Population Control. What makes populations of organisms increasing or decreasing in size… When...
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Transcript of Population Control. What makes populations of organisms increasing or decreasing in size… When...
Population Control
What makes populations of organisms increasing or decreasing in size… When new predators come When organisms leave the food web
But what controls how many organisms exist in a population in the first place?
What determines population? Why can’t we have 1,000,000 students here at Union Grove Middle? Space Teachers Supplies Student Behavior
These resources are
our limiting factors
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
Your fridge is like all of the resources (food, water, free space) in an ecosystem.
What if we want to throw a party?
Imagine Your Fridge
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.
Carrying Capacity
Key Point #2: We can read a carrying capacity graph to predict changes in population size
Time
Population size
Graph line = Population size at a
specific time
Dotted line = Carrying Capacity
Carrying Capacity
When a population is BELOW its carrying capacity, it will INCREASE in size
Birth rate exceeds death rates
Time
Population size
Carrying Capacity
But if it increases too much and rises ABOVE its carrying capacity, it will DECREASE in size
Death rate exceeds birth rate
Time
Population size
Carrying Capacity
When a population is BELOW its carrying capacity, it will INCREASE in size AGAIN!
Birth rate exceeds death rates
Time
Population size
Carrying Capacity
This happens over and over… but the increases and decreases get smaller and smaller…
Time
Population size
Carrying Capacity
Until eventually, the population size BECOMES STABLE AT THE CARRYING CAPACITY
Birth rate = death rate
Time
Population size
determined by
such asabove it
WORD BANK: water, carrying capacity, population increases, limiting factors, food, population decreases, space
below it
Carrying Capacity
Limiting Factors
Space
WaterFoodPopulation decreases
Population increases
RECAP…
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
On a piece of paper…
CHOOSE ONE, PART A: 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.
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.