Designing ecological and biodiversity sampling strategies

AbstractEmpirical studies of patterns in biodiversity and other ecological phenomena requirefield measurements. While finding a method of measurement at a predetermined sitecan be challenging, the locations at which samples are to be taken also have to bechosen. Despite many years of empirical field research in ecology, many studies seemto adopt designs which are poorly suited to their purpose. This paper discusses someof the key issues regarding sampling design in such studies.Objectives of the study should drive all aspects of design, hence clear andunambiguous objectives are a prerequisite to good design. These objectives mustinclude testing hypotheses. Most practical designs are hierarchical. Questions ofreplication and sample size can only be addressed once the hierarchy is understood,and the scales at which different objectives will be met are identified. Stratification isa key tool in making the design efficient for testing hypotheses. At any level in thehierarchy there are options of using either systematic or random sampling, withadvantages and disadvantages of both. High levels of unexplained variation aretypical in many ecological studies, and may mean no useful results are obtained. Thepaper discusses strategies for coping with high variation.iv