Transcript Population Ecology

Population Ecology
Why Study Populations?
A population is a group of organisms of
the same species that live in a given area.
Populations are the smallest unit that can
exhibit evolution.
Populations are the foundations of the
earth’s ecosystems.
Population Growth
The environment has a direct impact on
how populations grow and develop.
Population growth can be measured in one
of two ways. Exponential growth and
Logistic growth.
Exponential Growth
Represents the ideal
conditions available
for an organisms
growth.
Rapid increase in the
population.
The larger the
population gets the
faster it grows.
Number of Generations
Logistic Growth
 A type of population
growth that deals with
environmental factors
limiting it development.
 Contains 5 stages.
 Initial Growth
 Exponential Growth
 Slow Growth
 Slower Growth
 Steady State
Factors that Control
Population Growth
Density Dependent Factors
Density Independent Factors
Density- Dependent Factors
When factors that control population size
have more of an effect on larger
populations than smaller ones.
Examples: competition, predation,
parasitism, and crowding.
Competition
When populations are crowded they
compete for the necessities of life.
Competition between members of similar
but different species fuels evolutionary
change.
Example: Two different species of
herbivores (cows and kangaroos)
competing for the same stand of plants.
Predation
Almost every species serves as a food
supply for other species.
Predators kill and eat organisms, while the
prey are eaten.
Prey and predators evolved together over
a long period of time.
This type of relationship keeps an
ecosystem in balance.
Prey Predator Model
Prey Predator Relationship
50
Number of animals /acre
45
40
35
30
25
20
15
10
5
Rabbits
Foxes
0
1920
1930
1940
1950
Years
1960
1970
Parasitism
Parasites live off their host.
They work better in crowded conditions.
Few parasites kill their host.
Crowding and Stress
Most animals need a certain amount of space to
function properly.
Organisms will fight each other for space if they
are over crowded.
Stress causes changes in the normal hormonal
balances in organisms.
Large amounts of adrenaline given off during
stress may cause more fighting and less
breeding, lowering of the immune system,
altered female behavior.
Density- Independent
Factors
These factors are not related to population
size.
Most of them are natural occurrences.
Forest fires, hurricanes, volcanic
eruptions, cold or hot weather, and
drought.
Symbiosis
Relationships between organisms.
Commensalisms: One organism is
benefited and the other is not harmed.
Mutualism: Both organisms benefit from
the relationship.
Parasitism: One benefits and the other is
harmed.