2002 Program
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Dispersion and Spatial Distribution of Eight Orchid Species in the Caribbean National Forest, Puerto Rico
Lauri B. Brewster and James D. Ackerman
The dispersion and spatial distribution were analyzed for eight orchid species in the Caribbean National Forest of Puerto Rico. Thirteen species were encountered in the study sites, eight of which were used for analysis. The two most abundant species were Pleurothallis ruscifolia and P. pruinosa (respectively). Green's Index of Dispersion was used to categorize dispersion on hosts as being regular, random, or clumped. A regular dispersion pattern was revealed for P. ruscifolia, and the remaining seven species exhibited a random distribution. The distance between conspecific populations was analyzed for each species, and the general distribution was what would be expected for orchids—hyperdispersal. The small, hyperdispersed populations observed creates reason to believe that genetic drift is important in the genetic differentiation of these species. An analysis of gene flow and effective population sizes for these species needs to follow this study in order to fully assess the potential of genetic drift occurring in these orchids.
Redundancy between shrimps and invertebrates in leaf litter decomposition
Angela Bobeldyk and Alonso Ramírez
In tropical stream ecosystems, organisms occupy different niches in functional ecosystem processes. The 'redundancy hypothesis' suggests that the roles of organisms overlap enough such that in the absence of one species, others are able to keep ecosystem processes functional. Recent disturbances, such as dams and water extraction projects, have raised questions about effects of these events on stream ecosystems, especially pertaining to shrimps. Shrimps depend on being able to migrate from headwater streams to estuaries in order to complete their developmental life cycle. In this study, we examined the role of shrimps and other invertebrates in the process of leaf litter decomposition to see if in the absence of shrimps, if this process would be slowed. Our experiment consisted of three treatments: a control, shrimp exclusion, and invertebrate exclusion. We found that the decay rates of Cecropia schrebreiana did not differ significantly between the control and shrimp exclusion leaf packs. However, control leaf packs possessed few to no shredding invertebrates (insects and juvenile crabs), whereas shrimp exclusion leaf packs had an increasingly abundant population of shredding invertebrates. Finally, we found that in the absence of shrimps, smaller invertebrates were able to decay leaves at a similar rate to shrimps, thus demonstrating a compensatory effect.
Land Use and Hurricane Disturbance History of a Caribbean Forest Effects on Woody Debris
Angelina Samreny, Jill Thompson, Nicholas Brokaw
Woody debris (WD) plays many vital roles in ecosystems- from being the habitat for a myriad of organisms to being a nutrient and carbon resource for the ecosystem. The rate of deposition and the biomass of WD deposited, however, vary greatly among ecosystems. Because of hurricane disturbance to the Luquillo Experimental Forest (LEF) of Puerto Rico, it was predicted that the amount of WD there would be greater than the amount found in other tropical forests. Indeed this was the case when the biomass of WD from an LEF plot of land was compared to that of two other tropical forests. Furthermore, the land use history of the LEF has significantly affected the tree species composition there. In one plot, CC3, of the LEF human disturbance was so severe that Casearea arborea- a secondary, fast-growing, relatively low-density, tree species recolonized the area. Another plot, CC4, suffered minimal human disturbance so the dominant tree species is Dacryodes excelsa- a primary, slow-growing, high-density species. Thus it was predicted that in a hurricane, CC3 should be more prone to tree destruction, especially due to the quality of wood of the dominant tree species there. Hence, CC3 should have more WD than CC4 due to the effect of hurricanes and land use history of these plots. This hypothesis also was supported by the experimental data.
Variations in the reproductive effort of Pitcairnia angustifolia (Bromeliaceae) related to light environment and vegetative structures
Belmarie Samalot-Roque and Denny S. Fernandez
A plant's life history depends solely on the habitat conditions to which it is subscribed. The outcome of major activities such as reproduction often depend on the adequate acquisition of resources. In the family Bromeliaceae, specifically members of the subfamily Pitcairnioideae are well adapted to living conditions such as growing on rocks, also these do not posse's tanks or trichomes. It is believed that the bromeliads of this subfamily are the ancestors of the most rosette-like known bromeliads. Pitcairnia angustifolia belongs to this subfamily and is found along different habitat conditions on Quebrada Sonadora at Luquillo Experimental Forest. To determine how light environment, and vegetative structures affect the reproductive effort of the plant, hemispherical photographs analysis and measurements of the leaves were compared to different reproductive effort variables in P. angustifolia. Results suggested that the amount of direct sunlight radiation does not affect any of the reproductive effort variables although it does influence leaf length of the plant. Indirect solar radiation has an effect on the length of the inflorescences when related to the leaf maximum length. The leaf maximum length does affect the following reproductive variables: inflorescence length, inflorescence number and the amount of nectar production. The plant showed a strong preference to rocky substrates vs. soil substrates.
