bluuebunny/crossref_metadata_2025 huggingface dataset:
The Wilcoxon Signed Rank Test for Paired Comparisons of Clustered Data
Authors: Rosner Bernard , Glynn Robert J. , Lee Mei‐Ling T.
Published: March 2006

Summary The Wilcoxon signed rank test is a frequently used nonparametric test for paired data (e.g., consisting of pre‐ and posttreatment measurements) based on independent units of analysis. This test cannot be used for paired comparisons arising from clustered data (e.g., if paired comparisons are available for each of two eyes of an individual). To incorporate clustering, a generalization of the randomization test formulation for the signed rank test is proposed, where the unit of randomization is at the cluster level (e.g., person), while the individual paired units of analysis are at the subunit within cluster level (e.g., eye within person). An adjusted variance estimate of the signed rank test statistic is then derived, which can be used for either balanced (same number of subunits per cluster) or unbalanced (different number of subunits per cluster) data, with an exchangeable correlation structure, with or without tied values. The resulting test statistic is shown to be asymptotically normal as the number of clusters becomes large, if the cluster size is bounded. Simulation studies are performed based on simulating correlated ranked data from a signed log‐normal distribution. These studies indicate appropriate type I error for data sets with ≥20 clusters and a superior power profile compared with either the ordinary signed rank test based on the average cluster difference score or the multivariate signed rank test of Puri and Sen (1971, Nonparametric Methods in Multivariate Analysis, New York: John Wiley). Finally, the methods are illustrated with two data sets, (i) an ophthalmologic data set involving a comparison of electroretinogram (ERG) data in retinitis pigmentosa (RP) patients before and after undergoing an experimental surgical procedure, and (ii) a nutritional data set based on a randomized prospective study of nutritional supplements in RP patients where vitamin E intake outside of study capsules is compared before and after randomization to monitor compliance with nutritional protocols.
Structured Additive Regression for Categorical Space–Time Data: A Mixed Model Approach
Authors: Kneib Thomas , Fahrmeir Ludwig
Published: March 2006

Summary Motivated by a space–time study on forest health with damage state of trees as the response, we propose a general class of structured additive regression models for categorical responses, allowing for a flexible semiparametric predictor. Nonlinear effects of continuous covariates, time trends, and interactions between continuous covariates are modeled by penalized splines. Spatial effects can be estimated based on Markov random fields, Gaussian random fields, or two‐dimensional penalized splines. We present our approach from a Bayesian perspective, with inference based on a categorical linear mixed model representation. The resulting empirical Bayes method is closely related to penalized likelihood estimation in a frequentist setting. Variance components, corresponding to inverse smoothing parameters, are estimated using (approximate) restricted maximum likelihood. In simulation studies we investigate the performance of different choices for the spatial effect, compare the empirical Bayes approach to competing methodology, and study the bias of mixed model estimates. As an application we analyze data from the forest health survey.
Construction of Resolvable Spatial Row–Column Designs
Authors: Williams E. R. , John J. A. , Whitaker D.
Published: March 2006

SummaryResolvable row–column designs are widely used in field trials to control variation and improve the precision of treatment comparisons. Further gains can often be made by using a spatial model or a combination of spatial and incomplete blocking components.Martin, Eccleston, and Gleeson(1993,Journal of Statistical Planning and Inference34,433–450) presented some general principles for the construction of robust spatial block designs which were addressed by spatial designs based on the linear variance (LV) model. In this article we define the two‐dimensional form of the LV model and investigate extensions of the Martin et al. principles for the construction of resolvable spatial row–column designs. The computer construction of efficient spatial designs is discussed and some comparisons made with designs constructed assuming an autoregressive variance structure.
Tests for Independence between Marks and Points of a Marked Point Process
Authors: Guan Yongtao
Published: March 2006

Summary A convenient assumption while modeling a marked point process is that the observations (i.e., marks) and the locations (i.e., points) are independent. We propose new graphical and formal testing approaches to test for this assumption. The proposed graphical procedures are easy to obtain and can be used to diagnose the nature and range of dependence between marks and points. The formal testing procedures require only minimal conditions on marks and thus can be applied to a variety of settings. We illustrate these procedures through a simulation study and an application to some real data.
Sensitivity in Metric Scaling and Analysis of Distance
Authors: Krzanowski W. J.
Published: March 2006

SummaryAssessing the sensitivity or sampling variability of multivariate ordination methods is essential if inferences are to be drawn from the analysis, but such assessment has to date been notably absent in many applications of multidimensional scaling (MDS). The only available technique seems to be the one byDeLeeuw and Meulman(1986,Journal of Classification3,97–112) who proposed a special jackknife in a general MDS setting, but this method does not appear to have been widely used to date. A possible reason for this is that it is perceived to be computationally daunting. However, if attention is focused on classical metric scaling (principal coordinate analysis) then known analytical results can be used and the apparent computational complexity disappears. The purpose of this article is to set out these results, to indicate their use in more general analysis of distance, and to illustrate the methodology on some biometric examples.
An Extension of the Cormack–Jolly–Seber Model for Continuous Covariates with Application toMicrotus pennsylvanicus
Authors: Bonner S. J. , Schwarz C. J.
Published: March 2006

