The Comparative Demography of Semelparous Lobelia Telekii and Iteroparous Lobelia Keniensis on Mount Kenya

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Abstract
Two species of rosette-forming Lobelia grow in the alpine zone of Mount Kenya. L. telekii grows on dry rocky slopes and is usually semelparous (monocarpic); L. keniensis grows in moist valley bottoms and is usually iteroparous (polycarpic). L. telekii plants usually produce only a single rosette; L. keniensis plants usually branch to produce multi-rosette individuals. In both species there was a minimum and a maximum rosette size at reproduction. Rosette size at reproduction was positively correlated with inflorescence size in both species. In L. keniensis there was a minimum size at which single rosettes began to branch that was similar to the minimum flowering size. Distinct wet and dry periods of weather were identified, each about 15 mo. long. For both species, rosettes grew faster and had higher survivorship in the wetter sites and during the wetter period than in the drier sites or during the dry period. Predation by rock hyrax (Procavia johnstoni) of larger L. telekii plants in the dry period resulted in a bimodal size-specific mortality pattern. During the dry period and immediately after it hyrax killed over half the larger L. telekii rosettes in the study site. L. telekii rosettes flowered at a larger size and produced larger inflorescences in the wetter sites than in the drier sites. L. keniensis plants with more rosettes flowered more frequently than plants with fewer rosettes. In L. telekii mortality before reproduction was higher than in L. keniensis for all size classes, excluding the smallest seedlings. Mortality of multi-rosette L. keniensis plants (death of all constituent rosettes) was very low and restricted to the drier sites. The evolution of semelparity in Mount Kenya Lobelia may have been favored by the demonstrated higher adult mortality and greater time between reproductive episodes shown by L. keniensis plants in drier sites.