As a college biology student, I learned about the Isle Royale wolf-moose study in multiple classes. This study was often discussed as the "exemplar" of long-term population ecology research, and in many ways it is exceptional. During my first visit to the park with Marvin Roberson, the Michigan Chapter’s decades-long forest ecologist (now retired), conversations with scientists and park staff gave me a much broader perspective on this study and the park’s history.
Though scientists often like to study ecological dynamics on islands due to their comparative simplicity with the mainland, things are rarely as simple as they appear in ecology. To the casual observer today, it is easy to assume that wolves and moose have long been on Isle Royale, giving us this excellent opportunity to study their population dynamics for decades. That observer might be surprised to learn that moose have only been present on the island since the early 1900s, and wolves since 1950. Maybe more surprising, both introductions are nearly impossible to separate from indirect, and possibly direct, human influences. Prior to widespread hunting and trapping on Isle Royale in the mid to late 1800s, Isle Royale’s mammal composition looked completely different: woodland caribou and Canada lynx were the dominant large mammals. While north shore Lake Superior Ojibwe subsistence hunting had long occurred seasonally on Isle Royale, the introduction of firearms and Euro-American hunting brought hunting of both large mammals to unsustainable levels, ultimately leading to both’s extinction on the island by the 1930s. Forest regrowth following heavy logging on the island also provided plenty of accessible food, priming the island for a soon-to-be booming moose population.
Here’s where things get even more interesting: for both wolves and moose, their natural introduction paths are muddled by stories of human intervention. Wolves likely crossed over to Isle Royale on an ice bridge that forms periodically (though less often now) from Ontario, but the evidence that both male and female individuals immigrated in time to produce a breeding population is shaky, and around the same time, four wolves were introduced to Isle Royale from the Detroit Zoo. Whether or not these wolves actually contributed to the initial population or all four quickly died out is unclear. On the other hand, moose are excellent swimmers and are often assumed to have arrived on Isle Royale via swimming 14 miles from the mainland (they don’t typically walk across ice). Both a male and female swimming this distance, far even for moose, within close succession of each other is possible if a bit of a stretch. There is also some limited evidence to suggest that moose may have been intentionally introduced by a private club for hunting. Regardless of how exactly they got there, humans have long been influencing animal populations on the island, first by eradicating lynx and caribou, and then by altering the habitat and food resources to benefit moose, and indirectly wolves via the increased prey population.
In 2018-2019, following a decline in the wolf population and subsequent overbrowsing of the island’s vegetation by moose, the park made the controversial decision to introduce new wolves. The wolf population decline is attributed to reduced migration due to changes in ice bridge formation, the introduction of canine parvovirus by 1980, and the outsized effects of random mortality and inbreeding due to the small population size. By 2018, there were only two heavily inbred wolves left. During this period, the moose population boomed, beginning concerns about a possible mass starvation event as the moose ate through their food sources.
Even years after wolf relocation, effects of excessive moose browse to the island’s vegetation were visible during my trip. To my pleasant surprise, I was able to fill my summer berry quota from abundant thimbleberry bushes covering most of the park. However, when we visited Passage Island, which has never had moose, hares, or small rodents, thimbleberries were just one small component of a much more diverse understory. This discrepancy later made sense when the park’s ecologist, Lynette Potvin, told me that moose don’t eat thimbleberries (their loss). It’s no wonder that they were thriving everywhere that moose were eating their competition! Lynette also took me to a research exclosure, where moose were fenced out. The most notable difference was that the aspen saplings, a moose-preferred food source, were growing taller inside the exclosure than outside. Changes in Isle Royale vegetation as a result of moose preferences have long been documented. The Environmental Impact Statement for wolf introduction described detrimental effects on the once common ground-hemlock and Canada yew. Balsam fir today is also much less common than it was in the 1800s.
All of these impacts and more of large, predator-free moose populations led to the consideration of introducing new wolves to the shrinking Isle Royale population starting in 2015. The decision to relocate wolves from Minnesota and Ontario into the National Park inevitably sparked debate about the appropriateness of this level of human intervention into a capital-W Wilderness area. At the end of the day, for me, this question cannot be answered without taking the past and future into account. Wolves have been on Isle Royale for less than a human lifespan, and their original populations were at least moderately influenced by humans. The wolf decline was also not entirely unexpected; as the Park admits in the Environmental Impact Statement, the consequence of existing on an island with increasingly fewer links to the mainland is more extreme population fluctuation and frequent local extinction events. Population reductions as a result of disease or conflict within-species can lead to negative inbreeding effects in the remaining small population without the introduction of new individuals (and their genes) from immigration.
This brings us to the future: As climate change continues to reduce the frequency and duration of the ice bridge connection between the park and the mainland, will we continue to artificially add wolves to the population to prevent future inbreeding effects? An Isle Royale without wolves would lead to widespread ecosystem shifts, eventually resulting in fewer food sources for moose. Balsam fir, aspen, birch, and other preferred food species would likely continue to decline, at least over the short-term, and other wildlife would be affected by the loss of wolves. Long-term, this would change the sustainable population levels of moose and beaver populations and could lead to the eventual loss of moose from the island. The question becomes, however, if preventing these changes is worth committing to a likely need for regular “artificial immigration” events in the wilderness area. When asked about reintroduction during Environmental Impact Statement preparation, one subject matter expert stated: “I do not believe that any mix of wolf genetics introduced will result in long-term viability without human intervention given limited or no natural immigration events.” Another expert mentioned that there was at least a chance that they might persist for the lifespan of the Statement - 20 years.
In light of the history of lynx and caribou extirpation from the island, logging and mining, and the murky origins of wolf and moose, perhaps Isle Royale has been closer to a “living laboratory” in the past century than we’d like to believe. In 2018, we made the choice to continue experimenting. Twenty or thirty years down the line, we’ll likely have the same choice to make: Let nature run its course in what we've designated as a wilderness area - natural, untrammeled, and undeveloped - or continue applying resources to maintain a population in a climate where it’s no longer viable. Allowing wildlife and vegetation change to play out in the absence of an apex predator may feel and look bad in the short-term, but ecosystems don’t operate on the 20-year time scale of an Environmental Impact Statement. They respond and shift over decades, centuries, even thousands of years.
So, this is why we go to Isle Royale. To expand our perspective, connect with park staff and scientists, maintain our place at the decision-making table, and ultimately share the tangible effects of the decisions made with all of you.