SummaryRecent developments in the Cormack–Jolly–Seber (CJS) model for analyzing capture–recapture data have focused on allowing the capture and survival rates to vary between individuals. Several methods have been developed in which capture and survival are functions of auxiliary variables that may be discrete, constant over time, or apply to the population as a whole, but the problem has not been solved for continuous covariates that vary with both time and individual. This article proposes a new method to handle such covariates by modeling changes over time via a diffusion process and using logistic functions to link the variable to the CJS capture and survival rates. Bayesian methods are used to estimate the model parameters. The method is applied to study the effect of body mass on the survival of the North American meadow vole,Microtus pennsylvanicus.
Seemingly Unrelated Measurement Error Models, with Application to Nutritional Epidemiology
Authors: Carroll Raymond J. , Midthune Douglas , Freedman Laurence S. , Kipnis Victor
Published: March 2006

Summary Motivated by an important biomarker study in nutritional epidemiology, we consider the combination of the linear mixed measurement error model and the linear seemingly unrelated regression model, hence Seemingly Unrelated Measurement Error Models. In our context, we have data on protein intake and energy (caloric) intake from both a food frequency questionnaire (FFQ) and a biomarker, and wish to understand the measurement error properties of the FFQ for each nutrient. Our idea is to develop separate marginal mixed measurement error models for each nutrient, and then combine them into a larger multivariate measurement error model: the two measurement error models are seemingly unrelated because they concern different nutrients, but aspects of each model are highly correlated. As in any seemingly unrelated regression context, the hope is to achieve gains in statistical efficiency compared to fitting each model separately. We show that if we employ a “full” model (fully parameterized), the combination of the two measurement error models leads to no gain over considering each model separately. However, there is also a scientifically motivated “reduced” model that sets certain parameters in the “full” model equal to zero, and for which the combination of the two measurement error models leads to considerable gain over considering each model separately, e.g., 40% decrease in standard errors. We use the Akaike information criterion to distinguish between the two possibilities, and show that the resulting estimates achieve major gains in efficiency. We also describe theoretical and serious practical problems with the Bayes information criterion in this context.
A Hybrid Model for Nonignorable Dropout in Longitudinal Binary Responses
Authors: Wilkins Kenneth J. , Fitzmaurice Garrett M.
Published: March 2006

SummaryThis article presents a likelihood‐based method for handling nonignorable dropout in longitudinal studies with binary responses. The methodology developed is appropriate when the target of inference is the marginal distribution of the response at each occasion and its dependence on covariates. A “hybrid” model is formulated, which is designed to retain advantageous features of the selection and pattern‐mixture model approaches. This formulation accommodates a variety of assumed forms of nonignorable dropout, while maintaining transparency of the constraints required for identifying the overall model. Once appropriate identifying constraints have been imposed, likelihood‐based estimation is conducted via the EM algorithm. The article concludes by applying the approach to data from a randomized clinical trial comparing two doses of a contraceptive.
Detecting Pulsatile Hormone Secretions Using Nonlinear Mixed Effects Partial Spline Models
Authors: Yang Yu‐Chieh , Liu Anna , Wang Yuedong
Published: March 2006

Summary Neuroendocrine ensembles communicate with their remote and proximal target cells via an intermittent pattern of chemical signaling. The identification of episodic releases of hormonal pulse signals constitutes a major emphasis of endocrine investigation. Estimating the number, temporal locations, secretion rate, and elimination rate from hormone concentration measurements is of critical importance in endocrinology. In this article, we propose a new flexible statistical method for pulse detection based on nonlinear mixed effects partial spline models. We model pulsatile secretions using biophysical models and investigate biological variation between pulses using random effects. Pooling information from different pulses provides more efficient and stable estimation for parameters of interest. We combine all nuisance parameters including a nonconstant basal secretion rate and biological variations into a baseline function that is modeled nonparametrically using smoothing splines. We develop model selection and parameter estimation methods for the general nonlinear mixed effects partial spline models and an R package for pulse detection and estimation. We evaluate performance and the benefit of shrinkage by simulations and apply our methods to data from a medical experiment.
Additive Risk Models for Survival Data with High‐Dimensional Covariates
Authors: Ma Shuangge , Kosorok Michael R. , Fine Jason P.
Published: March 2006

SummaryAs a useful alternative to Cox's proportional hazard model, the additive risk model assumes that the hazard function is the sum of the baseline hazard function and the regression function of covariates. This article is concerned with estimation and prediction for the additive risk models with right censored survival data, especially when the dimension of the covariates is comparable to or larger than the sample size. Principal component regression is proposed to give unique and numerically stable estimators. Asymptotic properties of the proposed estimators, component selection based on the weighted bootstrap, and model evaluation techniques are discussed. This approach is illustrated with analysis of the primary biliary cirrhosis clinical data and the diffuse large B‐cell lymphoma genomic data. It is shown that this methodology is numerically stable and effective in dimension reduction, while still being able to provide satisfactory prediction and classification results.
Haplotype‐Based Association Analysis in Cohort and Nested Case–Control Studies
Authors: Chen Jinbo , Chatterjee Nilanjan
Published: March 2006

