Summary Population studies - IEB syllabus

POPULATION STUDIES
Ecology  the study of the interactions of organisms with their physical and
biological environments
Population ecology  concerned with the irregular rising and falling size of a
population, and both the physical and social aspects that regulate these fluctuations




FACTORS AFFECTING SIZE OF A POPULATION
 Natality – birth rate in animals or the production of
seeds in a plant
 Mortality – death rate
 Immigration – individuals moving (In)to a population and
stay
 Emigration – individuals leave (Exit) a population and do
not return
 Humans  birth rate, number of births per 1000 people
peryear
 death rate, number of deaths per 1000
people peryear
 Populations grow when birth and immigration exceed
death and emigration
 Populations decline when death and emigration exceed
birth and immigration
 Remain stable when birth and immigration
approximately equal death and emigration
 In a closed population  i.e. a fishpond, there is no
immigration or emigration, the only factors affecting
change in population numbers will be births and deaths
REGULATION OF POPULATIONS
 If a few individuals enter an unoccupied area, where there is no shortage of
food or any other resources and no predators - they will reproduce and grow
exponentially in population.
 As the numbers increase – there is more pressure on the available resources
 builds up environmental resistance, which causes birth rate and
immigration to decrease and the death and emigration to increase.
 ENVIRONMENTAL RESISTANCE – the total number of factors that stop a
population from reproducing at its maximum rate
 A balance is reached  population stabilizes at a particular point, this is the
carrying capacity
 CARRYING CAPACITY  the population density that the environment can
support