In this installment, wildlife ecologist and conservation biologist, Dr. Justin Suraci shares his experiences, as a Raincoast fellow, studying predator-prey relationships in the Coastal Douglas-fir (CDF) ecosystems of the Gulf Islands. He also unpacks the cascading impacts of removing carnivores from these landscapes and makes recommendations for better coexisting with carnivores in heavily populated regions.
What are the ecological impacts of large carnivore absence in the Gulf Islands?
To give you some context, I spent a lot of time between 2012 and 2014 researching this exact question: what are the downstream ecological effects of the historical loss of large carnivores from the Gulf islands? Historically, there was a full suite of predators on the Gulf Islands including cougars, wolves, and black bears. Indeed, they occasionally still make it out there. While I was doing my research, I received data from BC Conservation Officers showing the number of calls that they got regarding large predators on Salt Spring and other larger Gulf Islands. These data showed that every year a handful of larger predators make it from Vancouver Island out to the Gulf Islands, but largely because of complaints from the locals, they don’t usually last there very long.
Other than the handful of attempted migrants from Vancouver Island, these carnivores have been largely extirpated from the Gulf Islands for the better part of the last century. There is not very good data on this, but I think it is safe to say there has been roughly a hundred years of very limited predator presence. The consequences of their extirpation include a range of cascading effects down the food chain, perhaps best exemplified in the Gulf Islands by the high abundance of smaller predators (i.e. mesopredators), specifically raccoons, and a high abundance (some might even say hyper-abundance) of blacktail deer.
Some of my research focused on the impacts of raccoons in the absence of their large carnivore predators, and we found that raccoons severely deplete their own prey on the islands where they occur. They deplete nesting songbird populations, potentially also impacting songbird diversity, and have measurable effects on communities of intertidal and nearshore subtidal organisms, mostly crabs and fish. They forage and eat at such an intense level that their impact on nearshore communities is actually sort of impressive, for lack of a better word, given the otherwise really high abundances of some of these marine species.
Likewise, an overabundant deer population can have substantial impacts on terrestrial ecosystems where their browsing activity dramatically reduces foliage on trees and shrubs, and limits understory growth. Such high ungulate abundances can also potentially leave a demographic gap in tree ages because they stop any new saplings from establishing and growing to maturity. Similar to the raccoon example, these impacts are not one-offs, they can have cascading effects on other wildlife. A reduction in foliage does not just limit tree growth and structural diversity, but also limits habitat. Reduction in songbird abundance, especially among populations that tend to nest nearer to or on the ground, could potentially be attributable to deer abundance on the Gulf Islands.
There are worldwide declines in predator abundance. What are the primary drivers behind this decline?
There are two big ones that immediately spring to mind. The first is habitat fragmentation. Large carnivores, in particular, are wide ranging with slow life histories (i.e. they take longer to reach maturity, have longer gestation periods, have fewer offspring per breeding cycle, etc.). They need more room to roam compared to other species in order to find sufficient prey and establish territories. And connectivity between populations, another casualty of fragmentation, is just as essential. As an example, there is good cougar habitat in the Santa Monica Mountains of California. However, it is surrounded by human development, thus restricting cougar movement in and out. Isolated populations like the one in the Santa Monicas could gradually disappear through inbreeding suppression or random events like disease. This means that even if a carnivore population is well-established with access to seemingly sufficient habitat, an absence of connectivity limiting movement and gene flow puts that population at risk.
The second driver of declining predator abundance is direct persecution. Historically, large predators have been actively removed from the landscapes across North America. Cougar, wolf, and bear numbers have been dramatically reduced in their historical ranges, because they’re seen as threats to people’s lives and livelihoods, and in many cases treated like pests. This sort of active persecution has only really slowed down in the last half century, but still does occur.
How do declines in predator abundance affect ecosystem integrity?
People sometimes use the term “ecosystem collapse” to describe the cascading consequences of large predator loss. That cascade starts with the removal of an apex predator (e.g. wolf) from the top of the food chain, thus releasing lower trophic level species like herbivores (e.g. deer) and smaller predators (e.g. racoons) from any level of suppression. In some cases that suppression might have been due to actual predation, while in others it may have been the result of the suppressive effects of fear.
