Caribbean Slope Research Articles

Late-Holocene paleoenvironmental change at mid-elevation on the Caribbean slope of the Cordillera Central, Dominican Republic: a multi-site, multi-proxy analysis

High-resolution proxy records from the circum-Caribbean region indicate significant variation in Late Holocene climate, especially precipitation, attributed primarily to shifts in the mean annual position of the Intertropical Convergence Zone (ITCZ). The paleoenvironmental and cultural impacts of this Late-Holocene climate variability have been analyzed intensively in the western Caribbean, and to a lesser extent in the southern Caribbean. However, the occurrence and impacts of Late Holocene climate shifts in the eastern Caribbean, especially in island interiors, has not been well documented. Here we present sediment records of Late-Holocene paleoenvironmental change from two lakes located on the Caribbean slope of the Cordillera Central in the Dominican Republic that span the last ∼3000years. Sediment characteristics, pollen, charcoal, biogenic carbonate assemblages and isotopic composition, and bulk sedimentary carbon isotope values in Laguna Castilla and Laguna de Salvador indicate extreme shifts in hydrology, vegetation, and disturbance regimes in response to climate change and human activity in the lake watersheds. Close correspondence between the hydrological histories of the lakes and trace metal concentrations in sediments of the Cariaco Basin indicate that precipitation variability here responds to the same controls, and may similarly reflect shifts in the mean annual position of the ITCZ. Human occupation of the watersheds appears to be closely linked to severe dry periods and may indicate larger scale cultural responses to precipitation variability on the island of Hispaniola. Prehistoric human populations strongly affected vegetation and disturbance regimes in the lake watersheds. Impacts may have lasted several centuries and may have been more severe than impacts of modern populations.

Distribution models for the amphibian chytrid Batrachochytrium dendrobatidis in Costa Rica: proposing climatic refuges as a conservation tool

ABSTRACTAim We use novel data on the occurrence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in Costa Rica to model its potential distribution in that country.Location Lowland and montane areas of Costa Rica.Methods We use published and new data on the presence of B. dendrobatidis on 647 amphibians (35 species). Screening was performed through histological techniques by which 156 sites were surveyed. Of these, 21 were found to have the amphibian chytrid. Maxent, a presence‐only distribution modelling technique, was used to create 100 predictions of B. dendrobatidis occurrence, of which the most accurate 10 (based on area under the receiver‐operating characteristic curve) were chosen to create a composite distribution model. This approach increased confidence in model predictions, distinguishing areas of high probability of occurrence and low variability across model runs (higher confidence) from those with high probability but high variability (lower confidence).Results Predicted distribution patterns were not uniform along Costa Rica's mountains, where most amphibian declines have occurred. The pathogen was predicted to occur with greater probability on the Caribbean slopes than on the Pacific slopes. While high temperature seems to constrain the distribution of the pathogen, areas that also have small amounts of rainfall during the driest period of the year were predicted to have low probability of B. dendrobatidis occurrence.Main conclusions The model predicts that the Santa Elena Peninsula and the Central Valley have low probabilities of B. dendrobatidis occurrence, suggesting that they could function as refuges for amphibians. In such refugial areas, one could expect B. dendrobatidis to be absent, or to be present in low abundance (rendering an epidemic outbreak of chytridiomycosis unlikely). Craugastor ranoides, which belongs to a group of frogs particularly sensitive to chytridiomycosis outbreaks, persists in the hot and seasonally dry Santa Elena Peninsula but disappeared in the nearby colder and more humid Guanacaste Volcanic Chain. This information suggests that climatic refuges, where environmental conditions prevent disease outbreaks, could be an important component in amphibian conservation.

A New Species of Cyclanthera (Cucurbitaceae) from Alajuela Province, Costa Rica

Cyclanthera lalajuela Hammel & J. A. González, known only from the Caribbean slope of Alajuela Province, Costa Rica, is described. The combination of trifoliolate leaves with conspicuous, sessile glands at the base of the leaflets and unarmed fruits distinguish it from all other species in the genus.

