bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen Fixation in Bryophytes, Lichens, and Decaying Wood along a Soil‐age Gradient in Hawaiian Montane Rain Forest
Authors: Matzek Virginia , Vitousek Peter 
Published: March 2006

ABSTRACTWe determined rates of acetylene reduction and estimated total nitrogen fixation associated with bryophytes, lichens, and decaying wood in Hawaiian montane rain forest sites with underlying substrate ranging in age from 300 to 4.1 million years. Potential N fixation ranged from ca 0.2 kg/ha annually in the 300‐year‐old site to ca 1 kg/ha annually in the 150,000‐year‐old site. Rates of acetylene reduction were surprisingly uniform along the soil‐age gradient, except for high rates in symbiotic/associative fixers at the 150,000‐year‐old site and in heterotrophic fixers at the 2100‐year‐old site. Low fixation at the youngest site, where plant production is known to be N‐limited, suggests that demand for N alone does not govern N fixation. Total N fixation was highest in sites with low N:P ratios in leaves and stem wood, perhaps because epiphytic bryophytes and lichens depend on canopy leachate for mineral nutrients and because heterotrophic fixation is partly controlled by nutrient supply in the decomposing substrate; however, differences in substrate cover, rather than in fixation rates, had the largest effect on the total N input from fixation at these sites.
Food Web Structure and Basal Resource Utilization along a Tropical Island Stream Continuum, Puerto Rico
Authors: March James G. , Pringle Catherine M. 
Published: March 2006

ABSTRACTTropical stream food webs are thought to be based primarily on terrestrial resources (leaf litter) in small forested headwater streams and algal resources in larger, wider streams. In tropical island streams, the dominant consumers are often omnivorous freshwater shrimps that consume algae, leaf litter, insects, and other shrimps. We used stable isotope analysis to examine (1) the relative importance of terrestrial and algal‐based food resources to shrimps and other consumers and determine (2) if the relative importance of these food resources changed along the stream continuum. We examined δ15N and δ13C signatures of leaves, algae, macrophytes, biofilm, insects, snails, fishes, and shrimps at three sites (300, 90, and 10 m elev.) along the Río Espíritu Santo, which drains the Caribbean National Forest, Puerto Rico. Isotope signatures of basal resources were distinct at all sites. Results of two‐source δ13C mixing models suggest that shrimps relied more on algal‐based carbon resources than terrestrially derived resources at all three sites along the continuum. This study supports other recent findings in tropical streams, demonstrating that algal‐based resources are very important to stream consumers, even in small forested headwater streams. This study also demonstrates the importance of doing assimilation‐based analysis (i.e., stable isotope or trophic basis of production) when studying food webs.
Winds under the Rain Forest Canopy: The Aerodynamic Environment of Gliding Tree Frogs
Authors: McCay Michael G. 
Published: March 2006

ABSTRACTMovement of air under the canopy of a forest affects the gliding of animals such as frogs, snakes, geckos, and squirrels; the dispersal of pollen, seeds, and spores; as well as convective transport of heat and carbon dioxide. Wind speed profiles were measured under the canopy of a lowland rain forest during the morning, afternoon, and night at three sites in Costa Rica to determine the aerodynamic environment in which tree frogs maneuver while gliding. During the course of a day, average and maximum wind speeds were highest in the morning and midday, and lowest at night. Wind speeds under the canopy were highest near the top of the canopy and were lowest near the canopy floor in the morning and afternoon, and exhibited little variation with respect to height at night. Turbulence intensity (a common measure of gustiness) was constant (ca 1) for all times of day, heights in the canopy, and sites, but the absolute magnitudes of wind gust speeds were higher during the day than at night. Power spectral densities revealed that most of the variation in wind speeds occurred at frequencies that could potentially affect the gliding of tree frogs. Tree frogs (and many other gliding animals), however, glide at night and thereby avoid the higher wind speeds that occur by day. Computer simulations of the dynamic motions of frogs while gliding revealed that the night levels of wind gusts have little effect on the direction of gliding of tree frogs.
Do Tropical Storm Regimes Influence the Structure of Tropical Lowland Rain Forests?
Authors: Gouvenain Roland C. de , Silander John A. 
Published: March 2006

