When to switch from simple random to probability-based sampling in mapping and monitoring of rare habitats and species? (original) (raw)

Many habitats and species of conservation concern are too rare to be adequately represented in a simple random sample of observation units, e.g., for monitoring purposes. Here, we explore possibilities and limitations of a promising alternative approach, probability-based sampling, by which the probability of being sampled is a function of the predicted probability of occurrence in a potential sampling unit. We compare probability-based vs. random sampling for rare and common target phenomena by simulating variables at three nested sample levels allowing investigation of, e.g., presence or absence of a habitat, presence or abundance of a species in the habitat, and properties of this species, and by deriving theoretical limits for the different sampling designs based on a priori knowledge of the properties of the system. We show that the lower limit for target prevalence, allowing for reliable estimation of its properties, can be expressed as a function of the acceptable precision, ...