SummaryGenetic epidemiologic studies often collect genotype data at multiple loci within a genomic region of interest from a sample of unrelated individuals. One popular method for analyzing such data is to assess whether haplotypes, i.e., the arrangements of alleles along individual chromosomes, are associated with the disease phenotype or not. For many study subjects, however, the exact haplotype configuration on the pair of homologous chromosomes cannot be derived with certainty from the available locus‐specific genotype data (phase ambiguity). In this article, we consider estimating haplotype‐specific association parameters in the Cox proportional hazards model, using genotype, environmental exposure, and the disease endpoint data collected from cohort or nested case–control studies. We study alternative Expectation‐Maximization algorithms for estimating haplotype frequencies from cohort and nested case–control studies. Based on a hazard function of the disease derived from the observed genotype data, we then propose a semiparametric method for joint estimation of relative‐risk parameters and the cumulative baseline hazard function. The method is greatly simplified under a rare disease assumption, for which an asymptotic variance estimator is also proposed. The performance of the proposed estimators is assessed via simulation studies. An application of the proposed method is presented, using data from the Alpha‐Tocopherol, Beta‐Carotene Cancer Prevention Study.
A Mixed‐Effects Regression Model for Longitudinal Multivariate Ordinal Data
Authors: Liu Li C. , Hedeker Donald
Published: March 2006

SummaryA mixed‐effects item response theory model that allows for three‐level multivariate ordinal outcomes and accommodates multiple random subject effects is proposed for analysis of multivariate ordinal outcomes in longitudinal studies. This model allows for the estimation of different item factor loadings (item discrimination parameters) for the multiple outcomes. The covariates in the model do not have to follow the proportional odds assumption and can be at any level. Assuming either a probit or logistic response function, maximum marginal likelihood estimation is proposed utilizing multidimensional Gauss–Hermite quadrature for integration of the random effects. An iterative Fisher scoring solution, which provides standard errors for all model parameters, is used. An analysis of a longitudinal substance use data set, where four items of substance use behavior (cigarette use, alcohol use, marijuana use, and getting drunk or high) are repeatedly measured over time, is used to illustrate application of the proposed model.
Spatial Association between Speciated Fine Particles and Mortality
Authors: Fuentes Montserrat , Song Hae‐Ryoung , Ghosh Sujit K. , Holland David M. , Davis Jerry M.
Published: March 2006

Summary Particulate matter (PM) has been linked to a range of serious cardiovascular and respiratory health problems, including premature mortality. The main objective of our research is to quantify uncertainties about the impacts of fine PM exposure on mortality. We develop a multivariate spatial regression model for the estimation of the risk of mortality associated with fine PM and its components across all counties in the conterminous United States. We characterize different sources of uncertainty in the data and model the spatial structure of the mortality data and the speciated fine PM. We consider a flexible Bayesian hierarchical model for a space‐time series of counts (mortality) by constructing a likelihood‐based version of a generalized Poisson regression model that combines methods for point‐level misaligned data and change of support regression. Our results seem to suggest an increase by a factor of two in the risk of mortality due to fine particles with respect to coarse particles. Our study also shows that in the Western United States, the nitrate and crustal components of the speciated fine PM seem to have more impact on mortality than the other components. On the other hand, in the Eastern United States, sulfate and ammonium explain most of the fine PM effect.
Nonparametric Estimation of Stage Occupation Probabilities in a Multistage Model with Current Status Data
Authors: Datta Somnath , Sundaram Rajeshwari
Published: March 2006

Summary Multistage models are used to describe individuals (or experimental units) moving through a succession of “stages” corresponding to distinct states (e.g., healthy, diseased, diseased with complications, dead). The resulting data can be considered to be a form of multivariate survival data containing information about the transition times and the stages occupied. Traditional survival analysis is the simplest example of a multistage model, where individuals begin in an initial stage (say, alive) and move irreversibly to a second stage (death). In this article, we consider general multistage models with a directed tree structure (progressive models) in which individuals traverse through stages in a possibly non‐Markovian manner. We construct nonparametric estimators of stage occupation probabilities and marginal cumulative transition hazards. Empirical calculations of these quantities are not possible due to the lack of complete data. We consider current status information which represents a more severe form of censoring than the commonly used right censoring. Asymptotic validity of our estimators can be justified using consistency results for nonparametric regression estimators. Finite‐sample behavior of our estimators is studied by simulation, in which we show that our estimators based on these limited data compare well with those based on complete data. We also apply our method to a real‐life data set arising from a cardiovascular diseases study in Taiwan.
Quantification of the Prentice Criteria for Surrogate Endpoints
Authors: O'Quigley John , Flandre Philippe
Published: March 2006

