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

Truman P. Young
Journal of Ecology
Vol. 72, No. 2 (Jul., 1984), pp. 637-650
DOI: 10.2307/2260073
Stable URL: http://www.jstor.org/stable/2260073
Page Count: 14
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The Comparative Demography of Semelparous Lobelia Telekii and Iteroparous Lobelia Keniensis on Mount Kenya
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Abstract

(1) Two species of rosette-forming Lobelia grow in the alpine zone of Mount Kenya. Lobelia telekii grows on dry rocky slopes and is usually semelparous (monocarpic); Lobelia keniensis grows in moist valley bottoms and is usually iteroparous (polycarpic). Lobelia telekii plants usually produce only a single rosette; Lobelia keniensis plants usually branch to produce multi-rosette individuals. (2) 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 Lobelia keniensis there was a minimum size at which single rosettes began to branch that was similar to the minimum flowering size. (3) Distinct wet and dry periods of weather were identified, each about 15 months 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. (4) Predation by rock hyrax (Procavia johnstoni) of larger Lobelia 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 Lobelia telekii rosettes in the study site. (5) Lobelia telekii rosettes flowered at a larger size and produced larger inflorescences in the wetter sites than in the drier sites. Lobelia keniensis plants with more rosettes flowered more frequently than plants with fewer rosettes. (6) In Lobelia telekii mortality before reproduction was higher than in Lobelia keniensis for all size classes, excluding the smallest seedlings. Mortality of multi-rosette Lobelia keniensis plants (death of all constituent rosettes) was very low and restricted to the drier sites. (7) The evolution of semelparity in Mount Kenya Lobelias may have been favoured by the demonstrated higher adult mortality and greater time between reproductive episodes shown by Lobelia keniensis plants in drier sites.

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