Assessing the Scale of Prehistoric Human Impact in the Neotropics Using Stable Carbon Isotope Analyses of Lake Sediments: A Test Case From Costa Rica

AbstractAnalyses of pollen and other terrestrial microfossils in sediment profiles from neotropical lakes can complement and extend archaeological studies by documenting the timing of prehistoric human disturbances within watersheds. However, assessing the scale of prehistoric human impact from sedimentary microfossil assemblages alone is often difficult. We explore here the utility of combining stable carbon isotope (δ13C) analyses of lake sediments and isotopie mixing models to improve our ability to gauge the extent of prehistoric human disturbance recorded in sediment profiles. Our test case involves the analysis o f a sediment core from Laguna Bonillita on the central Caribbean slope of Costa Rica that spans approximately the last 2,700 calendar years. Variations in the δ13C values of the Laguna Bonillita sediments suggest that human population growth and environmental impacts in the watershed were at their maximum ~cal yr 300 B.C. This finding is in keeping with archaeological evidence of rapid regional population growth at this time but differs from initial interpretations of the sediment record that were based on pollen and charcoal analyses alone. We believe that the use of stable carbon isotope data from sediment profiles can improve estimates of the scale of prehistoric human impact and in doing so improve the contributions of paleoecological research to archaeology.

Beta diversity along environmental gradients: implications of habitat specialization in tropical montane landscapes

1. Understanding how species in a diverse regional pool are spatially distributed with respect to habitat types is a longstanding problem in ecology. Tropical species are expected to be specialists along environmental gradients, and this should result in rapid compositional change (high beta diversity) across landscapes, particularly when alpha diversity is a small fraction of regional diversity. Corollary challenges are then to identify controlling environmental variables and to ask whether species cluster into discrete community types along a gradient. 2. We investigated patterns of avian species' distributions in the Tilarán mountains of Costa Rica between 1000 m and 1700 m elevation where a strong moisture gradient exists. High beta diversity was found with both auditory counts adjusted for detectability and extensive capture data, revealing nearly complete change in community composition over a few kilometres on the Pacific slope. As predicted, this beta diversity was roughly twice as high as on temperate mountainsides. 3. Partial Mantel analyses and canonical correspondence analysis indicate that change in species composition is highly correlated with change in moisture (and correlated epiphyte cover) at different distances from the continental divide on the Pacific slope. Altitude was not a good predictor of change in species composition, as species composition varies substantially among sites at the same elevation. 4. Detrended correspondence analysis and cluster analysis revealed a zone of rapid transition separating a distinct cloud forest community from rainshadow forest. On the Caribbean slope, where a shallower moisture gradient was predicted to result in lower beta diversity, we found lower rates of compositional change and more continuous species turnover. 5. Results suggest that habitat specialization of birds is likely a strong ecological force generating high beta diversity in montane landscapes. Despite overall rapid rates of species turnover, zones of relatively coherent composition could be identified. 6. Landscapes with such high beta diversity are common in the tropics, although little studied. They offer high benefit/cost opportunities for conservation, particularly as climate change threatens to alter the species composition of communities of habitat specialists.

Blood parasites (Haemoproteus and microfilariae) in birds from the Caribbean slope of Costa Rica

AbstractWe studied blood parasites in wild birds within Hitoy Cerere Biological Reserve and Barbilla National Park in Costa Rica during the rainy season of 2004. We examined blood samples from 248 and 114 birds, respectively. Protozoan parasites of the genus Haemoproteus as well as microfilariae were found. Prevalence of Haemoproteus in birds was 0.8% and 4.4% in Hitoy Cerere and Barbilla, respectively, and differences were significant. Prevalence of infection by microfilariae was 8.1% and 3.5%, respectively, however, differences were not significant. Based on morphological characteristics, we divided microfilariae into two groups and nine morphotypes. In Hitoy Cerere, there were microfilariae of all nine morphotypes whereas in Barbilla we only found two morphotypes.