SummaryIn a recent discussion on the Prentice criteria for surrogate endpoints (1989) and the role of meta analyses in this context,Alonso et al.(2004,Biometrics60,724–728) expand on a number of points. Among these is a suggestion to base a measure of the degree at which an endpoint meets the Prentice criteria on a likelihood reduction factor. Although new in this context, the suggestion has been studied elsewhere and the measure of Alonso et al., as presented, requires some modification if it is to be useful in general situations. As it stands it depends upon the censoring mechanism, even when independent of the failure mechanism. This is, however, easily fixed. The measure suggested by Alonso et al. can be seen to fit in with a well‐established theory so that, once corrected for the presence of censoring, it can be employed with confidence. Of particular interest is the wide availability of a standard SAS program producing a coefficient which can be immediately transformed to provide an estimate of the population quantity behind the Alonso et al. proposal.
Active Pollination ofFicus surby Two Sympatric Fig Wasp Species in West Africa
Authors: Kerdelhué Carole , Hochberg Michael E. , Rasplus Jean‐Yves
Published: March 2006

Ceratosolen silvestrianusandC. arabicusare two species of agaonine fig wasps that co‐occur in the figs ofFicus surin West Africa. Our work in the Ivory Coast shows that both are active pollinators, and that they may be found together in the same syconia. In our study area,C. silvestrianusis much more abundant thanC. flabellatus. We found no competitive effect for oviposition sites onC. silvestrianus, and hypothesize that habitat preferences allow the coexistence of two sympatric active pollinators in the sameFicushost in the Ivory Coast.

En Afrique de I'Ouest, deux espéces d'hyménoptéres Agaoninae,Ceratosolen silvestrianusetC. flabellatus, sont associées àFicus surNotre étude en Côre d'Ivoire a montré que toutes dew pollinisent activement, et peuvent se développer ensemble au sein d'une même figue. Dans notre lieu de récolte,C. silvestrianusest bien plus abondant queC. fibellatus. Nous n'avons pas mis en évidence pourC. silvestrianus, de coût liéá la compétition avecC. flabellatus. La présence de deux pollinisateurs actifs sur un même site pourrait être due á I'existence d'une mosaïque d'habitats différents, abritant chacun préférentiellement une des deux espéces.
Asymbiotic Nitrogen Fixation and Litter Decomposition on a Long Soil‐Age Gradient in Hawaiian Montane Rain Forest1
Authors: Thompson Matthew V. , Vitousek Peter M.
Published: March 2006

We determined rates of decomposition and asymbiotic nitrogen fixation in the leaf litter of Cheirodendron spp. on the Hawaiian Islands. Leaf litter was collected from four sites on a long soil‐age gradient (300 yr to 4.1 M yr) and decomposed at two sites that differed widely in substrate age and nutrient availability. Rates of decomposition were higher in litter decomposed at the older site, where nutrient availability was greater. A substantial amount of nitrogen and phosphorus immobilization occurred in litter decomposed at the older site, with more immobilization occurring in litter with lower initial nitrogen and phosphorus concentrations, suggesting both supply and demand controls on nutrient immobilization. Potential rates of nitrogen fixation were very low in the first 25 d (0–5 nmol acetylene/gdw/h), rose to much higher rates by 70 d (20–45 nmol), and then declined by 140 d. We found no significant difference in rates of potential nitrogen fixation between sites of decomposition, but there was a strong substrate effect, with higher rates in litter with low lignin, low nitrogen, and high phosphorus. Where significant immobilization of nitrogen occurred for decomposing Cheirodendron, nitrogen fixation could have comprised no more than 10 percent of immobilized nitrogen. Overall, rates of nitrogen fixation were dependent on the source of the decomposing substrate but not on the site of decomposition, while short‐term decomposition and nutrient immobilization were strongly dependent on the site of decomposition but not as much on the source of the decomposing substrate.
Correlating Stem Biomechanical Properties of Hawaiian Canopy Trees with Hurricane Wind Damage1
Authors: Asner Gregory P. , Goldstein Guillermo
Published: March 2006

Hawaiian forests are subject to the effects of periodic hurricane conditions. Hurricane Iniki struck the island of Kauai, Hawaii on September 11, 1992 with winds exceeding 200 km/h and caused defoliation, felling of trees by snapping and uprooting, and standing tree mortality due excessive limb and leaf loss. The purpose of this study was to evaluate if measured wood mechanical characteristics could be correlated with stem failure of trees under windstorm conditions. A field survey indicated that post‐hurricane stem condition (snapped, uprooted, or standing) differed among five common canopy species and was significantly correlated with stem apparent elastic modulus (relative flexibility). Species that tended to snap had significantly higher apparent elastic moduli than those that remained standing or were uprooted. Wood density and stem diameter were not significantly related to stem failure mode. Native trees had a higher percentage per species of standing individuals but also had increased uprooting. Nonnative tree species were more often snapped and fewer were standing after the hurricane. The higher incidence of stem failure for introduced canopy trees may increase the spread of alien understory species following wind disturbance events. These relationships provide a simple means to predict relative differences in stem failure due to high wind conditions and should be considered in planning reforestation efforts on the Hawaiian Islands.
Dispersal of Spores of Mycorrhizal Fungi in Scats of Native Mammals in Tropical Forests of Northeastern Australia
Authors: Reddell Paul , Spain Alister V. , Hopkins Michael
Published: March 2006

