Download POPULATION GROWTH What determines the size of a population

POPULATION GROWTH
What determines the size of a population and where a population can live?
Available resources  Land, food, Shelter, Predators, Competitors
When these factors are ideal, populations thrive, when they are not, populations
decline and can become endangered.
Population graphs show how populations of organisms change over a period of time.
What is different about the 2 population graphs below?
GRAPH A: EXPONENTIAL GROWTH
This shows a population of bacteria over a time period of 4 h. The bacteria reach
a maximum population of4000 bacteria in 4 h.
REGION
DESCRIPTION
REASON
C
OF GROWTH
A
Increasing
Few animals so
slowly
reproduction is
B
slow
B
C
Increasing at a
More bacteria to
faster rate
reproduce
Increasing
Large numbers
rapidly
of bacteria
reproducing (eg.
1000 reproduce
 2000)
A
This is called EXPONENTIAL GROWTH. The bacteria appear to be growing
rapidly and do not seem to be limited by resources. However, most ecosystems
have limited resources and therefore, it is not possible for populations to grow
exponentially forever.
Graph B: LOGISTIC GROWTH
This shows a population of water fleas over a time period of 160 days. The water
fleas reach a maximum population of 135 fleas in 90 days and maintain this
population.
C
B
A
REGION GROWTH
A
Few organisms reproducing  slow growth
B
More organisms reproducing  rapid growth
C
# Organisms born = # organisms dying  stable (no increase or
decrease in population) This is known as a balance or equilibrium.
A population will remain stable but fluctuate slightly at C, the CARRYING
CAPACITY  the number of organisms that an ecosystem can support (without
causing harm to the environment)
A population will remain stable but fluctuate slightly at the CARRYING CAPACITY.
LIMITING FACTORS  Factors that place an upper limit to the size of a population.
They can be abiotic or biotic.
FOOD, SPACE and other important resources (sunlight, water, nutrients in the soil) DECREASE because
they are shared between more organisms  increases death rate  decreases population.
COMPETITION between organisms with the same niche increases  increases death rate  decreases
population.
PREDATION increases because it becomes easier to hunt and catch prey  increases death rate 
decreases population.
DISEASE spreads more easily in crowded environments.