Genetic variation and recent population history of the tropical garAtractosteus tropicusGill (Pisces: Lepisosteidae)

The tropical garAtractosteus tropicusbelongs to one of the few extant lineages of early bony fishes. The genetic variation detected both within and among 11 natural populations ofA. tropicusin Mesoamerica along with the implications for their recent history are presented. Sequences from cytochromeb(307 bp) and cytochrome oxidase subunit II (607 bp) were used as data sources. Apparently, the populations of this fish have decreased in size because of anthropogenic pressures, such as habitat degradation and destruction. The observed values for nucleotide diversity (0·0016 ± 0·0018) and haplotype diversity (0·477 ± 0·302) suggest low levels of genetic variation. Nonetheless, most of the populations studied are currently in a period of genetic stasis. Recent isolation by distance, reduced gene flow and translocation were inferred as the processes maintaining this stasis. Phylogenetic analyses showed reciprocal monophyly between the haplotypes from Guatemala and the other populations. This, together with the observed genetic variation, suggests that the Guatemalan haplotypes might represent a new species. The haplotypes, other than those from Guatemala, exhibited a geographic pattern consistent with two main reproductive populations, one from the Pacific and the other from the Gulf of Mexico–Caribbean slope of Mesoamerica. Pleistocene glacial and interglacial periods might be responsible for moulding the heterogeneity in the genetic structure observed during this study.

Feeding Habits, Fine Structure and Microhabitat Preference of Euthyplocia hecuba (Hagen, 1861) (Ephemeroptera: Euthyplociidae) Nymphs from Honduras

The Euthyplociidae are a tropical and subtropical Ephemeropteran group. The aim of this study was to augment knowledge on some aspects of the biology and ecology of Euthyplocia hecuba (Hagen, 1861) nymphs. Mayflies were collected in the Rio El Padre, located on the Caribbean slope of Honduras. Diet, microhabitat preference and some fine morphological aspects of the nymphs were examined. E. hecuba nymphs are very specialised organisms that occupy a specific ecological niche in the lotic/benthic community. Immature stages show an evident preference for life in soft and fine substrata. They are detritivorous burrowers that ingest large amounts of fine particles deposited by river flow in sedimentation areas. They show peculiar morphological adaptations for life in this particular substratum, such as mouthparts modified for digging and collection of fine organic sediments, digging legs with shovel-like tibiae and massive femora, and filamentous gills.

New Costa Rican species of the genus Kritacris (Acrididae, Proctolabinae)

Two new species, K. dicronophallus and K. licrophallus, are described from the Caribbean slope of Costa Rica, and new localities are given for K. arboricola, the type of the genus. The genus is redefined and a key provided. The three species differ principally in their phallic structures, external differences are minimal and confined to small differences in coloration and the female subgenital plate.

Poecilocloeus (Acrididae, Proctolabinae) is not confined to Amazonia

Abstract Poecilocloeus septentrionalis is described from the Caribbean slope of Costa Rica. This is the first record of the genus from outside the Amazon basin, where it is highly speciose, with some 50 described species. The new species is morphologically a typical member of its genus.

