Science Focus Topic 6 Notes: Succession and Change in Ecosystems | Print |
The gradual process by which some species within an ecosystem replaces other species is called succession.

Primary succession
is the gradual growth of organisms in an area that was previously bare ? like a rocky slope. Organisms to first appear are those that can cling to the rock and grow, such as mosses and lichens. These organisms break down the rock and died. Other organisms use the nutrients to begin to grow.

Examples of areas in which a community has never lived before would be:

  • new lava or rock from a volcano that makes a new island or a new landscape
  • a sand bar that arises from shifting sands in the ocean
  • exposure of igneous rock surfaces by a land slide
  • a meteor makes a depression that fills with rainwater or fresh water from underground streams.
Secondary Succession

The gradual growth of organisms in an area after a disturbance, such as a fire, or when a large tree falls, is known as secondary succession.

Changes Caused by Human Activity

Humans affect the environments around them in many ways, including activities and technologies such as: forestry, industrial processes, transportation, urban development, construction and farming. When an ecosystem is changed by human activity, there can be unexpected consequences.
Some species thrive when change occurs (eg.
Cowbirds), while some species suffer (eg. Warblers )

Some Species Adapt Better Than Others


Cowbirds adapt to farmland easily,
while others cannot.


The coyote has been able to adapt to the spread of urban areas, whereas other animals, such as the wolf have not

Pest Control

Pests that can affect human health and crops are a major problem. Besides controlling the pest population a pesticide can also damage other organisms that are not targeted. This occurs with a pesticide that is designed to kill lygus bugs (who damage canola crops). The pesticide will also kill bees. If the pesticide kills the pest predators, then the pest population may actually increase.

Biological Control

Using their own natural enemies is another way to control pests. This method is known as biological control

Introduced Species

Biological control can however cause other problems. The species that is introduced may have no natural predators and will overtake the area (using up the food supply) so that other organisms cannot survive.

This happened when zebra mussels were introduced into the Great Lakes. It has become a major problem.

Introducing a species not natural to a particular area
can cause more problems than what it solves.

Purple loosestrife ? sometimes called the ?beautiful killer? ? was introduced into North America has taken over valuable wetland habitat, pushing out native species.

Species In Danger

Many species in North America and in Canada specifically are in danger of
extinction. If a species becomes extinct, it can no longer be found anywhere in the world. Sometimes the organism is only lost in a large region. If this occurs, the species is extirpated. If a particular species is in danger of becoming extinct, or extirpated, it is placed on the endangered species list. There are special protection programs and laws made to protect endangered species.
Canada?s Endangered Species
Alberta?s Endangered Species

How Can You Help?

Recovery programs are in place or being developed to assist the species with repopulating an area. Volunteering to help is a great way to get personally involved.
Learn More at Alberta Government Website
Sustainable Resource Development