Competitive Abilities of Rare and Common Plants: Comparisons Using Acaena (Rosaceae) and Chionochloa (Poaceae) from New Zealand

• Published in: Conservation biology Vol. 16; no. 4; pp. 975 - 985
• Main Authors: Lloyd, Kelvin M., Lee, William G., Wilson, J. Bastow
• Format: Journal Article
• Language: English
• Published: Boston, MA, USA Blackwell Science Inc 01-08-2002; Blackwell Science; Blackwell
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biological competition; Biological taxonomies; Conservation biology; Conservation, protection and management of environment and wildlife; Demecology; Ecological competition; Environmental conservation; Forest habitats; Fundamental and applied biological sciences. Psychology; Habitat conservation; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Plants; Plants and fungi; Species; Tillers; New Zealand; Oceania; Monocotyledones; Growth; Soil fertility; Interspecific comparison; Rosaceae; Environmental factor; Experimental study; Plant conservation; Rare species; Competitive ability; Gramineae; Dicotyledones; Angiospermae; Agrostis capillaris; Interspecific competition; Spermatophyta; Population dynamics; Comparative study
• ISSN: 0888-8892; 1523-1739
• DOI: 10.1046/j.1523-1739.2002.01033.x

It is commonly suggested that rare plant species are poor competitors. However, the study of rarity and competitive ability has, like much of the research on rare species, been hindered by insufficient sample size, scarce use of experimental methods, and lack of comparison with common species. We used a within-taxon comparative approach to test for differences in competitive ability between rare and common species in two genera, Acaena (Rosaceae: six rare and four common species) and Chionochloa (Poaceae: four rare and five common species). We grew plants in replicated experiments at two levels of soil fertility and with two levels of competition, in monoculture or mixed with the introduced grass Agrostis capillaris. Competitive response was measured as relative yield, relative tiller increase, and change in live-leaf fraction. Rarity was measured by geographic range size, defined as the number of 10-km grid squares occupied by each species in New Zealand. The relationship between competitive ability and geographic range size was tested with correlations. Within Acaena, four of the rare species had high competitive ability, but there was no general relationship between competitive ability and rarity at either high or low levels of fertility. Differences in competitive ability appeared related to differences in ecological distribution rather than to rarity or commonness in a geographic sense. Within Chionochloa, common species tended to be stronger competitors than rare species, with the relationship being significant at the low level of fertility. Several of the common Chionochloa species have expanded their geographic ranges relatively recently, consistent with their greater competitive ability. Conversely, rare Chionochloa species occupy specialized habitats that may be interpreted as refuges from competition. Disparate results from Acaena and Chionochloa do not support the notion that rare species are generally poor competitors. Although rare species may have low competitive ability in some cases, it should not be assumed to be a cause of rarity for all rare species.