Showing papers in "Biotropica in 2005"

Research priorities for neotropical dry forests

Abstract: El conocimiento actual de las dimensiones humanas y biof´isicas de los cambios en los bosque secos tropicales y sus efectos acumulativos esta en las etapas iniciales del descubrimiento acad´emico En este articulo, introducimos una serie de art´iculos cient´ificos asociados a este n´umero especial sobre bosques secos en los Neotropicos Estos art´iculos provienen de una distribuci´on muy variada de sitios en las Am´ericas y van desde las aplicaciones de sensores multi- e hiperspectrales, hasta el estudio del efecto que los huracanes causan en la regeneraci´on de los bosques secos Presentamos a la comunidad cient´ifica los resultados de un taller dirigido a la discusi´on de aquellas prioridades de investigaci´on en bosques secos La discusi´on se enfoca a lo largo de los v´inculos que se necesitan entre percepci´on remota, ecolog´ia y ciencias sociales La incorporaci´on las ciencias sociales dentro de la investigaci´on ecol´ogica podr´ia contribuir dram´aticamente al entendimiento de los bosque secos tropicales, as´i como tienen len a posibilidad de ayudar en el desarrollo de v´inculos importantes entre ciencia y pol´itica dirigida al manejo de los recursos presentes en este importante ecosistema

Catastrophic Population Declines and Extinctions in Neotropical Harlequin Frogs (Bufonidae: Atelopus)1

Abstract: We surveyed the population status of the Neotropical toad genus Atelopus, and document recent catastrophic declines that are more severe than previously reported for any amphibian genus. Of 113 species that have been described or are candidates for description, data indicate that in 42 species, population sizes have been reduced by at least half and only ten species have stable populations. The status of the remaining taxa is unknown. At least 30 species have been missing from all known localities for at least 8 yr and are feared extinct. Most of these species were last seen between 1984 and 1996. All species restricted to elevations of above 1000 m have declined and 75 percent have disappeared, while 58 percent of lowland species have declined and 38 percent have disappeared. Habitat loss was not related to declines once we controlled for the effects of elevation. In fact, 22 species that occur in protected areas have disappeared. The fungal disease Batrachochytrium dendrobatidis has been documented from nine species that have declined, and may explain declines in higher elevation species that occur in undisturbed habitats. Climate change may also play a role, but other potential fact ors such as environmental contamination, trade, and introduced species are unlikely to have affected more than a handful of species. Widespread declines and extinctions in Atelopus may reflect population changes in other Neotropical amphibians that are more difficult to survey, and the loss of this trophic group may have cascading effects on other species in tropical ecosystems.

Trap Spacing and Transect Design for Dung Beetle Biodiversity Studies1

Abstract: Standardized sampling methods are essential for comparing species diversity and abundance patterns across different studies and sites. Although dung beetles are widely used as a focal taxon in biodiversity studies, nothing appears to be known about the effective sampling area of dung-baited traps. Mark-recapture experiments using Canthon acutus showed that at least 50 m between traps should minimize trap interference, and that wind affects trap detectability. Consequently, we propose a standardized dung beetle sampling design.

Predicting the Distribution of the Amphibian Pathogen Batrachochytrium dendrobatidis in the New World

Abstract: One application of ecological niche modeling is predicting suitable areas for the establishment of invasive species. Herein, I model the fundamental niche of the chytrid fungus Batrachochytrium dendrobatidis, a pathogen linked to amphibian declines on several continents. Niche models were generated with the Genetic Algorithm of Rule-Set Prediction using point distribution data of the pathogen and digital maps of environmental variables integrated in a GIS environment. The distribution of regions suitable for B. dendrobatidis in the New World is extensive and includes significant portions of: (1) Sierra Madre Occidental pine-oak forest; (2) Sonoran and Sinaloan dry forest; (3) Veracruz moist forest; (4) Central America east from the Isthmus of Tehuantepec; (5) Caribbean Islands; (6) temperate forest in Chile and western Argentina south of latitude 30°S; (7) Andes above 1000 m of altitude in Venezuela, Colombia, and Ecuador; (8) eastern slopes of the Andes in Peru and Bolivia; (9) Brazilian Atlantic forest; (10) Uruguay, Paraguay, and northeastern Argentina; (11) southwestern and Madeira-Tapajos Amazonian tropical rainforests. The regions with the highest suitability for B. dendrobatidis include habitats that contain the world's most diverse amphibian faunas. Models were built with New World localities, but also showed strong predictability for B. dendrobatidis localities in the Old World. Out of a total of 59 reported Old World localities for B. dendrobatidis, 56 occurred within regions with high predicted suitability. I also present analyses of the environmental envelope of B. dendrobatidis and discuss the implications of the results for the conservation of amphibians in the neotropics.

Allometric models for tree volume and total aboveground biomass in a tropical humid forest in Costa Rica.

Abstract: Allometric equations for the estimation of tree volume and aboveground biomass in a tropical humid forest were developed based on direct measurements of 19 individuals of seven tree species in Northern Costa Rica. The volume and the biomass of the stems represented about two-thirds of the total volume and total aboveground biomass, respectively. The average stem volume varied between 4 and 11 Mg/tree and the average total aboveground biomass ranged from 4 to 10 mg/tree. The mean specific gravity of the sampled trees was 0.62 ± 0.06 (g/cm3). The average biomass expansion factor was 1.6 ± 0.2. The best-fit equations for stem and total volume were of logarithmic form, with diameter at breast height (R2 = 0.66 − 0.81) as an independent variable. The best-fit equations for total aboveground biomass that were based on combinations of diameter at breast height, and total and commercial height as independent variables had R2 values between 0.77 and 0.87. Models recommended for estimating total aboveground biomass are based on diameter at breast height, because the simplicity of these models is advantageous. This variable is easy to measure accurately in the field and is the most common variable recorded in forest inventories. Two widely used models in literature tend to underestimate aboveground biomass in large trees. In contrast, the models developed in this study accurately estimate the total aboveground biomass in these trees.

