|LUQ Research Categories||Project Title||Project Description or Abstract||Investigators|
|Animal population dynamics||Anole Population Dynamics||
The population activity, abundance, density, and spatial distribution of anoline lizards (genus Anolis) were investigated in tabonuco rain forest of the Luquillo Mountains, Puerto Rico. A summary of the aspects of anole biology relevant to food web structure and organization in tabonuco forest were developed from these studies. The anole activity in different habitats was studied in relation to the changes in canopy structure before and after Hurricane Hugo (September 1989). The drastic reduction in canopy structure immediately following the hurricane confined anole activity to the lower few meters of the forest. Anolis stratulus, a canopy species, apparently responded to changes in microclimate. Relative abundance estimates based on vertical transect surveys were A. stratulus (82%), A. gundlachi (11%), and A. evermanni (7%). Vertical surveys documented that A. stratulus was the most abundant anole species in the forest and inhabited the canopy at estimated population densities of 25,870~7005 (dry season) and 21,333~6638 (wet season) individuals/ha. Field studies demonstrated the importance of small diameter perches in the structural habitat of this species. Individual A. stratulus occupy small, ellipsoidal home ranges and/or territories (males only) with a mean diameter of 6.2 ñ 1.2 m layered within the 10-14 m thick canopy. This three-dimensional habitat partitioning has not previously been noted for a vertebrate species and may account for the ability of A. stratulus to reach extremely high population densities. On Caribbean islands where there are no large animals such as those found in mainland ecosystems (e.g., tapirs, jaguars), anoles constitute a substantial portion of the total animal biomass. Their abundance, widespread ecological distribution, and functional role as higher order consumers make them important components of insular animal communities throughout the Caribbean. Recent studies have demonstrated their importance in structuring food webs on Caribbean islands (Schoener and Toft 1983; Schoener and Spiller 1987), and Reagan (1986) described the role of anoles as important consumers in the food web of tabonuco forest at El Verde.
|Animal population dynamics||Avian populations Long-Term Monitoring||
The project is part of the study of the resilience of populations after multiple disturbances. This study uses long-term population measurements of key species as a baseline to evaluate changes in populations in response to disturbance. The distribution of counts at 40 points in the Luquillo Forest Dynamics Plot allows correlation of population changes at each point with changes in plant and animal species and abundance at the same point.
|Robert B. Waide|
|Community composition||Bisley Vegetation Plots||
Relationships between landforms, soil nutrients, forest structure, and the relative importance of different disturbances were quantified in two subtropical wet steepland watersheds in Pueno Rico. Ridges had fewer landslides and treefall gaps, more above-ground biomass, older aged stands, and greater species richness than other landscape positions. Ridge soils had relatively low quantities of exchangeable bases but high soil organic matter, acidity and exchangeable iron. Valley sites had higher frequencies of disturbance, less biomass, younger aged stands, lower species richness and soils with more exchangeable bases. Soil N, P, and K were distributed relatively independently of geomorphic setting, but were significantly related to the composition and age of vegetation. On a watershed basis, hurricanes were the dominant natural disturbance in the turnover of individuals, biomass, and forest canopy. However. turnover by the mortality of individuals that die without creating canopy openings was faster than the turnover by any natural disturbance. Only in riparian areas was forest turnover by treefall gaps faster than turnover by hurricanes. The same downslope mass transfer that links soil forming processes across the landscape also influences the distribution of landslides, treefall gaps, and the structure and composition of the forest. One consequence of these interactions is that the greatest aboveground biomass occurs on ridges where the soil nutrient pools are the smallest. Geomorphic stability, edaphic conditions, and biotic adaptations apparently override the importance of spatial variations in soil nutrients in the accumulation of above-ground biomass at this site.
|Community composition||Bromeliad Invertebrate Diversity in Dominica||
A study of the bromeliad invertebrate fauna in forests at three elevations in Dominica, as part of cross site studies on bromeliad invertebrates in different tropical localities.
|Community composition||Bromeliad Invertebrate Diversity in the LEF||
Tank bromeliads form complex, but discrete, microcosms whose biological, physical and chemical parameters can be sampled in their entirety. Plants impound canopy litter and throughfall water, and form a microhabitat for mainly detritivorous animal communities. This study of their fauna provided a natural way to examine diversity, and also the relationship between diversity and habitat parameters at different elevations in the LEF.
