2008 Program
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Abundance and behavior of a litter snail (Megalomastoma croceum) in Puerto Rico
Daniel M. Dlugos and Chelse Prather
Gastropods are some of the most abundant but understudied organisms in tropical forests. Current research focuses on the diversity of snails and not their ecology. Often times litter snails are more ignored than more easily visible arboreal snails. Megalomastoma croceum is one of these litter snails, and may exceed densities of more than 5 individuals per square meter. This study took place at the Tabonuco forests of El Verde Field Station, Puerto Rico, and looked at abundance and behavior of this litter snail. The hypothesis was that M. croceum would be more abundant in the old coffee plantations of El Verde. Although the coffee plantations were found to have the highest abundances biomass of snails, abiotic variables did not explained the difference. Snail activity was high both during the day and at night, however activity peaked after rainfall and at night. More study is needed to determine what is driving both snail abundances and behavior.
Analysis of dissolved organic carbon quality in two tropical Puerto Rican streams receiving sewage
Maylen Pérez, Jorge Ortiz and Debora Figueroa
The transport of dissolved organic carbon from rivers to the ocean constitutes an important link in the global carbon cycle. Carbon exists in rivers as dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), almost half of which is made up of aromatic humic compounds. Aside from affecting the transport, solubility and toxicity of certain metals, DOC also affects pH, the depth of the photic zone, and other aspects of rivers that determine how well organisms can take up carbon for energy. Since the quality of carbon affects its turnover rate, studies quantifying the effects of urbanization on DOC quality in rivers are important for understanding how urban development affects the transport of carbon downstream, and thus the trophic structure of these ecosystems. Studies of this measure have been conducted mostly on forested, temperate watersheds, but few consider the effects of sewage effluents on the DOC quality of tropical urban streams. In order to quantify the effects of Waste Water Treatment Plant sewage effluents in two tropical streams in Puerto Rico, a study was conducted in the Río Bairoa in Caguas and in the Río Fajardo. DOC quality in water samples was assessed by three methods: Specific UV absorbance (SUVA ), analysis of biological oxygen demand (BOD) and chemical oxygen demand (COD). BOD and SUVA analyses both suggested a higher concentration of refractory material in the natural river water than in the sewage effluents, which contradicted our original hypothesis. Transformations of BOD that corrected for carbon quantity seemed to contradict this result, but were not statistically significant. Further research is necessary to determine if this contradiction is accurate or due to large variations or insufficient sampling. Analyzing the effects of sewage effluent on tropical urban streams constitutes an important contribution to the study of carbon and nutrient cycles, as well as to the understanding of the effects of urbanization on tropical fresh water ecosystems.
The role of decomposer on leaf litter decomposition of native and exotic tree species in a tropical Puerto Rican stream
Ashley Recupito and Alonso Ramírez
Lower incidences of shredder are present within tropical streams compared to its temperate stream counterpart. Due to a lack of shredder in tropical streams, scientist hypothesize that tropical streams rely on microbial processing in order to turn allocthonous organic matter into fine particles that serves as an energy source for streams. In this study, I hypothesize that 1) litter breakdown rate (k) will be greater for native leaf species versus the exotic leaf species. 2) Differences in litter breakdown between native and exotic species of leaf will be due to the presence of invertebrates, therefore by excluding invertebrates, the breakdown rates will display no difference between native and exotic leaf species. 3) Native leaf species will have a greater diversity of decomposers present than exotic leaf species, but heterogeneous mixtures of native leaves will have the greatest abundance and diversity. Four leaf bag treatments using A. glutinosa (control exotic), C. schreberiana (native), D. excelsa (native), and M. bidentata (native) along with course and fine mesh bags where placed in Quebrada Sonadora at El Verde research area, Puerto Rico. In contradiction to our hypotheses, the exotic species decomposed at a faster rate than the native species. In addition, homogenous bags decomposed faster than heterogeneous bags.
