Predators, Prey and People: How Humans Effect the Trophic Cascade
The distribution of humans worldwide has had an instrumental effect on the food chains that were already in play. Never before has a species dominated all terrains, all ecosystems and all creatures with a tool so powerful none could contest: the human mind. We as humans have such a rich history that we often forget what the world was like without us. It is because of this that sometimes we fail to see our impact before it is too late. With the rise of the field of conservation biology–a crisis discipline dedicated to the recovery of species nearing extinction or extirpation–we have the unique opportunity to understand how our actions impact the creatures around us, and what measures can be taken to mitigate or prevent negative outcomes (Pickett et al 1992).
The danger of human impacts is the effect they have on animal behaviour; sometimes the behaviours that adapted over millions of years for their survival become nothing more than another nail in their coffin. In my blog post, I will discuss the current threats facing the mountain caribou, how human impacts are altering the behaviour of these animals and their predators, as well as the conservation efforts that are currently being used to mitigate or remove these human-caused stresses.
HUMANS, WOLVES AND MOUNTAIN CARIBOU
In British Columbia, no one can escape hearing of this conflict time and time again, whether it be from the mouth of politicians, biologists or sadly, Miley Cyrus. Human practices have placed caribou in a particularly vulnerable position when it comes to their respective predators. The caribou has survived thus far due to their dual migratory approach, by which they migrate to higher elevations in the winter, their calving area(s) in spring, and then disperse to find food at lower elevations in the summer (Lankester and Mahoney 2001). If all goes according to plan, they can survive in these mountainous areas with a plethora of ground and arboreal lichen for food, relatively unscathed by the jaws of predators. The removal of caribou habitat essentially strips them of their protection and food, to the point where survival can only come from ‘boldly travelling to areas no caribou has traveled before!’ However, what started as one small step for caribou quickly became one giant leap for wolves. Thus, with the addition of humans in this equation, we now have three perspectives to consider: the caribou, the wolves and the humans.
CARL THE CARIBOU
Let us start with the caribou. Imagine, if you will, a joyful caribou named Carl. Now, all Carl the Caribou wants is to make it through winter and start a family that he can call his own. When winter comes, it is time for Carl and his chums to climb the steep terrains to bask in a predatorless paradise! However, once poor Carl reached the wintering grounds, it was not the paradise that is was before. All of the trees were either gone or had toppled to the ground, ridding the area of arboreal lichen and canopy cover (Chichowski 1996). All that is left for Carl “et al” to do is scavenge what they can from the deadwood and finish off the ground lichen (Chichowski 1996). However, unlike before, even a great deal of the ground lichen is trapped under an impenetrable sheet of ice (Sharma et al 2009)! With food dwindling and a lack shelter, Carl’s herd must wander back down into the crosshairs of their predators in search of the resources they need to survive (Sharma et al 2009). Thankfully, Carl is able to last until spring. Now it is time to head to the calving grounds! His herd makes it just in time for them to start mingling with the other caribou, but another challenge awaits; somehow the wolves were able to make it up to the calving grounds, too (Bergerud et al 1984)! Now there is nowhere left for him poor Carl to be safe . . . He will probably die.
WALTER THE WOLF
Walter the Wolf, on the other hand, is having a great year! The winter months are usually rough and dangerous for Walter’s pack, which resorts to taking on prey more capable of defending themselves, such as moose (Seip 1992). Oh, how Walter longs for the easy summer months, where prey like caribou frolic right onto his dinner plate. Well, Walter is in luck! Here come the caribou, dazed and desperate, stumbling into the path of those that eat them. Who is Walter the Wolf to deny this bountiful feast that has been so generously handed to him?
With the profitable winter coming to a close, Walter figures his pack is about to run out of luck. The calving grounds are out of reach and it is not like the caribou will just stroll into the valley again. He is perfectly content with relying on more difficult prey after such a successful winter, but then he hears an interesting sound. Following it, Walter the Wolf and his pack find a beautifully packed trail in the snow leading right up the steep hill side to the calving grounds. They struggle at first, higher and higher they climb, but they are finally able to enter the calving grounds and engorge themselves on the simplistic caribou. Why not?
