Why are keystone species important in an ecosystem?

Keystone species are crucial to an ecosystem because they play a critical role in maintaining its structural integrity and overall balance. These species disproportionately influence their environment relative to their abundance or biomass. They can affect the population sizes of other species and the structure of the community. For example, the presence of a keystone predator can regulate herbivore populations, which in turn helps maintain plant diversity. Without these key species, ecosystems can become unbalanced, leading to a decrease in biodiversity and changes in the ecosystem's physical environment.

The other options do not accurately reflect the significance of keystone species. For instance, stating that they have a minor impact contradicts the very definition of a keystone species, as their impact is substantial and vital. Additionally, while keystone species can sometimes be numerous, their importance is not related to their numbers but rather to their roles in ecological processes. Finally, keystone species can exist year-round or seasonally, but their significance is not tied to their seasonal presence; it is their functional role within the ecosystem that is paramount.