The relation between biodiversity and ecosystem function: Do insects consume leaf litter in tropical stream in Puerto Rico?
Vilmarie Figueroa-Nieves and Alonso Ramírez
The relationship between biodiversity and litter decomposition is a topic that has received little attention in tropical streams. It is known that several types of insects and shrimps are responsible for decomposing leaf litter in Puerto Rican streams. Studies in temperate zones have shown that insects, known as shredders, are important in the breakdown of leaf litter. There is little information about insect shredders in tropical streams. The objective of our study was to determine if insects play a role in the process of litter decomposition in tropical streams in Puerto Rico and to determine if the diversity of insects consuming leaf litter varies spatially within Luquillo Experimental Forest (LEF). We assessed variation in the amount of leaf litter and insect species in five streams. Results show that aquatic invertebrates in the LEF are dominated by species mainly consuming fine organic material. Shredders were relatively rare, only 3 out of 23 taxa were shredders: Calamoceratidae (Trichoptera) and shrimps and crabs. Our study indicates that insect shredders play a minor role in leaf litter decomposition as few taxa were found and were present in low numbers. Non-insects, such as shrimps, are more important in processing leaf material.
Light environments and plant recruitment in subtropical wet forest community within different past land use history
Eric Botts and Denny Fernandez
Like many tropical areas, the tropical wet forests in the Luquillo Mountains of Puerto Rico have been disturbed by human land use. All of the Luquillo Experimental Forest has been affected by land use in some way. Some areas were used for agricultural purposes as recently as the 1940s. These areas display notable differences in tree species present, as well as overall species diversity. The light environment generated by the canopy is a major determining factor in the species composition of seedlings present in the understory. It is possible that change in tree recruitment is a lasting legacy of human land exploitation, and that changes in the light environment of the understory are a factor in perpetuating that legacy. Two 16-point grids were designated, one in a former shaded coffee plantation, and another in an area with little or no recent human use. Three equidistant 1m 2 plots were positioned around each point. Hemispherical photography was used to determine canopy structure and the resulting light environment. The Leaf Area Index (LAI), LAI deviation, percent visible sky, Global Site Factor, Direct Site Factor, and Indirect Site Factor were used to characterize the light environment. Counts of seedling species and individuals within each species were made within each plot. The seedling counts of the three plots around each grid point were combined to generate one count per point. Species richness and overall abundance were recorded. Species diversity was then calculated using the Shannon and Simpson indices. ANOVA was used to determine significant differences in all canopy structure and seedling diversity factors between the two grids in the two forest areas. Correlation between indices in both grids was assessed. A significant difference was found in LAI Deviation, but no on species diversity indices. Canopy structure was found to be heterogeneous. A correlation was found between the LAI and LAI Deviation and both diversity indices in the coffee plantation, but no in the native forest. This suggests that the light environment is not related to the seedling species diversity, and that canopy structure and seedling species diversity are both being affected by a common factor in both areas. Further experimentation to test the relationship between species diversity and other environmental factors, such as soil composition, are necessary to determine the main cause of the continuing legacy of land use.
Reproductive biology of Lepanthes selenitepala and Lepanthes rubripetala: Two endemic orchids of Puerto Rico
Elana Peach-Fine and José J. Fumero-Cabán
The orchid family (Orchidacea) is one of the largest families of flowering plants. Approximately one third of all orchid species have specialized to attract pollinators without providing any nectar reward, these are referred to as deceptive species. Currently there is no conclusive theory as to the origins and maintenance of deception in the orchid family. Key variables have been identified, but further research is needed to understand this evolutionary phenomenon. We studied the reproductive biology of two Puerto Rican Lepanthes species, L. selenitepala and L. rubripetala. Additionally a pollinator study of these orchids was conducted and lab observations of a third, proportedly cleistogamous Lepanthes species, L. dodiana, were made. Reproductive studies were inconclusive for L. selenitepala, but a very high fruit set, 29%, lead to suspicions of autogamy. L. rubripetala was shown to be self-incompatible. The flowering of L. dodiana proved this individual to not be entirely cleistogamous, but questions remain about its breeding system. The pollinator study yielded no direct observations of a pollination event, but 13 fungus gnats (Diptera: Sciaridae), suspected pollinators, were captured in water pan traps.
