Wednesday, August 17, 2011

Yellowstone and Beyond: Fear as an Ecosystem Engineer by Moderator Cristina Eisenberg


Imagine that you are walking alone in downtown New York City at 11 p.m. You move quickly and don’t linger, looking over your shoulder regularly, your senses on high alert. In this high-crime city, every shadow, every dark alley contains the potential of danger. Now imagine you are walking downtown in the small town in Kansas where you grew up. It is 11 p.m. Your pace is relaxed, as you stroll from block to block. You pause and look at shop windows and take your time. And so it is for elk when wolves are in an ecosystem versus when they are not. Ecologist Joel Berger termed this effect the ecology of fear.

The ecology of fear has deep roots. Staying alive during the early Pleistocene involved escaping large creatures with sharp teeth and claws, such as saber-toothed tigers and dire wolves. Thus prey species evolved behavior driven by survival. Vigilance—time spent head up, looking for threats—is essential for survival in systems with apex predators, but comes at the expense of time spent eating. Fear inspired by the threat of predation also influences feeding choices animals make—and this in turn can affect how plants grow.

Vigilant elk/
Photo credit: Cristina Eisenberg
For example, in Yellowstone National Park, William Ripple and Robert Beschta found that wolves keep elk more wary and alert, thereby reducing consumption of plants such as aspen and willows in places that have escape impediments. And also working in Yellowstone, researcher John Laundre and his colleagues described landscapes inhabited by apex predators such as wolves as landscapes of fear.

How does fear shape ecosystems?


Alpha female wolf on an elk carcass
in a high predation risk area/
Photo credit: Dave Moscovitz

As a scientist, one of my leading research questions has to do with whether elk avoid risky places (thick forests, downed wood, steep embankments) in which it is more difficult to detect and escape an apex predator, such as a wolf. To answer this question I put in 180 miles of transects in Glacier National Park, Montana, and Waterton Lakes National Park, Alberta, in which I measured elk presence. One morning, when I resumed work in an area where the previous day I had put a transect into thick forest and quantified it as having high predation risk, I found an alpha female wolf standing in my transect, feeding on a freshly killed elk. She calmly looked up at me and my field crew, the heart of the elk in her mouth. The following year I found that elk were not spending much time browsing on the aspen in this particular area, thereby enabling young saplings to grow into adult trees. This vivid demonstration of the ecology of fear in action provided me with a powerful reminder of how wolves and other apex predators can be ecosystem engineers.


Wolf on a carcass/Parks Canada/
Photo credit: Cristina Eisenberg
What are the long-term consequences of the ecology of fear?

How might managers simulate the ecological effects of fear in landscapes where it is impractical to have apex predators?

Do you think cougars have different effects on prey behavior than wolves?

Why or why not?

3 comments:

Mark LaRoux said...

I'll give a personal account of the ecology of fear....first an article from 2008:
http://enewscourier.com/x1037417238/Was-bear-a-danger/print
(anthropocentric fear?) We get 1 or 2 bears a year crossing from north Georgia/east Tennessee to Mississippi (both remote areas) usually during summer and they run the population gauntlet of north Alabama between them. It just so happens that I had led a group of cub scouts at camp Chalakee (on the south side of Tennessee river in Alabama) and saw some unmistakable bear scat as we were hiking. "No way that's bear scat in north Alabama" I kept saying in my mind, but knew instinctively there was something very different about this campout. Bears in north Alabama? I got very little sleep camping, I'm sure my blood pressure was high, and the weekend of scouting fun was great for the kids, but I was kind of on edge the whole weekend. Sublime would be the best description. Just knowing something was out there made the night uncomfortable.
Long term consequences of ecology of fear?
(humans/pets) We used to complain about the recent coyotes that have eliminated many small dogs and cats in our neighborhood (wooded hills around 1500 feet). Our neighbors have become 'meso-westernized' in a way...no dog/cat food left outside, put the cats in at night, etc. I'm sure the pets change their behavior when they catch scent of the coyote scat (my 90 lb. black and tan howls in excitement when she catches their scent). The added benefit of coyotes is the reduction in other meso-predators...--feral cats have to hunt in the daylight, --possums and raccoons are lessened to minor roles and stay in the trees longer, --Allegheny woodrats don't eat as much seeds in raccoon feces eliminating one cause of diease for them,--fence lizards sun longer, etc...the whole cascade of slow changes 'helps' in small almost inperceptable steps. These are just coyotes (maybe a bobcat). Imagine what a more than occassional bear would do. Or a mountain lion. It would be like a sheriff coming to town to run off the riff-raff. But only as long as the sheriff is in town.
To keep the effects of fear, we need a constant full-time predator that keeps the stress up, not part-timers that leave no reminder they were there. Hunters swoop in, shoot something before the others can react, and leave in a rush, leaving the animals that saw the hunt to view us as aliens from UFO's...no scent markings, no scat, no young, rarely even females (and almost never in estrus due to the pill anyway). Gut piles, food wrappers, and shotgun shells are all that remains. Maybe we should be leaving more markings that we are an apex predator (yes, I'm saying 'go' in the woods). If not, at least run dogs through these wilds to keep the meso-predators in the trees or under ground for a while.
Cougars are great ambush predators, while wolves will just plain wear an animal out through numbers and small injuries. This is a lot like watching different forms of martial arts: some traditional Phillipine styles use multiple sticks that can wear you out while Japanese/Okinawan uses a 'key strike' that puts you down in a weak moment. The healthy elk look at wolves almost in defiance saying "Bring it on big boy" and keep them in sight, while the ninja strike of a large cat makes them fear a whole area or ecosystem...a situation. Do any animals follow a cougar? A bear? (Other than researchers) My guess is that cougars follow human hunters to figure out how they are hunting, not to stalk them. Considering how namy kills we make on deer, I would too.
Sorry for the rambling...very interesting topic though.

