Gray Wolves
Yellowstone National Park and The Future
William Georgenes - ENVS 117 at Santa Clara University
December 8th, 2022
Introduction
The Gray Wolf population in Yellowstone National Park has undergone a significant change in recent years. Once nearly eradicated from the region, conservation efforts have helped the gray wolf population make a significant recovery. As of the Yellowstone Wolf Project’s 2021 annual report, there are 97 Gray Wolves living in the park which play a crucial role in maintaining the balance of the park’s ecosystem (National Parks Service, 2021). Much has changed within Yellowstone National Park since the introduction of the wolves, and I hope to find out more about how the wolves have moved in space and size and how we can prolong the beneficial effects and potentially apply similar interventions in other ecosystems.
Wolf Facts
Genus: Canis (Latin word meaning “dog”)
Species: lupus (Greek word meaning
“wolf”)
Average body mass: males 110 pounds (50
kg); females 90 pounds (41 kg)
Primary food sources in
Yellowstone: Winter: elk (>96%), bison (3-4% and increasing
in recent years; deer (1.5%); Spring: elk (89%), bison (7%), deer
(7.1%); Summer: elk (85%), bison (14.1%), deer (<1%)
Elk killed per year per wolf: 18-22 elk/wolf/year
Average lifespan in Yellowstone: 4-5 years
Sources: (National Parks Service, 2022) and (Almberg ES, 2011)
What is a Keystone Species?
A keystone species has a disproportionately large impact on its environment relative to its abundance. This means that even though it may not be the most abundant species in an ecosystem, it plays a crucial role in maintaining the balance of that ecosystem. If a keystone species is removed from an ecosystem, a chain of events will occur that drastically changes the structure and biodiversity of that ecosystem (Denchak , 2022). There are three types of keystone species: predators, ecosystem engineers, and mutualists. Predators control the population of pray species. Example: Gray Wolf. Ecosystem engineers are species that create, control, and destroy a habitat. Example: Beaver. Mutualists are when multiple species interact in a beneficial symbiotic way that benefits everyone. Example: Bees (National Geographic Society, 2022).
Data
Data from The National Park Service allows us to look at and analyze the movement of gray wolves and the territories of each pack on Yellowstone Park over time, starting from the introduction in 1995. The population of gray wolves has fluctuated and packs of wolves have been created and others have dispersed over the years. Population and location data can help us better understand the Yellowstone National Park ecosystem with the addition of gray wolves and what we can do to maintain and improve the ecosystem going forward.
Wolf Pack Movement
Wolf packs are groups of wolves that live and hunt together. They typically consist of a breeding pair of wolves, known as the alpha male and alpha female, and their offspring. The size of a wolf pack can vary, but in Yellowstone National Park, the average pack size is 11.8 individuals (U.S. Department of the Interior). Wolf packs have complex social structures and communication systems, and they are known for their intelligence and adaptability. Territory is always part of the competition. The most desired areas are the ones with the most prey. In the first five years that the wolves were introduced to the park, around three quarters of their diet had been elk, but recently, bison has been becoming a more popular food source. The diet of gray wolves in the park is closely tied to the availability of prey, and it may vary depending on the time of year, but it is the main reason the packs compete for territory.
Take a look at these interactive maps of the wolf pack territories In Yellowstone National Park in 1995, 2007, 2015, 2019 to see the formation, disappearance, and movement of the packs. Hover your cursor over the different shaded regions to see the name of the pack. Alternatively, view the key below the figures.
Figure 1. Wolf pack territories in Yellowstone Park in 1995
These were the packs formed from the original 31 wolves that were placed in Yellowstone Park. Nine pups were born in the spring of 1995, and 14 in the spring of 1996. This began the rise of the gray wolf population for the next several years.
Figure 2. Wolf pack territories in Yellowstone Park in 2007
The wolf population in 2007 is 171, one of it’s highest recorded years since introduction.
Figure 3. Wolf pack territories in Yellowstone Park in 2015
Notice how the wolf packs themselves are always changing along with the size and area that each of them take up.
