Wolf Predation Improves Moose Herd Health

If there is any place in this world I call home, it’s the hills of West Virginia. I have many fond memories of growing up in the Mountain State. One of those memories came to mind recently while reading an article on the influence of wolf predation on the health of moose herds.

I remember all the excitement surrounding the beginning of deer season each year. My father didn’t hunt but nearly everyone else I knew did. It was a big deal when deer season opened in late November, usually the Monday before Thanksgiving. Many of my friends would spend the next two weeks in the woods hunting with their families, hoping to kill a buck with a large rack.

Because most of the students would have skipped classes anyway, many schools closed their doors the week of Thanksgiving. This closure made it possible for students to hunt with their families when deer season opened at the beginning of that week.

Hunting is a way of life in West Virginia. Beyond the sport, hunting provides an important source of food for many people. Many of my classmates’ families depended on a successful deer hunting season to help put food on their tables for most of the year.

Hunting is also vital for wildlife management in states like West Virginia. If it wasn’t for deer hunting to cull the herds, the number of deer would reach such high levels that many of these animals would starve or suffer from parasites and other infectious diseases. Hunting’s significant role prompts ecologists to ask two related scientific questions: 

  • Is hunting the best way to cull herds of deer and other herbivores?
  • How does hunting compare to predatory activity as the means to promote healthy herbivore populations?

A recent study executed by a research team from Michigan Technological University (MTU) addresses these questions and more. The team characterized wolves’ effect on the health of moose populations living in the Isle Royale National Park, located on an archipelago of islands in Lake Superior off the coast of Michigan’s upper peninsula.1

Key to addressing these two questions is understanding the influence of selective pressure on group health. Selective pressure results when predators target specific members of the prey group, such as juveniles, older members of the group, and those that are sick from parasite infections and other communicable diseases or noncommunicable genetic disorders.

Common wisdom dictates that selective pressure benefits the health and reproductive fitness of the herd, though, as the authors of the study point out, precious little evidence for this outcome exists based on empirical data. Their study remedies this problem.

The Isle Royale Study
Over the span of 45+ years (1959–2007), MTU researchers studied the wolf and moose populations of Isle Royale. They carried out aerial surveys in the winter and ground surveys during the summer months. As part of this study, the investigators wanted to understand the role that wolves play in maintaining healthy moose populations. This required that they examine moose carcasses to determine the cause of death and the age of the individuals at the time they died. For juveniles, they estimated their age at the time of death from tooth eruption patterns. For adults, they measured age based on microanatomical features of the teeth.

The three primary causes of moose deaths are starvation, accidents, and predation. The researchers could determine if the moose experienced starvation and malnutrition at the time of its death from its bone marrow. A careful analysis of the surroundings near the location of its death helped the researchers determine if the moose died from predation.

The researchers also assessed the moose remains for evidence of osteoarthritis. This disease condition has a genetic component. For this reason, the researchers used the arthritic condition of the moose as a proxy to assess the effects of predatory activity on the prevalence of a noncommunicable genetic disease in the herd. Many noncommunicable genetic diseases would remain invisible to the researchers. Osteoarthritis is an exception because evidence of this disease can be detected in moose skeletal remains.

Through this study, the MTU investigators learned that wolves avoided preying on healthy, prime-aged moose. Instead, they preferred juveniles and older individuals. 

They also noticed that the wolves preferentially killed prime-aged individuals with severe osteoarthritis. This makes sense because osteoarthritis hampers moose mobility, making these individuals vulnerable. Ironically, the researchers failed to find evidence indicating that osteoarthritis in older individuals increased their susceptibility to wolf predation. Upon reflection, this finding make sense. Older moose are already at increased risk for predation. So many other factors already make individuals in this age category vulnerable that they overwhelm the effects caused by the loss of mobility due to osteoarthritis. For example, older individuals suffer from a decline in vison, audition, and cognition. They are more sedentary because of muscle mass loss and declining aerobic capacity. All of these factors make older individuals easy prey for wolves.

The MTU researchers also learned that the occurrence of osteoarthritis in moose populations was much higher during years when the wolf numbers were down and was lower during years when the wolf numbers were high. In other words, the moose population was healthier during years when wolves’ predatory activity increased. This finding demonstrates the influence that selective predation has on herd health.

