Does niche limitation exist?

Abstract

Three sets of data are examined for evidence of niche limitation expressed as a deficit of variance in the number of species per sample, as compared to a null model with species occurring independently of each other. An agricultural field of permanent pasture was sampled with contiguous quadrats. It showed no variance deficit but rather a significant variance excess. Subdividing the field floristically or environmentally to achieve greater homogeneity did not reduce this excess. A fixed dune slope was sampled by a line of contiguous quadrats and analysed as quadrat sizes in the range 20 mm × 20 mm to 1 m × 20 mm. There was no variance deficit at any quadrat size; at quadrat sizes up to 100 mm × 20 mm there was significant variance excess. Reanalysis of Patrick's (1968) diatom data gave a variance deficit one year (but P = 0.5) and an excess the next. It is questionable whether the concepts of niche limitation, and hence of species packing, are meaningful if they cannot be demonstrated even in favourable circumstances. -from Authors Show more