A melange of curves - further dialogue about species-area relationships

Scheiner (2003) presented a classification of species-area curves into six types based on the pattern of sampling and how the data are combined to form the curves. Gray et al. (2004) contended that five of those types should be termed 'species-accumulation curves', reserving 'species-area curve' for those based on island-type data. Their proposition contradicts 70 years of usage and confounds curves that are area-explicit with those that are area-undefined. In exploring these issues, I highlight additional aspects of species-area and species-accumulation curves, including the assumption of nesting in Type IV (island) curves, how to convert area-unspecified curves into area curves, and the effects of the grain of the analysis on the properties of the curve. Further exploration, theoretical development, and dialogue are needed before we will understand all the biology that species-area curves summarize.