2000 Program
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Reproductive success and evolutionary characteristics of Pitcarnia angustifolia (Bromeliaceae)
Soto, I. and E. Melendez-Ackerman
Pitcairnia angustifoliais common along the streambed of the Quebrada Sonadora at the Luquillo Experimental Forest. It presents features that are related with hummingbird pollination. At the Luquillo Experimental Forest hummingbirds occur in low densities. A way to offset low pollinator abundance is by self-pollination or self-compatibility. In this experiment I studied the breeding system of Pitcairnia angustifolia, I specially tested for autogamy, apomixis and cost to selfing. The results suggest that the plant may be both autogamous and apomictic but results are inconclusive. The data showed that P. angustifolia is self-compatible and contrary to expected assuming inbreeding depression, cross pollinations abort fruits at a higher rate relative to self pollination suggesting outbreeding depression. Given our results, traits that promote outcrossing should be favored by selection in El Verde populations of P. angustifolia.
Pollination and reproductive systems in Lepanthes rupestris
Rivera, M. and J. Ackerman
The orchid genus Lepanthes is an enigma. There are over 600 species in the genus yet nothing is known of its pollinators and very little is known of its pollination biology although it has been suggested that pollination is by deception and by flies. We tested the hypothesis that insect abundance was related to fruit production, with the largest populations of orchids receiving the most visits. We placed sticky traps around Lepanthes rupestris populations and monitored fruit production and pollinia removals in all plants. We found no relationship between fruit production, and plant habitat (lithophytic vs. epiphytic), or insect abundance (total and by insect order). Such lack of pattern suggests that pollinator attraction is not based on size of floral display at any level and that the infrequent pollinator visits are consistent with the deception pollination hypothesis.
Interaction of light environment and substrate in an epiphytic lithophytic orchid
Rodriguez, E. and D. Fernandez
This study analyzed whether or not vegetative growth and development were limited by light availability, substrate quality and/ or their interaction in the epihytic orchid, Lepanthes rupestris. To that effect, 21 populations occurring on both tree hosts or on rocks were monitored. Every month measurements on the number of leaf were sampled in 9 individuals per population as an estimate of individual growth. We also counted all individuals within each population. Photon Flux density (PFD) was also quantified for each population as an estimate of light quality. A regression analysis showed that PFD and substrate were not a good predictors of photosynthetic growth area or population size in this orchid suggesting that these orchids do not respond differently (for the range under consideration) neither to variations in PFD nor substrate.
Effects of past land use on tree biodiversity in a tropical wet forest
Kalawani, R. and J. Zimmerman
Past studies have suggested that anthropogenic effects may influence plant biodiversity in tropical forests. This study examined two adjacent areas within the Luquillo Experimental Forest with very different land uses. One area was used as a coffee plantation that had been abandoned in the 20's. The other area had been selectively logged and never cut over. Transects were established between the areas and tree species were recorded. Significant differences in forest species composition were between both areas and were evident even at the boundaries between these two areas suggesting that effects of past land use may persist over long periods of time.
Arthropod biodiversity along an elevational gradient in the Luquillo Experimental Forest
Mickelwaite, E. and P. Klawinski
Species richness refers to the number of species in a certain taxon within a given period of time and space. The set of biotic and abiotic factors influencing a species in a given environment affects species density and therefore species richness. For the year 2000, we collected a total of 128 samples of spiders from the Luquillo Experimental Forest throughout the four forest types found there. Last year in 1999, a total of 64 samples were collected in the same areas. Sampling was developed by Coddington et al. (1991), which includes aerial, ground, leaf litter and vegetation beating searches. The data reveals a general trend of decreasing species richness with increasing altitude, which corresponds with a decrease in net primary productivity due to limiting environmental factors at higher elevations. Comparing 2000 data with data from 1999, there was an increase in the total number of species detected, from 40 to 69. In addition the dominance of the most prevalent species on the mountain, Leucauge regnyi, has decreased significantly. This suggests an overall increase in species evenness over the past two years, which may be indicative of the successional recovery of the vegetation structure after Hurricane Georges in 1998.
Interactions between Prestoea montana and Earthworms in a Tropical Wet Forest of Puerto Rico
Cortes, J. and X. Zou
Prestoea montana, also known as sierra palm, is a dominant sub-canopy tree in the tabonuco forest of the Luquillo mountains. Palms accumulate calcium in soils around stem bases due to their funnel-shaped canopy. To examine the influence of this plant species on the abundance and community structure of soil fauna, we sampled earthworms in areas close to and away from the bases of P. montana in an upland and in a riparian site at the tabonuco forest in the Luquillo mountains. We also carried out a soil sampling to determine pH and water content. We found that: (1) the density of both, soil-feeding endogeic and litter-feeding anecic earthworms did not differ between areas close to and away from the P. montana stem bases in the upland and riparian sites; (2) the fresh and dry weights of both species did not differ significantly among locations in the riparian site. Our results may suggest that calcium is not the limiting factor determining earthworm abundance in the Topical wet Forest of Puerto Rico.
The effects of population size on the reproductive success of Lepanthes rupestris
Goranova, G. and R. Tremblay
It has been suggested that population size plays an important evolutionary role in angiosperm by influencing reproductive success. Mating patterns among such plants,pollen removal and delivery, are governed by a mobile animal-pollinator. Reproductive success can be measured by determining pollen movement and fruit set, consequently the pollinator may determines the reproductive success of individuals and populations. If the pollinator is influence by the size of the plant population then natural selection and genetic drift may be influence by population size. No relationship have been found that correlated with reproductive success (male or females), including number of adult plants, or number of flowers produced.