ABSTRACTIt has been suggested that the average canopy height of Madagascar's lowland rain forests is shorter and the average tree density is greater than in other tropical lowland rain forests of the world. The cause was hypothesized to be frequent cyclone disturbances. We compared the structure of the lowland rain forests in Madagascar to the structure described in published accounts of other tropical lowland rain forests. We found that the eastern coastal lowland forests of Madagascar have short canopy heights relative to that of many other lowland tropical rain forests, and that these Malagasy forests also have relatively high tree densities. On a worldwide basis, there is a significant correlation between short forest canopies and occurrence of tropical cyclones. The association between high tree density and occurrence of tropical cyclones is valid for Africa, but the pattern does not hold up globally.RÉSUMÉII a été conjecturé que la taille moyenne de la canopée des forȩts basses ombrophiles de Madagascar est moindre, et que la densité des arbres est plus grande, que pour d'autres forȩts tropicales ombrophiles du monde. L'hypothèse a été avancée que les perturbations fréquentes des cyclones en sont la cause. Nous avons compare la structure des forȩts ombrophiles de basse altitude de Madagascar avec la structure d'autres forȩts tropicales ombrophiles du monde. La hauteur de la canopée des foréts de I'est de Madagascar est relativement plus courte que celles de beaucoup d'autres forȩts tropicales humides de basse altitudes, et la densité des arbres est relativement élevée. A l'échelle globale, il y a une relation entre courte canopée et perturbations par les cyclones. La relation entre densité des arbres et perturbations par les cyclones est validée par cette étude seulement pour le continent Africain.
Variation in Growth and Demography of a Knob‐scaled Lizard (Xenosaurus newmanorum: Xenosauridae) from a Seasonal Tropical Environment in México
Authors: Lemos‐Espinal Julio A. , Smith Geoffrey R. , Ballinger Royce E. 
Published: March 2006

ABSTRACTWe studied growth and demography in a population ofXenosaurus newmanoruma lizard that lives in rock crevices in the tropical cloud forests of Mexico. Growth rates varied with season (faster in the wet season) and year (faster in 1995 and 1997, slower in 1996 and 1999). Males and females did not differ in growth rate. Proportion of reproductive females varied from year to year, with 1996 having the lowest proportion of reproductive females (32.5%) compared to the other years (all >75%). The age/size structure changed slightly among years, but did not differ between the wet and dry seasons. On average, the sex ratio was female‐biased; however, the proportion of males in the population was greater in the dry season than in the wet season. Our results suggest that, like other lizards, growth and demographic characteristics of this population fluctuate with the proximate environment on both a seasonal and annual timescale.RESUMENEstudiamos los patrones de crecimiento y la demografia de una población deXenosaurus newmanorum, una especie de lagartija que vive en las grietas de las rocas de los bosques de niebla de México. La tasa de crecimiento corporal varió en función de la época del año (más rápida en la época húmeda), y en función del año (más rápida en 1995 y 1997, y más lenta en 1996 y 1999). No hubo diferencias significativas en las tasas de crecimiento corporal de machos y hembras. La proporción de hembras reproductivas varió de ańo a ańo, 1996 fue el ańo con menor proporción de hembras reproductivas (32.5%) comparado con el resto de los ańos (todos ellos > 75 %). La estructura de las clases de edad de esta población fluctuó levemente entre los años, pero no hubo diferencias entre las estaciones húmedas y secas. En promedio la proporción de sexos estuvo sesgada hacia las hembras; aunque la proporción de machos en la población fue mayor en la época seca que en la época húmeda. Nuestros resultados sugieren que, al igual que otras lagartijas, las características demográficas y de crecimiento corporal de esta población pueden fluctuar con base a factores próximos a escalas estacionales y anuales.
Age and Long‐term Growth of Trees in an Old‐growth Tropical Rain Forest, Based on Analyses of Tree Rings and 14C1
Authors: Fichtler Esther , Clark Deborah A. , Worbes Martin 
Published: March 2006

