Abstract:Tropical forest demography and dynamics were examined in three inventory plots across a precipitation gradient in central Panama. The harsh dry season of 1998 that accompanied the 1997-98 El Niño was spanned by censuses at all three sites. The wet and intermediate plots were similar in total species richness, the dry site somewhat lower in diversity; all three sites differed substantially from each other in species composition. Forest-wide growth of large trees was higher at the wet and intermediate sites than at the dry site, but sapling growth was highest at the dry site and lowest at the intermediate site. Forest-wide growth differences were reflected by individual species, for example, saplings of species at the dry site grew faster than saplings of the same species at the intermediate site. Forest-wide mortality was lowest at the dry site and highest at the wet, and this difference was also reflected by individual species. We suggest that low mortality and growth in the drier forest was due to the longer annual dry season and higher deciduousness, and that high sapling growth at the dry site was due to greater light penetration to the forest floor. Growth rates were elevated at aU three sites during 1998, possibly due to reduced cloud-cover during the El Niño. Contrary to expectation, mortality during 1998 was not elevated at wet and intermediate sites during the El Niño drought, but was at the dry site. Finally, we found that some species performed poorly at one site and declined in abundance, while having stable or increasing populations at another site, demonstrating that the communities are not at equilibrium.

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Aim The composition of communities is known to be influenced by biogeographical history, but also by local environmental conditions. Yet few studies have evaluated the relative importance of the direct and indirect effects of multiple factors on species diversity in rich Neotropical forests. Our study aims to assess drivers of change in local bird species richness in lowland tropical rain forests.Location Thirty-two physiographic subregions along the corridor of the Panama Canal, Panama.Methods We mapped the distributions of all forest-dwelling bird species and quantified the environmental characteristics of all subregions, including mean annual rainfall, topographic complexity, elevational variability, forest age and forest area. Plant species richness, believed to be correlated with structural complexity, was estimated by interpolation through kriging for subregions where data were unavailable.Results The study region has a strong rainfall gradient across a short distance (65 km), which is also accompanied by steep gradients in plant and bird species diversity. Path analysis showed that precipitation strongly affected plant species diversity, which in turn affected avian diversity. Forest age and topography affected bird diversity independently of plant diversity. Forest area and its proportion occurring in the largest two fragments of each subregion (habitat configuration) were also positive correlates of bird species richness.Main conclusions Our results suggest that plant species richness, known to be influenced in part by biogeographical history and geology, also affects bird species assemblages locally. We provide support for the hypothesis that bird species richness increases with structural complexity of the habitat. Our analysis of the distributions of the region's most disturbance-sensitive bird species showed that subregions with more rainfall, more complex topography and older forests harboured not only richer communities but also more sensitive species; while subregions with the opposite characteristics usually lacked large fractions of the regional forest bird community and hosted only common, widely distributed species. Results also emphasize the importance of preserving forest diversity from habitat loss and fragmentation, and confirm that larger, continuous forest tracts are necessary to maintain the rich avian diversity in the region.

This field study of female and immature migratory rufous hummingbirds (Selasphorus rufus) reveals that their feeding territories are closely regulated in size to maintain environmental reserves of energy per individual. Columbine (Aquilegia formosa) produces nectar about four times as fast per nectary as Indian paintbrush (Castilleja miniata) but territories have similar daily caloric productivity regardless of their floral species composition.Une étude en nature de femelles et d'oisilons du colibri migrateur Selasphorus rufus démontre que les territoires où ils se nourrissent sont délimités de façon à ce qu'il y ait dans le milieu une réserve constante d'énergie par individu. L'ancolie (Aquilegia formosa) produit son nectar environ quatre fois plus vite par nectaire que la castilléjie Castilleja miniata, mais les territoires ont des productivités caloriques quotidiennes semblables, quelle que soit la composition de la population florale.[Traduit par le journal]

Recent withdrawal of the U.S. military from the Republic of Panama has exposed 64,000 ha of lowland forest in the former Canal Zone to possible development. The forests form a 16-km-wide strip reaching 65 km from the Caribbean Sea to the Pacific Ocean and function as the water supply for the canal and as home to one of the world's richest terrestrial biotas. We present an overview of the distribution of bird diversity in the forests of the canal area based on 10 years of inventories. A total of 498 terrestrial species has been recorded, of which 177 occur only in lowland forests. More species reside in Caribbean-than in Pacific-slope forests and in the largest forest tracts. The Panamanian government, recognizing the importance of the forests for protection of biodiversity and for proper functioning of the canal, has created two national parks and a national monument in the canal area. One large park, Soberania National Park, currently contains 92% of the region's forest-dwelling species. Two large tracts on the Caribbean coast, the Achiote Road forest and the Fort Sherman forest, are not designated as national parks but are recognized as important forest areas. Those two forests harbor species found nowhere else in the canal corridor. Extensive fragmentation, disconnection of forested corridors between foothills and lowlands, and anthropogenic degradation of forests near towns have altered regional bird-community dynamics. Some dynamics occur on large spatial scales, such as the poorly understood movements of elevational and transisthmian migrants. Long-term maintenance of bird species diversity in the canal area will require preservation of the large forest tracts and reestablishment of a forested connection from the canal corridor lowlands to the Chagres lowlands and foothills in the east. Such conservation activities will be challenging to execute given the region's growing human population and desires for a stronger national economy. We recommend protection of remaining forests and active enforcement of protection laws to reduce hunting and further intrusions. Distribución de la Diversidad de Aves en un Paisaje Neotropical Vulnerable Resumen: El reciente retiro de militares de E.U.A. de la República de Panamá ha expuesto 64,000 ha de bosque bajo en la antigua Zona del Canal a la posibilidad del desarrollo. Los bosques forman una franja de 16 km de ancho que se extiende desde 65 km del Mar Caribe hasta el Océano Pacífico y funciona como fuente de agua para el canal y como hábitat para una de las biotas más ricas del mundo. Presentamos una visión general de la distribución de la diversidad de aves en los bosques delárea del canal basada en 10 años de inventarios. Se han registrado 498 especies terrestres, de las cuales 177 solo ocurren en bosques bajos. Más especies residen en los bosques del lado de Caribe que del Pacífico y en las mayores extensiones de bosques.El gobierno panameño, reconociendo la importancia de los bosques para la protección de la biodiversidad y para el adecuado funcionamiento del canal, ...