Fig. 12. Curves of competitive ability along an enk~ronmental gradient as predicted from the "relaxed" version of the competitive hierarchy model (Keddy 1989a). Shown at bottom are realized niches (observed in nature under the effects of competition). Two kinds of competitive dominance are distinguished: I . in the sense of the narrow competitive hierarchy model (CHM-dominance). and 2. actual dominance (ACT-dominance) in nature, in terms of the more relaxed version of the model (see text for further explanation of 2 model versions). The borders of realized distributions derive from the intersection points of competitive ability curves of neighbouring species. Thus. a species:species boundary is set by neither the final exhaustion of tolerance of low resource levels (that would coincide with zero competitive ability), nor by competitive exclusion of other species by a CHM-dominant species through its whole fundamental niche. Black sections of gradient indicate where occupying species are CHM-dominants. Hatched areas indicate sections uhere a CHM-dominant species becomes an ACT-subordinate, and a CHM-subordinate becomes an ACT-dominant (thus excluding the CHM-dominant from this section of gradient).
...read more