Competition in Mixtures of the Annual Hypochoeris Glabra and Perennial H. Radicata

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Abstract
(1) The annual Hypochoeris glabra and the perennial H. radicata were grown in mixed plantings in a glasshouse to determine their responses to competition and to examine the production that perennials should be superior to annuals in their ability to compete for resources. Dry weight allocation patterns during growth were also studied, because the predicted difference in competitive ability is based on the assumption that annuals allocate proportionally more resources to reproduction than perennials. (2) Mixtures were grown at total densities of 740, 1452 and 4033 plants m-2, with the species arranged in a type of replacment series. Responses of plants to competition over a four-month growth period were assessed by measuring rosette (vegetative shoot), root and reproductive dry weights of plants from three sequential harvests, which were begun when plants first initiated inflorescences. (3) Increased density reduced dry weight at harvest for both species, indicating that competition had occurred. During the experiment, annuals allocated more resources to reproduction than did perennials: 71% of harvested annual plants flowered, compared with less than 1% for the perennial. For annual plants, increased density delayed the initiation of inflorescences. (4) At harvest, perennials had greater vegetative dry weight than annuals, a difference that could be attributed to size differences among seedlings. Regressions of rosette weight on root weight indicated that annuals tended to allocate more dry weight to rosettes with increases in root weight than perennials, although these differences were mostly non-significant. (5) Estimates of the effects of interspecific and intraspecific competition, based on rosette, root and reproductive dry weights, showed that the perennial H. radicata was similar to the annual H. glabra in ability to compete for resources under the experimental conditions. For annual and perennial Hypochoeris, there was little evidence for an association between life-history and competitive ability, even though the assumption that annuals allocate proportionally more resources to reproduction was valid for the experiment.