ABSTRACTIn an old‐growth tropical wet forest at La Selva, Costa Rica, we combined radiocarbon (14C) dating and tree‐ring analysis to estimate the ages of large trees of canopy and emergent species spanning a broad range of wood densities and growth rates. We collected samples from the trunks of 29 fallen, dead individuals. We found that all eight sampled species formed visible growth rings, which varied considerably in distinctiveness. For five of the six species for which we combined wood anatomical studies with 14C‐dates (ring ages), the analyses demonstrated that growth rings were of annual formation. The oldest tree we found by direct ring counting was a Hymenolobium mesoamericanum Lima (Papilionaceae) specimen, with an age of ca. 530 years at the time of death. All other sampled individuals, including very large trees of slow‐growing species, had died at ages between 200 and 300 years. These results show that, even in an everwet tropical rain forest, tree growth of many species can be rhythmic, with an annual periodicity. This study thus raises the possibility of extending tree‐ring analyses throughout the tropical forest types lacking a strong dry season or annual flooding. Our findings and similar measurements from other tropical forests indicate that the maximum ages of tropical emergent trees are unlikely to be much greater than 600 years, and that these trees often die earlier from various natural causes.
Flower Color, Hummingbird Pollination, and Habitat Irradiance in Four Neotropical Forests1
Authors: Altshuler Douglas L. 
Published: March 2006

ABSTRACTPollinator visual systems differ considerably among broad groupings such as bees, bats, and birds, and it has been proposed that factors shaping the diversity of flower color in tropical plants include differences in pollinator perceptual abilities. Within the pollinators of the Neotropics, one major difference between taxa is that hummingbirds perceive color well across a broad range of wavelengths from 300–660 nm whereas most bees perceive color well over a narrower range spanning 300–550 nm. Thus, hummingbirds can see red and other long‐wavelength reflection much better than bees. Another factor that could potentially influence flower color in tropical forests is the difference in light availability among habitats such as gaps, canopy, and forest understory. I conducted a survey of floral color in four Neotropical forests using a portable spectroradiometer to provide an unbiased measure of color reflectance. The primary pollinator agents and light habitats of each plant species were classified using primary literature or accounts of direct observations by experts. Flower color was not influenced by differences in light availability between open and closed habitats but was influenced by pollinator visual systems. Specifically, insect flowers reflected across a broad range of the spectrum but hummingbird flowers reflected mostly long‐wavelength light (typically median wavelength <585 nm). Thus, hummingbird‐pollinated flowers are not tuned specifically to hummingbird color sensitivity but instead may decrease conspicuousness to bees and other insects that have poor visual sensitivity to long‐wavelength color.
Genetic Variation of Mantled Howler Monkeys (Alouatta palliata) from Costa Rica1
Authors: Zaldivar Maria E. , Glander Kenneth E. , Rocha Oscar , Aguilar Gabriel , Vargas Elida , Gutierrez‐Espeleta Gustavo A. , Sanchez Ronald 
Published: March 2006

ABSTRACTWe examined genetic diversity of howler monkeys (Alouatta palliata) from Costa Rica. Blood samples of howler monkeys were collected at various locations in Costa Rica, and electrophoresis of total plasma proteins yielded no variation. We also conducted starch gel electrophoresis of red cell isozymes and did not find variation for any of the 14 loci analyzed (i.e., ACP, ADA, CA2, EST, GPI, IDH, LDH‐1, LDH‐2, MDH, PGD, PGM‐1, PGM‐2, SOD, and TPI). These findings were compared with the levels of genetic variation for A. seniculus and A. belzebul from one Brazilian population. Four of the 14 isozymes (ADA, GPI, PGD, and SOD) showed more than one allele for these species. Both A. seniculus and A. belzebul from Brazil showed similar levels of genetic variation. The potential causes of the low genetic variation in A. palliata from Costa Rica are discussed.
Succession and Micro‐elevation Effects on Seedling Establishment of Calophyllum brasiliense Camb. (Clusiaceae) in an Amazonian River Meander Forest1
Authors: King Rachel T. 
Published: March 2006

