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.