POPULATION ECOLOGY
Population - a group of organisms of the same species inhabiting a defined
area so close to each other that random interbreeding takes place
Restrictions:
• individuals in the population must all be the same species
• Individuals in the population must all be in the same defined area
• Individuals in the populations must be able to breed with each other
POPULATION SIZE
Population parameters - the 4 things that can make a population size
change
1. Birth rate/natality - increases the number of individuals in a set time
2. Death rate/morality - decreases the number of individuals in a set
time
3. Immigration - when individuals move into the area from somewhere
else & join the population, increasing the size
4. Emigration - individuals move out of the population area to
somewhere else, decreasing the size
Immigration
Emigration
THE NUMBER OF
INDIVIDUALS IN THE
POPULATION
Natility Mortality
Open population - when all 4 population parameters can happen at the
same time
,Closed population - when its not possible for immigration & emigration to
happen
BIRTH RATE
Natural increase in population due to reproduction
Written as % per unit time
DEATH RATE
Natural decrease in population
Causes of death
- disease
- old age
- predation
Written as % per day/year
Increasing population = positive growth
Decreasing population = negative growth
GROWTH CURVE
Graphs drawn to show how the size of a population changes with time
GEOMETRIC / EXPONENTIAL GROWTH:
Shows population increasing
Lag phase - population numbers increase slowly to begin as there are only
few individuals reproducing
, Accelerating growth phase - the population grows more quickly and the
slope of the graph gets steeper
Limiting factors - anything that tends to slow down increasing growth
- food - space - access to mate
- water - diseases - natural disasters
- space - predation
Eventually, limiting factors will stop the growth of a population completely
Environmental resistance - the effect of limiting factors
Decelerating growth phase - when limiting factors start to have an effect
on population growth and changes the growth curve direction
Equilibrium phase - the level where the environmental resistance and the
reproductive pressure are equal
Carrying capacity - when reproductive pressure and environmental
resistance are balanced
Population - a group of organisms of the same species inhabiting a defined
area so close to each other that random interbreeding takes place
Restrictions:
• individuals in the population must all be the same species
• Individuals in the population must all be in the same defined area
• Individuals in the populations must be able to breed with each other
POPULATION SIZE
Population parameters - the 4 things that can make a population size
change
1. Birth rate/natality - increases the number of individuals in a set time
2. Death rate/morality - decreases the number of individuals in a set
time
3. Immigration - when individuals move into the area from somewhere
else & join the population, increasing the size
4. Emigration - individuals move out of the population area to
somewhere else, decreasing the size
Immigration
Emigration
THE NUMBER OF
INDIVIDUALS IN THE
POPULATION
Natility Mortality
Open population - when all 4 population parameters can happen at the
same time
,Closed population - when its not possible for immigration & emigration to
happen
BIRTH RATE
Natural increase in population due to reproduction
Written as % per unit time
DEATH RATE
Natural decrease in population
Causes of death
- disease
- old age
- predation
Written as % per day/year
Increasing population = positive growth
Decreasing population = negative growth
GROWTH CURVE
Graphs drawn to show how the size of a population changes with time
GEOMETRIC / EXPONENTIAL GROWTH:
Shows population increasing
Lag phase - population numbers increase slowly to begin as there are only
few individuals reproducing
, Accelerating growth phase - the population grows more quickly and the
slope of the graph gets steeper
Limiting factors - anything that tends to slow down increasing growth
- food - space - access to mate
- water - diseases - natural disasters
- space - predation
Eventually, limiting factors will stop the growth of a population completely
Environmental resistance - the effect of limiting factors
Decelerating growth phase - when limiting factors start to have an effect
on population growth and changes the growth curve direction
Equilibrium phase - the level where the environmental resistance and the
reproductive pressure are equal
Carrying capacity - when reproductive pressure and environmental
resistance are balanced
