Evol Ecol Res 4: 1097-1117 (2002) Full PDF if your library subscribes.
Diversity, productivity and scale in Wisconsin vegetation
Samuel M. Scheiner1,2* and Sharon Jones2
1Division of Environmental Biology, National Science Foundation, 4201 Wilson Boulevard, Arlington, VA 22230 and 2Department of Life Sciences, Arizona State University West, Phoenix, AZ 85069, USA
Address all correspondence to Samuel Scheiner, Division of Environmental Biology, Room 635, National Science Foundation, 4201 Wilson Boulevard, Arlington, VA 22230, USA.
The relationship between diversity and productivity remains a contentious issue in ecology. Although some have asserted that the relationship is always hump-shaped, a comprehensive literature survey found no single relationship. We conducted a comprehensive examination of the components of scale (grain, focus and extent) across a geographic hierarchy (e.g. spatially defined) and two overlapping ecological hierarchies defined by formations and community types.
We examined how species richness of terrestrial vascular plants varies with net primary productivity in 901 stands scattered across the state of Wisconsin, USA. We found no single relationship between species richness and productivity. Instead, the relationship depends on the components of scale (grain, focus or extent) and hierarchy (ecological or geographic). For the state as a whole, the relationship was U-shaped. Such U-shaped relationships, while found previously, have been noted rarely and ignored completely by theory. For the geographic hierarchy, with increasing extent the relationship went from hump-shaped to negative to U-shaped. Increasing the grain resulted in the opposite pattern, the relationship going from U-shaped to negative to hump-shaped. With increasing focus, the relationship became negative. For the ecological hierarchy among community types, increasing the grain changed the relationship to negative, whereas for the among-formation hierarchy, increasing the grain eliminated any relationships. In contrast, increasing the focus among community types strengthened the U-shaped relationship, but similarly eliminated it among formations. Decreasing the extent – examining individual formations or community types – generally eliminated the relationship, although a negative relationship was found for prairies and sand barrens, a positive relationship was found for bracken grasslands, and U-shaped relationships were found for northern upland forests. These results have implications for how we study the effects of scale, its components, the effects of sampling bias, and the scale at which various causal mechanisms might be operating.
Keywords: diversity, mean similarity, productivity, scale, species richness, terrestrial vascular plants, Wisconsin.
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