Quantifying the extent of river fragmentation by hydropower dams in the Sarapiquí River Basin, Costa Rica

Abstract Costa Rica has recently experienced a rapid proliferation of dams for hydropower on rivers draining its northern Caribbean slope. In the Sarapiquí River Basin, eight hydropower plants were built between 1990 and 1999 and more projects are either under construction or proposed. The majority of these dams are small (<15 m tall) and operate as water diversion projects. While the potential environmental effects of individual projects are evaluated prior to dam construction, there is a need for consideration of the basin‐scale ecological consequences of hydropower development. This study was a first attempt to quantify the extent of river fragmentation by dams in the Sarapiquí River Basin. Using simple spatial analyses, the length of river upstream from dams and the length of de‐watered reaches downstream from dams was measured. Results indicated that there are currently 306.8 km of river (9.4% of the network) upstream from eight existing dams in the Sarapiquí River Basin and 30.6 km of rivers (0.9% of the network) with significantly reduced flow downstream from dams. Rivers upstream from dams primarily drain two life zones: Premontane Rain Forest (107.9 km) and Lower Montane Rain Forest (168.2 km). Simple spatial analyses can be used as a predictive or planning tool for considering the effects of future dams in a basin‐scale context. In the Sarapiquí River Basin, we recommend that future dam projects be constructed on already dammed rivers to minimize additional river fragmentation and to protect remaining riverine connectivity. Copyright © 2007 John Wiley & Sons, Ltd.

Seasonal variation in the stable isotopic composition of precipitation in the tropical montane forests of Monteverde, Costa Rica

Climate and land use change may diminish orographic clouds over tropical montane forests, stressing biota and water resources during dry seasons. From 2003 to 2005 we measured the stable isotopic composition of precipitation and throughfall in Monteverde, Costa Rica, to distinguish convective, wet season rainfall associated with the Intertropical Convergence Zone (ITCZ) from dry season, orographic rain produced by northeasterly trade winds. While event‐to‐event fluctuations of δ18O and δ2H are high, monthly samples reveal a seasonal signal that may be used to trace water through the hydrologic cycle. Deuterium excess indicates that water evaporated from land is an important flux to the region during the transitional and dry seasons when winds from the Caribbean slope dominate. Following the shift to convective rainfall at the start of the wet season, when the western equatorial winds influence the Pacific slope of Costa Rica, d excess values become depressed. Yet as the wet season progresses, d excess begins to climb. These data suggest that several months of rain are needed following an acute dry season on the northern Pacific slope before a terrestrial evaporative signal is detected in wet season precipitation. The evaporative flux may result from a wet season expansion of surface water bodies and flooding of seasonal wetlands.

Soluble Reactive Phosphorus Transport and Retention in Tropical, Rainforest Streams Draining a Volcanic and Geothermally Active Landscape in Costa Rica. : Long-Term Concentration Patterns, Pore Water Environment and Response to ENSO Events

Soluble reactive phosphorus (SRP) transport/retention was determined at four sites in three rainforest streams draining La Selva Biological Station, Costa Rica. La Selva is located at the base of the last remaining intact rainforest transect from 30 m above sea level to 3000 m along the entire Caribbean slope of Central America. Steam SRP levels can be naturally high there due to regional, geothermal groundwater discharged at ambient temperature. Monitoring since 1988 has revealed distinctive long-term differences in background SRP and total P (TP) for three streams in close proximity, and identified the impact of ENSO (El Nino Southern Oscillation) events on SRP-enriched reaches. Mean interannual SRP concentrations (± standard deviation) were 89 ± 53µg/l in the Salto (1988–1996), 21 ± 39µg/l in the Pantano (1988–1998), and 26 ± 35µg/l in the Sabalo (1988–1996). After January, 1997 the separate upland-lowland contributions to discharge and SRP load were determined monthly in the Salto. SRP in Upper Salto was low (19 ± 8µg/l, 1997–2002) until enriched at␣the upland-lowland transition by regional groundwater. Mean SRP concentration in Lower␣Salto (108 ± 104µg/l) was typically highest February–April, the driest months, and lowest July–September, the wettest. SRP concentration was positively correlated to the inverse of discharge in Lower Salto when ENSO data were omitted (1992 and 1998–1999), but not in the Upper Salto, Pantano, or Sabalo. TP was positively correlated to the inverse of discharge in all three streams when ENSO data were omitted. High SRP springs and seeps along the Lower Salto contributed 36% of discharge but 85% of SRP export 1997–2001. Annual SRP flux from the total Salto watershed (1997–2001) averaged 2.9 kg/ha year, but only 0.6 kg/ha year from the Upper Salto. A dye tracer injection showed that pore water environments were distinctly different between Upper and Lower Salto. Upper Salto had high surface water–pore water exchange, high dissolved oxygen, low SRP, and low conductivity similar to surface water, and Lower Salto had low surface water–pore water exchange, low dissolved oxygen, high SRP, and high conductivity reflecting geothermal groundwater influence. SRP export from the Salto was controlled by regional groundwater transfer, which in similar volcanic settings could be a significant P source. However, ENSO events modified the SRP concentration in the Salto suggesting that long-term monitoring is required to understand underlying SRP dynamics and P flux to downstream communities.