Amphibian Declines in Brazil: An Overview1

Abstract: Population declines have previously been reported for at least 31 amphibian species in Brazil, in the families Leptodactylidae (19), Hylidae (7), Centrolenidae (2), Dendrobatidae (2), and Bufonidae (1). In five Brazilian museum collections, we found no entries of new records dating back to at least 15 yr ago for 13 of these species. We suggest that these taxa be studied in more detail to verify their status and to generate basic ecological data. Museum data indicate that the remaining species have been recently found in areas of reported crashes, or elsewhere. Several apparent declines in Brazil can be associated with habitat loss, interspecific interactions, natural fluctuations, or lack of intensive sampling. Personal observations and field data also indicate possible declines in the states of Parana and Ceara as well as in highlands within the Cerrado biome, in the state of Minas Gerais. Records suggest declines of montane and stream-associated populations of Brazilian amphibians in apparently pristine habitats. Field work is necessary to confirm these cases and to examine whether factors associated with similar extinctions in other parts of the globe-such as pathogens and climate change-are also related to local disappearances. To clarify pending questions and perhaps circumvent new cases, it is important to invest in short- and long-term field studies, and in the maintenance and expansion of museum collections.

Tree Phenology in Adjacent Amazonian Flooded and Unflooded Forests

Abstract: Most phenological studies to date have taken place in upland forest above the maximum flood level of nearby streams and rivers. In this paper, we examine the phenological patterns of tree assemblages in a large Amazonian forest landscape, including both upland (terra firme) and seasonally flooded (vand igapforest. The abundance of vegetative and reproductive phenophases was very seasonal in all forests types. Both types of flooded forest were more deciduous than terra firme, shedding most of their leaves during the inundation period. Pulses of new leaves occurred mainly during the dry season in terra firme, whereas those in the two floodplain forests were largely restricted to the end of the inundation period. Flowering was concentrated in the dry season in all forest types and was strongly correlated with the decrease in rainfall. The two floodplain forests concentrated their fruiting peaks during the inundation period, whereas trees in terra firme tended to bear fruits at the onset of the wet season. The results suggest that the phenological patterns of all forest types are largely predictable and that the regular and prolonged seasonal flood pulse is a major determinant of phenological patterns in vand igap´ o, whereas rainfall and solar irradiance appear to be important in terra firme. The three forest types provide a mosaic of food resources that has important implications for the conservation and maintenance of wide-ranging frugivore populations in Amazonian forests.

Amphibian declines in Latin America : Widespread population declines, extinctions, and impacts

Abstract: Amphibian populations are in decline throughout Latin America; all families of frogs have experienced declines, but the species associated with aquatic habitats in upland areas have been most affected. Declines in Latin America were most common during the 1980s, but new declines continue to be reported. The causes of declines are varied, but they have most often been associated with habitat loss, a pathogenic fungus, and climate change. Scientists are just beginning to grasp the ethical and biological implications of losses of this magnitude. In this Special Section, we provide a general summary of the phenomenon and introduce five contributed papers that provide new data and new insights into Latin American declines.

Crop size and fruit neighborhood effects on bird visitation to fruiting Schefflera morototoni trees in Puerto Rico

Abstract: Studies of zoochorous seed dispersal systems often consider crop size, yet seldom consider the kinds and amounts of fruits surrounding parent plants (the fruit neighborhood) when attempting to explain among-plant variation in fruit removal. We studied avian frugivory at 24 Schefflera morototoni trees from February to May 1998 in central Puerto Rico. The number of fruits removed by avian seed dispersers per visit was similar among focal trees (typically 2–4). In contrast, visitation rate was highly variable (range: 0–71 visits per 4 h). We used multiple regression analyses to evaluate the relative roles of crop size (focal tree ripe fruit abundance) and fruit neighborhood variables (measured within 30 m of focal trees) in affecting visitation to focal trees by avian frugivores. Visitation rate was positively related to crop size (although this variable was only significant in one of four regression models considered) and negatively related to the presence or abundance of conspecific fruits, suggesting that trees competed intraspecifically for dispersers. Relationships between visitation and heterospecific fruits were mixed—some kinds of fruits appeared to enhance visitation to focal trees, while others seemed to reduce visitation. In most regression models, neighborhood variables had larger effects on visitation than focal tree fruit crop size. Our results highlight the important effects of local fruiting environments on the ability of individual plants to attract seed dispersers.

Vegetation Structure, Composition, and Species Richness Across a 56‐year Chronosequence of Dry Tropical Forest on Providencia Island, Colombia

Abstract: We compared vegetation structure and species richness across a 56-yr chronosequence of six replicated age classes of dry tropical forest on the island of Providencia, Colombia, in the Southwest Caribbean. Stand age classes were determined using sequential, orthorectified panchromatic aerial photos acquired between 1944 and 1996 and Landsat 7 ETM + satellite imagery from 2000. Along the chronosequence we established 59 plots of 2 × 50 m (0.01 ha) to document changes in species richness, basal area, tree height, stem density, and sprouting ability. All woody trees and shrubs >2.5 cm diameter at breast height (DBH) were censused and measured. Although woody species density reached a peak in stands from 32 to 56 yr old, rarefaction analysis showed that species richness increased linearly with stand age and was highest in stands 56 yr old or greater. Nonparametric, abundance-based estimators of species richness also showed positive and linear associations with age. Basal area and mean tree height were positively associated with age since abandonment, while sprouting ability showed a negative relationship. Our results indicate rapid recovery of woody species richness and structural characteristics along this tropical dry forest chronosequence.

Amphibian Population Declines in Latin America: A Synthesis1

Abstract: The loss of global amphibian biodiversity has been well documented in recent years. The greatest information from Latin America came from countries such as Costa Rica, Panama, Ecuador, and Puerto Rico. The five papers in this special section illustrate the critical status of Latin American amphibians and further demonstrate certain commonalities of amphibian population declines within the region. These studies provide a framework by which future research and management could proceed in all tropical regions. RESUMEN En los pasados anos se ha documentado la perdida de biodiversidad de anfibios en muchas partes del mundo. La mayor informacion con respecto a America Latina proviene de trabajos realizados en Costa Rica, Panama, Ecuador y Puerto Rico. Los cinco trabajos de esta edicion especial ilustran el estado critico de los anfibios en America Latina y demuestran que existen algunos elementos comunes en los patrones de disminuciones poblacionales de anfibios en la region. Estos estudios proveen un marco de referencia para futuras investigaciones y desarrollo de planes de manejo en regiones tropicales.

