Population Growth:Lag Phase:• Little or no population growth• Period of adaptation or preparation for growth.Exponential Phase:• Birth > death• No factors limiting growth.• More individuals available for reproduction.• True exponential growth is only usually seen in cell populations.• Cannot last forever. Stationary Phase:

• Birth = death• CARRYING CAPACITY - This is the maximum size population a particular environment can support.

Death Phase:• Birth < death• Occurs when all resources have been used up.

Population Growth:Environmental Resistance:All the factors that may limit (slow down) population growth. How many can you think of?

This S-shaped curve is typical for species colonising new habitats.Populations enter the death phase if one factor becomes in short supply.

Available food Predation Parasitism Disease

Overcrowding Competition Accumulation of toxic waste Weather

Once a population has been established then birth and death rates usually affect population growth.IMMIGRATION and EMIGRATION could also play a part!What is the difference between emigration and migration?

Limiting Population Growth:There are two types of factors that can slow down growth or cause a population crash!DENSITY DEPENDENT FACTORSDENSITY INDEPENDENT FACTORS

Density Dependent Factors:Effect increases as the size of the population increases! Accumulation of toxic waste Disease Parasitism Sometimes food supply

Density Independent Factors:Factors have the same affect on organisms no matter how many there are! Usually sudden or violent abiotic factors – floods, fires, etc

Fluctuation in Numbers:Population size is usually regulated by the balance between birth and death rate.This does not mean that the number of individuals stays exactly the same, just that the population has reached EQUILIBRIUM.What is equilibrium?

Most populations have numbers that fluctuate near an equilibrium point known as the SET POINT.What will happen if the population rises above this set point?What will happen if the population falls below this set point?If the population rises above this set point then a density dependent factor usually increases MORTALITY or reduces breeding so the population declines.If the population falls below the set point then environmental resistance is temporarily relieved so that the population can rise again.

Populations may fluctuate on a regular basis in a predictable manner.Can you think of reasons why?

Patterns in weather, such as rainfall or temperature may cause fluctuations (e.g. annual).

These population oscillations are regulated by a process called

NEGATIVE FEEDBACK.

Competition:All organisms have to struggle to survive! Plants compete for light, space, water and nutrients. Animals compete for food, shelter, space and mates.There are two types of competition:• INTRASPECIFIC COMPETITION• INTERSPECIFIC COMPETITION

Intraspecific competition:• Competition between individuals of the same species.• Density dependent type of competition because more individuals means less resources.

Interspecific competition:• Competition between individuals of different species.• Usually between species occupying the same or similar niches within an ecosystem.• Two species cannot occupy the same niche in a specific habitat!