Measuring populations

Measuring populations - sampling

• Usually use transect or quadrat to sample

• Count number of organisms per sample area, then calculate numbers per m2 (or m3)

Measuring populations - transects

Used to establish main features eg – slope, water features, rocks, distribution of major plant life – trees, shrubs, etc

Drawing profiles

• Profiles show main living and non-living features including vegetation, slope, soil, etc

Drawing transects

• Transects show main living features including vegetation type, distribution and height

Measuring populations - quadrats

Used to establish population densities or distribution patterns eg – population number/unit area, percentage cover of different plant species

Drawing quadrats

• Quadrats show distribution patterns

Using quadrats to estimate population numbers

The diagram opposite shows the plants observed in a 6m x 6m plot.

Key:Bunchgrass species Cattail species

Estimate the population density for these two plants.

If this is a sample from a 100 m2

area, estimate the population of each of the plants in this area.

Measuring populations – capture-recaptureCapture organisms and tag/identify in some way, then release back to ecosystemGo back later and recapture. Count the number of recaptured organisms with tags

Estimate population using formula: Number in first sample x number in second sample number tagged in second sample

Capturing techniques 1

Pit traps:These involve

Organisms caught this way include

Animal traps:These involve

Organisms caught this way include

Capturing techniques 1

Pit traps:These involve digging a hole that

animals fall into. Many are put along a fence line, so animals are forced to walk over them

Organisms caught this way include arthropods, small amphibians and reptiles (depending on size of pit)

Animal traps:These involve cages or traps with bait to

attract animals to enter.Organisms caught this way include

small to medium sized mammals, reptiles and birds

Capturing techniques 2

Nets or scoops (Net-trawling):These involve

Organisms caught this way include

Tullgren funnel:This involves

Organisms caught this way include

Capturing techniques 2

Nets or scoops (Net-trawling):These involve use of nets, scoops or

trawling nets to capture animals in water or air.

Organisms caught this way include flying invertebrates eg insects (air nets), invertebrates and fish (trwl nets)

Tullgren funnel:This involves a light source over soil

sample, that forces the animals to move to the bottom and fall through the mesh.

Organisms caught this way include small invertebrates eg insects, worms, slaters, etc

Tracking and tagging

Ways of marking, tagging or tracking organisms after capture include

Some issues with these techniques include

Tracking and tagging

Ways of marking, tagging or tracking organisms after capture include radio collars, ear tags, ear notches, GPS transmitters, microchips, painting.

Some issues with these techniques include risk of harm to the tagged animal, ease of placing tag, length of time tag needs to remain in place, expense, size of animal

Measuring abiotic factorsFactors include • Climatic conditions eg

rainfall, temperature, humidity, wind, sunlight

• Presence of water and its quality eg salinity, turbidity, oxygen content

• Soil type and quality eg salinity, pH, fertility