Field investigation
Method overview
For abundance in an area, generate random coordinates and place quadrats without bias. For a gradient, place quadrats at regular intervals along a transect. Identify species, count/estimate abundance, measure the abiotic factor and repeat sufficiently.
Apparatus set-up
Diagramquadrats; transect tape; random-number generator; identification key; ruler; abiotic sensors
Independent variable
distance along gradient or environmental factor
Dependent variable
abundance, frequency or distribution of organisms
Control variables
quadrat size; sampling effort; season/time; identification method; observer; measurement method
Apparatus
quadrats; transect tape; random-number generator; identification key; ruler; abiotic sensors
Safety
Assess terrain/weather; avoid harmful organisms; minimise habitat damage and replace moved objects.
Scientific rationale
Random sampling reduces selection bias; systematic transects reveal change along a gradient; repeats improve representation.