1. Limits on Populations and Communities in Ecosystems
Who Eats Who part 5
Limits on Populations and Communities in Ecosystems

2. Biotic Potential
Biotic potential – is the maximum number of offspring that a species could produce with unlimited resources.
There are 4 factors that influence biotic potential:
Birth potential
Capacity for survival
Breeding frequency
Length of reproductive life
Poccket INB

3. Birth Potential The maximum number of offspring per birth.
Ex. Whooping cranes lay two eggs per year and usually only one chick survives.

4. Capacity for Survival
The number of offspring that reach reproductive age.
Ex. The female sea turtle lays many eggs, but only a few of her offspring even reach the sea and fewer still reach maturity.

5. Breeding Frequency
The number of times that a species reproduces each year.
Ex. Elk mate only once per year, during the fall.

6. Length of Reproductive Life
The age of sexual maturity and the number of years the individual can reproduce.
Ex. African elephants reach sexual maturity at about 15 years of age, but may reproduce until they are 90.

7. Limiting Factors Factors that cause a population to increase
Factors that cause a population to increase
Factors that cause a population to decrease
Abiotic
favourable light
too much or too little light
favourable temperature
too cold or too warm
favourable chemical environment
unfavourable chemical environment
Biotic
sufficient food
insufficient food
low number of predators
high number of predators
few or weak diseases and parasites
many or strong disease and parasites
ability to compete for resources
inability to compete successfully for resources

8. Carrying Capacity
Populations commonly fluctuate because of an interaction of the many biotic and abiotic limiting factors.
However, the ecosystems are able to remain in equilibrium, when none of the populations exceed the carrying capacity.
Carrying capacity – the maximum number of individuals of a species that can be supported by an ecosystem.

9. Limits of Tolerance
In the mid-1800’s, Justus von Liebig noted that certain substances must be present in order for plants to grow.
He found that if any one of these substances is present in low amounts, the growth of the plant is reduced, regardless of the quantity of other substances.
This became known as the law of the minimum: the nutrient in the least supply is the one that limits growth.

10. In 1913, Victor Shelford added to von Liebig’s work by noting that too much of a factor can harm an organism.
This principle is called Shelford’s law of tolerance, which states that an organism can survive within a particular range of an abiotic factor.

11. A species maximum population size is possible when an abiotic factor is at an optimum or an ideal within the range of tolerance.
However, many abiotic factors act on a species at any given time.
Most species have a broad range of tolerance for some factors and a narrow range for others.

12. Density-Independent Factors
Density-Independent Factor – a factor in an ecosystem that affects members of a population regardless of population density.

13. Density-Dependent Factors
Density-Dependent Factor – a factor in an ecosystem that affects members of a population because of the population density.

14. Factors that Cause Changes in Populations
Density-independent factors
Density-dependent factors
flood
food shortage
fire
competition for mates, breeding areas
spraying with pesticides
habitat
change in climate or temp.
disease
destruction of habitat
introduction of exotic species
drought
increased predation
competition for water and other resources