The loss of this suppressive effect of apex predators then leads to increases in herbivory and/or predation levels by mesopredators beyond any historical precedent for the ecosystem. In other words, the higher intensity of herbivory from ungulates once they have been released from any control from large predators might be beyond the capacity of local plant communities to withstand. In the short term, this means substantial defoliation and sustained high herbivory with no top-down control could even lead to a shift in ecosystem type.
A classic example of this ecological collapse is the islands in Gatun Lake in Panama. The lake was created by flooding a huge area to create the Panama Canal, which created a number of islands out of hilltops in what was formerly contiguous forest. These islands were too small for larger predators to persist, so species like jaguars eventually died off or swam away. Following the loss of those large predators, there was a slow, but well tracked decline of the ecosystem, as hyper herbivory led to the loss of understory plants, which led to the loss of bird species.
“Cascade” is a really good term for what it means, with these losses on the top leading to ecosystem-wide change. Interestingly, though we know this happens, there are few examples that have been well documented by western scientists. For example, all across North America, the removal and replacement of top predators with herds of cattle or sheep has led to large-scale ecosystem change, but there are not well-kept records of that change. So no doubt, the disruption or full collapse of predator-driven trophic cascades is not unique to the Panama Canal.
How do declines in predator abundance affect climate resilience?
There are a number of ways in which predator presence or absence could affect climate resilience. One potential pathway could be that the suppression of herbivores could conceivably lead to greater carbon sequestration potential in forested environments. That is, introduction (or maintenance) of predator populations would result in less herbivory of plant material, increasing carbon sequestration potential.
Another aspect of climate resilience is the ability of species to adapt to climate change by moving to and colonizing new environments with more favorable climate conditions. The effects of predator loss on range shifts could be incredibly variable as, presumably, the broader community of species will affect the potential for any particular species to track its climate niche. For instance, some species, like large herbivores, might find it easier to track their climate niche and colonize new habitats if large carnivores are absent while others could actually benefit from or even require the presence of large carnivores for successful colonization. For instance, some plant species that are heavily browsed by herbivores, or lower trophic level animals that are prey for mesopredators, may have an easier time colonizing climatically friendly habitats if large predators are present to suppress the herbivores and mesopredators that consume them. All that said, I’m not sure there’s much research yet on the subject of predators facilitating or not the climate adaptation of other species, but this seems like an important topic to explore further.
Are wildlife management strategies like culls or reintroductions effective? What are the challenges of reintroducing predators to the landscape?
Perhaps someone trying to manage caribou in Northern BC might say that culls are effective in the short term. Hypothetically, if there were only a handful of caribou remaining in the wild, then maybe killing nearby wolves would prevent them from hunting those last few caribou. However, that doesn’t address the problem that led to the caribou reduction in the first place. It is like putting a morally questionable band-aid over the underlying problem, rather than addressing it directly.
There is also well documented evidence of the ineffective removal of some species from their native territories. Coyotes are a good example. They are subject to culls in areas all across the American west, ostensibly to protect livestock or other agricultural interests. Research shows this can actually do more harm than good because, unless every single coyote has been killed (and hopefully no one is quite that effective), the removal of individuals alters the social landscape and can actually lead to increased conflict with coyotes. That is, the vacated territory of the coyotes killed will potentially be filled by other coyotes relatively quickly, and might be filled by more than one. In some cases, the practice of culling has been shown to lead to increased impacts on wildlife and/or other human values relative to unculled areas.
There is plenty of evidence to suggest that there are more effective methods to control the impacts of predators, specifically on livestock than direct removal. So an obvious challenge is filling the communication gap that exists to this day to convince land managers and decision makers that there are other, more effective ways to reduce human/carnivore conflict.
Ultimately, whether reintroductions are effective depends on what is meant by “effective.” Of course, sometimes they work. Take the classic Yellowstone example. Wolves were reintroduced to Yellowstone and we still have wolves in Yellowstone. So if the ultimate goal was to maintain a wolf population in Yellowstone, that was a very effective reintroduction. But the effectiveness of an introduction in some areas depends wholly on social buy-in. There are examples of failed reintroductions because no individuals survived past the first few years due to poaching. Preparing the social landscape for a reintroduction is a lot of work, often taking a complete culture shift, but it is absolutely necessary in some places.
