Where should wild species be sampled? New method based on isolation-by-distance objectively gives the answer

Random sampling is an important statistical assumption, but virtually impossible when sampling a wild species as we cannot know where all the individuals exist. While interpopulation or intrataxa sampling methods have been developed, there are currently few intrataxon sampling methods to objectively decide where to sample wild taxa. We suggest a new sampling method which computes appropriate sampling locations from coordinates, assuming geographical autocorrelation of phylogeny within a taxon (isolation-by-distance). The computed locations encompass the highest genetic diversity, providing a genetically representative sample. In addition, it can utilize presence/absence information during sampling to reoptimize sampling scheme. Comparing to the single existing method of the similar purpose, the merits of ours is unnecessity of environmental data resulting in easy application, and is theoretically deduced. We tested this method using published phylogeographical data. The test result was generally encouraging, but the method failed where species showed uniform genetic structure or recent distribution expansion which violate the assumption of geographical autocorrelation of phylogeny. Though simple, our method constructs a methodological and statistical foundation for sampling wild species, and is applicable to revising taxonomic study and conservation biology.