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Citation. Harpole, W.S.; Tilman, D. 2007. Grassland species loss resulting from reduced niche dimension. NATURE 446:791-793.
Abstract. Intact ecosystems contain large numbers of competing but coexisting species. Although
numerous alternative theories have provided potential explanations for this high
biodiversity, there have been few field experiments testing between these theories. In
particular, theory predicts that higher diversity of coexisting competitors could result
from greater niche dimensionality1, for example larger numbers of limiting resources or
factors. Alternatively, diversity could be independent of niche dimensionality because
large numbers of species can coexist when limited by just one or two factors if species
have appropriate trade-offs2. Here we show that plant coexistence and diversity result
from the 'niche dimensionality' of a habitat. Plant species numbers decreased with
increasing numbers of added limiting soil resources (soil moisture, nitrogen, phosphorus
and base cations), which is consistent with theoretical predictions that an increased
supply of multiple limiting resources can reduce niche dimension. An observational field study gave similar results. The niche dimension hypothesis also explained diversity changes in the classic Park Grass Experiment at Rothamsted. Our results provide an alternative mechanistic explanation for the effects of nutrient eutrophication on the diversity of terrestrial, freshwater and marine ecosystems.