Effects of Season and Vegetation Type on Community Organization of Dung Beetles in a Tropical Dry Forest1

Abstract: Dung beetles are important components of most terrestrial ecosystems. In tropical rain forests, dung beetle communities can be very rich in number of species and individuals, and they are known to be useful bioindicators of habitat disturbance. In contrast, very little is known about the organization of dung beetle communities in tropical dry forests. The aim of this study was to describe in detail the dung beetle community of a Mexican tropical dry forest and to assess the relative importance of rainfall seasonality and forest structure in affecting the temporal and spatial dynamics of this community. Dung beetles were captured with pitfall traps at the beginning of the rainy season, the middle of the rainy season, and the middle of the dry season, in two distinct forest types: deciduous forest (DF) and semideciduous forest (SDF) at the Estacion de Biologia Chamela. Both rainfall seasonality and forest structure affected the community organization of dung beetles. During both rainy periods, 14 species were captured, but only three during the dry season. Dung beetles captured during the dry season were only found in the SDF. When comparing the beginning and the middle of the rainy season, differences in abundance and guild structure were also observed between both periods and between forest types, but these differences were much less pronounced. RESUMEN Los escarabajos coprofagos constituyen un componente importante en la mayoria de los ecosistemas terrestres. En bosques humedos tropicales las comunidades de escarabajos coprofagos pueden tener muchas especies e individuos, y sirven como bioindicadores de perturbaciones de habitat. Por otro lado, se sabe muy poco acerca de las comunidades de estos insectos en bosque tropicales secos. El proposito de este estudio fue describir en detalle la comunidad de escarabajos coprofagos en un bosque seco de Mexico, y determinar la importancia relativa de la estacionalidad pluvial y la estructura del bosque en la dinamica de esta comunidad. Se capturaron escarabajos coprofagos colocando trampas de caida al principio de la epoca lluviosa, a mediados de la epoca lluviosa, y a mediados de la epoca seca, en dos tipos de bosque: bosque deciduo (BD) y bosque semideciduo (BSD) en la Estacion de Biologia Chamela. Tanto la estacionalidad como la estructura del bosque afectaron la organizacion de la comunidad de escarabajos coprofagos. En ambos periodos lluviosos se capturaron 14 especies, pero solamente tres durante la epoca seca. Los escarabajos de la epoca seca solo se encontraron en el BSD. Al comparar ambos periodos lluviosos, tambien se observaron diferencias en abundancia y estructura de gremios, entre el comienzo y la mitad de la epoca lluviosa, asi como entre los dos tipos de bosque, pero las diferencias fueron menos pronunciadas.

Factors Influencing Tree Phenology in Taï National Park, Côte d'Ivoire

Abstract: Entrained phenology patterns of tropical trees are expected to be sensitive to short-term fluctuations in typical rainfall and temperature. We examined 47 mo of data on the flowering, fruiting, and new leaf phenology for 797 trees from 38 species in the Tai National Park, Cote d'Ivoire. We determined the timing of the phenology cycles in relation to seasonal rainfall, temperature, and solar radiation. Regression analysis was used to examine how variations in rainfall and temperature influenced deviations in the peaks and troughs of phenology cycles. We also investigated whether populations that fruit during periods of community-wide fruit scarcity were those populations with relatively long- or short-fruiting duration. Flower, fruit, and leaf-flushing phenophases all exhibited 12-mo cycles. The broad peak in flowering began with the northward zenithal passing in April and ended with the southward zenithal passing in September. Fruiting peaks occurred in the long dry season, and leaf flushing peaked in the long dry season but continued into the wet season. Deviations from phenology cycles were largely attributable to short-term fluctuations in rainfall and/or temperature. Fruiting durations of species were related to the mean diameter at breast height. Species with long- and short-fruiting durations contributed equally to fruit abundance during periods of community-wide fruit scarcity. RESUME On s'attend a ce que les modeles phenologiques des arbres tropicaux soient sensibles aux fluctuations a court terme aux precipitations et temperature typiques. Nous avons examine 47 mois de donnees sur la floraison, la fructification, et la phenologie de nouvelles feuilles pour 797 arbres de 38 especes dans le Parc National de Tai, Cote d'Ivoire. Nous avons determine comment les cycles phenologiques ont ete orientes par rapport aux changement saisonniers des precipitations, de la temperature, et du rayonnement solaire. L'analyse de regression a ete adoptee pour examiner comment les variations des precipitations et de la temperature ont influence les deviations dans les pics et les creux des cycles phenologiques. Nous avons egalement etudie si les populations qui portent des fruits pendant des periodes de penurie de fruit a l'echelle communautaire etaient des populations a duree de fructification relativement longue ou courte. Les phenophases de floraison, de fructification et de feuillaison ont toutes montre les cycles de douze mois. Le large pic dans la floraison a commence avec le passage zenithal du nord en avril et pris fin avec le passage zenithal du sud en septembre. Les pics de fructification se sont produits pendant la longue saison seche, et le rougissement des feuilles a eu un pic pendant la longue saison seche mais a continue en saison des pluies. Les deviations des cycles de phenologie etaient en grande partie attribuables aux fluctuations a court terme dans les precipitations et/ou la temperature. Les durees des fructifications des especes etaient liees au diametre moyen a hauteur de poitrine. Les espece a longue et courte duree fructification ont contribueegalement a l'abondance de fruit pendant des periodes de penurie de fruit a l'echelle communautaire.

Secondary Forest Detection in a Neotropical Dry Forest Landscape Using Landsat 7 ETM+ and IKONOS Imagery1

Abstract: We integrate forest structure and remotely sensed data for four successional stages (pasture, early, intermediate, and late) of a tropical dry forest area located in the Sector Santa Rosa of the Guanacaste Conservation Area in northwestern Costa Rica. We used a combination of spectral vegetation indices derived from Landsat 7 ETM+ medium resolution and IKONOS high-resolution imagery. The indices (using the red and near-infrared bands) simple ratio and normalized difference vegetation index separated the successional stages well. Two other indices using mid-infrared bands did not separate successional stages as well. In a comparison of the successional stages with chronological age, there was no separability in the spectral reflectance among different age classes. Successional stages, in contrast, showed distinct groups with minimal overlap. We also applied a simple validation in another dry forest located in the Palo Verde National Park in the province of Guanacaste, Costa Rica, with reasonably good results. RESUMEN En este estudio, datos de campo y datos remotamente sensados son analizados para cuatro etapas sucesionales (pastos, temprano, intermedio y tardio) de un bosque seco tropical ubicado en el sector Santa Rosa del Area de Conservacion Guanacaste en el noroeste de Costa Rica. Utilizamos una combinacion de indices spectrales derivados imagenes satelitales, de mediana resolucion de Landsat 7 ETM+ y de alta resolucion de IKONOS. Los indices (usando las bandas de rojo e infrarojo cercano) de relacion simple (SR) e indice normalizado de diferencia vegetal (NDVI) separo bien las etapas sucesionales. Asi otros dos indices, usando las bandas de infrarojo medio no separaron las etapas sucesionales. En una comparacion de las etapas sucesionales con la edad cronologica, no existio separabilidad en la reflectancia espectral entre las diferentes clases de edad. Sin embargo, las etapas sucesionales mostraron grupos distinguibles con minima sobreposicion.Tambien aplicamos una simple validacion en otro bosque seco ubicado en el Parque Nacional Palo Verde en la provincia de Guanacaste, Costa Rica.