One hundred and thirty‐eight scat (faecal) samples from 17 mammal species native to forests of northeastern Queensland were examined for the presence of spores of both ectomycorrhizal and arbuscular mycorrhizal fungi. Spores of mycorrhizal fungi were found in 57 percent of scat samples representing 12 animal species (Aepyprymnus rufescens, Antechinus godmani, Bettongia tropica, Hypsiprymnodon moschatus, Isoodon macrourus, Melomys ceruinipes, Perameles nasuta, Rattus fuscipes, R. tunneyi, Thylogale stigmatica, Trichourur uulperula, Uromys caudimaculatus). Spores were absent in scats of Antechinus stuartii, Dasyurus hallucatus, Dendrolagus lumholtzi, Petaurus australis and Mesembriomys gouldii. Spores of ectomycorrhizal fungi occurred in 38 percent of scats, and all but one of these samples were from Eucalyptus‐dominated sclerophyll forests. Based on the frequency and abundance of spores in scats, five mammals were considered active consumers of hypogeous mycorrhizal sporocarps in sclerophyll forests (A. rufescens, B. tropica, I. macrourus, P. nasuta, and U. caudimaculatus). Individual scats of these animals generally contained a range of distinctive spore types. Spores of arbuscular mycorrhizal fungi were found in low abundance in almost 40 percent of scat samples collected, from both sclerophyll forest and rainforest habitats. We suggest that the majoriry of these spores were acquired incidentally through ingestion of soil during foraging activities on the forest floor. Glasshouse inoculation experiments in which seedlings of Eucalyptus grandis and Sorghum bicolor were inoculated with scat material from several species of mammal demonstrated that the spores of ectomycorrhizal and arbuscular mycorrhizal fungi retained some viability and colonized the roots of host‐plant seedlings. Insufficient information is known of the ecology of mycorrhizal fungi in Australia's tropical forests to speculate as to the implications of these findings for forest conservation and rehabilitation.
Structure and Dynamics of the Arboreal Termite Community in New Guinean Coconut Plantations21
Authors: Leponce Maurice , Roisin Yves , Pasteels Jacques M.
Published: March 2006

Whereas ant mosaics have been widely recognized and described in tropical ecosystems, data on space partitioning among arboreal termite colonies are rudimentary. During a long term field study in New Guinea, the distribution of arboreal termite species in coconut plantations as well as the extent and dynamics of competition between them were investigated. The three dominant species, Mirrocerotermes biroi, Nasutitermes princeps and N. novarumhebridarum, feed on the same items but never exploit the same tree. The resulting distribution pattern is a mosaic with two peculiarities. First, some extended areas around N. princeps colonies appear unexploited, as this species practices interference competition on a wide scale, defending large territories inter‐ and intra‐specifically. Second, interspecific relations are asymmetrical. In some plantations, large colonies of N. princeps expand their territory by destroying colonies of M. biroi, but when the pressure of N. princeps is relaxed, dense populations of colonies of M. biroi can recolonize the trees in a few years’ time. Territorial boundaries may thus change relatively fast. N. novarumhebridarum often colonizes dead trees and interferes less with the other species. These facts are consistent with each species’ reproductive investment strategy. Hypotheses are proposed to explain how the dominant species can coexist, even in long established plantations.
The Food Habits of Sympatric Jaguar and Puma in the Paraguayan Chaco
Authors: Taber Andrew B. , Novaro Andrés J. , Neris Nora , Colman Flavio H.
Published: March 2006

Food habits of jaguar and puma were studied in two regions of the Paraguayan Chaco. Biochemical analysis of 280 scats attributed 106 to jaguar and 95 to puma. Overall dietary overlap was 65 percent and they shared six of seven main prey types. For both cats 43 percent of prey items and 15 percent of prey biomass taken were mammal species kg, 23 percent of items and 29 percent of the biomass were from species 1–15 kg, and 27 percent of items and 53 percent of the biomass were from larger species. Birds, reptiles, and insects made up the remainder. In a developed region no significant differences between their diets were found, while in an undeveloped area more small mammals were taken by both species, and jaguar took more large prey than puma. The potential roles of competition and of differences in habitat structure and prey availability between the two areas on these species’ diets are discussed.

Se estudiaron los hábitos alimenticios de jaguar y puma en dos regiones del Chaco paraguayo. A través de un análisis bioquímico de 280 heces se asignaron 106 a jaguar y 95 a puma. La superposición trófica total fue 65 por ciento y compartieron 6 de 7 items presa principales. Para ambos gatos las especies de mamíferos de < 1 kg fueron el 43 por ciento de los items presa y el 15 por ciento de la biomasa de presas consumidas, 23 por ciento de items y 29 por ciento de la biomasa fueron de especies de 1–15 kg y 27 por ciento de items y 53 por ciento de biomasa heron de especies mayores. El resto heron aves, reptiles e insectos. En una región desarrollada no se encontraron diferencias significativas entre las dietas, mientras que en una región no desarrollada ambas especies consumieron más pequeños mamíferos y los jaguares consumieron más presas grandes que puma. Se discuten los posibles roles en la dieta de estas especies de la competencia y de diferencias en la estructura del hábitat, y la disponibilidad de presas entre las dos áreas.
Stand Characteristics and Leaf Litter Composition of a Dry Forest Hectare in Santa Rosa National Park, Costa Rica
Authors: Burnham Robyn J.
Published: March 2006

