Sampling Techniques

Ethics - handled carefully, shortest time possible, returned back to where they were found.

Pooter - small insects - sucking on a mouthpiece draws insects into a holding chamber via the inlet tube. A filter prevents insects going into the mouth.

Sweep nets - insects in long areas of grass.

Pitfall traps - small crawing invertevrates - a hole is dug in the ground - insects fall into it. Deep enough so that they don't crawl out - roof so it does not fill with water. Left overnight - nocturnal species can be sampled.

Tree beating - invetebrates living in a tree or bush - white cloth under a tree - tree is shaken to dislodge the invetebrates - animals will fall onto the sheet where they can be collected.

Kick sampling - organisms living in a river - the river bank is kicked to disturb the substrate - a net is held downstream for a set period of time to capture any organisms released into the flowing water.

Quadrats are used to sample plants and slow moving animals e.g. limpets or barnacles. - you must choose the correct size for the organism being studied

There are two main types of quadrat:

• Point quadrat - allows sampling of tall vegetation. It is a frame containing a horizontal bar - at set intervals alongthe bar, long pins can be pushed through to reach the ground - each species that touches the pin is recorded.

• Frame quadrat - consists of a square frame divided into a grid of equal sections. The type and number of species within each section of the quadrat us recorded.

To collect the most valid representative sample of an area, quadrats should be used following the random sample technique.

To study how the presence and distribution of organisms across an area of land varies, quadrats can be placed systematically along a line or belt transect.

There are three main ways of measuring the population of plants living in a habitat:

Density - if plants are large enough to be seen clearly, the number of them is counted in the quadrat (this gives the density per square metre). This is an absolute measure (not an estimate)

Frequency of occurence - used when individual members are hard to count. It is the number of times a plant species occurs in a given number of quadrats. It is often given as a %. It indicates the probability of finding a species in a series of quadrats examined in an area of interest.

Percentage cover - The percentage cover os each species (need a gridded quadrat). Lots of data can be collected easily and is useful when a particular species is abundant or difficult to count - it is an estimate by eye of the area within a quarat a species occurs.

• For each approach samples should be taken at many different points - more reliable results.
• The mean should then be calculated to get an avg value for an organism per square metre.
• To work out the total population in an area that has been sampled, multiply the mean value by the total area.
• Estimate abundance of each species using SACFOR (can be semi-quantative)

Animals are always moving/may be hidden, therefore it is difficult to calculate population size.

Capture-Mark-Release-Recapture is a technique used to estimate population size. (Motile)

• Involves capturing as many individuals of a species in an area as possible.
• The organisms are marked and then released back into the community.
• Time is allowed for the organisms to redistribute themselves.
• A second samples is taken and the proportion of marked individuals is used to estimate population size (greater no. of individuals marked from the recapture = smaller pop.)

The species evenness in an area can then be calculated by comparing the total number of each organism present. Populations of plants or animals that are similar in size or density represent an even population. Species evenness can be expresses as a ratio between the number of each organism present.

Abiotic factors are the non-living conditions in a habitat. They have a direct effect of the living organisms that live there.

e.g. light, water availability - to enable them to draw conclusions about organisms present and the conditions they need for survival, scientists normally measure these conditions at every sampling point.

Many abiotic factors can be measured quickly and accurately using a range of sensors, which are useful for a number of reasons:

• Rapid changes can be detected
• Human error is reduced
• High degree of precision
• Data can be stored or tracked on a computer.