Quadrat
Encyclopedia
A quadrat is a square
(of either metal
, wood
, or plastic
) used in ecology
and geography
to isolate a sample
, usually about 1m2 or 0.25m2. The quadrat is suitable for sampling
plants, slow-moving animals (such as millipedes and insects), and some aquatic organisms.
When an ecologist wants to know how many organisms there are in a particular habitat
, it would not be feasible to count them all. Instead, he would be forced to count a smaller representative part of the population, called a sample. Sampling of plants or animals that do not move much (such as snails), can be done using a sampling square called a quadrat. A suitable size of a quadrat depends on the size of the organisms being sampled. For example, to count plants growing on a school field, one could use a quadrat with sides 0.5 or 1 meter in length.
It is important that sampling in an area is carried out at random, to avoid bias. For example, if one were sampling from a school field, but for convenience only placed quadrats next to a path, this might not give a sample that was representative of the whole field. It would be an unrepresentative, or bias
ed, sample. One way one can sample randomly is to place the quadrats at coordinates on a numbered grid.
Long-term studies may require that the same quadrats be revisited months or even years after initial sampling. Methods of relocating the precise area of study vary widely in accuracy, and include measurement from nearby permanent markers, use of total station
theodolites, consumer-grade GPS, and differential GPS
.
Square (geometry)
In geometry, a square is a regular quadrilateral. This means that it has four equal sides and four equal angles...
(of either metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
, wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
, or plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
) used in ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and geography
Geography
Geography is the science that studies the lands, features, inhabitants, and phenomena of Earth. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...
to isolate a sample
Sampling (statistics)
In statistics and survey methodology, sampling is concerned with the selection of a subset of individuals from within a population to estimate characteristics of the whole population....
, usually about 1m2 or 0.25m2. The quadrat is suitable for sampling
Sampling (statistics)
In statistics and survey methodology, sampling is concerned with the selection of a subset of individuals from within a population to estimate characteristics of the whole population....
plants, slow-moving animals (such as millipedes and insects), and some aquatic organisms.
When an ecologist wants to know how many organisms there are in a particular habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
, it would not be feasible to count them all. Instead, he would be forced to count a smaller representative part of the population, called a sample. Sampling of plants or animals that do not move much (such as snails), can be done using a sampling square called a quadrat. A suitable size of a quadrat depends on the size of the organisms being sampled. For example, to count plants growing on a school field, one could use a quadrat with sides 0.5 or 1 meter in length.
It is important that sampling in an area is carried out at random, to avoid bias. For example, if one were sampling from a school field, but for convenience only placed quadrats next to a path, this might not give a sample that was representative of the whole field. It would be an unrepresentative, or bias
Bias
Bias is an inclination to present or hold a partial perspective at the expense of alternatives. Bias can come in many forms.-In judgement and decision making:...
ed, sample. One way one can sample randomly is to place the quadrats at coordinates on a numbered grid.
Long-term studies may require that the same quadrats be revisited months or even years after initial sampling. Methods of relocating the precise area of study vary widely in accuracy, and include measurement from nearby permanent markers, use of total station
Total station
A total station is an electronic/optical instrument used in modern surveying. The total station is an electronic theodolite integrated with an electronic distance meter to read slope distances from the instrument to a particular point....
theodolites, consumer-grade GPS, and differential GPS
Differential GPS
Differential Global Positioning System is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations....
.