Wolf Ecology and Prey Relationships on Isle Royale (Chapter 4)
Oct 26, This long-running study of wolves and moose on Isle Royale National Park Isle Royale reveal new info about predator-prey relationships. Jul 18, Isle Royale is home to both wolves and moose, which is not unusual. have been studying this predator/prey relationship for over 55 years. Wolf Ecology and Prey Relationships on Isle Royale, NPS Logo In response to changes in moose vulnerability, wolf predation began to increase in
Intensive culling ensures that limited food resources are utilized by the most vigorous members of the prey population. Wolf predation is essential to the healthy maintenance of a high moose population on Isle Royale. The role of predation may be clarified if we consider a hypothetical question: Malnutrition would take over as the principal direct and indirect source of mortality, affecting mainly calves and old moose in late winter and early spring. In the absence of predation, moose weakened by malnutrition may survive for months, competing with healthy moose for limited browse.
Calves would be born weaker and smaller than usual, and neonatal mortality probably would increase.Predator prey relationships
Thereafter calf mortality would be low, with the degree of loss to malnutrition in late winter and spring determined by winter weather. Over a series of mild winters the moose population would increase because of low adult mortality and relatively high calf survival. With the return of usual winter conditions mortality would greatly increase, and severe winters probably would cause large losses.
Long-term population levels of moose might well be lower without predation because of wasteful browse utilization. Thus wolves are essential to the maintenance of a healthy, high-density moose population on Isle Royale. Although wolves did not hold the population on Isle Royale below the level at which food supply and environmental conditions affected the welfare of moose, wolf predation increased during the s when moose, particularly calves and young adults, became unusually vulnerable.
As long as wolves and moose coexist on Isle Royale, wolf predation will remain the principal mortality factor operating on the moose herd. However, the degree of control exerted by predation will be determined largely by environmental influences principally food supply that act on moose reproduction as well as vulnerability to regulate numbers of moose.
Wolf Population Adjustments The recent partitioning of Isle Royale into two pack territories is a significant departure from the basic pattern of the s. The remarkable stability shown during the s demonstrated that effective natural controls were operative. The primary regulatory influence was believed to be food supply or social controls, or some combination.
Until recently wolf densities on Isle Royale and in other regions were not found to exceed one wolf per 25 km2 Pimlottleading to the inference that this was a maximum density beyond which wolves would not increase, perhaps because of social intolerance Huffaker High pup mortality in other wolf populations has been regarded as important in reducing their growth potential, and the finding of an apparently malnourished pup on Isle Royale in suggests that food shortages during the pup-rearing season were of regulatory significance Jordan et al.
However, Wolfe and Allen found that the wolf population, at a low level in the late s, did not increase immediately following a winter when moose vulnerability wa.
The emergence of a second pack of wolves on Isle Royale and the expansion of their population reflects an increased food supply stemming from greater vulnerability of moose and a higher beaver population.
Thus, the level of food resources available to Isle Royale wolves is proposed as the principal underlying variable which determines the number of stable packs and, ultimately, wolf population levels. In some cases "food supply" for predators may be correlated directly with prey densities, and predator populations will fluctuate in direct response to changes in prey levels. This is especially true of predators that are not as selective as wolves, such as lions preying on certain ungulates species Schaller and coyotes preying on jackrabbits Clark More selective predators, such as Isle Royale wolves, are particularly apt to respond to changes in numbers of vulnerable moose, rather than prey densities per se.
In this context the relationship of moose welfare to environmental influences is critical in understanding wolf population responses on Isle Royale. At the pack level, food plays an obvious role in regulating group size, since wolf-pack size is related to the size of their prey.
Packs feeding on Isle Royale moose have numbered between 15 and 20 wolves, those feeding on elk Cervus canadensis and mule deer Odocoileus hemionus contained between 6 and 14 members Carbyn a, band wolf packs feeding only on deer usually numbered 7 or less Mech ; Van Ballenberghe Food level can affect wolf populations directly, particularly through pup mortality and survival Van Ballenberghe and MechSeal et al.
In addition, the complex social organization found within and between wolf packs may provide for subtle influences on physiology and behavior that may be of regulatory importance. Territoriality among wolf packs apparently is a spacing mechanism which adjusts wolf densities to their food level. This explains the recent reorganization of the Isle Royale wolf population.