Factors Affecting Mortality and Resistance to Damage Following Hurricanes in a Rehabilitated Subtropical Moist Forest1

Abstract: The ability to resist hurricane damage is a property of both individuals and communities, and can have strong effects on the structure and function of many tropical forests. We examined the relative importance of tree size, species, biogeographic origin, local topography, and damage from previous storms in long-term permanent plots in a rehabilitated subtropical moist forest in Puerto Rico following Hurricane Georges in order to better predict patterns of resistance. Severe damage included uprooted trees, snapped stems, or crowns with greater than 50 percent branch loss. Hurricane induced mortality after 21 mo was 5.2 percent/yr, more than seven times higher than background mortality levels during the nonhurricane periods. Species differed greatly in their mortality and damage patterns, but there was no relationship between damage and wood density or biogeographic origin. Rather, damage for a given species was correlated with mean annual increment, with faster growing species experiencing greater damage, suggesting that growth rate may reflect a variety of life history tradeoffs. Size was also predictive of damage, with larger trees suffering more damage. Trees on ridges and in valleys received greater damage than trees on slopes. A strong relationship was noted between previous hurricane damage and present structural damage, which could not solely be explained by the patterns with size and species. We suggest that resistance of trees to hurricane damage is therefore not only correlated with individual and species characteristics but also with past disturbance history, which suggests that in interpreting the effects of hurricanes on forest structure, individual storms cannot be treated as discrete, independent events.

Tropical Dry Forests of Venezuela: Characterization and Current Conservation Status1

Abstract: Tropical dry forests are located predominantly in the northern portion of Venezuela, above 6°N. Although their potential extent covers ca 400,000 km2 (44% of the land), they currently occupy about 10 percent of this area. The diversity and complexity of Venezuelan dry forests increases from north to south along a gradient of decreasing severity of the dry season. A typical dry forest in Venezuela presents ca 110–170 species of plants from ca 40 to 50 families within an area of approximately 10 ha. Species composition and forest structure, however, are dependent on local landscape conditions (e.g., soil type, topography), and nearby forest types can be very different. Our analysis of five dry forest variants showed a maximum family similarity of 67 percent, although most values fell in the 50–60 percent interval. They are currently considered as one of Venezuela's most threatened ecosystems, but only 5 percent of extant dry forests are included in protected areas; this represents 0.5 percent of their potential extent. It is fundamental to promote the creation of at least 3 or 4 more large protected areas (ca 5000 ha), with different climatic and orographic characteristics, in combination with the recovery of threatened species, the restoration of degraded systems, and the implementation of sustainable development projects. Their apparent high resilience suggests that with the proper management we can restore and maintain the integrity of Venezuelan dry forests. RESUMEN Los bosques secos tropicales de Venezuela se ubican predominantemente al norte del pais, por encima de los 6°N. Aunque su distribucion potencial abarca ca 400,000 km2 (44 porciento del territorio terrestre), actualmente ocupan 10 porciento de esta area. La diversidad y complejidad de bosques secos en Venezuela aumenta de norte al sur, la direccion en la que el numero de meses secos disminuye de 8 a 3. Un bosque seco tipico en Venezuela presenta ca 110–170 especies de plantas, de ca 40–50 familias. La composicion de especies y la estructura de los bosques, sin embargo, son dependientes de las condiciones locales del terreno (e.g., tipo de suelo, topografia), por lo que tipos de bosque cercanos pueden ser muy diferentes. Nuestro analisis de cinco variantes revelo una similaridad entre familias de 67 porciento, aunque la mayoria de los valores cayo entre 50 y 60 porciento. Actualmente son considerados como uno de los ecosistemas venezolanos mas amenazadas, pero solo 5 porciento de los bosques secos remanentes estan incluidos en areas protegidas; esto representa 0.5 porciento de su distribucion potencial. Es fundamental promover la creacion de al menos 3 o 4 areas protegidas grandes adicionales (ca 5000 ha), con condiciones climaticas y orograficas diferentes, en combinacion con la recuperacion de especies amenazadas, la restauracion de sistemas degradados y la implementacion de proyectos de desarrollo sostenible. Su alta resiliencia aparente sugiere que con el manejo adecuado se podria restaurar y mantener la integridad de los bosques secos de Venezuela.

The Influence of Hurricane Winds on Caribbean Dry Forest Structure and Nutrient Pools

