Population Ecology ch20

Populations Population is the number of individuals in a certain location at a given time Population is the number of individuals in a certain location at a given time Factors that effect the population: Factors that effect the population: Immigration- IN – organisms moving in Immigration- IN – organisms moving in Emigration- EXIT – organisms moving out Emigration- EXIT – organisms moving out Death – fewer organisms Death – fewer organisms Birth – more organisms Birth – more organisms

Growth Rate Can be exponential:  Can be exponential:  Usually is calculated by: Usually is calculated by: Birth rate – death rate = growth rate Birth rate – death rate = growth rate If it is positive, then the population is growing If it is positive, then the population is growing If it is negative the population is shrinking If it is negative the population is shrinking

Why do populations stop growing exponentially?

Limiting Factor – something in the environment that limits the growth of a population Resources: Resources: Food, water, shelter, mates Food, water, shelter, mates Preditors Preditors Waste accumulates Waste accumulates Disease or injury Disease or injury

Carrying Capacity – the number of individuals an area can support for a long time This depends on limiting factors This depends on limiting factors Logistic growth curve: Logistic growth curve:

So…. In summary, What happens to a population when it gets too big? In summary, What happens to a population when it gets too big? Over use of resources = dies Over use of resources = dies Too much waste, poison = dies Too much waste, poison = dies Many individuals die, allowing resources to come back = life at a smaller population Many individuals die, allowing resources to come back = life at a smaller population

Energy Pyramids

Counting calories Every organism needs a certain amount of energy to be alive. Every organism needs a certain amount of energy to be alive. Once you are grown, if you eat more you gain weight and if you eat less you lose Once you are grown, if you eat more you gain weight and if you eat less you lose The average high school student should eat between 2000 and 3000 calories a day, adults The average high school student should eat between 2000 and 3000 calories a day, adults Animals are the same way: Animals are the same way:

Each organism only has so much energy available to it. Each organism only has so much energy available to it. 90% is lost 90% is lost SO…. Why are big, fierce animals rare? SO…. Why are big, fierce animals rare?