Embracing scale-dependence to achieve a deeper understanding of biodiversity and its change across communities

Although spatial scale plays a critical role in estimates of biodiversity, most empirical studies ignore scale or use only simple controls for sampling intensity. In a meta-analysis of studies that measured biodiversity responses to numerous ecological drivers across scales, we found nearly universal scale-dependence: effect sizes either greatly increased or decreased across scales, and nearly 10% switched directions across scales. Next, we show how accumulation and rarefaction curves can be used to dissect the effects of biodiversity scaling based on three components: total number of individuals (N), the shape of the species abundance distribution (SADs), and the pattern of spatial aggregation. In a second meta-analysis of studies with multiple rarefaction curves, ~30% of them crossed, and the three components of biodiversity were uncorrelated, contradicting conventional wisdom that most biodiversity measures are strongly intercorrelated. These results imply that there is no single 9magic metric9 or scale for measuring biodiversity, and that multiple measures and scales are necessary to quantify biodiversity patterns. We use a case study of nutrient additions in experimental ponds to illustrate how this multi-scale perspective reveals the responses of biodiversity to ecological drivers, and allows for a more informed search for possible mechanisms.