Determinants and spatial modeling of tree β-diversity in a tropical forest landscape in Panama

Abstract Questions: The objectives of this study were to clarify the extent to which environmental factors and geographical distance account for tropical floristic composition, and propose a methodology for delimiting the boundaries of floristic types based on species similarity. Location: The Panama Canal watershed. Methods: To assess which factors (climate, topography, geology and geographical distance) account for floristic composition, we performed Mantel tests on distance matrices and partitioned variation in species composition using canonical analysis. We used a permutation-based regression model computed on distance matrices and a hierarchical clustering of the tree composition to construct a predictive map of forest types of the Panama Canal Watershed. Results: We found that spatial variation alone explained 22–27% of species variation, while the fraction of species variation explained by environmental variables was smaller (10–12%); 13–19% of the variation was accounted for by the joint effect of environmental variation and geographic distance. The similarity-based map emphasizes the principal division in tree flora between the drier Pacific side and the wetter Caribbean slopes. Conclusions: The distribution of Panamanian tree species appears to be primarily determined by dispersal limitation, then by environmental heterogeneity. ‘Environmental segregation’processes do play an important role. Maps of broad-scale vegetation patterns based on thorough tree inventories can be used in conservation planning in the tropics.

Amphibians and Reptiles of La Selva, Costa Rica, and the Caribbean Slope: A Comprehensive Guide. By Craig Guyer and , Maureen A Donnelly. Berkeley (California): University of California Press. $60.00 (hardcover); $24.95 (paper). viii + 299 p + 207 pl; ill.; index. ISBN: 0–520–23758–7 (hc); 0–520–23759–5 (pb). 2005.

<i>Amphibians and Reptiles of La Selva, Costa Rica, and the Caribbean Slope: A Comprehensive Guide</i>. <i>By </i>Craig Guyer <i>and </i>, Maureen A Donnelly. <i>Berkeley (California): University of California Press</i>. $60.00 (hardcover); $24.95 (paper). viii + 299 p + 207 pl; ill.; index. ISBN: 0–520–23758–7 (hc); 0–520–23759–5 (pb). 2005.

TWO NEW SPECIES OF ELEUTHERODACTYLUS (ANURA: LEPTODACTYLIDAE) OF THE ALFREDI GROUP FROM EASTERN GUATEMALA

Two new species of frogs of the Eleutherodactylus alfredi group are described from Subtropical and Montane Wet Forests of the Montañas del Mico and the Sierra de Caral of the Caribbean slopes of Guatemala. They differ from other Guatemalan species in the group by having the fifth toe pad wider than the second, few melanophores on the abdominal area of the venter, and dorsal and ventral ground coloration. The species from the Sierra de Caral is larger in overall size and has smaller dentigerous fascicules than the one from the Montañas del Mico. These two species also differ between themselves in dorsal and ventral ground coloration.

