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Fieldwork
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 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 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 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