A to Z Definitions of the Most Important Ecological Terms

A glossary of the terms you need to know when studying ecology.

Ecology definitions
This sweet basset hound is brushing up on his ecological definitions. Getty Images

Acid Rain 

Precipitation that contains high concentrations of nitric and sulfuric acid. It is caused by pollutants in the air such as sulfur dioxide and nitrogen dioxide. Acid rain causes erosion, damage to vegetation, physical changes in aquatic species, and groundwater contamination.


The method by which living things change in order to survive in a particular climate or environment. 


The variety of species in an area.

The more genetically distinct species there are in an ecosystem, the healthier it is. Ecologist R. H. Whittaker categorized biodiversity as alpha, the number of species in an ecosystem; beta, the diversity between ecosystems; and gamma, the diversity of entire regions. 


Large regions often made up on several distinct ecosystems. There are six defined categories of biomes: tundra, conifer, deciduous forest, grassland, tropical, and desert. 

Carbon Footprint

The total amount of greenhouse gas emission by a person, event, or corporation.

Carbon Sinks

Areas (typically forests) that absorb carbon dioxide from the atmosphere.

Carrying Capacity 

The maximum population number of a species that an ecosystem can support without causing harm to other species.

Climate Change 

A statistical change in average weather patterns and conditions that may be leading to an overall warming of the Earth's temperatures.

Deep Ecology

A term coined by ecologist Arne Naess in his 1973 article “The Shallow and the Deep, Long-Range Ecology Movements,” that challenges humans to rethink ecology from the current human-centric focus to one that looks at the role of humans as members of the natural world.

Earth Day

A environmental holiday celebrated yearly on April 22, 1970.

The first Earth Day was organized by Wisconsin Senator Gaylord Nelson as a "teach-in" to raise awareness about environmental issues.


The study of the relationships between living things and their environment.


The interaction between living organisms in an environment, including plants, animals, fish, birds, microorganisms, water, and people, and their relationship with non-living components of the environment - such as soil, air, climate, and weather.


Genetic methods that species use to adapt to their environment.

Fossil Fuels

Coal, oil and natural gas that have been converted into burnable hydrocarbons. The burning of fossil fuels is thought to contribute to both pollution and global warming.

Global Warming

The rise of the Earth's average temperature that is thought to be caused by the accumulation of greenhouse gases in the atmosphere.

Greenhouse Gases

Gases, such as carbon dioxide, nitrous oxide, chlorofluorocarbons (CFCs), ozone, and methane, that trap solar energy as it is reflecting from the planet.


Where a particular species lives.


The mechanism an animal species uses to lower its metabolism, respiration, heart rate, and body temperature making it easier to survive in colder temperatures.

Keystone Species

A plant or animal species that plays a critical role in the overall health of an ecosystem. 

Nonrenewable Resource

Natural resources that cannot be replaced at the rate they are being used. Natural gas, coal, and oil are considered nonrenewable resources.

Renewable Resource

A resource, such as oxygen, water, solar energy, trees, and biomass that can be used and replaced naturally. 


A group of living organisms with similar genetic characteristics that enable them to breed with one another.


The classification of living things. Defined by botanist Carl Linnaeus in 1735 using the following categories:

  • ​Kingdom
  • Phylum
  • Subphylum
  • Superclass
  • Class
  • Order
  • Suborder
  • Family
  • Genus
  • Species