One hectare of tropical dry forest in Guanacaste Conservation Area, Costa Rica was mapped and all trees larger than 10 cm diameter at breast height (DBH) identified. The same hectare was sampled for leaf litter and the two data sets, forest and litter, were compared. Dominant and subdominant species of the forest are represented in the leaf litter, whereas rare tree species are highly variable in their representation in the leaf litter. Relative abundance of dominant and subdominant tree species is represented well by the litter although absolute rank‐order is nor identical between source forest basal area and leaf litter mass. The litter adds a significant component to the source forest data owing to the presence of vines and lianas, and more rarely small trees or shrubs. This indicates that litter studies may be able to add depth to forest diversity surveys. The source forest also was used to test foliar physiognomic reconstructions of climate that have been proposed recently by paleobotanists as an alternative to taxonomic affinities methods. The observed climate of the area does not conform to the climatic values that were predicted by application of these new methods.

Una hectárea de bosque seco tropical en el Area de Conservación de Guanacaste, Costa Rica fue mapeada, y todos los árboles mayores de 10 cm de dap fueron identificados. En la misma hectárea, se tomaron muestras de hojarasca y los dos colecciones de datos. bosque y hojarasca, fueron comparadas. Se encontró que las especies dominantes y subdominantes del bosque estaban representadas en las muestras de hojarasca, mientras que la presencia de especias arbóreas raras en las muestras de mojarasca fue muy variable. La abundancia relativa de especies arbóreas dominantesestá bien representada en la hojarasca aunque el área basal del bosque de origen y la masa de hojarasca no heron idénticos en rangos absolutos. La hojarasca añade un componente significativo a los datos del bosque de origen debido a la presencia de bejucos y lianas en la hojarasca, y más raramente árboles pequeños y arbustos. Estos datos indican que los estudios de hojarasca pueden incrementar la precisión de las estimaciones de la diversidad de los bosques. El bosque de origen fue usado tarnbien para examinar reconstrucciones del clima basados en la fisiognomia foliar recientemenre propuesras por paleobotánicas como una alternativa a métodos de afinidad raxonómicas. El clima observado en el área no corresponde con los valores climáticos que fueron predecidos por la aplicación de estos nuevos métodos.
Primary Herbivory by Wood‐Boring Insects along an Architectural Gradient of Rhizophora mangle
Authors: Feller Ilka C. , Mathis Wayne N.
Published: March 2006

We investigated the distribution of primary xylovores in Rhizophora mangle (red mangrove) first‐order branches, i.e., “twigs”, along an architectural gradient on Belizean mangrove cays. Greater structural diversity in R. mangle architecture, xylovore availability, occurrence of natural enemies, and habitat do not result in variable xylovore species richness. Despite large differences in architectural complexity, tall, fringe, dwarf, and sapling trees host the same set of primary wig borers. However, tall trees support greater diversity and abundance of twig inquilines than other tree forms. Primary twig borers have a key role in structuring these mangrove communities because their galleries and pupal chambers provide habitats for numerous species of secondary xylovores and inquilines. We also measured the amount of leaf area removed from R. mangle's canopy by wood‐ and leaf‐feeding herbivores. Vigorously growing tall and sapling trees sustain greater losses because of twig borers than dwarf trees. However, xylovory in fringe trees was not different from any of the other categories. Cumulative herbivory was greatest in the tall trees. In most cases, leaf‐area loss as an indirect or collateral result of primary xylovory equaled or exceeded leaf‐area loss as a direct result of folivory.
Effects of Species, Habitat, and Distance from Edge on Post‐dispersal Seed Predation in a Tropical Rainforest1
Authors: HOll Karen D. , Lulow Megan E.
Published: March 2006

We examined the effects of species, habitat type (open pasture, forest, and beneath isolated pasture trees), and distance from the forest/pasture edge (25 m and 250 m) on post‐dispersal seed predation of ten animal‐dispersed species near the Las Alturas Biological Station in southern Costa Rica. We also compared the amount of seed predation due to vertebrate and insect predators. Levels of seed predation were extremely species‐specific, ranging from 20–100 percent of seeds consumed during the 30 day study period. However, the proportion of seeds remaining was not correlated with seed size. Overall, seed mortality did not differ between the forest and open pasture habitats, but was significantly lower under isolated pasture trees. Individual species differed in which habitat they suffered the highest levels of predation. For eight of ten species studied, levels of seed predation did not vary significantly with distance from the foredpasture edge in any habitat. The majority of the post‐dispersal seed predation was due to mammalian predators. The results of this and other studies suggest that post‐dispersal seed predation may influence patterns of forest regeneration in disturbed areas.

