9.9 Endangered Species

7 min readjanuary 16, 2023

Jenni MacLean

Jenni MacLean

Riya Patel

Riya Patel

AP Environmental Science ♻️

252 resources
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Any organism including plants or animals can become endangered. Organisms are classified by the International Union for Conservation of Nature (IUCN) into the following categories. 

Image Courtesy of Wikimedia

Extinct (EX) – These species no longer exist and have become extinct.
Extinct in the wild (EW) – Survives only in captivity, cultivation and/or outside the native range, as presumed after exhaustive surveys.
Critically endangered (CR) – These species are at an extremely high risk of extinction in the wild and their population is declining at an alarming rate.
Endangered (EN) – These species are at a very high risk of extinction in the wild and their population is declining rapidly.
Vulnerable (VU) – Meets one of the 5 red list criteria and thus considered to be at high risk of unnatural (human-caused) extinction without further human intervention.
Near threatened (NT) – These species are at risk of becoming endangered in the near future.
Least concern (LC) – These species are considered to have a low risk of extinction and are not considered endangered.

Conservation Status Classification

IUCN uses five criteria to classify organisms and assess their conservation status. The conservation status of a species refers to its risk of extinction in the wild. These criteria are:
A) Reduction in population: The population size of the species has decreased significantly over a certain period of time.
B) Geographic range: The species has a restricted geographic range or habitat.
C) Population size: The species has a small population size, estimated to number fewer than 2,500 mature individuals, and is in decline.
D) Extremely small population size: The species has an extremely small population size, estimated to number fewer than 250 mature individuals.
E) Probability of extinction: A quantitative analysis has shown that the probability of the species becoming extinct in the wild is at least 20% within 20 years or five generations.
These criteria are used to classify species into the different categories of the IUCN Red List, such as Least Concern, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild, and Extinct. The criteria are intended to provide a consistent and objective way to assess the conservation status of a species, and to help prioritize conservation efforts.
Check out https://www.iucnredlist.org to look at the population status of thousands of plants and animals.

Risk Factors

Certain organisms are inherently more at risk for extinction than others due to their biology and ecology. The difference in reproductive rate, as well as the ability of an organism to adapt to environmental change, are two key factors that can influence the survival and extinction risk of a species.
R-selected species, such as mice, have a high reproductive rate and can quickly rebound from population losses. These species are typically short-lived and have many offspring that have a low chance of survival.
K-selected species, such as elephants, have a lower reproductive rate and take longer to recover from population losses. These species are typically long-lived and have fewer offspring that have a higher chance of survival.
Specialist species, such as orangutans, have a very specific niche and are adapted to a particular set of conditions. They can be particularly vulnerable to environmental changes and pressures, such as habitat loss, as they may not be able to adapt to new conditions.
Generalist species, such as pigeons, are able to adapt to a variety of different climates, food sources, and environmental challenges. They tend to be more resilient to environmental changes and pressures, but they can also compete with native species and alter the ecosystem.


Hunting, fishing, and other forms of harvesting are the most direct human influences on wild populations of plants and animals. Overharvesting occurs when individuals are removed from a population at a rate faster than the population can replace them. This can lead to population declines and even extinction, as seen in the case of the dodo bird on Mauritius.
Historically, market hunting has led to the overharvesting of many species, such as the American bison and passenger pigeon, causing dramatic declines in population numbers. However, with the implementation of regulations and legal protections, many species have been able to recover, such as the American bison.
Regulations such as hunting and fishing restrictions and limits on the number of animals that can be harvested have been implemented in many countries to prevent overharvesting. However, in some regions of the world, harvest regulations are not enforced, and illegal poaching continues to threaten species with extinction.
Illegal harvesting of rare animals, such as tigers, rhinoceroses, and apes, and rare plants, birds, and coral reef dwellers for private collections has become an increasing problem, and it's threatened the persistence of these species.

Plant/Animal Trade

The trade in plants and animals can represent a serious threat to the persistence of some species. Laws such as the Lacey Act in the United States and the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) were developed to control and regulate the trade of threatened and endangered plants and animals.
The Lacey Act, first passed in 1900, originally prohibited the transport of illegally harvested game animals across state lines. Today, the Act prohibits the interstate shipping of all illegally harvested plants and animals. CITES is an international agreement among 182 countries worldwide, which aims to control the international trade of threatened and endangered species.
Despite these laws and agreements, illegal trade in plants and animals continues to occur worldwide. Illegal trade in wildlife is estimated to be worth between 5 billion to 220 billion dollars annually. Illegal trade in wildlife and wildlife parts have been sent to United States ports over a 10-year period. The illegal trade in wildlife is driven by demand for fur, body parts thought to have medicinal value, and rare animals as pets.
Even legal trade in certain species can pose a potential long-term threat to species persistence. In the southwestern United States, for example, the growing movement to reduce water used by replacing grass lawns with desert landscapes has led to an increased demand for cacti and other desert plants collected from the wild, causing concern for these plant populations in the wild.


Countries have implemented a variety of strategies to address the decline in species and protect endangered and threatened species. One of the most important strategies is the implementation of legislation to protect habitats. The Endangered Species Act of 1973 in the United States, for example, aims to protect endangered and threatened species by preserving habitats from development.

Endangered Species Act

The Endangered Species Act (ESA) of 1973 is a federal law in the United States that aims to protect and recover species that are in danger of extinction throughout all or a significant portion of their range. The Act is administered by the U.S. Fish and Wildlife Service (FWS) and the National Oceanic and Atmospheric Administration (NOAA) and it is one of the strongest laws in the world for protecting endangered and threatened species.
The ESA provides for the listing of species as either "endangered" or "threatened" based on their risk of extinction. Once a species is listed, the Act requires the federal government to take actions to protect and recover it. This includes the designation of "critical habitat," which is defined as specific areas that are essential for the conservation of the species, as well as the prohibition of harming the listed species and their trade, including their fur or body parts.
The Act also implements the international CITES agreement, which regulates the trade of threatened and endangered species. To assist in the conservation of threatened and endangered species, the Act authorizes the government to purchase habitat that is critical to the conservation of the species and to develop recovery plans to increase the population of threatened and endangered species.
The ESA has been the center of much debate and controversy in recent years, as it can restrict certain human activities in areas where listed species live, including how landowners use their land. Despite this, the Act has had significant success in protecting and recovering endangered and threatened species, with several species being removed from the list as their populations have increased. However, efforts to weaken the ESA have been ongoing and it's important to continue to support and advocate for its protection.


Another key strategy is education, raising public awareness about the potential extinction of species and the impact of human actions on biodiversity. Through education, people can learn about the importance of conservation and take steps to support it.

Breeding Programs

Captive breeding programs in zoos and aquariums can also play a role in species conservation. These institutions can serve as education centers, while at the same time using the animals in captive breeding programs to rebuild populations of critically endangered species. Programs like the Smithsonian National Zoo and the San Diego Zoo have been instrumental in establishing populations of species like the black-footed ferret, red panda, and clouded leopard.


In addition, conservation organizations, non-governmental organizations, and research institutions have been working in collaboration with governments to address the decline in species, through research, monitoring, and conservation actions in the field, and also by creating protected areas, corridors, and reintroduction programs.
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