Changes in theEcosystems

Populations

• There are different characteristics that refer to the group of individuals or population in an ecosystem:

• Size of the population (Number of individuals)

• Density (Number of individuals/km2)

• Age distribution

Changes in Populations

• Population size, density or age distribution may vary. Populations are represented with population pyramids.

• We find 3 types of populations according to their growth:

Biotic potential

• Populations vary in their capacity to grow.

The maximum rate at which a population can increase when resources are unlimited and environmental conditions are ideal is termed the population's biotic potential.

Unlimited resources

Maximum growthrate

No predators

Variations in biotic potential

• Each species will have a different biotic potential due to variations in :

1. “Litter size“: how many offspring are born each time.

2. The breeding frequency : how often an individual can reproduce.

3. The species' reproductive span: how long an individual is capable of reproducing.

4. Survival rate: how many offspring survive to reproductive age.

Factor Rabbit Horse

Litter size High: 4-10+ Low: 1

Breeding frequency High: 30 days Low: 11 month

Reproductive span Short Long

Survival rate Poor Good

Biotic High Low

Potential

Unrestricted growth or J growth

• Ilimited resources.

• However, there are always limits to population growth in nature. Populations cannot grow exponentially indefinitely.

Environmental resistance

• Exploding populations always reach a size limit imposed by the shortage of one or more factors such as water, space, and nutrients or by adverse conditions such as disease, drought and temperature extremes.

• The factors which act jointly to limit a population's growth are termed the environmental resistance.

https://www.wou.edu/las/physci/ch371/lecture/popgrowth/carrying.htm

S growth of the population or Logistic growth

• Resources are limiting.

• The population increases untilit reaches it’s carrying capacity

Maximum number of individuals of a given species that an area's resources can sustain indefinitely without significantly depleting or degrading those resources.

• Below carrying capacity, populations normally increase.

• Above carrying capacity populations usually decrease.

https://www.wou.edu/las/physci/ch371/lecture/popgrowth/carrying.htm

Logistic growth

Population Growth

Regulating factors

• A factor that keeps population size at equilibrium is known as a regulating factor.

• Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight.

• The carrying capacity of an environment may vary for different species and may change over time due to a variety of factors, including: food availability, water supply, environmental conditions and living space.