2.1.15—Estimating population abundance

Use random sampling for equal selection chance, systematic sampling for even coverage, and transects when abundance changes along a gradient.

Choose from the ecological question, organism mobility and spatial pattern. Fixed intervals can bias results if they align with a repeating habitat pattern.

Use a belt transect to measure plants from shore to dune; use random quadrats to estimate a uniform meadow.

A line or belt transect, because the gradient is the question.

Systematic is not automatically unbiased if the interval matches a repeating pattern.