Population dynamics of Ludwigia leptocarpa (Onagraceae) and some factors affecting size hierarchies in a natural population

Rebecca W. Dolan, Butler University
R. R. Sharitz

Abstract

(1) Germination cohorts of Ludwigia leptocarpa, a semi aquatic annual plant were marked in the field at time of establishment and followed through the 1981 and 1982 growing seasons at a site in southern South Carolina. (2) Data from each cohort were pooled to determine demographic characteristics of the population as a whole, then analysed separately to determine the effect of time of germination on survivorship, relative growth rate, and adult size. (3) Changes in numbers of L leptocarpa fit a Deevey Type II survivorship curve. This and other characteristics of the species classify it as 'r-selected'. Aspects of the life history may reflect a 'bet-hedging' strategem that ensures establishment. (4) Differences in the time of germination are not responsible for differences in adult size, even when early germinating plants have as many as 35 days more for growth than late germmators. This, and the fact that differences occur even within single cohorts, implies that factors other than time of germination must influence plant size.

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