The Luquillo Long-Term Ecological Research Program (LUQ) focuses on understanding factors driving long-term change in tropical forest ecosystems in the Luquillo Mountains of Puerto Rico. Building from an earlier emphasis on natural disturbance (hurricanes, landslides, droughts, floods) and ecosystem response to disturbance, LUQ will continue studies of ecosystem structure and processes in mid-elevation tabonuco forest, extend research into other forest types along an elevation gradient, and begin investigations of regional-scale processes affecting the Luquillo Mountains. Four approaches will be used: long-term measurements and experiments, comparative analyses among different forest communities, gradient analysis from forest to urban ecosystems, and synthesis using conceptual and simulation models. Mounting evidence suggests that increasing hurricane intensity, declining rainfall in the mountains, and rising temperature in urbanized areas in the nearby lowlands can have significant effects on the ecosystems of the Luquillo Mountains. In this context, we ask: How do changes in disturbance regime and climate alter biogeochemical cycles, biotic structure, and ecosystem services in the Luquillo Mountains and northeastern Puerto Rico? This overarching question leads to three specific questions addressing key elements of our longterm conceptual framework, and nine hypotheses addressing these elements.

Leaffall Phenology in a Subtropical Wet Forest in Puerto Rico: From Species to Community Patterns

Zalamea, M. & González, G. (2008) Leaffall phenology in a subtropical wet forest in Puerto
Rico: from species to community patterns. Biotropica, 40, 295-304.

leaffall periodicity has been related to rainfall regime and dry season length. In weakly seasonal forests, where there is no marked dry season, other climatic factors could trigger leaf shed. In this study, we aimed to determine if other climatic variables (wind speed, solar radiation, photosynthetic photon flux density [PPFD], day length, temperature, and relative humidity) could be better correlated with patterns of litter and leaffall in a weakly seasonal subtropical wet forest in Puerto Rico. Leaffall patterns were correlated mainly with solar radiation, PPFD, day length, and temperature; and secondarily with rainfall. Two main peaks of leaffall were observed: April–June and August–September, coinciding with the periods of major solar radiation at this latitude. Community leaffall patterns were the result of overlapping peaks of individual species. Of the 32 species analyzed, 21 showed phenological patterns, either unimodal (16 species), bimodal (three species), or multimodal (two species). Lianas also presented leaffall seasonality, suggesting that they are subject to the same constraints and triggering factors affecting trees. In addition to solar radiation as a main determinant of leaffall timing in tropical forests, our findings highlight the importance of interannual variation and asynchrony, suggesting that leaffall is the result of a complex interaction between environmental and physiological factors.

behavioral thermoregulation in lizards: importance of associated costs

Raymond B. Huey
Behavioral Thermoregulation in Lizards: Importance of Associated Costs
Science 31 May 1974:
Vol. 184 no. 4140 pp. 1001-1003
DOI: 10.1126/science.184.4140.1001

The Puerto Rican lizard Anolis cristatellus behaviorally regulates body temperature in an open habitat but passively tolerates lower and more variable temperatures in an adjacent forest where basking sites are few and distant. Thermoregulation may be adaptive only when costs resulting from associated losses of time and energy are low.

Basal area growth for 15 tropical tree species in Puerto Rico

Parresol, B. R. 1995. Basal area growth for 15 tropical trees species in Puerto Rico. Forest . Ecology and Management; 73:211-219.

wildlife food and cover, and erosion control among other uses. Tree basal area growth data spanning 39 years are available on 15 species from eight permanent plots in the Luquillo Experimental Forest. The complexity of the rain forest challenges current forest stand modeling techniques. As a starting point individual tree basal area growth is modeled using the Chapman-Richards function constrained for hypothetical maximum tree size. In addition to initial tree diameter or basal area, significant explanatory variables are crown class, topographic position and degree of ground incline. Plots illustrate the differing growth patterns of the 15 tropical mixed/moist forest species. Two species exhibit exceptional growth. Buchenavia capitata (Vahl) Eichl. has basal area growth peaking at 87 cm2 year- ‘. The Manilkara bidentata (A. DC.) A. Chev. data show growth rates in excess of 60 cm* year-’ and the Chapman-Richards function indicates growth potential to a peak of 122 cm2 year-‘.

