Endangered Species (College Board AP® Environmental Science): Study Guide

How does a species become endangered?

What does it mean for a species to be endangered?

• A species is considered endangered when its population has declined to the point that it faces a high risk of extinction

• Endangered species are often listed under conservation laws such as

  • the U.S. Endangered Species Act (ESA)

  • the International Union for Conservation of Nature (IUCN) Red List

Factors that lead to endangerment

Overhunting and poaching

• Some species are hunted extensively for food, medicine, or trade

  • Example: African elephants are endangered due to ivory poaching

  • Unsustainable fishing practices have led to population declines in aquatic species like bluefin tuna

Limited diet and specialized needs

• Species with specific food sources or habitat requirements are more vulnerable to environmental changes

  • Example: Giant pandas rely almost entirely on bamboo, making them highly susceptible to habitat loss

Invasive species competition

• Non-native species introduced into an ecosystem can become invasive if they outcompete, prey on, or spread disease to native species

  • Example: The brown tree snake in Guam has caused the decline of native bird populations by preying on their eggs

Habitat destruction and fragmentation

• Deforestation, urban expansion, and agricultural land use reduce the available habitat for many species

  • Example: The Amazon rainforest, home to thousands of species, is being lost to logging and agriculture

  • Habitat fragmentation isolates populations, making reproduction more challenging and reducing genetic diversity

Climate change

• Rising temperatures, altered rainfall patterns, and extreme weather events affect many species

  • Example: Coral reefs are severely threatened by ocean warming and acidification, leading to coral bleaching

  • Polar bears are struggling to find food as Arctic ice melts

Adaptation & extinction

Why do some species face extinction while others survive?

• Not all species respond the same way to environmental changes

  • Species that can adapt quickly or relocate to new habitats have a better chance of survival

  • Those with specialized needs or slow reproductive rates are at greater risk of extinction

How species adapt to environmental changes

• Physiological adaptations:

  • Changes in body functions that help a species survive in new conditions

    • Example: Urban-dwelling blackbirds (Turdus merula)

    • Blackbirds living in cities have been shown to have higher stress tolerance and altered circadian rhythms, allowing them to better cope with noise, artificial lights, and human activity

• Behavioral adaptations:

  • Changes in behavior that increase survival chances

    • Example: Pink salmon (Oncorhynchus gorbuscha)

    • Due to warming ocean temperatures, populations in the Pacific Northwest have started migrating earlier to avoid higher temperatures that affect their spawning success

• Genetic adaptations:

  • Over generations, species may develop traits through natural selection to better fit their environment

    • Example: Tawny owl (Strix aluco) in Europe

    • Traditionally, tawny owls come in two color variations: gray and brown

    • Due to climate change and reduced snowfall, there has been a decline in gray-colored owls, as brown owls now have a survival advantage in less snowy environments

    • This is an example of natural selection in response to changing environmental conditions

Inability to adapt leads to greater extinction risk

Slow reproduction rates

• Species that reproduce slowly may not adapt fast enough to environmental changes

  • Example: Orangutans have long birth intervals, making population recovery difficult after habitat loss

Specialized diet or habitat requirements

• Species with specific needs struggle when their food source or habitat is altered

  • Example: Koalas depend almost entirely on eucalyptus leaves, making them vulnerable to habitat destruction

Inability to migrate or relocate

• If a species cannot move to a new area, it may not survive environmental changes

  • Example: Coral reefs cannot relocate as oceans warm, leading to coral bleaching and mass die-offs

Selective pressures

What are selective pressures?

• Selective pressures are environmental factors that

  • change the behaviors and fitness of organisms within an environment

  • influence which traits become more or less common in a population over time

• These pressures drive natural selection, determining which individuals survive and reproduce

  • Species that fail to adapt to selective pressures may decline or become extinct

Types of selective pressures

Predation pressure

• Predators act as a selective force, favoring traits that help prey survive

  • Example: Gazelles that run faster are more likely to escape predators and pass on their genes

Climate and environmental changes

• Temperature, weather patterns, and habitat shifts lead to species adaptations

  • Example: Galápagos tortoises from arid islands have evolved saddleback shells, which allow them to stretch their necks higher to reach food, such as cactus pads

  • In contrast, Galápagos tortoises from wetter islands have domed shells because food is more abundant and closer to the ground, so there is less selective pressure for a high-reaching neck

Availability of resources

• Food, water, and shelter availability affects survival and reproduction

  • Example: Finches on the Galápagos Islands evolved different beak shapes to specialize in different food sources

Disease and immunity

• Pathogens exert strong selective pressures, favoring individuals with resistance

  • Example: European rabbits evolved resistance to myxomatosis, a virus introduced to control their population

Human-induced pressures

• Hunting, pollution, habitat destruction, and climate change create strong selective pressures

  • Example: Elephants in some populations are evolving tusklessness due to selective hunting for ivory

Species competition & extinction

How does competition lead to species extinction?

• Species compete for limited resources, such as food, water, space, and mates

• When one species outcompetes another, the losing species may decline in population or face extinction

• Competition can be between native species or between native and invasive species

Competitive exclusion and species decline

• When two species compete for the same niche, one may outcompete the other, leading to competitive exclusion

  • Example: European starlings in North America have displaced native birds by taking over nesting sites

  • Some species can adapt and shift their niche, while others cannot and go extinct

• Invasive species often outcompete native species due to advantages such as:

  • Lack of natural predators in the new environment

  • Faster reproduction rates

  • Ability to tolerate a wider range of conditions

• The image above shows blue adapting to a new niche restricted to the top and bottom of the tree, avoiding competition

• This may help the species to survive

• However, if there is insufficient food to sustain the blue population, this species may become endangered or extinct

Protecting endangered species

Criminalizing poaching and illegal wildlife trade

• Many endangered species are targeted for their fur, horns, or medicinal value

  • Example: International bans on ivory trade aim to protect elephants from poaching

• Enforcement of anti-poaching laws and stricter penalties help deter illegal activities

Protecting natural habitats

• Habitat loss is the leading cause of species endangerment

• Conservation efforts focus on establishing national parks, wildlife reserves, and protected areas

Legislation and conservation policies

• Governments and international organizations enforce laws and agreements to protect species

  • Example: The U.S. Endangered Species Act (ESA) provides legal protection for species at risk

  • The CITES (Convention on International Trade in Endangered Species) regulates trade in endangered species to prevent exploitation

Captive breeding and reintroduction programs

• Breeding endangered species in captivity helps boost population numbers before releasing them into the wild

  • Example: The California condor was successfully bred in captivity and reintroduced to the wild

  • Zoos and conservation centers play a key role in these efforts

Ecotourism and community involvement

• Sustainable tourism generates revenue for conservation while educating the public

• Local communities benefit economically from conservation, making them more likely to protect wildlife

  • Example: Mountain gorilla ecotourism in Rwanda and Uganda has helped fund conservation programs and protect gorilla populations