HARRY THE HUMAN
Harry is . . . well, there is no way delicate way of putting this . . . Harry is an ignorant ass. When he isn’t out driving his gas guzzling hummer and spraying aerosol cans in the air in a bold protest to global climate change, Harry is in charge of selecting which areas should be logged for the forestry industry. It is not as if he is particularly passionate about it, he just enjoys the perk of being able to drive around the company snowmobile on his own time.
This fall, when asked where Harry’s people should log, he neglected to steer them clear of Carl’s winter range. What is Harry to do? With the mountain pine beetle epidemic there has been an influx in cuts, and it just so happens that the habitat Carl the Caribou wants is of great timber value (Chichowski 1996). Habitat destruction is exhausting work, and at the end of the day, all Harry wants to do is ride that company snowmobile up the highest hills. Lucky for Harry, he came across Carl’s calving grounds! Snowmobiling and wildlife viewing all in one day? Harry is one happy human! What Harry fails to acknowledge is that he paved a glorious road for Walter and his pack to enjoy the same scenery. Unfortunately, Walter intends to do a little bit more than view the wildlife. Smooth move, Harry the Human.
This relationship between the three species–humans, wolves and caribou–is not one that can be maintained. One of them is going to fall. Spoiler alert: it is the caribou. The original solution to merely preserve caribou habitat is only part of the solution. Even if those winter and calving ranges are preserved, the ground lichen may be inaccessible due to an unusually cold winter, or that season may be shortened to give predators early access to calving grounds, or recreational activities can even build trails for those predators to reach the caribou anyway (Lenart et al 2002; Seip 1992). In more recent years, recreation has been prohibited in these areas, but they cannot be managed 24/7; there will always be the odd skier or snowmobiler to go for a ride, unaware of their impact (Wolfe et al 2007). Even public education efforts have proved relatively ineffective, because many people engaging in these recreational activities are not locals, but rather, tourists (Wolfe et al 2007). This causes a lot of difficulties in managing the human user.
As for the management of wolves, methods have been less than inventive. Conservationists and managers approached the problem in the default manner: a culling. What many of these conservationists failed to acknowledge is that culling is one of the least effective methods of managing a wolf population (Lessard et al 2005). Extermination of the wolf is one thing, but simply removing a pack in a particular area will be a frivolous effort. A wolf pack can either be territorial or very mobile depending on the circumstance. If they find a profitable area, that pack is likely to stay to claim it, as they no longer need to travel long distances to meet their needs. Contrary to popular belief, culling this pack will do more harm than good, because it will result in rapid repopulation (Petersen 2011). This is to say that you have removed the wolves from a very profitable resource pool, which will allow neighbouring packs to enter to reclaim it (Lessard et al 2005; Petersen 2011). In the end, there will be a large influx of wolves into the area attempting to claim the territory as their own, causing a greater amount of predation (Lessard et al 2005). What managers have been doing is issuing year-round culling of wolves to mitigate this problem, which is an extremely expensive option with no stability in sight (Vors and Boyce 2009).
Finally, there are the caribou–the poor, doomed caribou. Their herd populations have reached such low numbers that every impact has become significant. Causes of mortality include hunting (misidentified shootings), train and vehicle collisions, starvation and predation, all of which are resulting in populations that are no longer self-sustaining (Wittmer et al 2005). In the matter of human-caused accidents, there has been little conservation effort. To counteract starvation, many managers have been hesitant in installing food supplementation stations, but have been resorting to it quite often in recent conservation (Newsome et al 2014). The problem with supplementation is that is creates a human-dependence and also congregates the animals to make hunting far easier their predators (Newsome et al 2014). However, there are not many other options to mitigate the effect of global climate change on food availability.
IS THERE HOPE FOR CARIBOU?
Personally, I believe that the survival of the caribou rests in the hands of my generation of conservation biologists. Old methods have proved unsuccessful in getting the mountain caribou back on their hooves, but new methods may prove more effective. One local biologist I have spoken to, Doug Herd, has set his sights on culling moose and deer, instead. He claims that after decades of ineffective wolf culls, it is time to no longer focus on the predator, but the resource pool they are so fond of in the area. If the territory is no longer desirable, the influx of wolves will be halted in time and allow the ecosystem to hopefully achieve stability. I think most managers will move forward with this strategy in the future, which may be the best chance the mountain caribou have!