What term describes species that have a disproportionately large effect on their environment relative to their abundance?

The term that describes species which have a disproportionately large effect on their environment relative to their abundance is "keystone species." Keystone species play a critical role in maintaining the structure of their ecological community. The removal of a keystone species can lead to significant changes in the ecosystem, often resulting in the decline or extinction of other species, thereby altering the community's composition and dynamics.

For instance, in many ecosystems, certain predators are considered keystone species because they maintain the population balance of prey species, which in turn affects the entire food web and habitat structure. This concept illustrates that not all species in an ecosystem contribute equally to its health and functionality; some have a heavier influence that can be vital for ecological stability.

In contrast, flagship species are often large or charismatic animals used as symbols for conservation efforts but do not necessarily have a direct ecological impact relative to their abundance. Endemic species are those that are native and restricted to a specific geographic area, while invasive species are non-native organisms that can disrupt local ecosystems but do not inherently carry the keystone function of influencing environmental dynamics significantly.