Investigamos el efecto de la especie, el tipo de hábitat (pastizal abierto, bosque, y debajo de árboles aislados en el pastizal), y la distancia a la orilla del bosque, sobre la depredación de semillas de diez especies dispersadas por animales cerca de la Estación Biológica Las Alturas en el sur de Costa Rica. Además comparamos la depredación causada por vertebrados e insectos. Los niveles de depredación fueron muy variables entre especies, entre el 20 y 100 por ciento fué depredado durance los 30 dias del estudio. No hubo correlación entre la proporción de semillas no depredadas y su tamaño. No existió una diferencia entre el bosque y el pastizal en la mortalidad total de las semillas, pero la mortalidad fue menor debajo de 10s árboles aislados. La depredación de semillas de diferentes especies varió en relación al hábitat. Para ocho de las diez especies los niveles de depredación no variaron en relación con la distancia a la orilla del bosque en ninguno de 10s hábitats. La mayoría de la depredación fué ocasionada por mamíferos. Los resultados de éste y otros estudios sugieren que la depredación de semillas influye en la regeneración del bosque en tierras degradadas.
Bird Populations in Rustic and Planted Shade Coffee Plantations of Eastern Chiapas, México
Authors: Greenberg Russell , Bichier Peter , Sterling John
Published: March 2006

Much of the remaining “forest” vegetation in eastern Chiapas, Mexico is managed for coffee production. In this region coffee is grown under either the canopy of natural forest or under a planted canopy dominated by Inga spp. Despite the large differences in diversity of dominant plant species, both planted and rustic shade coffee plantations support a high overall diversity of bird species; we recorded approximately 105 species in each plantation type on fixed radius point counts. We accumulated a combined species list of 180 species on repeatedly surveyed transects through both coffee plantation types. These values are exceeded regionally only by moist tropical forest. Of the habitats surveyed, shade coffee was second only to acacia groves in the abundance and diversity of Nearctic migrants. The two plantation types have similar bird species lists and both are similar in composition to the dominant woodland—mixed pine‐oak. Both types of shade coffee plantation habitats differ from other local habitats in supporting highly seasonal bird populations. Survey numbers almost double during the dry season—an increase that is found in omnivorous migrants and omnivorous, frugivorous, and nectarivorous resident species. Particularly large influxes were found for Tennessee warblers (Vermivora peregrina) and northern orioles (Icterus galbula) in Inga dominated plantations.
Tree and Liana Enumeration and Diversity on a One‐Hectare Plot in Papua New Guinea1
Authors: Wright Debra D. , Jessen J. Heinrich , Burke Peter , de Silva Garza Hector Gomez
Published: March 2006

Enumeration of a one hectare plot at 900 m a.s.l in Papua New Guinea revealed 693 individuals of 228 tree and liana species ≥ 10 cm DBH. A 0.1 hectare subplot contained 302 individuals of 106 species 2.5 ≥ DBH < 10 cm. Lauraceae, Moraceae, and Myristicaceae were the most important families in both size classes. This site is very diverse compared with other tropical forests, and like other species‐rich sites worldwide, it has high aseasonal rainfall and high rates of natural disturbance.
Microhabitats and Water Relations of Epiphytic Cacti and Ferns in a Lowland Neotropical Forest1
Authors: Andrade José Luis , Nobel Park S.
Published: March 2006

The pattern of canopy distribution and some water relations characteristics of the epiphytic cacti Epiphyllum phyllanthus and Rhipsalis baccifera and the epiphytic ferns Polypodium crassifolium and Polypodium phyllitidis were examined in the tropical forest of Barro Colorado Island, Panama. The epiphytic cacti were 6‐fold more succulent than the epiphytic ferns, which had a 9‐fold higher root: shoot ratio. The four species, especially the cacti, were more abundant on the deciduous trees Ceiba pentandra, Platypodium elegans. and Tabebuia guayacan than on the evergreen Anacardium excelsum. The water‐holding capacity of the bark was 2‐fold higher for A. excelsum and T. guayacan than for C. pentandra and P. elegans; the main crotches of the latter species intercepted 2‐fold more rainfall than those of the former. Well‐watered plants of all epiphytic species showed similar total daily transpiration. After 2 weeks of drought, daily transpiration decreased an average of 48 percent for the cacti and 73 percent for the ferns. After 4 weeks of drought, daily transpiration decreased 80 percent for the cacti and was eliminated for the ferns; succulence then decreased an average of 29 percent for the cacti and 98 percent for the ferns, but all species recovered fully within 2 d after rewetting. The epiphytic ferns had a low relative capacitance (0.16 M/Pa), causing these presumably C3 plants often to be under water stress. A high relative capacitance (0.50 M/Pa) and crassulacean acid metabolism allowed the epiphytic cacti to occur most frequently on the driest sites of this tropical forest.
Within‐Crown Flowering Synchrony in Strangler Figs, and Its Relationship to Allofusion1
Authors: Thomson James D. , Dent‐Acosta Sara , Escobar‐Píramo Patricia , Nason John D.
Published: March 2006

We studied flowering phenology at the level of individual branches within strangler fig trees to determine (1) whether branches bloomed asynchronously within trees and (2) whether asynchrony, if observed, could be ascribed to genetically different branches of mosaic trees (i.e., trees formed by spontaneous grafting of genetically different individuals) undergoing individual flowering cycles that were out of phase with each other. Although asynchrony was fairly common, it most often reflected individual branches failing to bloom during one flowering episode, then coming back to bloom in synchrony at the next episode. We detected fewer mosaic trees than expected, and found only a very weak suggestion that mosaic trees may show less within‐tree synchrony than simple trees.
Pollen Flow, Fecundity, and the Adaptive Significance of Heterostyly in Palicourea padifolia (Rubiaceae)1
Authors: Ree Richard H.
Published: March 2006