Multi-scale analysis of species introductions: combining landscape and demographic models to improve management decisions about non-native species

Brown, K.A., Spector, S.& Wu, W. (2008)Multi-scale analysis of species introductions:
combining landscape and demographic models to improve management
decisions about non-native species. Journal of Applied Ecology, 45,

1. Non-native, invasive species can affect biological patterns and processes at multiple ecological scales. The multi-scalar effects of invasions can influence community structure, ecosystem processes and function, and the nature and intensity of ecological interactions. Consequently, efforts to assess the spread of invasive species may benefit from a multi-scale analytic approach. 2. We analysed results from landscape- and population-scale models for Syzygium jambos , a nonnative tree in the Luquillo Mountains of Puerto Rico, to demonstrate a multi-scale approach that can be used to inform management decisions about invasive plants. At the landscape-level, we used an Ecological Niche Modelling approach to predict environmentally suitable habitats for the target plant. At the population-level, we constructed matrix projection models to determine the finite rate of population increase ( λ ) for S. jambos . We then extrapolated λ values to the landscape-scale to obtain a distribution map of λ values for the Luquillo forest. 3. The landscape analyses suggested that the most environmentally suitable habitats were those most similar to where S. jambos had already been observed. The population-level analyses showed that four of the seven populations had λ values less than 1, indicating that they were projected to be below replacement. The λ distribution map showed that S. jambos growth was highest in areas where it was most common and lowest in areas where it was most rare. 4. Our analyses further suggested that the importance of different drivers of invasion and the environmental variables that mediate them appear to be strongly scale-dependent. Past disturbances seemed most important for controlling invasions at fine-spatial scales; while abiotic environmental variables modulated coarse-scale invasion dynamics. 5. Synthesis and applications. We have shown that a multi-scale analytic approach can be used to manage invasive species by simultaneously targeting susceptible life stages and rapidly growing populations in a landscape. The utility of this approach stems from an ability to: (i) map the distribution of habitats that can potentially sustain λ values above replacement; (ii) identify populations to manage or monitor during selected stages of an invasion; (iii) forecast the probability for a target species to increase above a critical threshold abundance; and (iv) set priorities for control and monitoring actions.

Effects of different types of conditioning on rates of leaf-litter shredding by Xiphocaris elongata, a Neotropical freshwater shrimp

Crowl, Todd A.; Welsh, Vanessa; Heartsill-Scalley, Tamara 2006. Effects of different types of conditioning on rates of leaf-litter shredding by Xiphocaris elongata, a Neotropical freshwater shrimp.. J. N. Am. Benthol. Soc., 25(1):198-208.

Temperate headwater streams with closed canopies rely on inputs of terrestrially derived organic matter to provide the major energy basis for their food webs. Microbial colonization, or conditioning, makes leaf litter more nutritional and palatable to stream detritivores, but few studies have investigated the relative importance of litter source to macroshredders in tropical streams. We determined the source (terrestrial, aquatic, or aerial), quantity, and species composition of allochthonous inputs into the Quebrada Prieta, a tropical headwater stream in Puerto Rico, as a first step toward understanding the importance of conditioning history to rates of tropical leaf-litter processing by decapod consumers. Fresh leaves of 4 common species of leaves were treated by exposing them to different conditions for 2 wk. These exposure treatments (conditioning histories) represented routes by which leaves might enter streams and included submersion (aquatic input), incubation on the streambank soil (terrestrial input), and suspension above the ground (aerial input). Conditioned leaves were placed in small experimental microcosms with or without shrimp (Xiphocaris elongata) for 20 d. Shrimp significantly increased the rate of decomposition of all leaf species independent of conditioning history. Conditioning history had little effect on breakdown rates independent of the presence of shrimp. One species (Rourea surinamensis) had faster mass loss when the leaves were conditioned as aquatic inputs rather than as terrestrial or aerial inputs. Our results indicate that conditioning history has little effect on the ability of some macroconsumers to alter detrital foodweb dynamics in tropical streams. Tropical stream ecosystems may function differently from temperate ecosystems because of the dominance of large detritivores such as shrimps.

phytogeographical trends, centers of high species richness and endemism and the question of extinction in the native flora of puerto rico

Figueroa Colón, J. C. 1996. Phytogeographical trends, centers of high species richness and endemism, and the question of extinctions in the native flora of Puerto Rico. . The scientific survey of Puerto Rico and the Virgin Islands: an eighty year assessment of the island's natural history. Annals of the New York Academy of Sciences. New York: The Academy; pp. 89-102.