|Ecosystem dynamics||Canopy Arthropods (Canopy invertebrate responses to Hurricane Hugo)||
We study the canopy invertebrate responses to Hurricane Hugo, tree species, and recovery time since 1991. Some of the results include: Hurricane disturbance affects invertebrate abundances significantly. Changes in functional organization are consistent with comparable studies of arthropod responses to canopy removal during harvest in temperate forests. Tree species also affected invertebrate abundances significantly, but invertabrate communities did not differ significantly between the three early successional and three later successional tree species. Leaf area missing, an indicator or herbivore effect on canopy processes, showed significant seasonal and annual trends, as well as differences among tree species and hurricane treatments. Herbivore abundances and leaf area missing were not related to concentrations of nitrogen, phosphorous, potassium, or calcium in the foliage. This study demonstrated that invertebrate community structure and herbivory are dynamic processes that reflect the influences of host species and variable environmental conditions.
|Timothy D. Schowalter|
|Vegetation dynamics||Canopy Structure||
There are two main goals in this project. One one-time goal was to measure the dimensions of gaps present at El Verde research area, and the other continuing goal is to record changes in three dimensional canopy structure in three one- hectare sized plots, one each in tabonuco, colorado, and cloud forests.
|Ecosystem dynamics||Canopy Trimming Experiment (CTE)||
Hurricanes are important drivers of periodic disturbances on tropical forests of the Luquillo Mountauns. The immediate impact of this disturbance is on the canopy biomass which is redistributed from the canopy compartments to the detrital pool of the forest floor hence creating a wide opened canopy. The Canopy Trimming Experiment (CTE) is a long-term experiment designed for two purposes: 1) to decouple the effect of canopy disturbance (e.g., increasing light levels, temperature, moisture, etc.) from those of increased detrital inputs on rates of germination, growth, survival, detritus processing, nutrient cycling, soil conditions, and trophic structure, and 2) to increase the frequency of simulated hurricane effects above background levels to once every six to ten years. Climate change models predict increased frequency and intensity of Caribbean hurricanes (Emmanuel 1987, Goldenberg et al. 2001), and the goal is to evaluate predictions regarding the effects of an increased rate of hurricane disturbance on tabonuco forest (Sanford et al. 1991). The interaction of biotic and abiotic processes, all modified by the disturbance, are key in determining ecosystem responses because they regulate critical ecosystem fluxes and storage associated with detritus decomposition. These processes define detrital dynamics and play a central role in the recovery of forest structure and function after disturbance. Therefore, a third component of this experiment was to implement a series of short-term biotic manipulations nested within the large-scale CTE design, consisting on faunal manipulations to measure the strength of interactions between autotrophic and detrital food webs in the context of hurricane-associated disturbance, which allowed to asses the important components of the foodwebs. The overall hypothesis is as follow: Short-term dynamics of key response variables after disturbance will be a function of the interaction between microclimate and detrital inputs, whereas long-term dynamics (particularly of SOM and NPP) will be a function of detrital inputs.
CTE Litter Basket Decomposition Experiment: The objective was to determine how green litter deposition and canopy opening associated with a hurricane independently and together affect rates of decomposition of pre-existing litter and green hurricane litter. In addition, changes in litter quality and quantity and changes in microenvironment were hypothesized to bring about changes in abundance of white-rot litter basidiomycete fungi and their activity in translocating nutrients between litter cohorts. Fungal connectivity was determined between litter cohorts that were demarcated with screens. Analysis of nutrient concentrations and content will determine which litter cohorts became nutrient sources and which ones became sinks following canopy opening and/or deposition of green litter. Litter moisture, fungal connectivity to the pre-weighed senesced leaf cohort and leaf mass loss were all slowest in the treatment with canopy trimming and debris removal and fastest in the closed canopy with added debris. Addition of green leaf litter ameliorated the environment in the senesced litter layer below and buffered it from effects of canopy opening, resulting in similar fungal connectivity and mass loss in control and trimmed canopy plus debris plots.