ABSTRACTI investigated the effects of successional stage and micro‐elevation on seedling establishment of Calophyllum brasiliense (Clusiaceae), a common canopy tree of seasonally flooded lowland forest along the Manú River meander zone in southeastern Peru. To compare seedling establishment between microhabitat types, I planted C. brasiliense seeds in a fully crossed experimental design of three successional stages (early, mid, and mature) and two micro‐elevations (levees and backwaters). Seedling establishment success in this study was affected by both successional stage and micro‐elevation, but micro‐elevation was most important in mid‐successional habitats. In general, seedlings in early succession experienced better conditions than in mature forest; light levels were higher, herbivory lower, and seedling growth higher. In mid‐successional forest, micro‐elevation determined habitat quality; backwaters had higher light levels, lower herbivory, and higher seedling growth and survival than levees. Mid‐successional backwaters were similar in quality to early successional forest for seedling establishment, while levees in that same successional stage were the poorest microhabitats for establishment. Although mid‐successional backwaters are similar to early succession for seedling establishment, in the long run, seedlings that establish in mid‐succession have a lower chance of reaching reproductive size before their habitat ages to mature forest than members of their cohort that established in early succession. I hypothesize that successful recruitment for C. brasiliense in the Manú River meander system requires dispersal to early successional habitat.
Foliar C:N Ratio of Ferns along an Andean Elevational Gradient1
Authors: Wegner Caroline , Wunderlich Meike , Kessler Michael , Schawe Marcus 
Published: March 2006

ABSTRACTWe studied the concentration of leaf N and C among 183 fern species along an elevational gradient at 1700 to 3400 m in humid montane forest in the Bolivian Andes at different levels of taxonomic resolution. For two species of Elaphoglossum sampled 8 and 14 times, respectively, there were no elevational trends. Similarly, a contrast of 22 species with wide elevational amplitudes sampled at their highest and lowest locations did not show any change in C or N contents, or in C:N ratios with elevation. At the community level, however, the mean values of C:N ratios for (a) all species found at a given elevation showed a significant decline with increasing elevation and (b) among epiphytic species, higher ratios (i.e., lower relative N content) than among terrestrial species at the same elevation. These trends were opposite to those of the upper soil layer, in which C:N ratios increased with elevation.
Lizard Assemblages from Natural Cerrado Enclaves in Southwestern Amazonia: The Role of Stochastic Extinctions and Isolation1
Authors: Gainsbury Alison Melissa , Colli Guarino Rinaldi 
Published: March 2006

ABSTRACTWe used null model analyses to investigate the existence of structure in lizard assemblages from open vegetation enclaves in Rondónia, southwestern Amazonia, in relation to species richness, species co‐occurrence, diet, and size overlap. These enclaves presumably have been isolated since the Holocene, providing a history of long‐term isolation. We assumed that the presence of structure in lizard assemblages from the Rondónia enclaves is consistent with the notion that extinctions are a deterministic process, some species being more prone to extinction than others. We grouped enclaves into four categories: latosoil cerrado, sandy cerrado, transitional forest, and rocky field. We collected 14 Cerrado lizard species, consisting of five families in all sampled areas. Analyses of species richness, co‐occurrence, diet overlap, and size overlap patterns suggested lack of organization in the assemblages. The assemblages from the rocky fields of Guajarí–Mirim and the sandy cerrados in Vilhena were significantly structured in diet overlap, whereas the remaining assemblages lacked structure. This probably resulted from phylogenetic inertia and not from ecological interactions. Our results suggest that extinctions proceeded in a stochastic fashion and that historical factors had a dominant role in shaping lizard assemblages in detriment of present‐day ecological factors. In addition, we identified endemic species in the enclaves as well as a tight association between unique ecogeographic features of the landscape and species occurrences. We propose that conservation measures in the region must adequately preserve these features to ensure the survival of the species.
Morphological Variation in Two Facultative Epiphytic Bromeliads Growing on the Floor of a Swamp Forest1
Authors: de Freitas Cecília A. , Scarano Fabio R. , Blesboer David D. 
Published: March 2006

ABSTRACTThe epiphytic tank bromeliads Nidularium procerum (a CAM plant) and TV. innocentii (a C3 plant) can be found as terrestrial plants in the understory of a Brazilian swamp forest. They occur in segregated patches differing in light and flooding regimes; however, plants of each species are found in the other species preferred habitat in a narrow boundary zone where the two populations meet. Although ecophysiological factors were previously thought to dictate the distribution of these species at this site, we suggest that their current distribution is probably related to colonization history and subsequent competition for space.
New Perspectives in Comparative Ecology of Neotropical Rain Forests: Reflections on the Past, Present, and Future
Authors: Powers Jennifer S. 
Published: March 2006

