior two years after the re-introduction of grey wolves to Yellowstone National Park.
John Laundre: That first year we looked at areas where both the elk and wolves [roamed] and areas of the park the wolves hadn’t gotten to yet, because they [had been] released in the northern part of the park.
So you had the advantage of observing areas where wolves were and comparing to areas where they hadn't populated yet.
By the second year we could easily see that in areas where the wolves were released the elk were a lot more fearful. In areas where the wolves still hadn’t gotten to, [it] was like scene out of the Disneyland. The elk were bounding around and not paying too much attention at all.
What did fear look like?
Well it’s a kind of apprehension. They spend more time lifting their head and looking around. And their calves were right by their sides. You could tell they were afraid of being attacked.
You coined the ecological term, “landscape of fear.” What does that mean?
Predators have what we call “level of lethality,” which is the fact that the level of ability to catch varies with habitat. No predator is an expert in all habitats.
Wolves are more lethal in open areas because they run them down. Cougars on the other hand sneak up on their prey and so they’re more lethal on forest edges.
So the landscape contains levels of varying risk for prey. So the level of fear within the prey changes across the landscape as the vegetation changes. And this also changes what we call the lethality of the predator.
Presumably the landscape of fear is not innate but something learned. So if the wolves had not roamed Yellowstone for 70 years, how could the elk know to be afraid of them?
Right. Well there are anecdotal stories about when the wolves were first released they ran among the elk and the elk viewed them just as big coyotes, nothing to be afraid of, until they killed couple of them. When you see you neighbor being killed you start to get the idea that this is something you need to be afraid of.
But the surprising conclusion that came out of Yellowstone is that fear itself is what changed the behavior of elk not the number of killings by wolves.
Yes. Of course predators do kill their prey. But they’re not very efficient at killing. The average estimate of efficiency is about 20 percent. That means that 80 percent of the time, the animals are surviving a near death experience.
That is where the learning comes in. They learn that they come closer to being killed if they’re caught out in the open than if they’re caught in the woods. If you escape death you learn where you escaped and you learn how you escaped.
In fact many [ecologists] feel that predators manage the fear of their prey. Like a good hunter they may not overhunt an area. For instance, if hunters go out and hunt an area, soon the animal will become difficult to find. So hunters might let the area rest.
The longer something doesn’t happen the lower our guard goes. [And this same phenomena occurs within the predator-prey relationship.]
How has the landscape of fear impacted the entire ecosystem?
Well, we know what the impact is when there is no landscape of fear. The large ruminants decimate their habitat. In the Eastern US, for instance, we’re suffering the consequences of not having large predators. The deer are eating up the forest.
What we are seeing in Yellowstone now is the process of rejuvenation of habitat because elk are afraid to basically move around the habitat freely grazing. For instance Willows and Aspens have recovered tremendously in the park.
I understand there are studies that proved that just evidence of the existence of a predator can instill fear and alter species' diets.
Yes. And there is a study coming out soon where researchers presented scents, scats and vocalizations of a predator but never presented the actual predator. And they saw how these things change the behavior of the prey animals. So there are a lot of neat designs that can be done. Some that demonstrate that behavior change can come not from just killing but just the presence of predator.
This of course reminds us of the classic presence of scarecrows in a corn field.
Right, but there has to be a certain degree of lethality. The scarecrow eventually doesn’t work because he is not lethal. This is why the plastic owls don’t work after a while. They work initially because the crows see them and stay away until they catch on that the owl has been sitting there a long time.
How can this landscape of fear help us manage entire ecosystems?
One of the things I’m looking into right now is the impact of the landscape of fear. We talk about scaring the prey. But predators will also kill, and the killing depends upon how much safe or risky habitat exists in the landscape.
One can envision an area that’s 70 percent safe and 30 percent risky. The prey can avoid the dangerous areas and so in that particular habitat I would predict the prey population will be pretty plentiful but the predator population will be lower.
Now let’s switch it, and say it’s 70 percent risk and 30 percent safe. Now what we have is an area where the predator is fairly lethal, and we'll have a lower level of prey. What I argue is we can mange this predator-prey relationship by managing the landscape.
Can you give us an example?
Yes, take bighorn sheep. Forest fires keep a lot of areas open and bighorn sheep need open areas. When we suppress the fire [which we want to do] the trees and the shrub grow back. That provides ideal hunting habitat for cougars. Then many say we have to control the cougar. But we don’t need to control the cougar. We need to control the habitat.
We need to look at the land [or habitat] and understand what balance of risky versus safe habitat will provide us a balance of predator and prey.
So landscape becomes a very, very strong management tool. Once we understand what the landscape of fear is for a particular species then we can go in an manage the habitat depending on what our conservation goals are.
Another example is the cottontail rabbit population. It’s declining mainly because the shrub cover is declining, and that is happening mainly because of over-browsing by deer. So its “safe habitat” is declining and it is more vulnerable to predation by foxes and coyotes.
The answer is not to control the foxes and coyotes but to somehow instill fear into the deer to allow the appropriate safe habitat for cottontails to come back.
This post was originally published on Smartplanet.com