Sampling Populations
Key Concepts
The purpose of field sampling is to gather information about a population and its environment,
including:
Population estimation, density, distribution, environmental gradients and profiles, zonation
and stratification
Stratified sampling is conducted through considered:
Site selection
Choice of ecological surveying techniques
Methods to minimise bias
Presentation and analysis of collected data
Stratified Sampling
The purpose of stratified sampling is to identify individual species in an ecosystem and
consider their interactions with the biotic and abiotic factors in the ecosystem, habitat or
microhabitat.
It enables ecologists to divide a large population into similar sub-groups or strata.
Strata are formed based on a common characteristic in the population
o Eg: canopy, understorey and ground cover vegetation would be three different
strata in a rainforest
Advantages of Stratified Sampling
Stratified random sampling is superior to simple random sampling because the process of
stratifying reduces sampling error and ensures a greater level of representation.
The choice of stratified random sampling ensures adequate representation of all subgroups.
When there is uniformity within strata and comparative difference between strata, the
estimates can be as precise (or even more precise) as with the use of simple random
sampling.
o Measurement of the relationships between environmental variables may be more
statistically significant
Zonation
Zonation is a community pattern in which there a visible strata or zones caused by changes
in abiotic and biotic factors.
The most illustrative examples of zonation are found in locations where environmental
conditions vary greatly over a short distance.
,
Key Concepts
The purpose of field sampling is to gather information about a population and its environment,
including:
Population estimation, density, distribution, environmental gradients and profiles, zonation
and stratification
Stratified sampling is conducted through considered:
Site selection
Choice of ecological surveying techniques
Methods to minimise bias
Presentation and analysis of collected data
Stratified Sampling
The purpose of stratified sampling is to identify individual species in an ecosystem and
consider their interactions with the biotic and abiotic factors in the ecosystem, habitat or
microhabitat.
It enables ecologists to divide a large population into similar sub-groups or strata.
Strata are formed based on a common characteristic in the population
o Eg: canopy, understorey and ground cover vegetation would be three different
strata in a rainforest
Advantages of Stratified Sampling
Stratified random sampling is superior to simple random sampling because the process of
stratifying reduces sampling error and ensures a greater level of representation.
The choice of stratified random sampling ensures adequate representation of all subgroups.
When there is uniformity within strata and comparative difference between strata, the
estimates can be as precise (or even more precise) as with the use of simple random
sampling.
o Measurement of the relationships between environmental variables may be more
statistically significant
Zonation
Zonation is a community pattern in which there a visible strata or zones caused by changes
in abiotic and biotic factors.
The most illustrative examples of zonation are found in locations where environmental
conditions vary greatly over a short distance.
,
