What determines population?

1. Three main factors determine whether a population increases or decreases: number of births, number of deaths, or number of individuals that move into or out of an area. • Immigration is the movement of individuals into an area (Into = Immigration) • Emigration is the movement of individuals out of an area (Exit = Emigration)

2. Under ideal conditions, with unlimited resources and space, a population will experience exponential growth. • Actual populations stabilize rather than growing endlessly.

3. These resources are our limiting factors What determines population? • Why can’t we have 50,000 students here at Ballakermeen? • Space • Teachers • Supplies • Student Behaviour

4. Limitations on Populations • There can never be an unlimited number of organisms in a population in an ecosystem. • Why?

5. An ecosystem can only support as many organisms as it has resources and space for • Carrying capacity = maximum number of organisms that can live in one population in an ecosystem over time • Every species has a different carrying capacity. Food and water, space, and predators are the limiting factors that determine carrying capacity for a population

6. Imagine Your Fridge Your fridge is like all of the resources (food, water, free space) in an ecosystem. What if we want to throw a party?

7. Imagine Your Fridge We can keep inviting people, as long as there’s enough food in the fridge. But with each new guest, there’s less to go around.

8. Imagine Your Fridge The fridge won’t replenish magically, and I don’t have the money to keep putting food in the fridge forever. So too many guests means that… So too many animals means that… Someone goes hungry… Not enough food/water/free space… And leaves the party.  And organisms die. 

9. A population growth curve can be used to predict changes inpopulation sizeand to identifycarrying capacity

10. Carrying Capacity • When a population is below its carrying capacity (B), it increasesin size • Plenty of food and space • Birth rate is higher than death rate

11. Carrying Capacity • When a population is above its carrying capacity (A), it decreases in size • Not enough food and space; or too many predators • Death rate is higher than birth rate

12. Carrying Capacity • This happens over and over… but the increases and decreases get smaller and smaller…

13. Carrying Capacity • Eventually, population size stabilizes at the carrying capacity (C) • Stabilizes= stays the same • Birth rate = death rate

14. On what date did the rabbits reach their carrying capacity?

15. Why does the rabbit population increase in the highlighted region?

16. CFU 3 A fire kills grass and other producers in the ecosystem. What will happen to the carrying capacity for rabbits?

17. determined by such as above it below it WORD BANK: water, carrying capacity, pop. size increases, limiting factors, food, pop. size decreases, space

18. Summary • An environment can only support as many organisms as there is available food, water, and free space • Carrying capacity = maximum number of organisms that can live in an ecosystem based on these limiting factors • We can read a population growth curve to predict changes in population size • Below carrying capacity = increase in size • Above carrying capacity = decease in size • Over time, population stabilizes at carrying capacity

19. Exit Ticket • What are three limiting factors that determine the carrying capacity of a population in an ecosystem? • What is happening to the population at point A in the graph and why? • What is happening to the population at point B in the graph and why? • What is the carrying capacity for the population based on the graph shown?

20. 1. When did the rabbits reach carrying capacity? How do you know? • 2. What is happening to the population during June? • 3. What are some potential factors that could limit the rabbit population?

21. Population Growth Practice