Species loss

Species loss, particularly the extinction of species that is caused by human activities, has increasingly concerned scientists in a number of fields. The Endangered Species Act (1973) is the central piece of legislation concerned with preventing species loss in the United States.

Background

Public and scientific concern about species loss stems from several factors and encompasses a variety of viewpoints. Ethically, many people believe that species have value in and of themselves and that humankind does not have the right to cause the extinction of any species. A species may also have an unknown potential to enrich human life and health. The latter argument is important in that many synthetic medicines and commercial products were first produced by plants and animals. The loss of species could mean the loss of beneficial new products for human society. Species that exist today are the result of millions of years of evolutionary success, and to lose species is to lose that evolutionary history. From a resource management point of view, ecologists and land managers alike are concerned about the effects that species loss may have on the function and stability of biotic communities.

The ramifications of species loss are not easily predictable. The food-web relationships among species in a community may or may not be known and, if known, may not have been measured. Relationships such as predation, competition, and parasitism link species into complex community relationships. One way species are linked is by trophic levels within the community food chain, which is more accurately described as a food web. Starting with plants at the base of the web, trophic levels begin with producers, followed by several successive levels of consumers: herbivore, first-level carnivore, second-level carnivore, and so on, up to top carnivore. Omnivores feed both as herbivores and as carnivores and thus feed at more than one trophic level. Finally, decomposers feed on dead organisms and their waste products from all trophic levels.

Species-Removal Studies

Species-removal studies provide some indication of what may occur when a species becomes extinct. In more than 90 percent of predator-removal studies, population densities of prey species in the trophic level immediately below the predator have shown a significant increase or decrease. In many cases, the change in was twofold. Rarely has the removal of predator species had no effect on the population density of its prey. However, not all studies have shown the expected increase in prey density; many have shown an unexpected decrease.

For species that possibly compete with one another, more than 90 percent of competitor-removal studies have shown an increase in the “remaining competitor” population density. Several factors may influence the strength of community response in species-removal experiments. For example, a predator may prey more heavily on a large, aggressive prey species and thus allow the coexistence of a less aggressive, competitor prey species. If the predator is removed, the aggressive prey may increase in density while the less aggressive one may actually decrease. Studies in aquatic communities indicate that the higher the trophic level in which species removal occurs, the greater the effect on population densities at lower trophic levels.

The ramifications of species loss can be only partially predicted with knowledge of community food webs. The size and direction of population density change within a community may or may not be as expected. It is safe to predict, however, that species loss will cause changes in most instances.

Wildlife Protection and Endangered-Species Legislation

Concern about species loss in North America can be traced back at least as far as 1872, when legislation offering limited protection to the buffalo was passed by Congress. This legislation was passed at the height of buffalo exploitation by market hunters and during the US Army’s policy of fighting Native American tribes by cutting off their food supply. However, President Ulysses S. Grant vetoed the legislation, and the buffalo was almost lost. Only a few hundred remained by 1900. The first National Wildlife Refuge was set aside by President Theodore Roosevelt in 1902 to protect egrets from extinction by feather hunters. Three years later, the Wichita Mountain National Wildlife Refuge was set aside to protect one of the small remnant herds of buffalo. Several North American species and subspecies are now extinct because of similar exploitations: the passenger pigeon, Carolina parakeet, heath hen, Merriam’s elk, and Badlands bighorn sheep are some of the best-known examples.

During the 1960s, increasing concern about an accelerated species extinction rate attributable to human exploitation and disturbance of the environment culminated in the first federal protective legislation for endangered species, the Endangered Species Preservation Act of 1966. This act was limited to listing endangered birds and mammals and funding research on their population and habitat acquisition. This legislation was expanded in 1969 to include all vertebrate animal species and some invertebrates. The definitive protection legislation is the 1973 Endangered Species Act. This act set procedures for listing threatened and endangered species, called for the designation of critical habitats for each threatened or endangered species, and mandated the development of recovery plans for these species. The act prohibits the use of federal funds for projects that would harm threatened or endangered species. The coverage of the 1973 act was also expanded to include plants and invertebrate animals (except pest insects), subspecies, and distinct vertebrate populations. In 2023, twenty-one species of birds, fish, mussels, and bats, along with one species of plant, were declared extinct in the United States. The year was the fiftieth anniversary of the Endangered Species Act.

Beginning in 1966, the United States Fish and Wildlife Service (USFWS) assumed the legal responsibility of compiling and maintaining an official threatened and endangered species list. There are formal petitioning processes for placing additional species on the list and for removing them from the list. Petitions may be initiated by the USFWS or by private organizations. Petitions are reviewed by scientific panels using all available information on the species. If sufficient information is available to support the petition, a proposed addition to the list is published in the Federal Register and other appropriate places to solicit public comment. Final decisions about listing, “down-listing” (for example, changing a species designation from “endangered” to “threatened”), or “delisting” are made by the USFWS. The ultimate goal of the listing process and the implementation of a recovery plan is to increase the abundance and distribution of a species to the point of being able to remove it from the threatened and endangered species list.

Bibliography

Ellis, Richard. The Empty Ocean: Plundering the World’s Marine Life. Island Press, 2003.

"Endangered Species." U.S. Fish & Wildlife Service, DOI, www.fws.gov/program/endangered-species. Accessed 10 Jan. 2025.

Garbutt, Nick, and Mike Unwin. 100 Animals to See Before They Die. Bradt Travel Guides, 2007.

Goodall, Jane, Thane Maynard, and Gail Hudson. Hope for Animals and Their World: How Endangered Species Are Being Rescued from the Brink. Grand Central Publishing, 2009.

Maclaurin, James, and Kim Sterelny. What Is Biodiversity? University of Chicago Press, 2008.

McGavin, George. Endangered: Wildlife on the Brink of Extinction. Firefly Books, 2006.

Nakamura, Kate. “22 Animals That Went Extinct in the US in 2021—And How to Take Action for Biodiversity." Global Citizen, 14 Dec. 2021, www.globalcitizen.org/en/content/animal-extinct-biodiversity-2021/. Accessed 10 Jan. 2025.

Pimm, Stuart L. The Balance of Nature? Ecological Issues in the Conservation of Species and Communities. University of Chicago Press, 1991.

Ricklefs, Robert E., and Dolph Schluter, editors. Species Diversity in Ecological Communities: Historical and Geographical Perspectives. University of Chicago Press, 1993.

Schuldheisz, Christine. "Twenty-one Species Delisted from the Endangered Species Act Due to Extinction." US Fish & Wildlife Service, 16 Oct. 2023, www.fws.gov/press-release/2023-10/21-species-delisted-endangered-species-act-due-extinction. Accessed 10 Jan. 2025.

"Species at Risk." Government of Canada, 13 May 2024, www.canada.ca/en/services/environment/wildlife-plants-species/species-risk.html. Accessed 10 Jan. 2025.

Strong, Donald R., Jr., et al., editors. Ecological Communities: Conceptual Issues and the Evidence. Princeton University Press, 1984.

Wilson, Edward O. The Future of Life. Vintage, 2003.