Sample shape, spatial scale and species counts: Implications for reserve design Original Research Article

The optimal design of nature reserves has been a hotly debated topic for some years. One contentious issue has concerned the ideal shape of reserves, with several researchers suggesting that reserves should be as nearly circular as possible to minimize edge-related degredation and potential ‘peninsularity’ effects. This paper demonstrates an advantage to non-circular reserves: given the spatial autocorrelation of environmental conditions and species ranges, elongated samples should tend to capture a greater diversity of conditions and, consequently, a greater number of species. To test this idea, samples of 16 cells, arranged as 4 × 4 squares, 2 × 8 rectangles and 1 × 16 lines were considered in mapped plant distributions at spatial scales ranging from cells of 1 m2 to 2500 km2. Overall, elongated samples tended to capture significantly larger numbers of species than did their square counterparts, as predicted. The degree of elongated sample advantage was very similar at all but the smallest of the scales considered, suggesting that the pattern of species turnover (β-diversity) is nearly scale-independent or fractal in nature. As the advantages of elongation are largely scale-independent and the only documented disadvantages (edge effects) are very scale-dependent, the optimal shape of a reserve for species sampling should shift as a function of reserve size, with large reserves becoming increasingly elongated.