Mr. Chapman
Biology 20
Norquay School
Biotic & Abiotic Factors
Biotic and Abiotic Factors
All ecosystems are made up of living and non-living components. These parts are referred to as
biotic and abiotic factors.
Biotic factors – living things, such as plants, animals, fungi and bacteria. Each organism plays a
particular role in the ecosystem.
Abiotic factors – nonliving things such as moisture, temperature, wind, sunlight, and soil. The
balance of these factors determines which living things can survive in a particular
environment.
Brainstorm: Come up with a list of biotic and abiotic factors that may be present inside of an
aquarium.
Biotic Factors
Abiotic Factors
Ecosystem Changes
Ecosystem may look similar from one year to the next, with similar numbers of plants and
animals. Ecosystems, however, are always undergoing changes. For example, a long period of
increased precipitation might allow one plant species to grow better than others. As the plant
continues to grow, it may crowd out other plant species, changing the community’s
composition. Though the total number of plants in the community may remain the same, the
Mr. Chapman
Biology 20
Norquay School
Biotic & Abiotic Factors
species have changed. As these cyclic changes occur, an ecosystem falls into a balance, which is
known as an approximate equilibrium.
An ecosystem is a complex web of biotic and abiotic factors. Although
humans do not always consider themselves part of the ecosystem, we do
rely on the environment for survival. All species are affected by changes
to the biotic and abiotic factors in an ecosystem.
Biodiversity
Relationships within an ecosystem are very complicated. Imagine taking a string and connecting
it to every biotic and abiotic factor that you influenced or ever influenced you. Soon, you would
have a massive web of organisms and nonliving things attached to strings, revealing a large
amount of biodiversity.
Biodiversity – the assortment, or variety, of living things in an ecosystem. An area with a high
amount of biodiversity has a large assortment of different species living near one another.
The amount of biodiversity in an area depends on many factors, including moisture and
temperature. Some areas of the world have unusually large amounts of biodiversity. For
instance, tropical rain forests (which are moist and warm environments) cover about a little
under 7% of Earth’s surface. However, these areas account for 50% of the planet’s animal and
plant species. Such an area is referred to as a hot spot.
Mr. Chapman
Biology 20
Norquay School
Biotic & Abiotic Factors
Keystone Species
The complex relationships in ecosystems mean that a change in a single biotic or abiotic factor
(a few broken strings in the web) can have a variety of effects. Sometimes the change might
barely be noticed, but other times it can have a deep impact. In some cases, the loss of a single
species may cause a ripple effect felt across an entire ecosystem. An organism such as this is
known as a keystone species.
Keystone species – a species that has an unusually large
effect on its ecosystem.
One example of a keystone species is the beaver. By felling
trees to construct dams, beavers change free-flowing stream
habitats into ponds, wetlands, and meadows. This
modification leads to a cascade of changes within their ecosystem.
Mr. Chapman
Biology 20
Norquay School
Biotic & Abiotic Factors
A number of things are changed by the work done by beavers. They include the following:
Exercise: Read the first paragraph of page 396, which describes the importance of the Pacific
Salmon. Then, in approximately ½ to ¾ of a page, explain what makes the Pacific Salmon a
keystone species.