If we give species half a chance, they will take it.Dr. Justin Suraci
In some cases, however, large carnivores will reintroduce themselves into their historic ranges. There are examples of this happening in Europe and parts of the US, usually preceded by some reduction in human pressures. In the European example it seems to have been the combined result of a handful of changes in hunting laws and frankly just changes in social values. Now, throughout much of continental Europe there has been a recolonization of wolves, lynx, and brown bears. So clearly, if this can happen there, where there is a huge population of people, it can certainly work in regions across North America where there are way fewer people. It is just a matter of getting those people on board.
If we want to maintain ecosystems in a natural, high performing state, the full suite of species that coevolved in those ecosystems needs to be present. While natural habitat and the species that depend on it for survival are intrinsically valuable and deserve to be maintained and protected for their own sake, there are some that assert that more convincing arguments need to be made to secure much needed social buy-in for coexistence. Sometimes, communities need to be reminded of the value that predator species provide.
I’m currently working on a project with cougar data from the Olympic Peninsula of Washington state. The idea is to map the services and disservices provided to humans by the presence of healthy cougar populations. For example, by controlling local deer populations, cougars may reduce occurrences of vehicle collisions or improve agricultural outputs by reducing crop grazing. Potentially, an argument can be made that the services provided by the presence of carnivore species outweighs potential disservices, such as livestock deportation.
I think there is still work to be done on the Gulf Islands for peaceful coexistence with carnivores. In many ways, it may be better in terms of social buy-in for carnivores to reintroduce themselves into their historic ranges than for them to be reintroduced by the government. In the Gulf Islands specifically, large carnivore migrants often don’t last long since, as mentioned above, it is commonplace for people to call conservation officers to have wolves, bears, and cougars removed when they visit an island. Yet, if these animals are still showing up in these places it may serve as an indication that their island habitats are still places they would like to spend time.
Maybe, rather than removing carnivores, islands should have plans in place for when they appear, such as keeping garbage bins properly sealed and keeping pets indoors. A bit of interpretive signage and community outreach to encourage a few slight behavioral changes can help to facilitate coexistence. There is plenty of precedent for this even on neighbouring Vancouver island, but certainly elsewhere in North America, so it seems like it could happen in the Gulf islands.
The Santa Cruz mountains, just north of the city of Santa Cruz in California, are an interesting example. The mountains are sandwiched between the coast, Santa Cruz, and the huge cities of San Francisco and San Jose. There is a lot of development pushing into the greenspace provided by the mountains, but cougars are using the whole area. Many individuals have been collared and some have wide enough territory to live way out in the woods feeding on only deer, others are pushed right up against the suburbs and occasionally pass through people’s yards. For the most part, people don’t even notice that they are living next to large wild cats, even though there might be one cruising through their backyard a few times a week. Even still, the amount of conflict there is minimal, and I find that to be super encouraging.
What can be done to restore ecological balance to the CDF?
Beyond what has already been covered, I would reiterate that the key thing that we can do as conservationists is whatever it takes to get the social buy-in. Otherwise, we can basically leave the system alone and I think it would largely recover itself. There is evidence that species are likely to recolonize any area where we remove a sufficient amount of human pressure to allow them to do so. If we give species half a chance, they will take it.
The main takeaway in my mind is that it’s largely a social problem. We need to help communities warm up to the idea of coexisting with wildlife. Once they do, the wildlife are there and ready to coexist.
About Justin Suraci
Dr. Justin Suraci is a wildlife ecologist and conservation biologist interested in how interactions between predators and prey shape ecological communities, and how these interactions are impacted by human activity. Dr. Suraci’s work draws on behavioral, community, and movement ecology to develop conservation solutions for wildlife predators and prey in an increasingly human-dominated world. He currently holds a Lead Scientist position at Conservation Science Partners, based in Truckee, California.
Suraci, J.P., Clinchy, M., Dill, L.M., Roberts D., Zanette, L.Y. (2016). Fear of large carnivores causes a trophic cascade. Nature Communications. 7:10698. DOI: 10.1038/ncomms10698
To celebrate the end of the year, we are so happy to be able to offer matching campaigns on two of our most pressing fundraising initiatives.
All donations to both the Southern Great Bear Rainforest tenure acquisition and our KELÁ_EKE Kingfisher Forest initiative, will be matched until the end of the year. This is a great opportunity for our supporters, like you, to make your impact go twice as far, while benefiting from tax deductions.