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Introduction to ecology review

Key terms

EcologyThe study of how organisms interact with one another and with their physical environment
BioticLiving, or once living, factor in an ecosystem
AbioticNon-living factor in an ecosystem
OrganismAn individual living thing
SpeciesA group of similar organisms that can mate and produce fertile offspring
PopulationA group of individuals that belong in the same species and live in the same area
CommunityAll the populations of all the different species that live together in a particular area
EcosystemAll the organisms that live in a place, along with their physical environment
BiosphereAll of the ecosystems on Earth
BiodiversityThe variety of organisms in an ecosystem


Ecology is studied at many levels and has grown increasingly important as technological and environment impacts have grown. We need to understand ecology so that we can design sustainable methods that reduce negative impacts on biodiversity.

Biotic and abiotic factors

Ecosystems are influenced by both biotic and abiotic factors.
Biotic factors include animals, plants, fungi, bacteria, and protists. Some examples of abiotic factors are water, soil, air, sunlight, temperature, and minerals.
For example, red pandas are distant relatives of raccoons and are found only in the eastern Himalayas. They spend most of their time in trees and eat a primarily vegetarian diet.
In recent years, the red panda population has dropped significantly, leading conservation groups to classify it as a vulnerable or endangered species.
Image credit: Red panda almost falling off by Sander van der Wel, CC BY-SA 2.0
Biotic factors, such as logging of trees and introduction of diseases from domestic dogs, played a major role in the decline of red panda populations. Although abiotic factors have been less important to date, changing temperatures could cause further habitat loss in the future.
Understanding the biotic and abiotic factors responsible for the decline in red panda numbers helps ecologists form conservation plans to protect the species.

Levels of ecology

Ecologists often work at five broad levels, sometimes discretely and sometimes with overlap: organism, population, community, ecosystem, and biosphere.
Ecosystem levels. Image from Wikimedia, CC BY 4.0
From smallest to largest:
  • Organism: Organismal ecologists study adaptations, beneficial features arising by natural selection, that allow organisms to live in specific habitats. These adaptations can be morphological, physiological, or behavioral.
  • Population: A population is a group of organisms of the same species that live in the same area at the same time. Population ecologists study the size, density, and structure of populations and how they change over time.
  • Community: A biological community consists of all the populations of different species that live in a given area. Community ecologists focus on interactions between populations and how these interactions shape the community.
  • Ecosystem: An ecosystem consists of all the biotic and abiotic factors that influence that community. Ecosystem ecologists often focus on flow of energy and recycling of nutrients.
  • Biosphere: The biosphere is planet Earth, viewed as an ecological system. Ecologists working at the biosphere level may study global patterns—for example, climate or species distribution—interactions among ecosystems, and phenomena that affect the entire globe, such as climate change.

Common mistakes and misconceptions

  • Dead organisms are not abiotic. Some people think that if an organism is no longer alive, it cannot be considered biotic. However, if something used to be alive, or was part of a living organism (such as a bone, or hair), it is still considered biotic.
  • Populations and communities are not the same. Although some people use those terms interchangeably at times, in biology, these terms have specific meanings. Populations consist of only one species in an area, while communities encompass multiple species.
  • Some people think that the loss of a few species is not a big deal. However, this could not be further from the truth! Biodiversity is crucial to the success of our planet because each species, no matter how big or how small, has an important role to play.
    In addition, a richer biodiversity allows organisms and ecosystems to adapt to environmental change, and also offers many contributions to medicine and agriculture as well!

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