Allochthonous Transfer Across the Stream-terrestrial Boundary in a Tropical Rain Forest
David Torres-Sanchez and Paul Klawinski
Insect, spider and anole abundance studies were made at the Luquillo Experimental Forest in Puerto Rico to determine interactions between aquatic emergent insects and these groups of organisms at three streams that differ in size and plant community structure. Stomach contents found in the anoles at the streams and in the forest were identified taxonomically in order to determine the source of energy used by two major species. The amount of energy produced (in terms of aquatic insect abundance) is significantly higher at the streams than in the forest. Spider abundance was also higher at the streams but the general abundance of anoles does not change among different distances. The abundance of the lizards' species seems to be influenced by the structure and the distance from the stream in which they are located, but their diet composition is more determined by their distance from the stream.
The Effect of Natural Disturbances on Genetic Diversity in Heliconia caribaea
Devon Treece and Elvia Meléndez-Ackerman
It is widely accepted that natural disturbances influence the structure and diversity of plant communities. This process is especially evident in the Luquillo Experimental Forest (LEF) in Puerto Rico where extensive data collection has revealed correlations between types and frequencies of disturbances and the plant communities contained in those disturbance regimes. Although the impact of natural disturbances on the level of the community is well understood, less is known about how these disturbances affect the biotic community at the level of the species. One plant species that is heavily affected by natural disturbances, namely hurricanes, in LEF is Heliconia caribaea, a clonal species that can quickly invade tree-fall gaps caused by hurricanes. We explored the usefulness of Amplified Fragment Length Polymorphisms (AFLP's) to investigate the differences in genetic diversity between sub-populations of H. caribaea located in areas of heavy disturbance versus areas of less disturbance. We have successfully determined 3 selective primer combinations for these analyses. Selective PCR products have been obtained for 6 sub-populations (3 high disturbance, 3 low disturbance) at LEF. These products will be run on polyacrylamide gels to compare the percentages of polymorphisms of each of the sub-populations.
Effect of Fertilization on Soil Acidity in the Luquillo Mountains
Stephanie Gieck, Mathew Warren and Xioming Zou
Ammonia fertilizers are known to cause acidification of the soil due to the nitrification process. This acidification results in a lower pH, increased exchangeable acidity, increased base neutralizing capacity, and lowered acid neutralizing capacity. It was hypothesized that these results would occur at two sites, El Verde and Pico del Este. The hypothesis proved to be true for El Verde, but at Pico del Este there was no significant difference found between the control and fertilization plots. It is possible that because the soils at Pico del Este are waterlogged, there is not enough oxygen for the nitrification process to acidify the soil and denitrification may even be occurring, which uses protons in the process. Denitrification may also account for the higher pH of the Pico del Este control soils compared to the El Verde control soils. Another possibility for the lack of acidification in Pico del Este and an overall higher pH is the presence of more soil organic matter. This may act as an acidification buffer.
Pollination and Speciation of Lepanthes (Orchidaceae): A case for natural selection, genetic drift, or both?
Grant T. Godden and James D. Ackerman
Broad-based studies of Lepanthes have contributed to much of our knowledge of orchid evolution, particularly with regard to genetic drift. However, the pollinators and pollination mechanisms for nearly all Lepanthes species remain a mystery, leaving a void in our understanding of the selective forces involved with pollinator specialization. In this investigation, we regularly censured six populations of Lepanthes rupestris Stimpson for a period of three weeks during the month of July, monitoring floral production, abundance, and visitation. Sticky traps were utilized in an effort to identify a fungus gnat pollinator. However, no insects with attached pollinia were observed and fungus gnat abundance at each population could not be correlated to floral visitation. Fruit set throughout the month of July was particularly low as a result of reduced floral longevity, which was correlated to cumulative precipitation.
Characterization of the plant diet of introduced pigs and goats in Mona Island Reserve, Puerto Rico
Carla Cortés and Elvia Melendez-Ackerman
The introduction of feral ungulates (i.e. goats and pigs) is one of the most common and impending threats to the biodiversity of island biotas around the world. Introduction of these animals to Mona Island, a dry forest Reserve located between the islands of Puerto Rico and Hispaniola occurred 500 years ago by Spanish settlers. While some data suggests that these animals may regulate some plant communities in the island, a detailed characterization of the diet of these animals is lacking. Current management of populations of these animals include a three month hunting season coordinated by the Department of Natural Resources and the Environment (DNRE) of the Commonwealth of Puerto Rico. We used this management strategy as an opportunity to directly characterize the plant species that make up the diet of these animals. This information could be valuable in identifying those species that might be most susceptible to herbivory by these animals. Preliminary results indicate that many plant species appear in the stomach of these animals including species highly toxic secondary compounds (e.g. Euphorbia petiolaris) and an endangered cactus endemic to the island (i.e. Harrisia portorricensis).