Ecology is the study of organisms, their relationships with their surroundings, and their relationships with other organisms. Something important to remember in ecology is that every element of a system is dependent on, and could not exist, without the other elements of that system. Everything is intertwined. The action of one organism creates consequences for all other organisms, either directly or indirectly. The world exists in a very delicate balance. Ecology studies how this balance is achieved, maintained, disrupted and regained.

The Basics of Ecology

Ecosystems and Communities

Based on climate and vegetation distributions, ecologists have divided the world into ecosystems based on the living and non-living functions in a system. Examples of ecosystems include grasslands, tropical forests and deserts.   An ecosystem is made up of communities - relationships between plants and animals living together.   Ecology studies the structure and function of the communities within these ecosystems.

Communities will differ from one location to the next, due to many factors such as: climate, soil types, types of plant species, and the types of animals that inhabit the area.  One such type is an island community; an isolated patch that is geographically separated from other similar areas. Such islands can occur naturally (as with actual islands), but most are either fragmented by man-made forces (such as clear-cutting or road creation), or by natural forces such as floods.  In island patches, the extinction rate is higher and genetic diversity slowly decreases with no injection of new species.

Edge communities are another type of community. Here diversity is greater than in islands, as edge communities are actually the meeting grounds for two communities. Edge communities have greater traffic flow than island communities because they are not isolated, and consequently there are more plant and animal species.

Within communities, there are interactions between plants and animals, plants and other plants, and animals with animals. Most of these interactions will take place in the form of competition, predation, parasitism and disease, and mutualism. Competition occurs when two or more niches (the role a species occupies in a community) overlap or when resources become scarce. The ability to be a successful competitor means survival in the community.

There are two types of competition.  The first, intraspecific competition, occurs between members of the same species. The second, interspecific competition, occurs between members of different species. Both of these may include the exploitation of resources, or interference by one member to prevent other members from attaining any resources. For example, weeds are very competitive plants.  They aggressively gain control of resources and establish roots and shoots quickly so as to prevent the establishment of other species.

Predation can impact the composition and numbers of different species in a community, especially in a competitive community or when resources are scarce. Predation is necessary in a community to keep species population numbers in check.

The effects of parasitism and disease on a community become very clear when there is an outbreak of either phenomenon. Many times outbreaks occur when the numbers of one species have grown chaotically, and the environment can no longer support it. When this happens, the area is said to have reached its carrying capacity. The clearing of land and the introduction of exotic species can also unleash parasites and disease.

Mutualism describes a relationship between two species where both can benefit; this type of interaction is very important to the survival of both species.   An example of this is flowers and honeybees - the bees get their nectar for honey from the flowers, and the flowers have a transportation method to distribute their pollen to pollinate other flowers.

Grasslands: A Major Ecosystem in the Qu'Appelle Valley

"At one time grasslands covered about 42 percent of the land-surface of the world, but now most of that area is under cultivation." (Smith 1996)

Most grasslands share the following characteristics:

  • High evaporation rates
  • Droughts
  • An almost essentially flat landscape
  • Inhabited by grazing and small burrowing animals
  • Low precipitation
  • High summer temperatures

Grasslands are very productive ecosystems when adequate moisture is present.   Grass species are the dominant plants of grasslands, and they will either grow in mats or bunches.   Other plants common to grasslands are various types of herbs. Very few woody species such as trees grow in a grassland, and any species that do grow will be somewhat stunted due to the temperature and moisture variances. All species that grow in this ecosystem must possess a high degree of drought tolerance due to the low and varying precipitation patterns of grasslands.   These plants will usually have deep roots so to reach the groundwater deep in the soil.   In fact most of a plant's mass is underground in its roots.   Some plants may have roots extending over 1 metre into the soil!   In a grassland, the thick cover of plants with deep roots hold the soil in place so soil erosion is significantly reduced.

The plants forming a grassland's cover usually do not grow very tall.   However, with this cover, the air close to the ground is still and provides a cooler environment than the air above. On grazed lands, where the cover is much shorter, the ground temperatures are higher and air currents are swifter.   As the growing season of the prairies progress, shorter species plants give way to taller ones, and the cover becomes diversified in height and composition.   The diverse vegetation of the grasslands supports a wide variety of herbivores such as grasshoppers, mice, rabbits, deer, and in the past bison.  

With a short warm season and with an abundance of vegetation that grows and dies and each year, a ground cover of dead plants builds up. The decomposers cannot breakdown all the plants that die each year. This litter ties up a great deal of grassland nutrients - it takes about 3 to 4 years before a grassland's organic matter will entirely decompose.   Here wildfires actually become periodically necessary as fires reduce this litter cover. Animals that graze will also help in litter reduction. By suppressing fires and grazing, the fuel will accumulate and a large, disastrous fire may occur.   Grassland management is vitally important if grasslands are to be conserved.