ABSTRACTIn an effort to understand variations in ecological patterns among lowland tropical rain forests, Alwyn Gentry and colleagues synthesized data sets from four of the premier Neotropical field stations–La Selva (Costa Rica), Barro Colorado Island (Panama), Cocha Cashu (Peru), and the Biological Dynamics of Forest Fragmentation Project (Brazil). To promote the kind of geographically comparative tropical ecology advocated in the 1990 Gentry book, the Organization for Tropical Studies and the Smithsonian Tropical Research Institute organized a course in 2001 that visited each of these field stations. Papers from some of the studies resulting from this course are highlighted in this special section. These studies are notable for the consistent methods applied across forests, and they underscore the acute need and bright future for comparative tropical ecology. Key site characteristics for each of the field stations are summarized here.RESUMENEn un esfuerzo de entender las variaciones en patrones ecológicos entre selvas tropicales de bajura, Alwyn Gentry y colegas sintetizaron bases de datos en las cuatro principales estaciones biológicos del Neotrópico: La Selva (Costa Rica), Barro Colorado Island (Panamá), Cocha Cashu (Perú), y el Proyecto de Dinámica Biológica de Fragmentación de Bosque (Brasil). Con el fin de promover el estudio ecologico tropical comparativa a nivel geográfico recomendada por Gentry en 1990 la Organización para Estudios Tropicales y el Smithsonian Tropical Research Institution organizaron un curso en el año 2001, el cual visitó cada una de éstas estaciones. Los artículos científicos de algunos de los estudios producto de este curso se presentan en esta sección especial. Estos estudios son notables debido a la consistencia en los metodología aplicada a través de los cuatro sitios. Asimismo, estos estudios denotan la necesidad y el potencial de Uevar a cabo mas investigación a nivel de ecología tropical comparativa. Caracteristicas importantes para cada una de las estaciones de campo son resumidos en esta sección.
Efectos de la Fragmentatión Sobre la Aborción y Depredación de Semillas en el Chaco Serrano
Authors: Chacoff Natacha P. , Morales Juan M. , Vaquera Maria del P. 
Published: March 2006

RESUMENLas interacciones entre plantas e insectos pueden ser afectadas por la fragmentacion de los hábitats. En este estudio, realizado en el Chaco Serrano de Argentina, investigamos los efectos de la fragmentación sobre la cantidad de semillas abortadas, depredadas y sanas de Acacia aroma y Cercidium praecox. Encontramos que los efectos de la fragmentaci6n fueron diferentes en cada especie. A medida que se redujo el área del fragmento, aumentó el número de semillas abortadas en A. aroma, mientras que la depredación pre‐dispersión disminuyó y la cantidad de semillas sanas aumento en C. praecox. El aumento de semillas abortadas en los fragmentos pequeños no produjo un número menor de semillas sanas disponibles para la dispersión. En las dos especies, los niveles máximos de depredacion por parte de brúquidos fueron cercanos al 35 por ciento, mientras que la aborción de semillas no superó el 7 por ciento. Debido a los altos niveles de daño y la especificidad de los brúquidos, los cambios producidos por la fragmentacióon pueden ser muy importantes para las poblaciones de estas dos especies. Los efectos de la fragmentación sobre la polinización y la depredación pre‐dispersión de semillas de estas fabáceas pueden generar una mayor disponibilidad de semillas para su posterior dispersión en ambientes fragmentados.ABSTRACTHabitat fragmentation can have consequences on plant reproduction through several interactions with insects. We studied the effects of habitat fragmentation in die proportion of aborted, predated and undamaged seeds of Acacia aroma and Cercidium praecox. We performed this study in the Chaco Serrano of Argentina. We found that fragmentation effects differed between species. In small patches, the number of aborted seeds of A. aroma increased and the number of pre–dispersal predated seeds and undamaged seeds of C. praecox decreased and increased, respectively. However, higher numbers of aborted seeds in small patches did not lead to fewer available seeds for dispersion. For these species, seed predation by bruchids was about 35 percent and aborted seeds were around 7 percent. Because of the elevated levels of damage and the high specificity of bruchids, the changes caused by habitat fragmentation may be very important for the populations of these two species. Habitat fragmentation effects on pollination and pre–dispersal seed predation of these legumes may determine higher availability of seeds for dispersion in fragmented habitats.