9.9 - Endangered Species

Learning Objectives

I. How Species Become Endangered

• Poaching: The illegal hunting and trade of animals or their parts. Poaching often targets exotic species, like elephants for their ivory tusks or rhinos for their horns. One strategy to fight poaching is to cut those valuable parts off the animals so they don’t get killed for them.

• Overharvesting / Hunting: A species can become endangered or extinct from being over-harvested. The American Bison was almost driven to extinction by hunting.

• Exotic Pet Trade: Species get removed from the wild and sold as pets. Tigers are a well-known example of a species taken from their natural habitat to be sold.

• Specialist Requirements: Species that are niche specialists, needing very specific habitats, resources, or food, are prone to endangerment.
• The koala is a great example, since it has narrow food requirements and relies on the eucalyptus tree. That makes specialists less tolerant or resilient to changing conditions, as seen during the Australian wildfires.

• Invasive Species: These are a huge threat to native species. Invasives are typically very aggressive about feeding and using habitat, so they can outcompete natives.
• The zebra mussel is a key example. Zebra mussels attach to native freshwater mussels by the hundreds, smothering them and taking their food. In Lake St. Clair and western Lake Erie, native mussels almost completely disappeared from open waters within a few years of the invasion. North America has more freshwater mussel species than anywhere else, and many were already endangered, so zebra mussels push them closer to extinction.

• Climate Change: A huge threat and one of the drivers pushing many species toward endangerment. Climate change can shift habitats, for example when cold boreal forests get too warm. If organisms can’t adapt fast enough, they’re prone to endangerment or extinction.

II. Protecting Endangered Species

• Preventing Poaching:
• Cutting off the valuable parts of the animal.
• Hiring armed guards and scientists to track vulnerable populations. Guards are often given the authority to arrest people or prevent illegal poaching.
• Increasing the severity of penalties or fines, like strict fines or jail time, to discourage poaching.

• Protecting Habitat Areas (Most Effective Way): Governments can purchase land or designate it as endangered species habitat, like a national park, wildlife preserve, or animal sanctuary.
• This is highly effective because it gives the species access to their natural habitat without disruption, and it gives them the space and time they need to reproduce and repopulate. It’s especially important for K-selected species like large mammals, elephants for example.

III. Key Legislation

• CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): An international agreement, signed in 1973, that controls trade in wild animals and plants and their parts. Trade in the most endangered species, like rhino horn and elephant ivory, is mostly banned, and trade in many others needs permits. It requires member countries to establish their own agency to monitor the import and export of protected species, including tusks, fur, and live organisms, and gives those agencies the authority to seize products and punish violators.

• Endangered Species Act (US Law): This U.S. legislation gives the Fish and Wildlife Service, the enforcement agency, the power to designate species as endangered or threatened, and to purchase and set aside land as habitat so those species can repopulate.
• Passed in 1973. The Fish and Wildlife Service handles land and freshwater species, and NOAA Fisheries handles most marine species like whales and sea turtles.
• It makes it illegal to take a listed species (kill, harm, capture, or harass it), lets the agencies protect critical habitat that a species needs to recover, and bars federal agencies from funding or approving projects that would jeopardize a listed species.
• Recovery examples: the bald eagle (removed from the list in 2007, helped by the 1972 DDT ban), the American alligator (1987), and the eastern Pacific gray whale (1994).
• Change in 2026: in July 2026 the two agencies removed their rule that counted major habitat destruction as illegal "harm," so destroying habitat on its own usually no longer counts as a take. Critical habitat rules for federal projects still apply, and states, tribes, and environmental groups have sued to undo the change (as of 2026).

IV. IUCN Red List and Endangered Status

• Least Concern: Species that are widely abundant and not currently threatened.

• Near-Threatened: Species close to qualifying as threatened, likely to become threatened in the near future.

• Threatened Classifications: Species with a high risk of extinction in the wild. From lower to higher risk, these are Vulnerable, Endangered, and Critically Endangered.

• Extinct in the Wild: Species that only exist in captivity, like in a zoo or sanctuary.

• Completely Extinct: Not a single member of the species is left on Earth.

V. Endangerment by Taxon

VI. Specialists vs. Generalists and Competition

• Specialists like the koala are more vulnerable, because they’re less likely to survive in a new habitat or adapt to new conditions and food sources.

• Generalists like the redback salamander have the advantage, because they thrive when conditions are changing rapidly and they can use many different resources.

• Ability to Move: Species that can move to a new area when conditions change, like many birds and ocean fish, are less likely to go extinct. Species that can't move far, or have nowhere to go, are at the highest risk: plants with slow seed dispersal, animals stuck in fragmented habitat, and mountaintop species. The American pika, a small mammal that overheats easily (it can die after a few hours at about 78°F), has disappeared from many low-elevation sites in the Great Basin, and it can only move uphill until it runs out of mountain.

• Competition: Interspecific competition, meaning competition between different species, can limit a species’ range and cause endangerment. For example, the endangered Shenandoah salamander is restricted to only three mountain peaks, because the widely abundant redback salamander fiercely protects its rock habitats and chases the Shenandoah off the lowlands.

• Selective Pressures: a selective pressure is any factor that changes which individuals survive and reproduce (their fitness), and so changes how organisms in that environment behave and what traits the population has over time. Predators, disease, climate, competition, and humans can all be selective pressures.

• Real Example (tuskless elephants): during Mozambique's civil war (1977 to 1992), poachers killed about 90% of the elephants in Gorongosa National Park for ivory. Females born without tusks were far more likely to survive, so tusklessness became much more common: about 18% of adult females had no tusks before the war, but about half of the females that survived it were tuskless, and they pass the trait on to their daughters (Campbell-Staton and others, 2021).

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