What role do keystone species play in an ecosystem?

Keystone species play a critical role in maintaining the structure and stability of an ecosystem. The correct answer highlights that these species have a significant impact on their environment that is disproportionate to their abundance. This means that even if they are not the most numerous organisms in an ecosystem, their presence or absence can lead to dramatic changes in the ecosystem's structure and function.

For instance, a keystone species might be a predator that helps control the population of herbivores, which in turn allows vegetation to thrive. Without the predator, herbivore numbers might explode, leading to overgrazing, which can drastically alter the plant community and the entire ecosystem. Thus, the influence of keystone species is a primary driver in maintaining ecological balance.

In contrast, the other options suggest misconceptions about keystone species. These species are not necessarily abundant or always top predators; rather, their unique roles contribute to ecological stability. Additionally, they do not inherently cause habitat destruction, as that implies a detrimental effect rather than the balancing influence they typically exert on an ecosystem.