24.1 population size

3 main phases of a population growth curve

phase 1 - a period of slow growth. The small number of individuals that are initially present reproduce increasing the total population. As the birth rate is higher than the death rate. the population increases in size

phase 2 - a period of rapid growth. As the number of breeding individuals increases, the total population multiplies exponentially. No constraints act to limit the population explosion

phase 3 - a stable state. Further population growth is prevented by external constraints. During this time the population size fluctuates but its overall size remains relatively stable. Birth dates are death rates are approximately equal

examples of limiting factors

abiotic factors - the non-living factors including temperature, light, PH, availability of water or oxygen, humidity

biotic factors - these living factors include predators, disease and competition

carrying capacity

the maximum population size that an environment can support is known as its carrying capacity

immigration

the movement of individual organisms into a particular area increasing population size

emmigration

the movement of organisms away for a particular area decreases population size

density independent factors

factors that have an effect on the whole population regardless of its size

eg. earthquakes, fires, volcanic eruptions, and storms