LIFE HISTORY AND DEMOGRAPHY OF A TWIG EPIPHYTE: A CASE STUDY OF ERYCINA CRISTA-GALLI (ORCHIDACEAE)

摘要

Little is known about the life history of twig epiphytes or about the demographical responses they have developed in order to survive in such an oligotrophic and often disturbed environment. In order to develop a model to further the understanding ofthe demographical adaptations of this type of plant, we present demographic data of Erycina crista-galli, and compare it with other epiphytes. In July 2004 two populations were selected: Union Roja (UR) and Santo Domingo (SD). 563 individuals were markedin SD and 592 in UR. The survival rates were: 0.439 seedlings, 0.22 juvenile, 0.49 reproductive_1, and 0.49 reproductive_2 for SD and 0.25 seedling, 0.41 juvenile, 0.32 reproductive_1 and 0.45 reproductive_2 for UR. The highest pseudobulb production rates were presented by reproductive in SD (1.47+-1.04), and by reproductive_2, in UR (0.94 +-1.10), while the seedling (0.37+-0.26 cm/year SD) was the life stage that showed the highest increase. The fecundities were of 1.00 +-0.00, and 2.00+-0.00 capsules/individual in reproductive_2 and of 2.00+-1.73, and 2.00+-2.00 capsules/individual in reproductive_2. Both populations were decreasing (X =0.5 SD and X=0.398 UR). The highest elasticity values were for r_2 (0.702 SD and 0.324 UR). There was no consistent difference in the elasticity values of fecundity, growth and stasis between E. crista-galli and the other species. The only demographic feature that appears to distinguish twig epiphytic orchids from other epiphytic orchids is the age of sexual maturity.