Cristina Eisenberg said...

Dear Mark,

Thank you for sharing your personal experiences with the ecology of fear. You have pointed out some very compelling reasons why fear can be a healthy component of ecosystems. The examples that you give, of finding bear scat in Alabama, or of how coyotes in the neighborhood change people's behavior,and that of small predators, such as feral cats--are powerful. Such stories can be found in all sorts of ecosystems, and I look forward to hearing more stories about this from readers.

You ask about the fear-based effects of cougars or bears. In places where there are wolves, cougars and bears do not provoke the same sort of fear as wolves do. This is because bears are omnivores that eat vegetation as well as meat. They opportunistically scavenge meat, and will often take elk calves and deer fawns, but do not typically kill adult elk and deer. Cougars are solitary stealth hunters, and the dynamics of their hunting strategy do not engender the same sort of vigilance behavior that wolves do, although scientists don't fully understand why this is so.

Cristina

Bob said...

In places where apex predators might not be tolerated, how can managers create healthier ecosystems?

In places where we can’t have keystone predators, do you think hunting by humans can be used to create similar effects?

I called Dr. Eisenberg’s OSU office a couple months ago, hoping to ask a similar question while prepping to fight to stop the WA Legislature from passing a cougar (Puma concolor) hound hunting bill. So I’m happy to see it’s not a frivolous question and is up for discussion. I’ve spent time trying to understand these questions, step in and help me here.

The experiments that fence out ungulates over a sizeable area appear to create diversity, with the fence acting in a sense as a keystone with influence broader than just the ungulates it controls. I believe the effects may be beneficial in the span of several lifetimes, but still, the fence introduces simplicity to the system, and long-term cannot perform as well as a system honed by thousands of millennia. The system will lack the energy transfer of prey scat and carcasses, as well as apex consumers spilling drops to the gods. Low level changes may not manifest for many years. Still, short-term improvements help to slow the more rapid downgrading, and though not optimal, buy time.

Assuming Homo sapiens arrived in the American sub-systems too late to influence evolutionary processes, it seems hunting acts as an additional trophic level, turning an odd-level system (green) to an even-level system (brown). Hence the second question. My considerations lead me to think “Not really,” but again, in the short-term it might slow degradation.

I have seen, and considered, the idea to allow year-round hunting of prey to more nearly simulate predation pressures. What would still be missing is the fear factor. Wolves are obvious as coursing predators, herds take an active part in the predation process. A herd will still see a Puma in the last phase of stalk and pounce predation, and will probably still fear margins. A hunter though, is an unseen killer, and when observed, just appears as another scavenger. So my hypothesis is that hunters would not change the browsing habits or utilization areas of prey species absent natural (traditional) apex consumers.

Also missing is the predator-prey-producer relationships and feedback forces. We don’t (generally) limit our families or practice infanticide or abandonment when times are hard. We are insensitive to life cycles and bottom-up and top-down forces. We go past tipping points, and we generally ignore science as we don’t have the will to stop ourselves.

I saw a PDF file from the 10th Mountain Lion Workshop that was a proposal by Dr. Gary Koehler and Richard Beausoleil of WA Dept of Fish & Wildlife proposing a distributed cougar hunt, keeping the total kill below the 12% lion recruitment rate both statewide and in local populations. It’s a science-based approach that, given we’re still going to hunt apex predators, attempts to minimize the disruption to not only cougars’ ecological services, but to the specie’s social structure as well. I’d personally prefer we let cougars manage cougars (and wolves manage wolves), and that we focus on becoming pseudo-keystones under (external, peer-reviewed) scientific parameters in those areas where we extirpated apex consumers.