Rates of decomposition depend on the particular interactions between producers and decomposer food webs. This interactions are determined by the intrinsic characteristics of both plant and decomposers and are as well influenced by abiotic factors. Field studies were designed to determine the influences of environmental parameters such as climate and microsite variation on the decomposition rates of five tree species from The Luquillo Experimental Forest (LEF). This also allowed us to determine the influence of leaf quality on the decomposer community and whether leaf physical, structural or phylogenetic relationships could be used as predictors of decomposition rates. Microcosms were used to separated the contribution of interactions between dominant plants and fungal species in decomposition rates. The rates of decomposition were determined by mass loss in both the field and microcosms experiments. In the microcosms systems, CO2 evolution by the decomposition of each of the five leaf litter substrates, by fungal species isolated from that particular leaf or from any of the other litter types, was obtained by using sodium hydroxide traps. There were significant differences in decomposition rates among leaf litter types both in field and microcosms experiments. There was also a significant effect of dry and wet periods in decomposition rates. Leaf litter decomposed faster under their tree sources than in a common plot. Among the leaf quality parameters, the lignin and nitrogen to lignin ratios were the best predictors of decomposition rates. Non polar elements, water soluble (simple sugars), P and Ca were positively correlated with percent mass loss (PML) while C was negatively correlated with PML. In the microcosms experiments we did not found specificity between fungi and their substrate (where the fungus was isolated), neither to substrates that were chemically, physically or structurally related to the plant were the fungi was originally isolated. Nevertheless, there were differential responses of particular fungi to plant substrates as well as influences of plant species on the fungal decomposers performance. The differential contributions of leaf species to carbon budgets (mass remaining and CO2 release) may be important in determining management practices for forest and agricultural systems. We found that species such as Manilkara bidentata may retain carbon in the ecosystem while other species such as Sapium laurocerasus decomposed rapidly and therefore, released nutrients quickly but with greater carbon losses. The absence of tight links between plants and fungal decomposer may indicate adaptation of fungi to changes in resource availability in a disturbed forest. Alternatively, this might indicate that the presence of a fungi in a particular substrate does not depend on the substrate's chemical o physical composition but on the presence of other members of the detrivoral community. Although the presence of generalist basidiomycetes made an important contribution to the decomposition of leaf species, the diversity of the decomposer and detrivoral community might be important in maintaining nutrient balances in the ecosystems since random encounters of plants, decomposers and detrivores may determine the residence time of a substrate on the forest floor.

Soil fungal communities respond to multiple abiotic and biotic factors that change along elevation gradients. This study documents changes in fungal and bacterial diversity, and abundance and composition of microbial functional groups along a subtropical elevation gradient. The elevation gradient is located in eastern Puerto Rico and is composed of five forest types each with characteristic vegetation. Soil samples were collected every three months from March 2003 thru March 2005. Soil fungal and bacterial communities were analyzed using fatty acid methyl esters (FAME) and TRFLP profiles. Diversity in this elevation gradient is higher at mid-elevations. Most G negative and G positive bacterial FAME were positively related to soil pH in MLR models, lower pH in mid-elevation forest soil may suppress bacteria favoring fungi. These data can be used as a benchmark for monitoring changes in microbial communities along elevation gradients caused by natural and anthropogenic disturbances, as well as global and regional climate changes.

