TOEFL Reading Practice Test #21

Wolves are apex predators that play a critical role in maintaining the balance of ecosystems. As predators at the top of the food chain, they regulate populations of herbivores such as deer and elk, which in turn influences vegetation and other animal species. Through their presence and behaviors, wolves drive a phenomenon known as trophic cascades, where changes at the top of the food chain ripple through entire ecosystems.

One of the most famous examples of a trophic cascade involving wolves occurred in Yellowstone National Park. Wolves were reintroduced to the park in 1995 after being absent for nearly 70 years. During their absence, elk populations had grown unchecked, overgrazing areas along riverbanks and reducing vegetation such as willow and aspen. This lack of vegetation led to soil erosion and negatively impacted other species, including beavers, which rely on trees for building dams. After wolves were reintroduced, they began preying on elk, reducing their numbers and altering their behavior. Elk started avoiding open areas near rivers, allowing vegetation to recover. With the return of trees and shrubs, beaver populations rebounded, creating habitats that benefited fish, birds, and other wildlife. This cascade of effects demonstrated the profound impact wolves have on ecosystem health.

Wolves also influence the behavior of prey animals, a process known as the “ecology of fear.” The mere presence of wolves causes herbivores to alter their grazing patterns and avoid areas where they feel vulnerable. This redistribution of grazing pressure helps maintain diverse plant communities and prevents overgrazing in specific areas. For instance, in regions with active wolf populations, studies have shown that vegetation near water sources tends to thrive because herbivores avoid these open spaces to reduce the risk of predation.

However, the role of wolves in ecosystems is not without controversy. In agricultural areas, wolves occasionally prey on livestock, leading to conflicts with farmers and ranchers. These incidents often fuel debates over wolf conservation and management. Some argue that wolf populations should be strictly controlled to prevent economic losses, while others emphasize their ecological importance and advocate for non-lethal methods of deterrence, such as electric fencing and guardian animals.

The challenges wolves face are not limited to human conflict. Habitat loss due to deforestation and urban expansion threatens their survival. Fragmented habitats reduce wolves’ access to prey and increase the risk of inbreeding, which can weaken populations over time. Climate change also poses emerging threats, potentially altering prey availability and the landscapes wolves depend on.

Despite these challenges, wolves remain a keystone species, meaning their presence is essential for ecosystem stability. Conservation efforts, including protected areas, reintroduction programs, and public education, have helped some wolf populations recover. However, ensuring the long-term survival of wolves requires balancing ecological, economic, and social priorities. Wolves are not just predators; they are vital players in the intricate web of life that sustains ecosystems.