Abstract: In 1998, we measured the effects of Hurricane Georges after it passed over long-term research sites in Puerto Rican dry forest. Our primary objectives were to quantify hurricane effects on forest structure, to compare effects in a large tract of forest versus a series of nearby forest fragments, to evaluate short-term response to hurricane disturbance in terms of mortality and sprouting, and to assess the ability of hurricanes to maintain forest structure. We sampled damage from 33 plots (1.3 ha) across a 3000-ha tract of forest as well as in 19 fragments. For stems with 2.5-cm minimum diameter, 1004 stems/ha (12.4%) suffered structural damage, while 69 percent of the undamaged stems were at least 50 percent defoliated. Basal area lost to structural damage equaled 4.0 m2/ha (22%) in south-facing native forests. Structural damage and defoliation increased with stem diameter and were more common in certain dry forest species. South-facing forests and those on ridgetops incurred more damage than north-facing forests or those comprised primarily of introduced species. Stem mortality was only 2 percent of all stems after 9 mo. Structural damage did not necessarily result in stem mortality. Hurricane-induced mortality was not associated with stem height or diameter, but was ten times greater than background mortality. Basal sprouting was proportional to the amount of structural damage incurred in a stand. Forest fragments experienced the same patterns of hurricane effects as the reference forest. The low, dense structure of Caribbean dry forest can be maintained by hurricane damage to larger stems and induction of basal sprouting to generate multistemmed trees. RESUMEN En 1998 medimos los efectos del Huracan George despues de que paso por sitios localizados en Puerto Rico y dedicados a la investigacion a largo plazo. Nuestros objetivos fueron cuantificar los efectos de huracanes en la estructura del bosque y comparar estos efectos en un bosque especifico con una serie de fragmentos de bosque que se encontraban en la proximidad a nuestra area de estudio. La evaluacion de la respuesta rapida del bosque seco debido a los efectos de huracanes se exploro en terminos de la mortalidad y regeneracion, asi como se estudio la habilidad de los huracanes de mantener la estructura del bosque. Para este estudio de muestreo, 33 parcelas con danos (1.3 ha) a lo largo de una seccion de 3000 ha de bosque asi como en 19 fragmentos de bosque. En tallos con ≥2.5 cm de diametro, 1004 tallos/ha (12.4%) sufrieron dano estructural, mientras que el 69 porciento de los tallos no danados fueron al menos en un 50 por ciento defoliadas. Perdidas en area basal debido al dano estructural fue equivalente a 4.0 m2/ha (22%). Bosques con pendientes en direccion sur y aquellos en los topes de las colinas presentaron mas danos que bosques con pendientes orientadas hacia el norte o aquellos que estaban constituidos principalmente de especies introducidas. Mortalidad en los tallos fue solamente un 2 porciento despues de 9 meses, asi como tambien se encontro que el dano estructural no contribuyo a la mortalidad de tallos. Mortalidad inducida por el huracan no se encontro asociada con el diametro o altura de los tallos o bien su diametro, pero fue 10 veces mas grande que la mortalidad de control. Los fragmentos de bosques experimentaron el mismo comportamiento que el bosque de referencia.

Effects of Season and Successional Stage on Leaf Area Index and Spectral Vegetation Indices in Three Mesoamerican Tropical Dry Forests1

Abstract: We compared plant area index (PAI) and canopy openness for different successional stages in three tropical dry forest sites: Chamela, Mexico; Santa Rosa, Costa Rica; and Palo Verde, Costa Rica, in the wet and dry seasons. We also compared leaf area index (LAI) for the Costa Rican sites during the wet and dry seasons. In addition, we examined differences in canopy structure to ascertain the most influential factors on PAI/LAI. Subsequently, we explored relationships between spectral vegetation indices derived from Landsat 7 ETM+ satellite imagery and PAI/LAI to create maps of PAI/LAI for the wet season for the three sites. Specific forest structure characteristics with the greatest influence on PAI/LAI varied among the sites and were linked to climatic differences. The differences in PAI/LAI and canopy openness among the sites were explained by both the past land-use history and forest management practices. For all sites, the best-fit regression model between the spectral vegetation indices and PAI/LAI was a Lorentzian Cumulative Function. Overall, this study aimed to further research linkages between PAI/LAI and remotely sensed data while exploring unique challenges posed by this ecosystem. RESUMEN En este estudio comparamos el indice de area de plantas PAI, el indice de area foliar (LAI), y la apertura de dosel para diferentes etapas sucesionales en tres sitios del bosque seco tropical: Chamela, Mexico; Santa Rosa, Costa Rica y Palo Verde, Costa Rica en la estacion lluviosa y seca. Ademas, examinamos las diferencias en la estructura de dosel para indagar los factores que mas influyen en el PAI/LAI. En forma adicional, exploramos las relaciones entre los indices espectrales de vegetacion derivados de imagenes satelitales Landsat 7 ETM+ y el PAI/LAI para asi crear mapas de PAI/LAI de la estacion lluviosa para los tres sitios. En este estudio encontramos que las caracteristicas especificas de la estructura del bosque con mayor influencia en PAI/LAI varian entre sitios y las mismas estan asociadas a diferencias climaticas. Las diferencias en el PAI/LAI y la apertura del dosel entre los sitios son explicadas tanto por el historial de uso del suelo y asi como las practicas de manejo del bosque. Para todos los sitios el mejor modelo de regresion entre los indices espectrales de vegetacion y el PAI/LAI es la funcion Cumulativa Lorentziana. En general, este estudio tiene como objetivo estudiar mas a fondo las relaciones entre el PAI/LAI y los datos colectados de manera remota, mientras se exploran otros retos particulares que plantea este ecosistema.

Sugar Preferences in Nectar‐ and Fruit‐Eating Birds: Behavioral Patterns and Physiological Causes1

Abstract: Sucrose, glucose, and fructose are the three sugars that commonly occur in floral nectar and fruit pulp. The relative proportions of these three sugars in nectar and fruit in relation to the sugar preferences of pollinators and seed dispersers have received considerable attention. Based on the research of Herbert and Irene Baker and their collaborators, a dichotomy between sucrose-dominant hummingbird-pollinated flowers and hexose-dominant passerine flowers and fruits was proposed. Data on sugar preferences of several hummingbird species (which prefer sucrose) vs. a smaller sample of passerines (which prefer hexoses) neatly fitted this apparent dichotomy. This hummingbird‐passerine dichotomy was strongly emphasized until the discovery of South African plants with sucrose-dominant nectars, which are pollinated by passerines that are able to digest, and prefer sucrose. Now we know that, with the exception of two clades, most passerines are able to assimilate sucrose. Most sugar preference studies have been conducted using a single, relatively high, sugar concentration in the nectar (ca 20%). Thus, we lack information about the role that sugar concentration might play in sugar selection. Because many digestive traits are strongly affected not only by sugar composition, but also by sugar concentration, we suggest that preferences for different sugar compositions are concentration-dependent. Indeed, recent studies on several unrelated nectar-feeding birds have found a distinct switch from hexose preference at low concentrations to sucrose preference at higher concentrations. Finally, we present some hypotheses about the role that birds could have played in molding the sugar composition of plant rewards.

