If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

All of the following terms appear in the videos or articles for this tutorial on local threats to biodiversity. The terms are arranged here in alphabetical order, and nouns are given in just their singular form unless the plural of the term is unusual.

biodiversity: the variety of life on Earth or some other specified geographic region of the planet; the diversity of life occurs at the genetic level, at the species level, at the ecosystem level, and in evolutionary lineages

carrying capacity: the maximum number of individuals of a given species that an area's resources can sustain indefinitely without significantly depleting or degrading those resources

cryptogenic: in general, something with obscure origins; a cryptogenic species is one whose origins in a particular area are unknown with regard to whether it is native or introduced by humans; crypto means “hidden”, and genic means “origin”

dead zone: an area of low oxygen in an ocean or lake that is harmful or lethal to aquatic organisms; usually caused by increased levels of nutrients such as nitrogen and phosphorus from agricultural fertilizers that are washed off the land and into the water where they cause blooms of algae and other phytoplankton; when the algae and phytoplankton die, the bacteria that decompose them also deplete the oxygen in the water

downstream effect: the spreading of a pollutant from its initial release site to other areas that are downstream for water-carried pollution or downwind for wind-carried pollutants; for example, pesticides from a farm field may run into a local river and be carried downstream or the pollutants from the smokestack of a factory will be carried downwind; pollution can have an impact far away from the place where the pollution was produced

exotic species: a species that is transferred intentionally or accidentally by human activities from its native habitat to one in which it does not occur naturally; also known as an introduced species

exponential growth: a pattern of population growth that results in an increasingly steep increase in the total population size over time; populations can continue exponential growth only as long as there are no limits to necessary resources; the human population has had exponential growth

generalist: an organism or species that can tolerate a wide range of environmental conditions, habitats and food sources; generalists also tend to have high reproductive rates and do well colonizing new areas; generalists are the opposite of specialists, but there is a continuum between them, not sharp, clear-cut boundaries

habitat: a general term for the type of environment in which an organism lives

hormone mimics: a chemical compound that acts like a naturally occurring hormone for some type of organism; some chemical pollutants are hormone mimics and interfere with the normal development or reproduction of organisms

introduced species: a species that is transferred intentionally or accidentally by human activities from its native habitat to one in which it does not occur naturally; also known as an exotic species

invasive species: an introduced species that becomes well-established in its new environment, spreads easily, and causes ecological and economic harm; invasive species frequently outcompete native species and lead to the decline or even extinction of natives; different types of plants, animals, fungi and microorganisms can be and are invasive species

land-use change: the conversion of natural habitat to some other use by humans; the change is frequently harmful for native organisms

light pollution: a form of pollution that involves excessive, misdirected, or obtrusive artificial light; light pollution can negatively impact wildlife in an area

native species: a species that occurs in an area naturally, rather than as the result of human activities

noise pollution: a form of pollution that  involves excessive, loud and artificial noise or sounds; noise pollution can negatively impact animals

overfishing: taking aquatic wildlife at rates too high to be sustainable; whether it is fish, crabs, lobsters, sea urchins or any other type of marine or freshwater species, overfished populations cannot reproduce quickly enough to counteract the harvesting, so the population size declines; species can be driven to extinction by overfishing

pathogen: a microorganism, such as a virus, bacterium, fungus or protozoan, that causes disease in its host; virtually all organisms are susceptible to pathogens

pollution: the presence, due to human activities, of one or more contaminants in a habitat that negatively impacts organisms and ecosystem function; the contaminant is also called a pollutant, and can be a chemical, a material like plastic or Styrofoam, sediment, noise, heat or light

population: all the individuals of a particular species that live in a specific geographic area; a species may be made up of one or more populations

reproduction: the biological process by which parents produce offspring

resource exploitation: the use of natural resources such as wood, coal, fish and fresh water by humans; resource exploitation is frequently non-sustainable, the rate and amount of extraction of the resource from the environment is too high to allow replacement of the resource through natural means and thus it limits the availability of the resources in the future

species richness: the number of different species in a given geographic area

urbanization: the conversion of a rural or natural area into a city environment; urbanization is an ongoing trend for the human population and is one of the biggest causes of land-use change