1. Biotic and Abiotic Population Influences within Ecosystems
Limiting factors
Tolerance
Biotic & Abiotic population influences
Symbiosis
Predator-Prey relationships
Population equation
Exponential growth

2. Limiting Factor
Abiotic factors determine where a species can live (temperature, precipitation, etc.)
Biotic factors determine the species’ success (number of predators, available food, etc.)
A limiting factor is any factor that places an upper limit on the size of a population.

3. Examples of limiting factors:
Availability of water & food would affect how many, if any, organisms can live in an area
Predators to an area would affect the number of organisms (prey) living in the area
Temperature of the area affects which animals live there (ex., polar bears will not be in a desert because they would overheat)

4. Factors that limit one population in a community may also have an indirect effect on another population.
Example:
lack of water limits the growth of flowers
less flowers = less food for caterpillars  less caterpillars
less caterpillars = less food for frogs  less frogs
less frogs  less snakes
less snakes  less owls

5. Tolerance
The ability of an organism to withstand a range of biotic and abiotic factors.
Different species have different ranges of tolerance.

6. Tolerance Optimal Zone = best conditions for the organism to survive
The further you go from the optimum zone, the lower your population

7. The range of tolerance are the conditions that the organism can continue to exist in.
Outside the range of tolerance, the organism will not survive.

8. Abiotic Impacts on the Biomes of the World

9. Biotic Influences
Carrying capacity - number of organisms of one species that an environment can support indefinitely (forever).

10. Do all organisms get along with each other?
How organisms live together in an ecosystem is called symbiosis.
There are 3 types of symbiosis:
Mutualism
Parasitism
Commensalism

11. Mutualism Both species benefit from the relationship.
E.g. Clown fish and sea anemones. Clown fish are protected from predators by the stinging tentacles of the sea anemones and in return, the anemone receives protection from animals that would prey upon it.

12. Parasitism One species benefits at the expense of another species.
Parasites usually don’t kill their host (the animal they live on). Why would they kill the thing that is providing them food and a home?
Example – ticks on a dog
A tick is a parasite that feeds off the nutrients in the dog’s blood. The dog doesn’t get the nutrients so it is harmed.

13. Commensalism
Occurs when one species benefits from a partnership (gets food, protection, etc.) without benefiting or harming the other.
E.g.   Tigers and golden jackals. These jackals will attach themselves to a particular tiger, trailing it at a safe distance in order to feed on the big cat's kills.

14. Symbiosis: Mutualism, Commensalism, and Parasitism

15. Predator – Prey Relationship
Predator – a type of consumer that will seek out and eat other organisms.
Prey – the animal that the predator eats.
Examples – cat & mouse; lion & antelope

16. Predator – Prey!!

17. Predator – Prey Relationship
In many cases they act to regulate each other.
E.g. If there are more predators, the population of prey will decrease. If prey numbers decrease, there is less food for the predators so their population decreases.

18. Predator = Lynx, Prey = Hare
Predator = Wolf
Prey = Moose

19. Population Factors How a populations change (increase or decrease)
Natality (Births)
Mortality (Deaths)
Immigration (Animals coming in)
Emigration (Animals leaving)

20. The Population equation
Population Factors
The Population equation
New Population =
Old Population + Natality + Immigration – Mortality – Emigration

21. Exponential Growth
Rapid, uncharacteristic growth which only occurs under certain circumstances for a short period of time
Can be seen when an organism enters a new habitat that has a lot of resources or when predators are removed

22. E.g. In South Africa, elephants became protected after many years of hunting for their tusks. This graph shows the result of the hunting ban instituted in 1960.