1. Ecosystems Part 3
Populations

2. Interactions in Ecosystems
Biotic Interactions:
Symbiosis
Predation
Competition
Battle at Kruger
What interactions are happening here?

3. Competition Intraspecific Competition Interspecific Competition
Members of the same species compete for the same resource in an ecosystem.
Ex: food, light, nutrients, space.
Ex: two wolves compete for a rabbit.
Interspecific Competition
Individuals of different species compete for the same resource in an ecosystem.
Ex: food or living space.
Ex: cheetah and lion compete for zebra.

4. Think about it...
Is there competition among plants?

5. Population
A group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce.

6. Think about it...
If all of the rocks are removed from a desert ecosystem, what would happen to the population of rock dwelling lizards, and in turn the animals which eat them?
A ten mile area of trees is removed from the tropical rainforest. How will this affect the amount of water and the amount of oxygen in the area?

7. Think about it... When does a population increase?
When does a population decrease?

8. Population
The size of the populations are continually adjusted by the species interactions with biotic and abiotic factors.
Populations tend to increase exponentially when there are abundant available resources.

10. Population Growth Exponential growth Accelerating population growth
“J”-shaped graph
Usually only occurs for a short time under certain conditions
Organism finds new habitat with lots of resources
When other pressures are removed (i.e. hunting ban)

11. Population Growth Population growth can’t happen forever.
If resources are used up the species is unable to survive long enough to reproduce.

12. Population Growth As population rises, resources decline.
If the growth is too rapid, resources are rapidly depleted and a population crash can occur.

13. Population Growth
More often what happens is that the resources slowly decrease, the growth rate slowly increases, and they meet.
Carrying Capacity
This is called an s-shaped or logistic curve

14. Population Decline... Swallow Population Decreasing in Canada CBC News
September 15, 2014

15. Limiting Factors
Factors that limit the growth, distribution, or amount of a population in an ecosystem.
As a population increases in size, each individual has access to fewer resources, limiting the growth of the population.

16. Types of Limiting Factors
Density Independent Factors
Do not depend on the number of members in a population.
Usually abiotic factors
Ex: natural phenomena, weather, fires, pollution, etc.

17. Types of Limiting Factors
Density Dependent Factors
Do depend on the number of members in a population.
Usually biotic factors
Ex: disease, parasites, predation, competition

18. Carrying Capacity
The largest population of a species that can be supported by an environment.
Controlled by:
Abiotic factors
Biotic factors
Limiting factors

19. Graphing Carrying Capacity
Population  y axis (vertical)
Time (year)  x axis (horizontal)

20. Graphing Carrying Capacity
If the line of the graph is:
Going up: population is increasing
Going down: population is decreasing
Horizontal (flat): population is at its carrying capacity for that species in that ecosystem.

21. During which months is the population increasing?
What is the carrying capacity of hares in Sackville?

22. When is the population at its carrying capacity?
What is happening to the population?