|LUQ Research Categories||Project Title||Project Description or Abstract||Investigators|
|Community composition||Community Ecology of Land Snails||
Terrestrial gastropods and walking sticks were sampled at 36-40 points on the grid at the Bisley Watersheds to investigate long-term population and community dynamics and response to disturbance. Terrestrial gastropods and walking sticks were sampled at 40 points on the Luquillo Forest Dynamics Plot at El Verde twice annually from 1991-2002 to investigate long-term population and community dynamics and response to disturbance.
Densities: Densities of invertebrates and apparency of plant species are estimated to investigate the effects of disturbance on long-term population dynamics, habitat associations, and spatial distributions.
Habitat: To investigate habitat associations of terrestrial invertebrates, apparency of 17 plant groups (species, genera, families) from 0-3 m from the ground was estimated at 36 points on the grid at Bisley Watersheds 1 and 2 in 1994 and 1999.
|Community composition||Community Ecology of Streams Snails||
Diadromous fauna, migrating between marine and coastal streams is dominant in the neotropics. However, the factors controlling their population distribution and size are poorly understood. The migratory snail Neritina virginea (Gastropoda: Neritidae), abundant in estuaries and coastal rivers in the Caribbean, was studied to understand those factors. The objectives of the study were three-fold: 1) to identify the factors controlling the distribution of diadromous fauna at different spatial scales, 2) to determine patterns and causes of massive upstream migrations and their importance for population persistence, and 3) to integrate this knowledge into conservation strategies for migratory species and stream management plans.
After a survey of 32 coastal streams around Puerto Rico (Greater Antilles), it was evidenced that physical variables operating at different levels of the spatial hierarchy controlled longitudinal distribution of N. virginea. The hierarchically organized variables were river-ocean connectivity (regional scale), instream barriers and water chemistry (stream-network scale), habitat hydraulics (reach scale) and nearbed-flow roughness and depth (habitat scale). However, michohabitat scale distribution depended upon habitat and reach scale context. At habitat scale, water depth in pools, and nearbed flow roughness in riffles were the most important controls. At the reach scale, spatial heterogeneity among and within streambed patches was related to flow refugia, therefore controlling sensitivity of N. virginea density to flooding disturbances.
In addition, the role of structures (bridges) and maintenance activities (downstream channel realignment) associated to road crossings over streams was assessed. By splitting the stream channel and deflecting the flow, bridge pilings altered upstream migration routes. In particular, migratory individuals used more frequently boulder-and-cobble riffle reaches and avoided gravel-bed run reaches. Impact assessment of channel realignment over a 70 m reach in lower Rio Mameyes (NE Puerto Rico) showed that increase in frequency of fine sediment patches contributed to local population depletion and high mortality of juvenile individuals migrating upstream. As a consequence a population located 100 m upstream became isolated and did not recover from a crash caused by a major storm flood occurred after the channel realignment. In conclusion, distribution and size of populations of diadromous fauna such as N. virginea in coastal streams is influenced by hierarchically organized variables. By affecting variables at microhabitat to reach scales, road crossings over streams contribute to reduce longitudinal connectivity, and isolate upstream populations of N. virginea.
|Effie A. Greathouse|
|Ecosystem dynamics||Decomposition Fungal-Plant Interactions||
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.
|Animal population dynamics||Diatom Population Dynamics||
Monthly collections of benthic diatoms are made at four sites in the Rio Mameyes of northeastern Puerto Rico. The sites range from an unpolluted closed canopy headwater stream within the National Forest, to a small, highly polluted coastal plain tributary that drains a golf course and surrounding suburban development. Diatoms are collected by cleaning a standardized area of randomly selected rocks from each site. The identification of the composition and abundance of diatoms in each site will be used to identify species and communities that reflect water quality and community response to floods, low flows, and water pollution.
|Animal population dynamics||Differential Abundance of Microbial Functional Groups along the Elevation Gradient from the Coast to the Luquillo Mountains||
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.
|Animal population dynamics||Earthworm Population Dynamics||
Plant communities may impose strong control on soil fauna populations. We compared and examined patterns of earthworm abundance, species composition, and distribution pattern of earthworms in tree plantations and secondary forests of Puerto Rico. Our results indicate that variation in plant species composition and soil properties between plant communities can trigger differences in earthworm abundance and distribution pattern within a tropical wet forest.
|Animal population dynamics||Ecological studies of dams and migratory fauna||
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.
|Effie A. Greathouse|
|Ecosystem dynamics||Effects and Recovery from Poisoning||
Quebrada Sonadora was poisoned with chlorine bleach 140 m upstream from the bridge of Road 186 in the LEF causing massive mortality of freshwater shrimps over a ~500 m reach (300 m a.s.l. , Fig. 1). The poisoning was discovered on 12 March 1999 and was estimated to have occurred on 10 March, based on the state of decay of thousands of dead shrimps observed along the river. No carcasses of Sicydium plumieri were observed. While no bleach bottles were found at the site of this poisoning, bleach bottles have been found at other stream poisonings documented in the LEF, and locals report that swimming pool tablets are also sometimes used in illegal chlorine poisonings. Chlorine is known to display rapid volatilization, transformation, and flushing in lotic waters; thus, LEF chlorine poisonings are pulse disturbances. When the poisoning was discovered, the benthos in pools of the poisoned reach was visibly and dramatically different than the pool benthos upstream. In downstream pools, shrimps were not observed, and thick layers of sediment and fine particulate organic matter (FPOM) coated the rocks. In pools upstream from the poisoning, xiphocaridid and atyid shrimps were active, and no visible sediment/FPOM was observed on rocks. In contrast, there were no pronounced differences in sediment/FPOM accrual between riffles above and below the poisoning. These visual observations of immediate effects suggested that the poisoning event represented a unique opportunity to quantify large-scale effects of shrimp removal for comparison to previous small-scale manipulative experiments conducted in the Sonadora and tributaries (Prieta, Toronja). In the first component of this project, from March 26 to April 6, 1999, we quantified differences between the first 100 m of the poisoned reach and a 100-m reference reach immediately upstream from the poisoned reach, and we conducted a manipulative experiment, adding freshwater shrimps (Xiphocaris elongata, Atya lanipes, Macrobrachium spp. ) to 3 poisoned pools for comparison to 3 poisoned pools in which no shrimps were added. In the second component of this project, from June 15 to July 28, 1999, we assessed recovery of the poisoned reach, comparing the upper 315 m of the poisoned reach to a 250-m reference reach immediately upstream from the poisoning.
|Animal population dynamics||Elevational Gradients of Gastropod Biodiversity||
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.
|Michael R. Willig|
|Food web dynamics||Experimental Food Web Manipulation||
Results of an experimental manipulation of the understory food web by controlling densities of Anolis lizards and Eleutherodatylus frogs and measuring the response of arthropods and plants (in terms of herbivory). These manipulations were performed by constructing exclosures that controlled the entrance and exit of anoles and coquies.