SCI 120: Discussion 4

Cause-and-Effect Model in Yellowstone

The removal of wolves from Yellowstone had a negative effect on the entire ecosystem. Without wolves, the elk and moose overpopulated the ecosystem, leading to overgrazing of vegetation, particularly along riverbanks. This loss of plant life caused soil erosion, destabilized rivers and reduced habitat for other species: SCI 120: Discussion 4.

Beavers usually rely on trees for food and dam-building, which declined and affected the flow of water and reduced aquatic habitats. The loss of trees also affected bird populations that depended on them for habitation and food. Scavengers also relied on the remains of wolf kills for food declined. The reintroduction of wolves restored many of these changes and brought the ecological balance back.

Relationship Between Wolves and Moose and Elk?

Wolves, moose and elk have a predator-prey relationship. Wolves hunt moose and elk, regulating their population and behavior. This helps to maintain the ecosystem by preventing overgrazing.

Effects of Wolf Removal on an Ecosystem?

The population of both moose and elk increased following the removal of wolves from an ecosystem. This led to overgrazing and habitat destruction, disruption of food chains. It also altered landscapes including rivers and forests.

How did this Affect the Beaver Population?

In the absence of wolves, elk and moose moved freely, overgrazing saplings and low-lying vegetation. They no longer needed to stay in safer areas, leading to habitat degradation along rivers.

Indirect Effect of Wolves on Beaver Populations

By controlling elk and moose populations, wolves indirectly support beavers by allowing vegetation such as willows and aspens to grow along rivers. More trees provide food and materials for beavers to build dams, which create stable aquatic ecosystems.

Why Does this Happen?

This occurs because predators influence the behaviour and numbers of herbivores (Bruers et al., 2024). When wolves are absent, herbivores overconsume vegetation, removing resources needed by other species.

Effect on Birds in the System?

`           Bird populations were reduced when trees were also reduced due to overgrazing. The smaller number of trees in the ecosystem meant fewer habitats. As vegetation increased with wolf reintroduction, the population of birds increased.

How does the Decline of Beavers Lead to a Decline in Aquatic Insect Populations?

Many aquatic insects thrive where water moves slowly; beavers create this kind of environment. Without beavers, these habitats disappear, reducing insect numbers. Since insects are a food source for fish and birds, their decline affects multiple species.

What did the Extermination of Wolves Affect the ‘Health’ Of Rivers?

Soil erosion along riverbanks increased because trees along the banks disappeared as a result of overgrazing (this happened due to the absence of wolves in the ecosystem). Riverbanks became unstable, leading to shallow streams instead of deep, structured waterways. This reduced water quality and negatively impacted aquatic life.

Effect of Wolf Kills (Carrion) on Other Animals

The remains of Wolf kills provided food for scavengers like foxes, coyotes, bears, and birds of prey (Wirsing & Newsome, 2021). Without this food source, many scavengers reduced in population and others migrated elsewhere in search of food.

Effect of Wolf Reintroduction on Bison and Elk Behaviour

When wolves were brought back to Yellowstone, elk and bison became more cautious and avoided open valleys and riverbanks where they could be easily killed by the wolves. This allowed vegetation to regrow in the ecosystem.

How Did this Affect the Vegetation Along Rivers?

As elk and moose avoided riverbanks after the re-introduction of the wolves in the ecosystem plants had a chance to grow again. Willows and aspens regrew and stabilized the riverbanks. Soil erosion also reduced and provided a good habitat for other species.

 How did this Affect the Beaver Population?

With tree populations recovering, beavers had enough food and materials to build dams. Their return created a slow-water environment that benefited fish, amphibians, and birds.

Why Wolves are considered a ‘Keystone Species’ in Yellowstone?

Wolves play a crucial role in maintaining ecological balance by regulating herbivore populations and influencing their behaviour (Bruers et al., 2024). Their presence supports vegetation growth, stabilizes rivers, and benefits other species.

 Keystone Species

These are animals or plants that play a key role in the entire ecosystem (Shukla et al., 2023). Their removal from the ecosystem can disrupt balance and cause ecosystem decline.

References

Bruers, S., Davis, A. J., Hojjat, S., Koskensilta, A., Lepeltier, T., & Pearce, D. (2024). Nature without Suffering: Herbivorisation of Predator Species for the Compassionate Stewardship of Earth’s Ecosystems. Journal of Applied Animal Ethics Research, 6(2), 175-204. https://doi.org/10.1163/25889567-bja10051

Shukla, I., Gaynor, K. M., Worm, B., & Darimont, C. T. (2023). The diversity of animals identified as keystone species. Ecology and Evolution, 13(10), e10561.https://doi.org/10.1002/ece3.10561

Wirsing, A. J., & Newsome, T. M. (2021). Scavenging effects of large canids. Integrative and Comparative Biology, 61(1), 117-131. https://doi.org/10.1093/icb/icab012

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