Inner‐crown Microenvironments of Two Emergent Tree Species in a Lowland Wet Forest

Abstract: Vascular epiphyte communities, comprising up to 25 percent of tropical forest flora, contribute to plant diversity and thus ecosystem-level processes; however, one of the proximal determinants of those communities, microclimate, is little studied Here we present the first comprehensive study of microclimates in the inner crowns of two emergent tree species, Hyeronima alchorneoides and Lecythis ampla, at La Selva Biological Station, Costa Rica We examined photon flux density, temperature, vapor pressure, and humidity in inner-crown branches during the wet and dry seasons and during the wet-season leafless phase of Lecythis In both seasons, the percentage daily PFD in foliated Lecythis crowns (9%, wet season; 11%, dry season) was significantly higher than in Hyeronima crowns (5%, both seasons), with the leafless wet-season PFD of Lecythis reaching 23 percent of full sun Temperature and vapor pressure varied less in Hyeronima than in Lecythis crowns during the dry season Microenvironmental conditions for epiphytes within Hyeronima crowns were more spatially and temporally homogeneous and were more buffered from ambient conditions than within Lecythis crowns Growing conditions within the crowns of the same trees and among different trees were measurably different and are likely to affect the structure and composition of the resident epiphyte communities

Species Turnover and Vertical Partitioning of Ant Assemblages in the Brazilian Amazon: A Comparison of Forests and Savannas1

Abstract: We measured beta diversity, or turnover in species composition, of ant assemblages inhabiting patches of forest and savanna (cerrado) near Alter do Chao, in the Brazilian Amazon. In addition, we assessed vertical partitioning of these assemblages by comparing the ground and lower vegetation strata within each habitat. Ants attracted to sardine baits were collected along transects in 39 savanna and 34 forest sites scattered over a 16 km × 16 km landscape. There were about twice as many species in the forest as in the savanna, and within both habitats, we collected more species on the ground than in the vegetation. Similar results were obtained when analyzing data at the level of individual transects, indicating that ant species richness is affected by both habitat and strata. About two-thirds of the species recorded in the savanna were also found in the forest. Within both habitats, a large proportion of the species found in the least species-rich stratum (vegetation) were also found in the richer one (ground). However, ordination analysis, using data from individual transects, revealed that different habitats and strata can be clearly discriminated from each other in terms of their ant species composition. Each habitat and stratum had a number of characteristic (indicator) species which, although generally not exclusive to that particular habitat and stratum, predominated there. Our findings indicate that habitat and strata specialization is an important factor governing the organization of ant communities in Amazonia. RESUMO Nos medimos a diversidade beta, ou o turnover na composicao de especies, de assembleias de formigas habitando florestas e savanas (cerrados) proximas a Alter do Chao, na Amazonia Brasileira. Alem disto, ao comparar em cada um dos habitats o solo com a vegetacao baixa, avaliamos se havia uma separacao vertical da fauna. Formigas atraidas a iscas de sardinha foram coletadas ao longo de parcelas em 39 areas de savana e 34 de floresta espalhadas por uma area de 16 × 16 km. Encontramos cerca de duas vezes mais especies na floresta do que na savana e, nos dois habitats, mais especies no solo do que na vegetacao. Resultados similares foram obtidos ao analisar os dados ao nivel das parcelas, indicando que a riqueza de especies de formigas e afetada tanto pelo habitat quanto pelo tipo de estrato. Cerca de dois tercos das especies da savana tambem ocorreram na floresta. Em ambos os habitats, uma alta proporcao das especies encontradas no estrato mais pobre em especies (vegetacao) tambem ocorreu no estrato mais rico (solo). Entretanto, a analise de ordenacao, usando dados das parcelas, revelou que diferentes habitats e estratos sao facilmente discriminados entre si em funcao da composicao de especies de formigas. Cada habitat e estrato apresentaram um numero de especies caracteristicas (indicadoras) que, embora em geral nao fossem exclusivas daquele habitat e estrato particular, predominaram ali. Nossos resultados indicam que a especializacao de habitats e estratos e um importante fator governando a organizacao de comunidades de formigas na Amazonia.

Clearing Width and Movements of Understory Rainforest Birds

Abstract: We assessed the capacity of three species of disturbance-sensitive understory birds to traverse a highway (50–75 m width) and large farm clearing (250 m width), by radio-tracking translocated individuals in central Amazonia, Brazil. Most individuals translocated across the highway (eight of nine birds) or moved within continuous forest (five of seven birds) returned to their home ranges, whereas none of five birds moved across the large clearing returned. Our results suggest that large clearings (>250 m width) can significantly reduce the movements of some understory rainforest birds.

Importance of Body Size in Determining Dominance Hierarchies among Diverse Tropical Frugivores1

Abstract: Most studies examining dominance hierarchies have focused at the intraspecific level. While some examples of interspecific hierarchies have been noted, these have usually been limited to a few species in the same taxonomic group that utilize resources in similar ways. Here, we examine evidence for dominance interference competition among vertebrates comprising a diverse frugivore community, including 19 species of birds, squirrels, and primates in a mature Central African rainforest. A total of 38 fruiting trees from 18 species were observed for 2058 h to record dominance interactions between foraging vertebrates. We show that interference competition occurs within and between taxonomically diverse species of vertebrates at fruiting trees. The resulting cross-taxonomic dominance hierarchy includes larger vertebrates, such as primates and hornbills, as well as smaller ones, such as squirrels and parrots. Within this hierarchy, the dominance rank of each species is highly correlated with body mass, and is shown to significantly affect the number of fruits removed from a given tree. Because a majority of tropical tree species depend on vertebrates to disperse their seeds, and particular vertebrates may preferentially disperse the seeds of specific tree species, results may have important conservation implications for the maintenance of tree diversity in regions where populations of larger frugivores have been depressed or extirpated.

