Ecosystems, Populations, and Relationships

Ecosystems & Population

Ecosystems

Ecosystems are complex, interactive systems that include both biological communities (biotic) and physical (abiotic) components of the environment. Organisms and populations of organisms are dependent on their environmental interactions both with living and nonliving factors.

​Ecosystems

As with individual organisms, a hierarchal structure exists; groups of the same organisms (species) form populations, different populations interact to form communities, communities live within an ecosystem, and all of the ecosystems on Earth make up the biosphere. Like individual organisms, ecosystems are sustained by the continuous flow of energy.

​Ecosystems

Ecosystems are dynamic in nature; their characteristics can vary over time. Disruptions to any physical or biological component of an ecosystem can lead to shifts in all its populations.

​Ecosystems

Biodiversity describes the variety of species found in Earth’s terrestrial and oceanic ecosystems. The completeness or integrity of an ecosystem’s biodiversity is often used as a measure of its health.

Multiple Choice

An ecosystem can be defined as _________

• All of the living and non-living things in an area.

• All of the living things in an area.

• All of the populations in an area.

• None of the above.

Ecosystems and Population

​Populations

A population is a group of organisms belonging to the same species that live in a particular area. Populations can be described based on their size, density, or distribution.

Population density measures the number of individual organisms living in a defined space. Regulation of a population is affected by limiting factors that include density-dependent, density-independent, abiotic and biotic factors.

Multiple Choice

In some environments, wolves prey on elk for their source of food. If all of the wolves were removed from the environment, what would likely happen to the population of deer?

• The wolf population would increase if reintroduced to the environment.

• The deer population would increase and become healthier.

• The deer population would decrease, because less fit deer would breed.

• The deer population would increase and start competing for food.

​Limiting factors

Density-dependent factors: Limiting factors that are density-dependent are those that operate more strongly on large populations than on small ones. Density-dependent limiting factors include competition (for food, water, shelter & space), predation, parasitism, and disease. These limiting factors are triggered by increases in population density (crowding).

​Limiting Factors

Density-independent factors Limiting factors that are density-independent are those that occur regardless of how large the population is and reduce the size of all populations in the area in which they occur by the same proportion. Density-independent factors are mostly abiotic (such as weather changes), human activities (such as pollution), and natural disasters (such as fires, hurricane, earthquake).

Multiple Choice

From the following options, select the one that best represents a density dependent factor.

• Predation

• Unusual weather

• Natural disaster

• Human interference

Multiple Choice

From the following options, select the one that BEST represents a density independent factor.

• Predation

• Disease

• Competition

• Natural disaster

Multiple Choice

What happens to a population and to competition when there is a reduction of

living space?

• The population expands and competition intensifies.

• Competition strengthens while the population contracts.

• The population increases as competition decreases.

• Competition weakens and the population decreases.

Multiple Choice

Which best determines the number of wolves that can live in an area?

• the amount of snow in the area each year

• the number of birds that live in the area

• the number of trees in the area

• the amount of food available in the area