These notes provide information on the topic of population ecology for IEB grade 12 Life Sciences. These notes include information on growth forms, ecological succession and human population graphs.
- Natality (birth rate)
- Mortality (death rate)
- Immigration (movement into an area)
- Emigration (movement out of an area)
If there is a fence or the immigration and emigration cannot happen then it is a closed population
Various counting techniques are used to determine population size
Census (direct method)
- Each individual organism is counted
- This is done using aeroplanes, helicopters and/or aerial photographs
Mark and recapture (indirect method)
- Individuals in an area are captured and marked
- The individuals are then released
- The animals are recaptured after some time (not enough for births and deaths to occur)
- The number of marked individuals is noted
- Population size is determined using the formula
¿ individuals captured ∈1 st sample × individuals captured∈2 nd sample
- Population
number of marked individuals∈2nd sample
Quadrat (indirect method)
- A square of known size is placed in an environment of known size
- The organisms within the square are counted and divided by the size of the area
- This method is repeated in random places within the environment
- Population size is determined using the formula
surface area of environment
- Population ¿ average organisms per quadrat ×
surface areaof quadrat
, Population Ecology
Population Growth
Geometric Growth (exponential growth)
Occurs when there are no predators, full reproductive potential and unlimited resources
- Ie: ideal environmental conditions
There is a distinct J shape population curve
- Slow start with a sharp rise
- Often a sudden standstill when conditions become unfavourable
- When conditions improve the cycle starts again
This growth form is often associated with bacteria, insects and fungi
Logistic Growth
Limiting factors change geometric growth the logistic growth
It begins with a few young individuals
There are 4 phases of growth
- Lag phase: individuals acclimate, reach sexual maturity and go through gestation
- Accelerating phase: natality is higher than mortality
- Decelerating phase: environmental resistance increases but natality higher than mortality
- Equilibrium phase: the population has reached carrying capacity and natality = mortality
This happens over a long period of time and once equilibrium is reached the population fluctuates
This growth form is characteristic of vertebrates
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