LEPANTHES CARITENSIS, AN ENDANGERED ORCHID: NO SEX, NO FUTURE?

Abstract

Persistence of any population depends on the ability of its members to reproduce, asexually or sexually. When reproductive success and/or survivorship are low, this may lead to population decline or in extreme cases extinction. Estimating population growth rate by matrix analysis is effective in determining population stability, although rarely used in orchids. The newly described epiphytic orchid Lepanthes caritensis, is limited to the Charco Azul area in the Carite Forest Reserve, Puerto Rico and occurs only on one species of tree, Micropholis guyanensis (Sapotaceae). Reproductive success, growth and survivorship of individuals of L. caritensis were recorded monthly for two years and a matrix analysis was applied to estimate the asymptotic growth rate of two populations. Reproductive effort was infrequent, few pollinaria were removed and fruit set was nil in both populations. Recruitment and mortality during the sampled years was 8.2% and 22.0% respectively. Mortality was significantly higher in juveniles as compared to adults (28.9% and 10.6% respectively). Recruitment of seedlings must have resulted from the presence of a seed bank or long distance seed dispersal. Intrinsic population growth rate was estimated at 0.995 and 0.999 for population one and two, respectively. Elasticity analysis suggests that non-reproductive adult stage in both populations is the most sensitive to change and would have the largest effect on the population growth rate as compared to other stages and reproductive success. The estimated half-life of Lepanthes caritensis populations is approximately 9.5 and 47 years for population one and two, respectively. Population persistance will depend on the consistency of the mortality rate and stochastic reproductive success.