Palicourea padifolia is a distlous shrub visited primarily by hummingbirds and bees in mid‐elevation rain forests in Costa Rica. At Las Cruces Biological Station, the population of P. padifolia is composed of equal numbers of pin and thrum plants and morphs are randomly distributed. Like the majority of distylous species, P. padifolia exhibits a self and intramorph‐incompatible mating system. The analysis of stigmatic pollen loads obtained from emasculated flowers shows that pollen flow between floral morphs is disassortative, which supports the Darwinian hypothesis concerning the adaptive significance of heterostyly. Pins experience greater disassortative pollination than thrums. Pins also set more seed than thrums, suggesting that the higher frequency of compatible pollen deposited on pin stigmas results in greater fecundity; alternatively, greater seed set in pins could be due to the differential allocation of resources to male and female function between morphs. Overall, seed set for the Las Cruces popularion of P. padifolia is much lower than the potential maximum. Factors which could contribute to seed set limitation include the frequency and/or spatial pattern of pollinator visits, pollen availability, and resource availability.
Reproductive Biology of the Monoecious Understory Palm Prestoea schultzeana in Amazonian Ecuador1
Authors: Ervik Finn , Feil Jan P.
Published: March 2006

Prestoea schultzeana is a monoecious, protandrous palm in the forest understory of Amazonian Ecuador. We studied its leaf production, population density, sexual expression, phenology, pollination, and the specificity of the floral visitors. On average, 1.4 leaves and 0.9 inflorescences are produced per individual per year. The number of staminate flowers per inflorescence is relatively constant compared with the number of pistillate flowers which varies greatly. Flowering occurs in staminate and pistillate phases of approximately 19 and 0–7 days duration, respectively. Flowers open in the morning, and staminate flowers abscise in the afternoon of the same day whereas pistillate flowers last for two days. Flowers are whitish‐yellow with a sweet odor and produce nectar. They were visited by Coleoptera (Chrysomelidae, Curculionidae, Nitidulidae, Ptiliidae, Staphylinidae), Hemiptera, Diptera (Drosophilidae, Syrphidae, Ceratopogonidae), Lepidoptera (Nymphalidae), and Hymenoptera (Formicidae, Halictidae). All examined individuals of the syrphid fly Copestylum sp. visiting pistillate flowers carried 100–500 grains of P. schultzeana pollen. Pollen occurred on all body parts, but especially on the legs, and this makes Copestylum sp. the most important pollinator. Most floral visitors were also frequent on the flowers of co‐occurring plant species; notably the palm Hyospathe elegans shared most visitor species with P. schultzeana.
Global Patterns of Pre‐Dispersal Propagule Predation in Mangrove Forests1
Authors: Farnsworth Elizabeth J. , Ellison Aaron M.
Published: March 2006

Mangroves in disparate families produce viviparous seedlings (propagules) that are attacked by many crab and insect predators both before and after dispersal. While post‐dispersal predation is viewed as an important factor in structuring many mangrove communities, pre‐dispersal predation rates and agents have been characterized for few species. Ten species of mangrove and 3299 propagules were surveyed for pre‐dispersal propagule predation at 42 sites around the world. Pre‐dispersal predation rates were variable among sites and species, ranging from 0 to 93 percent within sands, with a global total predation rate of 23.3 percent (across all propagules examined) and a mean level of 28.3 percent across sites. Grapsid crabs, Coleoptera and Lepidoptera were the primary predators identified. Forests near human population centers and stands occurring at high intertidal sites exhibited higher levels of propagule predation than those in unpopulated or low‐intertidal sites. Predation rates on a species were weakly, negatively correlated with conspecific seedling density at a site. To explore temporal variation in, and ramifications of pre‐dispersal predation for propagule growth and abscission dynamics, Rhizophora mangle propagules were monitored over two years at three sites in Belize, Central America. Predation did not significantly reduce hypocotylar growth of germinated propagules on the parent tree, but nearly doubled the abscission rate of premature propagules. Pre‐dispersal propagule predation is a ubiquitous feature of mangrove forests world‐wide, and must be accounted for in estimates of reproductive output, stand health, and propagule availability for forestry and restoration efforts.
Factors Influencing the Selection of Basking Perches on Cardon Cacti by Spiny‐Tailed Iguanas (Ctenosaura hemilopha)1
Authors: Blízquez M. Carmen , Rodríguez‐Estrella Ricardo
Published: March 2006

The selection of optimal basking perches to achieve preferred body temperatures and avoid predation risks is one of the most important behavioral decisions that a lizard makes. We studied perch selection by the spiny‐tailed Iguana (Ctenosaura hemilopha) in Baja California Sur where they bask on elevated cacti. The more important factor determining cardon selection by iguanas was the presence of old woodpecker holes which could be used as refuges within the top 50 cm of a branch. Other factors are the height of the cardon, the presence of some other holes and the number of branches of the plant. These data suggest that predation risk is the strongest factor affecting the selection of certain cardons as basking structures by spiny‐tailed iguanas. Because the holes are mainly old woodpecker nests, the choice of a cardon as a refuge‐perching site has to be related to a prior selection by woodpeckers.