'Pecking Order' of Four Plant Species from Pastures of Different Ages

Abstract

The rank order of competitive effects ('pecking order') was studied for four species collected as seeds from each of three different-aged pastures. Based on all pairwise comparisons of performance in mixtures, species rank order was linear for plants from each pasture but the position of species was not identical for each pasture. These rank orders showed no relationship to the rank orders of abundance in the field. Rank orders in four-species mixtures were similar, but not identical to those based on pairwise mixtures for plants from the two younger pastures. The extent to which one species was able to deny resources to another was generally independent of the age of the pasture from which the plants were collected. The extent to which the two components of a mixture made demands on the same resources decreased with increasing pasture age for two pairs of species. These results are contrasted with results from an earlier study involving the same four species collected as neighbouring clones, rather than as seeds. Rank order of suppressive effects on a given target differed depending on which species was the target and generally differed from rank orders based on all pairwise comparisons of performance in mixtures. 'Constancy' of rank order (with different targets) decreased with increasing age of the pasture from which plants were collected. The data suggest that a variable rank order of species against different targets may be a consequence of: 1) different degrees to which species make demands on the same resources when the target is changed, and/or 2) different degrees of beneficial effects on different targets, and/or 3) different relative competitive abilities against different targets.