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Designing e cological and biodiversity sampling strategies

Empirical studies of patterns in biodiversity and other ecological phenomena require field measurements. While finding a method of measurement at a predetermined site can be challenging, the locations at which samples are to be taken also have to be chosen. Despite many years of empirical field research in ecology, many studies seem to adopt designs which are poorly suited to their purpose. This paper discusses some of the key issues regarding sampling design in such studies. Objectives of the study should drive all aspects of design, hence clear and unambiguous objectives are a prerequisite to good design. These objectives must include testing hypotheses. Most practical designs are hierarchical. Questions of replication 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 is a key tool in making the design efficient for testing hypotheses. At any level in the hierarchy there are options of using either systematic or random sampling, with advantages and disadvantages of both. High levels of unexplained variation are typical in many ecological studies, and may mean no useful results are obtained. The paper discusses strategies for coping with high variation.