Annals of Botany 89: 205-211, 2002
© 2002 Annals of Botany Company
Sex Ratio and Reproductive Effort in the Dioecious Juniperus communis subsp. alpina (Suter)
elak. (Cupressaceae) Along an Altitudinal Gradient
1Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apdo. 1095, 41080 Sevilla, Spain
* For correspondence. Fax (+) 954557059, e-mail plortiz{at}us.es
Received: 24 July 2001; Returned for revision: 18 September 2001; Accepted: 29 October 2001.
The hypothesis that reproductive cost differs between sexes was tested in Juniperus communis subsp. alpina along an altitudinal gradient. Sex ratio (male : female) increased significantly with elevation, and above 2600 m it was significantly male-biased. The reproductive effort was markedly greater for females than for males at all elevations. However, over 3 years of study, the growth of the females, measured as elongation of the main axes, was similar to that of the males. In both sexes, growth decreased with increasing elevation. Neither size of the ripe seed cones, nor the number of developed seeds per cone varied with elevation. The percentage of filled seeds was significantly greater at higher elevations indicating more favourable conditions for wind pollination in these stands. However, cone production decreased with elevation and so, reproductive success of J. communis subsp. alpina in Sierra Nevada decreases towards both upper and lower altitudinal distribution limits. The results do not support the hypothesis of differential reproductive cost between sexes; thus, alternative arguments to explain the altitudinal variation of sex ratio are discussed.
Key words: Juniperus communis, Cupressaceae, altitudinal gradient, cone crop, growth rate, reproductive effort, sex ratio.
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