lesson 28 changes in the ecosystems
TRANSCRIPT
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.