Niche dimensionality and biodiversity

[Grassland species loss resulting from reduced niche dimension](http://www.nature.com/nature/journal/v446/n7137/abs/nature05684.html)

The idea of niche dimensionality is an analogy of ``space'' concept -- that the niche space is defined and separated by a series of ecological factors and their values. More such dimensions means that more subspaces or niches can be defined therefore more species may be supported.

Resource addition can make some limiting factors not limiting anymore, allowing fewer trade-off opportunities and thus reduce the dimensions of the niche space. Increased supplies of limiting resources can also change the [stoichiometry](http://www.m-w.com/cgi-bin/dictionary?va=stoichiometry) or decrease the heterogeneity of limiting resources.

The increase of resources does create new niches. However, most local species cannot occupy these new niches. Thus local species number and evenness both decline. The more the species are co-limited by multiple resources, the more likely they will be influenced in the face of diminishing limiting factors.

This concept can be considered as a formalised explanation of the effects of eutrophication. Traditionally eutrophication is interpreted as encouraging nutrient-demanding species so they outcompete those oligotrophic species. The notion of niche dimension provided us with a new perspective.

The question: is there other management actions other than increasing nutrient that can reduce niche dimensions? A guess is that any management that turns limiting factors to unlimiting ones may do so. Will the prohibition of grazing have the same effect on the grassland? It has been observed that biodiversity is higher in grazed plots than nongrazed plots (e.g. [(Taddese et al., 2002)](http://www.springerlink.com/content/vn024bc60xqrg2ca/)).