The MTU investigators determined that selective predation removes individuals that don’t contribute to reproductive fitness (older individuals and juveniles) and that are infirm from the herd. A key insight from this study revealed the role selective pressure plays in maintaining the genetic health of the herd. Selective predation not only removes individuals suffering from parasites and infectious diseases, but those suffering from noncommunicable genetic disorders. Thus, selective predation keeps the moose population at the height of genetic robustness. 

Scientific Implications
This work has important implications for wildlife management practices. Often, the Department of Natural Resources (DNR) in states like West Virginia relies on hunting to serve as the primary vehicle to cull herd numbers. This approach is necessary, yet, based on the MTU study, appears to be much less effective than allowing the herds to be culled naturally by predatory activity. When people hunt, they go after prime-aged individuals, reducing the overall reproductive fitness and genetic health of the herd population. When predators cull the herd, they improve the reproductive fitness and genetic health of the herd by means of selective predation.

This study also helps rehabilitate wolves’ image. Many people regard wolves as a nuisance predator and hunt and kill these creatures because they prey on cattle. In fact, in some states, bounties are placed on wolves. Yet, as the MTU study shows, wolves play a vital role in maintaining the health of naturally occurring herds. In fact, when wolf predation is at its zenith, the herds are at their healthiest. This finding should motivate DNRs to reevaluate their strategy to control wolf populations.

Philosophical Implications
This work also has important philosophical and theological implications. The insights gained from this study help theists provide a scientifically robust response to an aspect of the problem of natural evil—one of the most significant challenges skeptics level against God’s existence. 

Many skeptics decry the fact that nature is “red in tooth and claw.” Accordingly, they regard animal pain and suffering and the seemingly cruel, gratuitous death of animals in nature as fundamentally incompatible with God’s existence, or, at least with God’s goodness. If God is all-powerful, -knowing, and -good, why would he create a world with so much cruelty—a world soaked in blood? In other words, it seems justified to conclude that animal suffering and death is incompatible with the existence of a God who is omnipotent, omniscient, and omnibenevolent. So, either God doesn’t exist, or, if he does exist, he isn’t good.

These complaints assume that God doesn’t have any good reasons for creating a world with animal death, pain, and suffering. But if he does, then a world in which predation takes place, a world in which animal suffering is widespread, is rightly understood to be fully compatible with a God who is loving and good.

The MTU study suggests at least one reason why an all-powerful, -knowing, and -good God would create a world where animals kill one another. Predation plays a vital role in ecosystem health. Predation controls herbivore numbers by protecting against an ecological meltdown due to the loss of primary producers (plants). It also appears to keep the prey populations at their healthiest by removing individuals that are suffering from infectious agents and genetic diseases. Without predatory activity (and the ensuing blood-soaked animal death and dismemberment), there would be much more pain and suffering in ecosystems, not less.

As the psalmist reminds us:

You bring darkness, it becomes night,
    and all the beasts of the forest prowl.
The lions roar for their prey
    and seek their food from God.
The sun rises, and they steal away;
    they return and lie down in their dens.

Psalm 104:20–22

Resources

Is Cruelty in Nature Really Evil?” by Fazale Rana

Why Would God Create a World Where Animals Eat Their Offspring?” by Fazale Rana

Why Would God Create a World with Parasites?” by Fazale Rana (article)

Why Did God Create the Thai Liver Fluke?” by Fazale Rana (article)

Scientists Uncover a Good Purpose for Long-Lasting Pain in Animals” by Fazale Rana (article)

Of Weevils and Wasps: God’s Purpose in Animal Death” by Maureen Moser (article)

Animal Death Prevents Ecological Meltdown” by Fazale Rana (article)

Animal Death before the Fall: What Does the Bible Say?” by Lee Irons (article)

Animal Death and the Atonement” by Krista Bontrager (article)

Life from Death” by Fazale Rana (article)

Endnotes

  1. Sarah R. Hoy, John A. Vucetich, and Rolf O. Peterson, “The Role of Wolves in Regulating a Chronic Non-Communicable Disease, Osteoarthritis, in Prey Populations,” Frontiers in Ecology and Evolution 10 (April 20, 2022): 819137, doi:10.3389/fevo.2022.819137.

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