Regional-scale variation in litter production and seasonality in tropical dry forests of southern Mexico

Abstract: Highly seasonal rainfall creates a pulse of litterfall in the southern Yucatan peninsula region, with cascading effects on the timing of essential nutrient fluxes, microbial dynamics, and vegetation growth. I investigated whether forest age or a regional environmental gradient related to rainfall has a greater effect on patterns of litterfall in this increasingly human-dominated landscape. Litterfall was sampled in 10‐13 stands in each of three locations spanning a rainfall gradient of ca 900‐1400 mm/yr. Litter was collected monthly from November 1998 through January 2000 in mature forests and in secondary forests aged 2‐25 yr. Despite a substantial precipitation gradient, age was the only significant predictor of annual litter mass. Two- to five-yr-old forests produced significantly less litter than 12‐25-yr-old secondary forests (4.6 vs. 6.2 Mg/ha/yr), but the difference between older secondary forests and mature forests (9 percent) was not significant. Litter production increased with rainfall, but not significantly so. The pattern of litterfall was similar across locations and age classes, with a peak during late March or early April. However, litterfall seasonality was most pronounced in the old secondary and mature forests. Litterfall was more evenly distributed throughout the year in forests under 10 yr old. Seasonality of litterfall was also less pronounced at the wettest site, with less disparity between peak litterfall and off-peak months. Seasonality was not related to soil texture. Forest age and rainfall are important drivers of litterfall dynamics; however, both litter mass and degree of seasonality depended more strongly on forest age. Thus, the impact of land-use change on litter nutrient cycling is as great, if not greater, than the constraint imposed by the major natural environmental factor affecting tropical dry forests.

The utility of spectral indices from Landsat ETM+ for measuring the structure and composition of tropical dry forests

Abstract: There is a growing emphasis on developing methods for quantifying the structure and composition of tropical forests that can be applied over large landscapes, especially for tropical dry forests that are severely fragmented and have a high conservation priority. This study investigates the relationships between various measures of forest structure (annual woody increment, canopy closure, stand density, stand basal area) and composition (tree species diversity, tree community composition) measured in semi-deciduous tropical dry forests on islands in Lago Guri, Venezuela and three spectral indices derived from Landsat ETM+: Normalized Difference Vegetation Index (NDVI), Infrared Index (IRI), and Mid-Infrared Index (MIRI). Even though there were significant autocorrelations among spectral indices, there were significant differences in the relationships between spectral indices and forest attributes. IRI was not significantly correlated with any of the structural variables while MIRI was correlated with canopy closure and NDVI values were correlated with canopy closure as well as annual woody increment. NDVI and MIRI were both related to relative tree diversity and all three indices were associated with aspects of tree species composition. Based on the results of this study, it appears that spectral indices, and in particular NDVI, may be useful indicators of forest attributes in tropical dry forest habitats. Further research needs to be undertaken to identify if the results of this study can be applied to other tropical dry forests at a global spatial scale. RESUMEN Existe un interes cada vez mayor en desarrollar metodos para cuantificar la estructura y composicion de los bosques tropicales que se puedan aplicar a nivel de paisajes grandes, especialmente para los bosques secos tropicales que estan severamente fragmentados y tienen una alta prioridad para su conservacion. Este estudio investiga las relaciones entre las diferentes medidas de la estructura forestal (crecimiento anual, densidad de la copa, densidad de arboles, y area basal) y la composicion (diversidad de especies de arboles y composicion de la comunidad de arboles) en bosques secos tropicales semi-deciduos en las islas en el Lago Guri, Venezuela, con tres indices espectrales provenientes de Landsat ETM+: Normalized Difference Vegetation Index (NDVI), Infrared Index (IRI), and Mid-Infrared Index (MIRI). Aunque se obtuvieron autocorrelaciones significativas entre los indices espectrales, tambien se obtuvo diferencias significativas en las capacidades de proyeccion de cada indice para las cualidades del bosque que se midieron. IRI no fue correlacionado con las variables estructurales, pero MIRI fue correlacionado con, y los valores de NDVI eran correlacionados con la densidad de la copa y tambien el crecimiento anual de los arboles. NDVI y MIRI fueron relacionados con la diversidad relativa de especias y los tres indices fueron asociados a aspectos de la composicion forestal. De acuerdo con los resultados de este estudio, sugerimos que los indices espectrales y en particular el NDVI, pueden ser indicadores utiles de las caracteristicas generales de los bosques secos tropicales. Se necesitara llevar a cabo mayores investigaciones para determinar con precision si los resultados de este estudio pueden ser aplicados a los bosques secos tropicales en una escala espacial global.

Bee Populations, Forest Disturbance, and Africanization in Mexico1

Abstract: This study documents the stingless bees' (Meliponinae) recent displacement in the Yucatan (Quintana Roo, Mexico) and the effects of human-induced ecosystem disturbance on bee diversity Point observations of flower-visiting bees were made along transects in three communities with different degrees of human-induced ecosystem disturbance The community with the greatest anthropogenic disturbance had lower overall species richness of stingless bees and the highest degree of dominance of the Africanized honeybee (Apis mellifera scutellata), while the area with the most intact ecosystem had the highest diversity of stingless bees, though A mellifera was still the dominant species We observed aggressive competitive behavior involving physical attacks by A mellifera against stingless bees, indicating that Africanized honeybees are adopting new behaviors to compete better with dominant native pollinator species

Long Tongues and Loose Niches: Evolution of Euglossine Bees and Their Nectar Flowers1

Abstract: I examined relationships between tongue length of orchid bees (Apidae: Euglossini) and nectar spur length of their flowers in the genera Calathea, Costus, and Dimerocostus using phylogenetically independent contrasts Long-tubed flowers have specialized on one or several species of long-tongued euglossine bees, but long-tongued bees have not specialized on long-tubed flowers Whereas long tongues may have evolved to provide access to a wider variety of nectar resources, long nectar spurs may be a mechanism for flowers to conserve nectar resources while remaining attractive to traplining bee visitors RESUMEN Examine la relacion entre la longitud de las lenguas de las abejas de orchideas (Apidae: Euglossini) y la profundidad de las flores en los generos Calathea, Costus, y Dimerocostus usando un analisis filogenetico de contrastes independientes Las flores de tubos largos se han especializado en una o mas especies de abejas Euglossinis con lenguas largas, pero las abejas de lengua larga no se han especializado en flores de tubos largos Lenguas largas en las abejas probablemente han sido seleccionado para facilitar el acceso a diversas fuentes de nectar, mientras que en las flores, tubos largos podrian ser un mecanismo para conservar nectar, y a la vez, manteniendose attractivas a las abejas de forajeo “traplining”

Chimpanzee (Pan troglodytes) seed dispersal in an afromontane forest: microhabitat influences on the postdispersal fate of large seeds

Abstract: We examined the postdispersal fate of large seeds (≥5 mm) dispersed by chimpanzees in an afromontane forest to evaluate aspects of the effectiveness of seed dispersal by chimpanzees, Pan troglodytes. We assessed the influence of six microhabitat characteristics on seed persistence and germination in seeds dispersed in chimpanzee feces and “wadges.” A total of 257 fecal samples and 56 wadges were located over a 4-mo period by tracking a semi-habituated chimpanzee community on day follows. Forty-nine (19.1%) of the fecal samples contained large seeds from five different tree species. The majority of fecal samples with seeds contained seeds from the mature forest tree Olea capensis (Oleaceae) (83.7%). Forty-two wadges (75%) contained seeds from the mature forest tree Syzygium guineense (Myrtaceae). Seeds were monitored at their deposition site for removal and germination up to 49 d following deposition. We collected data on the microhabitat surrounding each fecal and wadge sample. Multivariate analyses indicated that while fecal and wadge samples were not clustered into particular microhabitats, there was little overlap in the microhabitats in which wadges and fecal samples were deposited. Significantly more seeds persisted over 49 d in wadges (67.9%) than in feces (30.3%). Elevation was the only microhabitat variable determined to have a significant influence on seed persistence, whereas slope was determined to have a significant influence on germination.

