Liana abundance, diversity, and distribution on Barro Colorado Island, Panama.

Lianas are a key component of tropical forests; however, most surveys are too small to accurately quantify liana community composition, diversity, abundance, and spatial distribution - critical components for measuring the contribution of lianas to forest processes. In 2007, we tagged, mapped, measured the diameter, and identified all lianas ≥1 cm rooted in a 50-ha plot on Barro Colorado Island, Panama (BCI). We calculated liana density, basal area, and species richness for both independently rooted lianas and all rooted liana stems (genets plus clones). We compared spatial aggregation patterns of liana and tree species, and among liana species that varied in the amount of clonal reproduction. We also tested whether liana and tree densities have increased on BCI compared to surveys conducted 30-years earlier. This study represents the most comprehensive spatially contiguous sampling of lianas ever conducted and, over the 50 ha area, we found 67,447 rooted liana stems comprising 162 species. Rooted lianas composed nearly 25% of the woody stems (trees and lianas), 35% of woody species richness, and 3% of woody basal area. Lianas were spatially aggregated within the 50-ha plot and the liana species with the highest proportion of clonal stems more spatially aggregated than the least clonal species, possibly indicating clonal stem recruitment following canopy disturbance. Over the past 30 years, liana density increased by 75% for stems ≥1 cm diameter and nearly 140% for stems ≥5 cm diameter, while tree density on BCI decreased 11.5%; a finding consistent with other neotropical forests. Our data confirm that lianas contribute substantially to tropical forest stem density and diversity, they have highly clumped distributions that appear to be driven by clonal stem recruitment into treefall gaps, and they are increasing relative to trees, thus indicating that lianas will play a greater role in the future dynamics of BCI and other neotropical forests.

Assessing evidence for a pervasive alteration in tropical tree communities.

In Amazonian tropical forests, recent studies have reported increases in aboveground biomass and in primary productivity, as well as shifts in plant species composition favouring fast-growing species over slow-growing ones. This pervasive alteration of mature tropical forests was attributed to global environmental change, such as an increase in atmospheric CO2 concentration, nutrient deposition, temperature, drought frequency, and/or irradiance. We used standardized, repeated measurements of over 2 million trees in ten large (16-52 ha each) forest plots on three continents to evaluate the generality of these findings across tropical forests. Aboveground biomass increased at seven of our ten plots, significantly so at four plots, and showed a large decrease at a single plot. Carbon accumulation pooled across sites was significant (+0.24 MgC ha(-1) y(-1), 95% confidence intervals [0.07, 0.39] MgC ha(-1) y(-1)), but lower than reported previously for Amazonia. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. Over all ten plots, the fastest-growing quartile of species gained biomass (+0.33 [0.09, 0.55] % y(-1)) compared with the tree community as a whole (+0.15 % y(-1)); however, this significant trend was due to a single plot. Biomass of slow-growing species increased significantly when calculated over all plots (+0.21 [0.02, 0.37] % y(-1)), and in half of our plots when calculated individually. Our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Instead, they suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability. More long-term studies are necessary to clarify the contribution of global change to the functioning of tropical forests.

The importance of demographic niches to tree diversity.

Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics.

Nonrandom processes maintain diversity in tropical forests.

An ecological community's species diversity tends to erode through time as a result of stochastic extinction, competitive exclusion, and unstable host-enemy dynamics. This erosion of diversity can be prevented over the short term if recruits are highly diverse as a result of preferential recruitment of rare species or, alternatively, if rare species survive preferentially, which increases diversity as the ages of the individuals increase. Here, we present census data from seven New and Old World tropical forest dynamics plots that all show the latter pattern. Within local areas, the trees that survived were as a group more diverse than those that were recruited or those that died. The larger (and therefore on average older) survivors were more diverse within local areas than the smaller survivors. When species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems.

Error propagation and scaling for tropical forest biomass estimates.

The above-ground biomass (AGB) of tropical forests is a crucial variable for ecologists, biogeochemists, foresters and policymakers. Tree inventories are an efficient way of assessing forest carbon stocks and emissions to the atmosphere during deforestation. To make correct inferences about long-term changes in biomass stocks, it is essential to know the uncertainty associated with AGB estimates, yet this uncertainty is rarely evaluated carefully. Here, we quantify four types of uncertainty that could lead to statistical error in AGB estimates: (i) error due to tree measurement; (ii) error due to the choice of an allometric model relating AGB to other tree dimensions; (iii) sampling uncertainty, related to the size of the study plot; (iv) representativeness of a network of small plots across a vast forest landscape. In previous studies, these sources of error were reported but rarely integrated into a consistent framework. We estimate all four terms in a 50 hectare (ha, where 1 ha = 10(4) m2) plot on Barro Colorado Island, Panama, and in a network of 1 ha plots scattered across central Panama. We find that the most important source of error is currently related to the choice of the allometric model. More work should be devoted to improving the predictive power of allometric models for biomass.

