Which category of organisms is not covered by the Endangered Species Act?

The Endangered Species Act (ESA) is designed to protect species that are at risk of extinction. Under this legislation, a wide range of organisms, including amphibians, birds, and insects, are covered. The purpose of the ESA is to conserve not only the listed species but also the ecosystems upon which they depend.

Bacterial species, however, are generally not included under the ESA. The act focuses primarily on vertebrate animals and certain invertebrates and plants, especially those that have a significant ecological, cultural, or economic value. While microorganisms are crucial to ecosystems, the legislative framework of the ESA does not extend to them, which is why bacterial species are the correct answer in this context. This distinction reflects the targeted nature of the Act in terms of conservation priorities and the criteria used for listing endangered species.