Wetlands - An Important Ecosystem

The Qu'Appelle Valley is heavily populated with wetlands, so it is necessary to understand their importance.   Wetlands provide many necessary services to nature and man. They:

  • Provide homes and food for water fowl, fish, reptiles and wildlife
  • Enhance the quality of water through filtering and reducing toxics, pollutants and over-abundant nutrients
  • Reduce flooding by storing rain water and overflows from rivers
  • Feed groundwater supplies


Diversity is a very important feature that impacts a community's survival.  Diversity is described as the community's abundance of different species of organisms and differing genes.  Diversity is affected by the age of a community, the variety of the environment, the climate, predation and disturbances.  The higher the diversity of an area, the easier it is to bounce back from changes such as a diseases. However, a community with low diversity can be easily destroyed by a change, and it has a less likely chance of recovering. Crop fields are a good example of low diversity communities - with only one or two crops produced, they are susceptible to disturbances such as diseases.   With higher degrees of diversity come increased gene pools. This increases a community's chances of survival through disturbances and other changes.   Increased diversity also increases a species' chance of adapting to new and changing environments.  Adaptation is key as only those who can adapt to can survive.


As previously mentioned, disturbances bring change to an ecosystem and are a natural necessary physical force. Disturbances create new community possibilities because they create room for new species to move in.   Disturbances are characterized by their intensity, frequency and scale.  Disturbances can be caused by fire, disease, over-grazing, forestry, mining, farming, landslides and glacier movement.  The Fort Qu'Appelle Geolog Tour shows that the Qu'Appelle Valley is the product of massive disturbances - it underwent at least four ice ages in which large glaciers cut through the valley, producing different effects with each ice age.  Disturbances vary in size; they may be large like a glacier or may be as small as a dog digging a hole in the yard. Examples of these disturbances exist all around. Stop 4 on the Fort Qu'Appelle Geolog Tour is an example of a recent disturbance because the land was cleared to extract gravel for a gravel pit.  


After a disturbance occurs, the community undergoes succession, which is the sequential replacement of one community by another. Communities are constantly progressing toward a stable, terminal community called the climax community. Each step along the way to the climax community is called a sere, and each seral stage is considered a separate community. Some seral stages will be quick, others may last so long that they seem to be the climax community. The climax community, while experiencing small-scale changes, will exist until a disturbance occurs again. Then the succession cycle will repeat itself. The climax community is achieved when succession slows down and the community reaches a state of stability and self-maintenance. Anytime along the process towards a climax community, a disturbance can occur that will start succession over again. The first plants to settle into a disturbed site are called pioneer species. These species prepare the site for later succussion plants to come in. Trembling aspen is an example of a poineer species in wooded communities, as it establishes quickly after a fire goes through.

Overall, the Qu'Appelle Valley may seem to have reached the level of climax community, as the last ice age ended 14,000 years ago.  However, varying stages of succession are occurring in many of the local communities in the valley due to constant disturbances such as flooding and increased human activity. For example, Stop 4 is in the first stages of succession with many weedy species establishing themselves. Unfortunately Stop 4 will stay in the primary stages of succession as long as activity continues in the gravel pit.   However, behind the gravel pits later succession stages have begun, and these are closer to achieving a climax community.  Can you spot any other examples of disturbances and succession among the stops from their pictures on this website?

There are two types of succession. The first is primary succession and occurs in areas that have not been occupied before, such as gravel, bedrock, or alluvial deposits like those Fort Qu'Appelle was built on.  After the ice retreated from the Qu'Appelle valley, primary succession would have occurred. The second type is secondary succession and it occurs where other organisms are already present. Secondary succession is the result of vegetation disturbance by humans, animals or nature.

Energy Flow in an Ecosystem - The Food Chain

Energy enters the system from the sun.   Photosynthetic plants and algae (primary producers) harness the sun's energy to convert water and carbon dioxide into carbohydrates, a process called photosynthesis. Plants with roots and algae also utilize the nutrients from soil and water to grow. These primary producers supply food to the primary consumers (herbivores), who in turn feed the secondary consumers. Secondary consumers, such as coyotes, in turn feed the tertiary consumers. Secondary and tertiary consumers are carnivores. Some organisms, such as humans are actually all three: primary, secondary and tertiary consumers and are referred to as omnivores. Decomposers, living in soil and water, feed on the dead decaying organic matter from all levels. Decomposers return the nutrients to the soil and water, which the primary producers take up and use.  This is called the food chain.  

At each level of consumption, the available energy gained from the food decreases. For example, a caterpillar that consumes a plant receives a high degree of energy. It uses the majority of the energy doing daily activities, but stores some energy for later growth. A bird then eats the caterpillar, but most of the initial energy was already used by the caterpillar, so the bird receives less energy than what was originally available. It would, in these terms, seem more efficient to skip a step and simply eat the primary producer. However, when looking at the food chain as a whole, skipping steps would prevent higher levels from receiving the nutrients they require. The food chain exists as a fragile system, and each level exists in delicate balance with every other level. By not sustaining the food chain and damaging the environment, humans can produce long-lasting ill effects on the environment that in turn will only hurt ourselves.

**The above information was compiled from Archibold 1995; Martin 1996; Miller 1998; and Smith 1996. Fuller details about these references are listed on the Reference page.

Page last updated on 2004-10-08
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