Isle RoyaleNational Park

Why is the Wolf population at Isle

Royale decreasing if they have no

predator?

By: Johanna Lund

Dictionary

Predator: any organism that exists by preying upon other organisms.

Prey: an animal hunted or seized for food, especially by a carnivorous animal.

Competition: to strive against another to attain a goal.

Wolves don’t have predators or do they?Gray wolves have had little trouble preying on the moose on Isle Royale. The moose have been weakened by an infestation of blood-sucking ticks. The tick’s population has exploded due to mild weather. Scientists have studied the delicate prey-predator balance between moose and wolves. Scientists believe global warming causes the ticks to overpopulate, this is bringing competition to the national park's wolf population.

Since 2002, the number of moose on the island has declined from 1,100 to 385, following a dramatic increase in winter ticks. The insects infest the moose, suck their blood, weaken them, and make them easy prey for wolves. When higher temperatures persist and the number of ticks increase, the wolves are dying out because there isn’t enough moose (their main food source).

Each winter, 80,000 ticks or more may live on the skin of a single moose. Moose sacrifice gallons of blood and much of their thick insulating fur to give life to these horrific little creatures. Scientists studying the moose and wolves have determined that as many as 100,000 ticks can infest a single moose. Sometimes, the ticks take so much blood the moose dies. Ticks bring  Lyme disease to their host , they carry around bacteria called spirochetes that can cause the infection, Lyme disease. This is only one disease moose get from ticks. Ticks can carry many other diseases. If ticks have been on other animals that have bad diseases they can carry it with them to the next animal and eventually spread it everywhere. When spring and fall temperatures are warmer, more ticks can breed. Moose rub against trees or try to bite the ticks, causing hair loss. With less hair, the animals spend more energy keeping warm and it causes them to die in the winter because they do not have a warm coat.

In the summer, the moose also spend less time foraging for food because they are weakened from tick bites, they spend more time helpless and sick. Those that don't bulk up enough in summer are less prepared for tough winters and wolf attacks. In the first few years after the tick numbers decreased, wolf numbers also rose because so many moose were easy prey. Once the wolf numbers rise, they go down because there is not enough food. Then the wolves start dying because of starvation. During the summer winter ticks exist only as unhatched eggs in the soil. In autumn the ticks hatch, crawl to the tops of grasses and wait to latch onto any unsuspecting moose that walks by. These young ticks feed and grow on the moose during the winter. In early spring, the ticks mate, the males die and the females drop from the moose to the soil where they lay their eggs.

We can easily understand the competition between the ticks and the wolves over the moose. If too many ticks are infesting the moose they die out, and there is not enough food for the wolves then their population decreases dramatically.

Now there is nine wolves left.

http://www.isleroyalewolf.org/node/44

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