Impact of Commercial Hunting on Monkey Populations in the Taï region, Côte d'Ivoire1

Abstract: We studied the impact of hunting on monkey species in the Tai National Park and adjacent forests in Cote d'Ivoire. The average wild meat consumption per capita per year was assessed from market surveys and interviews. We determined that the amount of primate wild meat being extracted in the Tai National Park and surrounding forests was 249 t in 1999. Hunting pressure was the highest on the larger primate species such as red colobus, Procolobus badius, black and white colobus, Colobus polykomos, and the sooty mangabey, Cercocebus torquatus atys. Estimates of population densities were based on line transect surveys. The maximum annual production of each species was calculated using the Robinson and Redford model (1991) and assuming unhunted conditions. Comparing current harvest levels with the maximum sustainable yield suggests that harvest of red colobus monkeys (Procolobus badius) is sustainable, whereas current off-take of the black and white colobus (Colobus polykomos), the sooty mangabey (Cercocebus atys), diana monkeys (Cercopithecus diana), and Campbell's monkeys (Cercopithecus campbelli) exceeds sustainability by up to three times. RESUME Nous avons etudie l'impact de la chasse sur les especes de singes dans le Parc National de Tai et ses principales forets peripheriques en Cote d'Ivoire. La consommation moyenne de viande de brousse par capita et par an a ete estimee a partir d'etudes de marches et d'interviews. Nous avons estime la quantite de viande de gibier d'origine simienne extraite du Parc National de Tai en 1999 a 249 t. La pression de la chasse etait plus forte sur les especes de singes de plus grande taille telles que le colobe bai, Procolobus badius, le colobe noir et blanc, Colobus polykomos, et le cercocebe enfume, Cercocebus torquatus atys. Les estimations de densite de populations ont ete faites par la methode des transects. La production annuelle maximale de chaque espece a ete calculee en utilisant le modele de Robinson et Redford (1991) en supposant des conditions sans chasse. La comparaison des prelevements avec la production maximale soutenable suggere que le prelevement en cours des colobes bais (Procolobus badius) est soutenable alors que celui de colobes noirs et blancs (Colobus polykomos), des cercocebes enfumes (Cercocebus torqatus atys), des cercopitheques dianes (Cercopithecus diana) et des mones de Campbell (Cercopithecus campbelli) excede le seuil de durabilite de jusqu'a trois fois.

Habitat Preferences of Ungulates in Hunted and Nonhunted Areas in the Calakmul Forest, Campeche, Mexico1

Abstract: We investigated habitat preference in the community of ungulates in the Calakmul Forest of Southern Mexico through systematically counting the tracks of six species in randomly placed transects. Tracks were associated with one of four major forest types according to Pennington and Sarukhan (1998). Forest type availability was estimated through 393 independent points on the same transects. We surveyed 90 transects in three hunted areas and one large nonhunted area, with a total of 206 km walked. A total of 1672 tracks of the six species were found. Brocket deer (Mazama americana and Mazama pandora) preferred low-dry forest in the nonhunted area and low-flooded forest in the hunted areas. Collared peccary (Pecari tajacu) was a generalist species in the nonhunted area, whereas in the hunted areas, it preferred the subperennial forest. White-lipped peccary (Tayassu pecari) was found only in subperennial forest in the nonhunted area and favored low-flooded forest in the hunted areas. White-tailed deer (Odocoileus virginianus) preferred low-flooded forest in the hunted areas, while it was a generalist in the nonhunted area. Tapir (Tapirus bairdii) preferred low-flooded forest in the hunted areas. The most evident habitat difference among hunted and nonhunted areas was a major use of low-flooded forest in the hunted areas for the species. Conservation of ungulate species in the Calakmul region requires protection of all major habitat types in hunted and nonhunted areas. RESUMEN Las preferencias de habitat en una comunidad de ungulados fueron estimadas a traves de conteos sistematicos de huellas de las seis especies en transectos situados al azar. Las huellas encontrados fueron relacionados con cada uno de los cuatro tipos de habitat mas frecuentes encontrados en el bosque tropical (de acuerdo con Pennington & Sarukhan 1998) de la Region de Calakmul en el sur de Mexico. La disponibilidad de los cuatro tipos de habitats fueron estimadas a traves del registro de 393 puntos independientes tomados en los transectos. Noventa transectos fueron caminados en tres areas con caceria y una gran area sin caceria con un total de 206 kilometros caminados. Se encontraron 1672 huellas de las seis especies. Los venados temazates (Mazama americana y Mazama pandora) prefirieron el bosque bajo seco en el area sin caceria y el bosque inundable en las areas con caceria. El pecari de collar (Pecari tajacu) prefirio la selva subperennifolia en las areas con caceria y no mostro preferencias en el area sin caceria, mientras que el pecari de labios blancos (Tayassu pecari) solo se encontro en la selva subperennifolia en el area sin caceria y prefirio el bosque bajo inundable en las areas con caceria. En estas mismas areas el venado cola blanca (Odocoileus virginianus) prefirio el bosque bajo inundable y fue un generalista en el area sin caceria. El tapir (Tapirus bairdii) prefirio el bosque bajo inundable en las areas con caceria. La diferencia mas evidente entre areas con caceria y sin caceria fue un mayor uso del bosque bajo inundable en las areas con caceria por las especies. Conservacion de los ungulatos en la region de Calakmul requiere proteccion de habitats en areas de caceria y areas sin caceria.