The ecological roles of diadromous fauna (freshwater shrimps, fishes, and snails) in Puerto Rico were studied in the context of examining consequences of their loss from streams above large (height >15 m) dams. Four sub-projects were conducted:

(a) Indirect upstream effects of dams: consequences of migratory consumer extirpation in Puerto Rico. This sub-project examined the effects of decimation of migratory fauna populations on stream ecosystem structure above large dams. We compared streams above large dams to streams without large dams, in terms of relative abundances of migratory fauna and ecosystem components affected by migratory fauna in previous in situ experiments. Previous research indicated that: (1) all native fishes and shrimps in Puerto Rico are extirpated from habitats upstream of large dams without regular spillway discharge because they are diadromous, whereas streams above large dams with regular spillway discharge have greatly reduced abundances of diadromous fauna, and streams without large dams have relatively natural fish and shrimp assemblages (Holmquist et al. 1998); and (2) small-scale experimental exclusion of native shrimps and fishes decreases leaf decay rates and increases epilithic organic and inorganic matter, chlorophyll a, carbon, nitrogen, carbon-to-nitrogen ratio (C:N), and chironomid biomass (Pringle et al. 1999, Crowl et al. 2001, March et al. 2001, March et al. 2002). We examined whether sites above large dams had higher levels of epilithic coarse organic matter, algae, fine organic and inorganic matter, carbon, nitrogen, C:N, and non-decapod invertebrates, consistent with previous findings of small-scale experimental shrimp and fish exclusions.

(b) Do small-scale exclosure/enclosure experiments have relevance for large-scale extirpation of migratory fauna? This sub-project took advantage of large dams to examine effects of experimental scale. Alteration of migratory stream populations due to large dams represents a large-scale (i.e. whole-catchment), long-term (i.e. decades) "extirpation experiment. " We compared this large-scale perturbation to four small-scale experiments (two exclusion experiments in sites with no large dams and two shrimp addition experiments in dammed sites) that we conducted in a subset of the sites sampled in sub-project (a). We examined whether small-scale experiments predicted effects at the large-scale in terms of direction and magnitude.

(c) Conservation and management of migratory fauna and dams in tropical streams of Puerto Rico. This sub-project was a review, in which we: (1) examined Puerto Rico's potential to serve as a window into the future of freshwater migratory fauna in tropical regions, given the island's extent and magnitude of dam development and the available scientific information on ecology and management of the island's migratory fauna, and (2) reviewed ecology, management and conservation of migratory fauna in relation to dams in Puerto Rico. Our review included a synthesis of recent and unpublished observations on upstream effects of large dams on migratory fauna and an analysis of patterns in free crest spillway discharge across Puerto Rican reservoirs.

(d) Ecological effects of non-migratory native and non-native fauna above large dams in tropical streams, Puerto Rico. This sub-project consisted of a set of electric exclusion experiments conducted above two of the dammed sites in sub-project a. Previous research demonstrated higher abundances of exotic fishes above large dams (Holmquist et al. 1998). Thus, these experiments examined whether exotic fishes affect stream ecosystem patterns and confound any interpretations in sub-project a regarding roles of migratory macroconsumers.

Elevational gradients are useful for assessing the manner in which animal species respond to environmental variation. Changes in elevation result in predictable changes in abiotic factors (temperature, precipitation) as well as in plant community composition and physiognomy, and may do so within a relatively small geographic area, minimizing the role of biogeographic or historical mechanisms in molding differences in animal species composition among sites. Paired elevational transects (250 m to 1000 m) in the Sonadora River watershed were sampled at 50 m intervals to decouple underlying environmental gradients that are associated with changes in elevation and that are hypothesized to structure animal communities. One transect (mixed forest) reflected changes in abiotic and biotic conditions, including forest type (i.e., tabonuco, palo colorado, and elfin forests), whereas the second transect reflected changes in environmental conditions but not forest type, as its constituent plots were all located within palm dominated forest. Gastropods on each plot were sampled 4 times during the summer of 2007 (wet season) on the mixed forest transect and 3 times during the summer (wet season) of 2008 on the mixed forest and palm forest transects. Sampling was conducted at night (2000-0400 h). Each time a plot was surveyed, 2 people searched all available surfaces (e.g., soil, litter, rock cover, vegetation, debris) up to a height of approximately 3 m for 15 minutes or until all substrates had been completely searched, whichever was longer. Sampling was not repeated at any one elevation until after the entire gradient was sampled.