Figure 4. Wolf pack territories in Yellowstone Park in 2019
Effect on the ecosystem
Since the introduction of the wolves, the Yellowstone Park ecosystem has seen great improvements. One of the primary ways that gray wolves benefit the ecosystem is by controlling the populations of their prey species. When wolves were nearly eradicated from the park, the populations of their prey species began to grow unchecked. By hunting and preying on elk, deer, and bison, wolves help to keep these species from overpopulating and overwhelming the park’s resources. This helps to maintain the balance of the ecosystem and prevent overgrazing of the park’s vegetation. Before the introduction of the wolves, the elk population in Yellowstone National Park went through a cycle of “booms and collapses” with fluctuations in the climate (Peterson, 2021). The winter season would end with hundreds of elk carcasses, starved to death, scattered around the park. With the wolves in the ecosystem, the elk population dropped and began to stay more consistent. Elk and other animals need to be more alert and tend to move a lot more in order to survive. This, and the regulation of population help to keep the balance of the ecosystem.
Figure 5. Gray Wolf Population in Yellowstone Park
The gray wolf population had a heavy increase for the first
several years until the noticeable decline beginning in 2007. The
primary cause of the decreasing trend is due to the decline in elk
population which makes up almost all of the Gray Wolves’ diet during the
winter season. Lack of available territory also fed into the population
decline. Although the population decline may initially seem bad, this is
a good outcome to have because the wolves are still playing their roll
as a keystone species in the ecosystem of Yellowstone National Park even
only with a population of 97, measured in 2021, with 29 of those wolves
being pups (Yellowstone
Wolf Project Reports, 2021). While many people visit the park to
observe the gray wolves, the lesser number of them may also be better
for the overall business of the park because there are less documented
cases of humans or domesticated animals getting in conflicts with the
wolves (Outdoor
News, 2019).
Applying keystone species re-introduction elsewhere
It is amazing to see all that the re-introduction of wolves has done for Yellowstone National Park in the last 25 years. How can we use what we learned from the wolves to help other ecosystems? There is work to be done all around the world, but an ecosystem that stands out to me as similar to Yellowstone is the Caribbean Coral Reefs. Although they are very different ecosystems, I believe similar interventions can be done to the coral reefs to help preserve them.
Parrotfish are colorful fish that live in and are a keystone species of the Caribbean Coral Reefs. Parrotfish spend almost all of their time eating algae off of the coral reef which keeps the reefs healthy and clean. The population of parrotfish is extremely low largely due to overfishing (Nature Conservancy, 2021). Similarly to how the wolves were hunted out of Yellowstone by humans. As we saw with the wolves, the abundance of prey (elk etc.) were balanced with the wolves present. I believe an active and monitored controlled addition of parrotfish into the Caribbean coral reefs could balance the ecosystem and help preserve the health of the reefs, based on the analysis of gray wolves in Yellowstone National Park.
Resources
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U.S. Department of the Interior. (n.d.). Tools and Data. National
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glimpse at 20 years of Wolf Spatial Ecology in Yellowstone (U.S.
National Park Service). National Parks Service. Retrieved December 1,
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Yellowstone, wolves have helped stabilize the ecosystem. Animals.
Retrieved December 6, 2022, from https://www.nationalgeographic.com/animals/article/yellowstone-wolves-reintroduction-helped-stabilize-ecosystem#
Denchak , M. (2022, August 8). Keystone Species 101. NRDC.
Retrieved December 6, 2022, from https://www.nrdc.org/stories/keystone-species-101
National Geographic Society. (2022, May 19). Keystone species.
National Geographic Society. Retrieved December 6, 2022, from https://education.nationalgeographic.org/resource/keystone-species
Almberg ES and Others. (2011). Infectious Diseases in
Yellowstone’s Canid Community. Yellowstone Science. Retrieved December
6, 2022, from https://irma.nps.gov/DataStore/Reference/Profile/2258812
Outdoor News, A. (2019, April 22). Wolf population
declining in Yellowstone National park. Outdoornews. Retrieved December
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