Wolves and moose on Isle Royale
In response to increased food resources, the single resident pack ranged in winter over only half of the island inand the second pack became established the following year on the remaining half. Without a shrinkage in the original pack's territory, a second pack could not have materialized. Similarly the increased size of the winter territory of the East Pack in the first 3 years of its existence was correlated with a decrease in the amount of food available to each pack member in winter.
This led to considerable spatial overlap and, in at least one case, direct mortality from inter-pack aggression. Social relationships within the pack may also be sensitive to food supply and thus influence pack size. Social stress, particularly for subordinate wolves, probably increases when food is short. Social restraints seem to reduce the incidence of breeding among adults in a pack. Their lives are historic because we have been documenting their lives for more than five decades.
This research project is the longest continuous study of any predator-prey system in the world. After 14 years Over time wolf abundance fluctuated a bit. But, after a series of mild winters moose abundance doubled.
After 22 years Then a series of severe winters, increased wolf predation, and moose abundance was cut in half. Wolves soared to 50 individuals. The wolf population crashes.
After 38 years With a reprieve from wolf predation, the moose population explodes. We begin to think, but cannot yet prove, that inbreeding among wolves explains why they languor in low abundance for over a decade. A year later Intense competition for a declining forage, an outbreak of winter ticks, and the severe winter.
Wolves and moose on Isle Royale - Wikipedia
They all conspired against the moose population which collapsed in Another decade passes Moose continue to dwindle. Ina wolf immigrates from Canada, bringing an infusion of new genes. The wolves increase erratically. After 53 years The wolf population eventually stumbles as the moose continue to be kept low by high rates of predation, ticks, and hot summers.
- Keep up with Mother Nature
- Two wolves survive in world’s longest running predator-prey study
- About The Project: Overview
Much of what we have learned is associated with having been patient enough to observe and study the fluctuations in wolf and moose abundances summarized above. The wolves and moose of Isle Royale also frequently reveal intimate details of their daily life experiences and they have inspired numerous artistic expressions. If we pay attention, they all tell us something important about our relationship with nature.
These insights and discoveries are all presented here for you. Building on the graph above and to develop a deeper understanding, here is more on the history of wolves and moose on Isle Royale.
Moose first came to Isle Royale in the early 20th century, and for fifty years, their numbers fluctuated with weather conditions and food abundance.
Wolves first arrived in the late s by crossing an ice bridge from Canada. The lives of Isle Royale moose would never be the same. Researchers began annual observations of wolves and moose on Isle Royale in The project began during the darkest hours for wolves in North America—humans had driven wolves to extinction in large portions of their former range.
The hope had been that knowledge about wolves would replace hateful myths and form the basis for a wiser relationship with wolves. Most studies in ecology last for a few years or less. Afterward, ecologists naturally draw conclusions about the nature of our environment.
Scientists did so after observing the wolves and moose of Isle Royale for a few years. Durward Allen, who initiated the Isle Royale wolf-moose project inwas a pioneer among ecologists for having the foresight to understand the value of continuing to observe where others would have drawn conclusions and moved on to study something different.
By the moose population had doubled, and one now had to admit there had been a major shift in the balance. The wolf-moose project was originally designed to continue for ten years.
Administrators of the day suggested that the project end. Durward found greater merit in continuing to lead these observations. Bythe study in its 22nd year, the moose population had tripled from its original size and then declined to half its maximum size. During that time, wolves more than doubled to fifty.
By now it was apparent. In particular, wolves in were abundant and moose had been on the decline for the better part of a decade. Would it be possible that wolves could drive their prey to extinction? No one had ever observed wolves and their prey long enough to know. The next two years were dramatic. Wolves plummeted from 50 to Canine parvovirus, a disease inadvertently introduced by humans, was largely to blame for the decline.
The Population Biology of Isle Royale Wolves and Moose: An Overview
With only 14 wolves, extinction was a real concern. The only way to know what would happen next would be to continue observing. The wolf population recovered partially during the mids, only to decline again.
For much of a decade wolf abundance remained in the low teens. It seemed plausible, but far from certain, that the low numbers were ultimately the negative consequences of inbreeding. All we knew for sure was that Isle Royale wolves are highly inbred and descended from just a single female and two males.