Leaf Production and the Cost of Reproduction in the Neotropical Rain Forest Cycad, Zamia Skinneri

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Abstract
(1) Leaf production and reproductive output were followed over 6.6 years for 180 individuals of Zamia skinneri, a cycad of tropical rain forest understorey. In this light-limited environment there were marked interactions between leaf production and cone (strobilus) production, indicating a significant ''cost of reproduction''. (2) At the population level, leaf production peaked in May.sbd.July each year, causing an annual cycle in the number of leaves on individuals. On the average, plants produced a total of 8.8 leaves in four episodes over the 6.6 years. (3) The median number of reproductive episodes for primary forest males and females was one over the 6.6-year period, but significantly more males produced cones two and three times. (4) Both cone production and total leaf production were correlated with an index of canopy openness as well as with plant size. (5) Reproductive individuals increased leaf number by an average of 28.sbd.41% one year prior to cone production. Very few reproductive individuals flushed new leaves in the year of reproduction, and female (but not male) leaf production was depressed for two years after cone production. (6) The low rate of leaf and cone production, and the correlation of leaf production and reproductive output with canopy openness over a very small range of values, indicate that Z. skinneri is highly light-limited. (7) The relation of leaf production to cone production and the depressing effect of reproduction on future cone production demonstrate a clear cost of reproduction, which in all aspects is higher for females than for males. (8) Evaluation of the lifetime consequences to long-lived organisms of different patterns of allocation to reproductive and vegetative structures will require long-term observations on individuals in their natural habitat.