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

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. 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 as above it WORD BANK: water, carrying capacity, population increases, limiting factors, food, population decreases, space below it Carrying Capacity Limiting Factors Space WaterFood Population 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.