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What determines population?

These resources are our limiting factors. What determines population?. Why can’t we have 1,000,000 students here at Wilson K-8? Space Teachers Supplies Student Behavior. Carrying Capacity.

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What determines population?

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  1. These resources are our limiting factors What determines population? • Why can’t we have 1,000,000 students here at Wilson K-8? • Space • Teachers • Supplies • Student Behavior

  2. Carrying Capacity • Key Point #1: 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 somewhere, based on the food, water, and free space there • Every species has a different carrying capacity. Food, water, and free space are the LIMITING FACTORS that determine carrying capacity

  3. 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?

  4. 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.

  5. 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. 

  6. Population size Dotted line = Carrying Capacity Graph line = Population size at a specific time Time Carrying Capacity • Key Point #2: We can read a carrying capacity graph to predict changes in population size

  7. Population size Time Carrying Capacity • When a population is BELOW its carrying capacity, it will INCREASEin size • Birth rate exceeds death rates

  8. Population size Time Carrying Capacity • But if it increases too much and rises ABOVE its carrying capacity, it will DECREASE in size • Death rate exceeds birth rate

  9. Population size Time Carrying Capacity • When a population is BELOW its carrying capacity, it will INCREASEin size • Birth rate exceeds death rates

  10. Population size Time Carrying Capacity • This happens over and over… but the increases and decreases get smaller and smaller…

  11. Population size Time Carrying Capacity • Until eventually, the population size BECOMES STABLE AT THE CARRYING CAPACITY • Birth rate = death rate

  12. determined by Carrying Capacity Limiting Factors such as above it Food Water Population decreases below it Space Population increases WORD BANK: water, carrying capacity, pop. size increases, limiting factors, food, pop. size decreases, space

  13. What are three factors that limit deer population size? • Why does population size decrease in the highlighted portion of the graph? • At which point does birth rate exceed death rate the most? • What is the carrying capacity of deer on WallaWalla Island? • At which point do deer exceed their carrying capacity?

  14. In what three years does population size most exceed carrying capacity? • Why does the population decrease after 1850? • Why does population size rise again after each big drop? • Identify three periods of time where birth rate exceeds death rate • What is the relationship between population size and carrying capacity between 1800-1840?

  15. Think…Pair…Share CHOOSE ONE, PART A: CHOOSE ONE, PART B: Bears eat salmon. If a disease causes massive amounts of salmon to die, what will likely happen to the bears? Explain why. If a population has exceeded its carrying capacity, what will happen to it? Explain why. • Lions hunt and eat wildebeest. If a hunter enters the grassland and kills all the lions there, what will happen to wildebeest population size? Explain why. • Bald eagles eat vertebrate fish. If humans pollute the water and many fish die, what will happen to bald eagle population size? Explain why.

  16. In 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 somewhere based on these limiting factors • We can read a carrying capacity graph to predict changes in population size • Below carrying capacity = increase • Above carrying capacity = decease • Over time, population stabilizes at carrying capacity

  17. Last example • What is the carrying capacity of rabbits in this ecosystem? • When is the carrying capacity for rabbits first reached? • Why does rabbit population size increase in the highlighted section of the graph?

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