Prevalencia de infección en la endocervix con el virus del papiloma humano en una población de prostitutas de la ciudad de Panamá / Prevalence of endocervix infection with the human papilloma virus in a population of prostitutes of Panama city

Durante el período comprendido entre Enero y Marzo de 1986 fueron examinadas 183 prostitutas para determinar la incidencia de ADN del virus de papiloma humano (VPH). Ellas acudían a las clínicas de Higiene Social, coordinadas por el Ministerio de Salud en diferentes Centro de Salud de la Ciudad de Panamá. A cada una de ellas se les efectuó una encuesta epidemiológica, el examen físico, y cultivos virales y bacterianos para la determinación de los agentes de enfermedades de transmisión sexual; además, se les hizo un hisopado del endocervix, para la detección del ADN del virus de papiloma humano (VPH). La infección con el virus se determinó con la técnica de hibridización in situ, en papel filtro de nitrocelulosa, bajo condiciones estrictas y no estrictas. De las 183 prostitutas estudiadas, 41 (22,4%) tenían uno de los tipos de VPH buscados; 31 (16.9%) presentaban los tipos 16-18, y 20 (10.9%) los tipos 6-11, bajo condiciones de hibridización estrictas. Se sugiere que el aumento de la promiscuidad sexual en la población estudiada incrementa el riesgo de infección con el VPH, tipo 16-18

Estudio controlado de casos de cáncer cervicouterino e infección con el virus papiloma humano en América Latina / Controlled study of cases of cervix uteri cancer and infection with human papilloma virus in Latin America

Se cree que los virus del papiloma humano (VPH) 16 y 18 son factores de riesgo para las displasias y neoplasias de la cervix uterina. Sin embargo, la mayoria de los estudios no han sido controlados y se hicieron por observación, en poblaciones de bajo riesgo para cáncer de la cervix uterina. Se informa aquí la fase piloto de un estudio controlado de cáncer invasor de la cervix uterina efectuado en Panamá y Costa Rica, a nivel nacional, y en la ciudad de Bogotá, Colombia, de julio a septiembre de 1985. Incluimos 46 casos nuevos de cáncer de cérvix y 51 controles, apareados por edad. Las participantes fueron entrevistadas y se tomaron muestras, para pruebas de detección del VPH y citopatología. La infección con VPH fue definida por la técnica de hibridización in situ del ADN viral, en condiciones estrictas y no estrictas, para la determinación de los VPH tipos 6, 11, 16 y 18. En más casos (91%) que en controles (63%) se detectó el VPH (condiciones no estrictas) y en más casos (67%) que en los controles (43%) se detectó el VPH 16 ó 18. El 50% de los maridos eran positivos, con cualquier tipo de VPH, sin que hubiese diferencia significativa entre los maridos de los casos y los maridos de los controles. La edad de la primera relación sexual fue el factor de riesgo más significativo para la infección con VPH 16 ó 18 (16/18) en todas las participantes. El fumar se asoció significativamente con el cáncer de la cérvix (52% de los casos vs 27% de los controles) pero no se asoció con la infección con el VPH

Métodos bioestadísticos en investigaciones científicas: modelos logísticos prospectivos en estudios retrospectivos / Biostatistic methods in scientific research: prospective logistic models in retrospective studies

Regresiones logísticas han sido utilizadas frecuentemente para analizar data retrospectiva. Existen dos métodos diferentes: el modelo logístico "prospectivo" considera la enfermedad como la variable dependiente, mientras que el modelo logístico "retrospectivo" considera el factor de riesgo como la variable dependiente. Téoricamente, el modelo retrospectivo es el correcto al considerar el esquema de muestreo utilizado en estudios caso-control. El modelo retrospectivo se complica, sin embargo, cuando el factor de riesgo tiene más de dos valores o cuando hay que tomar en consideración más de un factor de riesgo. Matemáticamente, ambos modelos resultan en la misma desigualdad relativa con respecto a los parámetros. Por consiguiente, el modelo prospectivo puede ser usado para estimar la desigualdad relativa en datos caso-control siempre que haya suficiente ajuste de covarianza