POPULATIONS & SUSTAINABILITY
A-LEVEL BIOLOGY
MODULE 6
POPULATION GROWTH CURVE
1) Birth rate > Death rate
2) No constraints act to limit population explosion
3) Fluctuations in external constraints (birth rate = death rate)
Exponential growth represented on a logarithmic scale b/C data span several orders of
magnitude
Limiting factors
1
,Period of exponential growth when ideal conditions and maximum growth rate
Abiotic: temp, light, pH, water or O2 availability, humidity
Biotic: predators, disease, competition and migration
Carrying capacity: max. population size an environment can support
Density independent factors
Have an effect on the whole population regardless of its size
Eg. natural disasters such as earthquakes, fires, volcanic eruptions and storms
COMPETITION
Result of interactions btw living organisms
Interspecific: 2 diff species compete for same resources →reduction in resources
available to both populations
- Less energy for growth/reproduction = smaller populations
Competitive exclusion principle
Less well adapted species outcompeted = decline in number so no longer exist in same
habitat as the better adapted species
Species using resources more effectively will ultimately eliminate the other
Intraspecific
Greater availability of resource = larger population supported
- Increase in size increases organism’s survival chance + reproductive success
2
, 1) Plentiful resource = all have enough to survive/reproduce
Increase in population size
2) Many more individuals share food/space available = limited resources so not
enough available for all to survive
Decrease in population size
3) Less competition:
- Smaller populations means less organisms are competing for the same resources
- More survive/reproduce →population growth
This cycle repeats
Predation
Predator kills and eats prey
Interspecific competition operating btw predator and prey species
Predators have evolved to become highly efficient in capturing prey
3
A-LEVEL BIOLOGY
MODULE 6
POPULATION GROWTH CURVE
1) Birth rate > Death rate
2) No constraints act to limit population explosion
3) Fluctuations in external constraints (birth rate = death rate)
Exponential growth represented on a logarithmic scale b/C data span several orders of
magnitude
Limiting factors
1
,Period of exponential growth when ideal conditions and maximum growth rate
Abiotic: temp, light, pH, water or O2 availability, humidity
Biotic: predators, disease, competition and migration
Carrying capacity: max. population size an environment can support
Density independent factors
Have an effect on the whole population regardless of its size
Eg. natural disasters such as earthquakes, fires, volcanic eruptions and storms
COMPETITION
Result of interactions btw living organisms
Interspecific: 2 diff species compete for same resources →reduction in resources
available to both populations
- Less energy for growth/reproduction = smaller populations
Competitive exclusion principle
Less well adapted species outcompeted = decline in number so no longer exist in same
habitat as the better adapted species
Species using resources more effectively will ultimately eliminate the other
Intraspecific
Greater availability of resource = larger population supported
- Increase in size increases organism’s survival chance + reproductive success
2
, 1) Plentiful resource = all have enough to survive/reproduce
Increase in population size
2) Many more individuals share food/space available = limited resources so not
enough available for all to survive
Decrease in population size
3) Less competition:
- Smaller populations means less organisms are competing for the same resources
- More survive/reproduce →population growth
This cycle repeats
Predation
Predator kills and eats prey
Interspecific competition operating btw predator and prey species
Predators have evolved to become highly efficient in capturing prey
3