Influence of moss thickness and stream current on the distribution of Lepanthes (Orchidaceae) on Quebrada Sonadora
Juan G. García Cancel and Elvia J. Meléndez-Ackeman
Epiphytes are a diverse group of plants that compromise over 10 % of the world total flora. In some humid tropical forests, such as the cloud forests, epiphytes may be the most species-rich life form. Lepanthes rupestris Stimson is perhaps one of the best studied orchids of the Neotropics. This is a self-incompatible orchid that exhibits patchy distributions and low reproductive rate due to infrequent pollination events. One hypothesis is that population recruitment and establishment may be related to the presence or degree of moss cover, but this hypothesis remains untested. This study assessed: 1. If any relationship exists between mosses thickness and L. rupestris seedlings growth, should there be a relationship it would tend to produce more seedlings in a medium thick moss. 2. If some species of mosses have a negative effect on the L. rupestris establishment then the lack of this (or these) moss(es) would provide a better habitat for seedlings and their numbers would be greater than in areas were they are present. Finally, 3. if the exposure to the direct strike of water and less exposure of sunlight limit the mosses establishment then intermediate areas, those protected by shade from direct sunlight and the direct strike of the main body of water during heavy rains yet with some humidity will be the best habitat for L.rupestris seedlings.
Orchid – phorophytic interactions: Exploring vegetative adaptation of tropical epiphytic orchids
Maria Carr and James D. Ackerman
Constituting approximately two-thirds of the family Orchidaceae, epiphytic orchids superbly demonstrate the vast diversity of orchids. Considering their small, isolated populations, tropical epiphytic orchids have proven excellent models for studies of evolution. This study involved four tropical epiphytic orchids from El Yunque National Forest, Puerto Rico (18°19'N, 65°45'W): Pluerothallis ruscifolia, Pluerothallis pruinosa, Jacquiniella globosa and Mormolyca pudica. We explored the more obscure thus overlooked vegetative adaptations of these orchids by investigating potential phorophyte specificity. There was no host-specificity found among these orchids. Out of 48 tree species that occurred within the plots, 33 of them were hosts to at least one of these orchids. Still, there were indeed patterns observed in that some hosts were preferred while others completely avoided. By comparing incidences of orchids within plots that were perhaps exposed to similar seed rain to the fitness of the orchids on those species of trees, we discovered that on the most orchid-loving trees, orchid individuals were not necessarily more fit. We postulated that this could be due to the orchid-mycorrhizal interactions being more influential on orchid fitness than the environmental conditions and resources provided by the host tree. A potential explanation for the patterns observed is that the fungi are distributed heterogeneously and that orchids have specialized to perform better when parasitizing particular species of fungi which, in turn, prefer particular species of trees. The last portion of our survey considered the influence of moss and/or lichen coverage, elevation and DBH of the host trees. Data provided that DBH and moss coverage both have some impact on the frequency of orchids on their hosts, although minimal and only applicable to certain species of orchids in certain stages of their life cycles.
The responses of Puerto Rican spider communities to disturbance in different forest types
Matthew Nielsen and Paul Klawinski
Disturbance and the succession which follows it play essential roles in all ecosystems. To better understand post-hurricane succession in sub-tropical forests we will study the changes in the spider community in the different forest types found in El Yunque national park (tabonuco, palo colorado , palm, and dwarf forest) in the summers following hurricane Georges. Since spiders depend heavily on vegetation structure, the state of the spider community will serve as a good indicator of the state of succession in the forest. To sample the spider community, we will use the protocol outlined by Coddington et al. (1991), which consists of aerial search, ground search, vegetation beating, and litter collection. We will use non-metric multidimensional scaling to analyze the changes to the community over time.