Amphibians and reptiles of La Selva, Costa Rica, and the Caribbean slope: a comprehensive guide

Acknowledgments Introduction Geography, Climate, and Vegetation A History of Herpetological Research at La Selva Diversity Conservation Amphibia Gymnophiona Caudata Anura Reptilia Testudines Squamata Crocodylia Additional Species Field Data Sheet for Amphibians and Reptiles Glossary Literature Cited Art Credits Index

The larva ofMecistogaster linearis, with notes on its abundance in lowland rainforest of Costa Rica (Odonata: Pseudostigmatidae)

Abstract The larva of Mecistogaster linearis is described and illustrated from specimens collected within or near the Rio Dantas Wildlife Refuge at the north-western border of the Barbilla National Park on the Costa Rican Caribbean slope. Characters of F-0 larvae permit easy separation from Megaloprepus caerulatus, a species coexisting with M. linearis. Diagnostic characters include overall colour, shape of head, prementum and caudal gills. Exuviae may be determined using shape of mandibles. Two types of branched setae are present on tibiae and tarsi. Most are 3-branched but on front tarsi they are instead feather-shaped. It is suggested that these setae are used for eye-cleaning. M. linearis was a relatively rare but regularly occurring species in the study area throughout the 3-year study period.

The mid‐domain effect applied to elevational gradients: species richness of small mammals in Costa Rica

AbstractAim The objective of this study was to comprehensively document and examine the alpha and gamma patterns of species richness in non‐volant, small mammals (rodents, shrews and mouse opossums) along a tropical elevational gradient. These data were used to determine the support for existing hypotheses of species richness encompassing mid‐domain null models, as well as climatic, and community overlap hypotheses.Location Field studies were conducted along a Caribbean slope of the Río Peñas Blancas watershed in the north‐eastern region of Costa Rica between 750 and 1850 m at 10 sampling sites.Methods Species richness and abundances of small mammals were surveyed for four seasons including three temporal replicates at each of five elevational sites: late wet season (2000), early wet season (2001), and dry season (2002), and one spatial replicate at five different sites within the same elevations during the late wet season (2001). Species richness at elevations below 700 m was compiled from specimen records from 23 US national and international collections. Predictions of a null model based solely on geometric constraints were examined using a Monte Carlo simulation program, Mid‐Domain Null.Results In 16,900 trap nights, 1561 individuals from 16 species were captured. Both alpha and gamma species richness peaked at mid‐elevation between 1000 and 1300 m, with richness declining both at higher and lower elevations. Most of the empirical curves of species richness occur within 95% prediction curves of the mid‐domain model, although deviations from the null model exist. Regression of the empirical richness on the null model predictions explained nearly half of the variation observed (r2 = 0.45, P = 0.002).Main conclusions The geometric constraints of montane topography appear to influence the diversity pattern of small mammals, although climatic conditions including an intermediate rainfall and temperature regime, and distance from the persistent cloud cap also are correlated with the pattern of species richness. The predictions of productivity, and community overlap hypotheses are not supported with the empirical data.

Morphological and behavioral adaptations in Bolitoglossa colonnea (Caudata, Plethodontidae) in relation to habitat use and daily activity cycle

Bolitoglossa colonnea is a member of the Bolitoglossa striatula group (sensu Wake and Lynch 1976) that inhabits low to intermediate elevations on the Caribbean slope of Costa Rica and Panama, and the Golfo Dulce area in southwestern Costa Rica and extreme western Panama. Due to their secretive habits and the low density in which these tropical salamanders generally occur, observations are rare and their natural history remains poorly known. Here we present data from field observations and a behavioral experiment that extend our understanding of the biology of this tropical salamander. Both Dunn (1926) and Taylor (1952) reported observing specimens of B. colonnea at night crawling on fallen logs and on low vegetation near a small fast-flowing stream. Bruce (1997) invariably found these salamanders close to the forest floor, either on the upper surfaces of broad-leaved herbaceous plants, on a pinnatifid fern, or on the vertical stem of a small plant. A single individual was observed crawling on leaf litter on the forest floor. The latter author remarked upon not being able to locate any salamanders during the