CTE Ferns: The species composition (diversity) and abundance of all of the ferns in all subplots of the CTE plots were assessed annually beginning in January, 2003 by the researcher. Ferns in all plant measurement subplots are also monitored and measured (by staff) at regular intervals and the experiment proceeds to detect changes in growth, diversity and abundance.
CTE Snail data: The objective of the CTE snail data is to determine how green litter deposition and canopy opening associated with a hurricane independently and jointly affect population dynamics and community composition of terrestrial gastropods. Because canopy openness can be expected to increase abiotic stress on gastropods, whereas litter deposition should provide increased resources and refugia, tradeoffs can be expected.
CTE Canopy Arthropods: This project addresses canopy invertebrate responses to CTE treatments, for comparison with invertebrate responses to canopy-opening hurricane disturbances dating from 1991. One year of pre-treatment and three years of post-treatment data are available. Statistical analyses are in progress.
CTE Litterbag Invertebrate Counts and Weights: A long-term experiment to increase the frequency of simulated hurricane effects above background levels to once every six years. The experiment will determine effects of repeated disturbance of the forest canopy and increased detrital inputs to the forest floor on germination, growth, survival, nutrient cycling, soil conditions, and trophic structure. Using leaf litter in litterbags, the aim of this part of the experiment was to examine the response of litter invertebrates to canopy disturbance [e.g., hurricanes], and to distinguish between the effects of canopy removal and detrital inputs. The effects of different litterbag mesh size and litter type [fresh or senescent] was also studied.
CTE Litter Basket Microbial diversity DNA data: Leaf Litter Microbial Communities at different stages of decomposition with and without canopy opening and debris deposition. Hurricanes are common disturbances affecting forest ecosystems in the Caribbean. Our objective was to determine the relative abundance and diversity of microorganisms in leaf litter at different stages of decomposition, and the influence of canopy opening and debris addition or removal. The study was conducted in the tabonuco forest (subtropical moist) at El Yunque Rain Forest, Puerto Rico. Three blocks with four treatment plots were established. TRFLP profiles of the 16S rDNA digested with MnlI and fungal ITS digested with HaeIII showed that the microbial communities at 17, 31 and 55 weeks were highly divergent among treatments. Ratio of fungal to bacterial phylotypes increased for closed canopy with debris addition. Leaf mass loss was slowest in the treatment with canopy trimming and debris removal. Microbial community changes through time can be related to microclimate and the availability of labile compounds. Fungi appeared to control the succession of microorganisms in decomposing leaves.
CTE soil and Leaf litter microbial community analysis: Microorganisms play an important role in the forest's restoration through their detritus dynamics. Our objective was to determine how the canopy openings and debris pulses affect the soil and leaf litter microbial community structure and composition in the forest before and after the canopy manipulation. We monitored the soil and leaf litter communities through the analysis of their cellular fatty acids also called ester linked fatty acid methyl ester (EL-FAME).
CTE trace gases: This research explores the trace gas dynamics from the Canopy Trimming Experiment
CTE soil solution chemistry: Soil solution was collected monthly from zero tension lysimeters installed in the CTE plots. Sampling began prior to cutting the canopy and continue to the present.
|Community composition||Community Composition of Litter Invertebrate||
A study of the litter invertebrate fauna in litter from palm and non-palm canopies in each of the three main forest types in the LEF was undertaken to distinguish between the effects of elevation and of litter quality and quantity on the composition and biomass of the litter invertebrate community.
|Community composition||Community Composition of Plants||
The composition of plant communities changes with elevation in the Luquillo Experimental Forest. The goal of this project is to document the patterns of these changes, and in particular, to determine whether the distributions of individual species are independent of one another, or whether they are related, in either a congruent or a hierarchical manner. Twenty-four permanent vegetation plots, each 50m by 20m are being established in the LEQ, with eight plots each along three rivers, the Sonadora, Icacos, and Mamayes. The plots are being established at every 100m in elevation, starting at 200m above sea level. All woody, free-standing stems greater than 1cm dbh are being marked, identified and mapped into 5x5 subquadrats. We anticipate that gradient analysis will show whether the distributions of species are coincident or independent, enabling us to evaluate whether separate, genuine plant communities exist in the LEQ. Because the plots are permanent, we also expect that they will also us to better evaluate how different vegetation types, at different elevations, respond to large scale disturbances, especially hurricanes.