Plants are in general exquisitely sensitive to differences in soil moisture availability, particularly when competing with each other. We have previously found that species segregate along soil moisture gradients in English wet meadows (Silvertown et al., 1999, Nature 400:61-63). Evidence from that study suggested that the pattern should be phylogenetically widespread. Here, we test that prediction by analysing the distribution of plants along soil moisture gradients in an entirely different community found in the Southern Hemisphere. Further, we use species in the family Restionaceae belonging to a clade endemic to the Cape Floristic Region to test the hypothesis that speciation in this group involved ecological radiation into novel niches in hydrological niche space.
Results/Conclusions
The distribution of species on hydrological gradients in fynbos plant communities was mapped at 8 sites in the Cape Floristic Region. At 7 of the 8 sites, in communities ranging from montane to coastal fynbos, species segregated along soil moisture gradients within plots only 50m X 50m. The phenomenon we discovered in N. temperate meadows in the N. Hemisphere is therefore also present in the quite different plant communities found in the Mediterranean climate of the Cape. This supports our earlier prediction that hydrological niches are a general phenomenon in plant communities. We are currently using a species-level phylogeny of the family Restionaceae (Hardy et al., 2008, Int. J Plant Sci., 169: 377-390) to test our prediction that radiation in this family involved ecological speciation into hydrological niche space.
