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Summary Population ecology notes
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This document contains notes on population ecology including definitions
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POPULATION ECOLOGYDEFINITIONS: METHODS TO ESTIMATE POPULATION SIZE:
§ Species = group of organisms which share characteristics close enough to allow them § Direct techniques = counting every individual & no statistical
to breed successfully calculations involved
§ Population = group of individuals of the same species, living in a defined area where o Census = actual head count / aerial photography
they may breed freely § Indirect techniques = estimate of population size, using part of
§ Community = consists of all populations in an area, interacting with one another population & then applying formula
§ Ecosystem = major interacting system consisting of all the organisms (biotic
components) and their non-living environment (abiotic components)
POPULATION REGULATION:
MARK-RECAPTURE TECHNIQUE:
§ Factors that affect population size = food availability, competition, QUADRAT: § Limited sample of organisms in population are
weather, territory, predation, disease
caught, tagged & released. After they have
§ Carrying capacity = number of organisms that an environment can § Frame of any shape & of dispersed amongst population, 2nd group is
support (if a population increases above carrying capacity, the known size is placed on area captured & number of animals captured is
environment deteriorates) (all individuals counted). counted as well as number of recaptured
§ Environmental resistance = population will rise & fall with changes in Repeated on number of animals in 2nd capture
environmental resistance randomly selected sites & § Accuracy dependent on:
o Density independent factors = affect population size no average calculated o marking mustn’t harm animal
matter how closely packed the population is § Accuracy dependent on: o mark mustn’t wear off between counts
o Density dependent factors = prevent overpopulation & result o accurate counting o individual must mix with rest of
in stable populations with slight fluctuations, which are o knowing area of population
affected by changes in population they are acting on (food quadrat o population should be closed (no
supply, shelter, space, disease, predation, competition) o random distribution of immigration/emigration)
each quadrat o no births/deaths during time of
POPULATION SIZE: o use of large enough investigation
number of quadrats to o chance of animal being captured
§ Immigration = organisms from outside the accurately calculate mustn’t change due to age/experience,
ecosystem, join the population average during investigation
§ Emigration = when organisms leave the ecosystem § Population size = no. § Population size = no. of individuals x total no. in
§ Mortality = number of deaths per year organisms in quadrat x habitat 2nd sample, divided by no. of marked individuals
§ Natality = number of live births per year size, divided by quadrat size in 2nd sample
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