Thermal Biology of Anolis Lizards in a Complex Fauna: The Christatellus Group on Puerto Rico

Thermal Biology of Anolis Lizards in a Complex Fauna: The Christatellus Group on Puerto Rico
Raymond B. Huey and T. Preston Webster
Vol. 57, No. 5 (Late Summer, 1976), pp. 985-994

To describe the thermal biology of the three trunk-ground species of the Anolis cristatellus group on Puerto Rico, an island with 10 species of Anolis, we obtained samples of air and body temperatures of A. gundlachi (shady perches, montane forests), A. cristatellus (shady or sunny perches in open or closed forests, lowlands to mid-elevations), and A. cooki (sunny perches in open, xeric lowlands). Average body temperatures parallel altitudinal and habitat association (lowest for A gundlachi, highest for A. cooki). Within a species, body temperatures are strongly correlated with air temperatures and thus vary with altitude, time of day, habitat, and weather. Observed differences between sympatric species in body temperatures and habitat probably reflect physiological requirements, but may be magnified by competition. Relative thermal niche breadth of individuals of these species is approximated and compared with data on species from simple anole faunas to evaluate hypotheses on the evaluation of thermal niche breadth. Extent of basking behavior is inversely related to associated costs for these species. In closed forests where costs of raising body temperatures are high, A. gundlachi and A. cristatellus rarely bask and seemingly are routinely passive to ambient conditions. In open habitats where costs are low, A. cristatellus and A. cooki frequently bask.

Why tropical forest lizards are vulnerable to climate warming

Huey, R.B. et al. (2009) Why tropical forest lizards are vulnerable to
climate warming. Proc. R. Soc. Lond., B, Biol. Sci. 276, 1939–1948

Biological impacts of climate warming are predicted to increase with latitude, paralleling increases in warming. However, the magnitude of impacts depends not only on the degree of warming but also on the number of species at risk, their physiological sensitivity to warming and their options for behavioural and physiological compensation. Lizards are useful for evaluating risks of warming because their thermal biology is well studied.We conducted macrophysiological analyses of diurnal lizards from diverse latitudes plus focal species analyses of Puerto Rican Anolis and Sphaerodactyus. Although tropical lowland lizards live in environments that are warm all year, macrophysiological analyses indicate that some tropical lineages (thermoconformers that live in forests) are active at low body temperature and are intolerant of warm temperatures. Focal species analyses show that some tropical forest lizards were already experiencing stressful body temperatures in summer when studied several decades ago. Simulations suggest that warming will not only further depress their physiological performance in summer, but will also enable warm-adapted, open-habitat competitors and predators to invade forests. Forest lizards are key components of tropical ecosystems, but appear vulnerable to the cascading physiological and ecological effects of climate warming, even though rates of tropical warming may be relatively low.

Recovery of a tropical stream after a harvest-related chlorine poisoning event

GREATHOUSE, EFFIE A.; MARCH, JAMES G.; PRINGLE; CATHERINE M. 2005. Recovery of a tropical stream after a harvest-related chlorine poisoning event.. Freshwater Biology 50, :603-615.

1. Harvest-related poisoning events are common in tropical streams, yet research on stream recovery has largely been limited to temperate streams and generally does not include any measures of ecosystem function, such as leaf breakdown. 2. We assessed recovery of a second-order, high-gradient stream draining the Luquillo Experimental Forest, Puerto Rico, 3 months after a chlorine-bleach poisoning event. The illegal poisoning of freshwater shrimps for harvest caused massive mortality of shrimps and dramatic changes in those ecosystem properties influenced by shrimps. We determined recovery potential using an established recovery index and assessed actual recovery by examining whether the poisoned reach returned to conditions resembling an undisturbed upstream reference reach. 3. Recovery potential was excellent (score ¼ 729 of a possible 729) and can be attributed to nearby sources of organisms for colonisation, the mobility of dominant organisms, unimpaired habitat, rapid flushing and processing of chlorine, and location within a national forest. 4. Actual recovery was substantial. Comparison of the reference reach with the formerly poisoned reach indicated: (1) complete recovery of xiphocaridid and palaemonid shrimp population abundances, shrimp size distributions, leaf breakdown rates, and abundances of oligochaetes and mayflies on leaves, and (2) only small differences in atyid shrimp abundance and community and ecosystem properties influenced by atyid shrimps(standing stocks of epilithic fine inorganic and organic matter, chlorophyll a, and abundances of chironomids and copepods on leaves). 5. There was no detectable pattern between any measured variables and distance downstream from the poisoning. However, shrimp size-distributions indicated that the observed recovery may represent a source-sink dynamic, in which the poisoned reach acts as a sink which depletes adult shrimp populations from surrounding undisturbed habitats. Thus, the rapid recovery observed in this study is consistent with results from other field studies of pulse chlorine disturbances, harvest-related fish poisonings, and recovery of freshwater biotic interactions, but it is unlikely to be sustainable if multiple poisonings deplete adult populations to the extent that juvenile recruitment does not offset adult shrimp mortality.
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