A catastrophic tropical drought kills hydraulically vulnerable tree species.

Drought-related tree mortality is now a widespread phenomenon predicted to increase in magnitude with climate change. However, the patterns of which species and trees are most vulnerable to drought, and the underlying mechanisms have remained elusive, in part due to the lack of relevant data and difficulty of predicting the location of catastrophic drought years in advance. We used long-term demographic records and extensive databases of functional traits and distribution patterns to understand the responses of 20-53 species to an extreme drought in a seasonally dry tropical forest in Costa Rica, which occurred during the 2015 El Niño Southern Oscillation event. Overall, species-specific mortality rates during the drought ranged from 0% to 34%, and varied little as a function of tree size. By contrast, hydraulic safety margins correlated well with probability of mortality among species, while morphological or leaf economics spectrum traits did not. This firmly suggests hydraulic traits as targets for future research.

Environmental Controls on Soil Microbial Communities in a Seasonally Dry Tropical Forest.

Several studies have shown that rainfall seasonality, soil heterogeneity, and increased nitrogen (N) deposition may have important effects on tropical forest function. However, the effects of these environmental controls on soil microbial communities in seasonally dry tropical forests are poorly understood. In a seasonally dry tropical forest in the Yucatan Peninsula (Mexico), we investigated the influence of soil heterogeneity (which results in two different soil types, black and red soils), rainfall seasonality (in two successive seasons, wet and dry), and 3 years of repeated N enrichment on soil chemical and microbiological properties, including bacterial gene content and community structure. The soil properties varied with the soil type and the sampling season but did not respond to N enrichment. Greater organic matter content in the black soils was associated with higher microbial biomass, enzyme activities, and abundances of genes related to nitrification (amoA) and denitrification (nirK and nirS) than were observed in the red soils. Rainfall seasonality was also associated with changes in soil microbial biomass and activity levels and N gene abundances. Actinobacteria, Proteobacteria, Firmicutes, and Acidobacteria were the most abundant phyla. Differences in bacterial community composition were associated with soil type and season and were primarily detected at higher taxonomic resolution, where specific taxa drive the separation of communities between soils. We observed that soil heterogeneity and rainfall seasonality were the main correlates of soil bacterial community structure and function in this tropical forest, likely acting through their effects on soil attributes, especially those related to soil organic matter and moisture content.IMPORTANCE Understanding the response of soil microbial communities to environmental factors is important for predicting the contribution of forest ecosystems to global environmental change. Seasonally dry tropical forests are characterized by receiving less than 1,800 mm of rain per year in alternating wet and dry seasons and by high heterogeneity in plant diversity and soil chemistry. For these reasons, N deposition may affect their soils differently than those in humid tropical forests. This study documents the influence of rainfall seasonality, soil heterogeneity, and N deposition on soil chemical and microbiological properties in a seasonally dry tropical forest. Our findings suggest that soil heterogeneity and rainfall seasonality are likely the main factors controlling soil bacterial community structure and function in this tropical forest. Nitrogen enrichment was likely too low to induce significant short-term effects on soil properties, because this tropical forest is not N limited.

Life history and phenology of Phylloicus pulchrus (Trichoptera: Calamoceratidae) in a tropical rainforest stream of Puerto Rico / Historia de vida y fenología de Phylloicus pulchrus (Trichoptera: Calamoceratidae) en una quebrada de bosque tropical lluvioso de Puerto Rico

Abstract Caddisflies are abundant, diverse, and important insects in freshwater ecosystems. However our knowledge on their life history is incomplete, in particular for the Neotropics. The objectives of this study were to describe the life history and phenology of Phylloicus pulchrus in the Luquillo Experimental Forest, Puerto Rico. Eggs and larvae were reared to determine the species lifespan and time in each instar. Larval instars were determined based on a head width vs. pronotal suture length correlation (N= 120). Larvae and benthic leaf litter were sampled monthly at a headwater stream for a year; all specimens were classified into instars based on their case size. Adult P. pulchrus were sampled monthly for a year with a light trap and at various times with a Malaise trap. Monthly environmental variables were related to species and sex abundance. There was a gradient of egg development where eggs (within compound masses) closest to the water were more developed. There were five larval instars and reared larvae showed longer development times and more variable body measurements in later instars. The best correlation for larval instar determination was case length-head width (Pearson= 0.90, P= 2.2e-16, N= 120). Phylloicus pulchrus has a multivoltine life cycle, with asynchronous larval development. Adult abundance was low. First to third instar larvae were influenced significantly by rainfall and rainfall seasonality had a negative significant effect on second instar larval abundance (ANOVA= 7.45, P= 0.02).Compound egg masses were probably oviposited by different females that gathered for oviposition. Phylloicus pulchrus follows the predominant developmental characteristic of Trichoptera of having five larval stages. Development times were longer than expected (longest times for a Phylloicus species) and may be an effect of laboratory rearing. The influence of rainfall (and seasonality) on different larval instars highlights the importance of this variable on early larval development. The cause of low adult abundance remains unclear, but may be related to low emergence rates and trap efficiency. Rev. Biol. Trop. 66(2): 814-825. Epub 2018 June 01.

Resumen Los tricópteros son insectos abundantes, diversos e importantes en los ecosistemas de agua dulce. Sin embargo el conocimiento sobre su historia de vida es incompleto, en particular para el Neotrópico. Los objetivos de este estudio fueron describir la historia de vida y fenología de Phylloicus pulchrus en el Bosque Experimental de Luquillo, Puerto Rico. Huevos y larvas fueron criadas para determinar la extención y tiempo de vida de cada estadio de la especie. Los estadios larvales fueron determinados basados en la correlación del ancho de cabeza vs. largo de la sutura pronotal (N= 120). Se muestrearon larvas y hojarasca béntica mensualmente por un año, todos los especímenes se clasificaron en estadios por el tamaño del estuche. Los adultos de P. pulchrus fueron recolectados mensualmente por un año utilizando una trampa de luz y varias recolectas con una trampa Malaise. Datos mensuales de variables ambientales fueron usados para explicar la abundancia total y por sexo de la especie. Se detectó un gradiente de desarrollo de los huevos donde los huevos (dentro de masa compuesta) más cercanos al agua estaban más desarrollados. Fueron cinco los estadios larvales y las larvas criadas mostraron tiempos de desarrollo más largos y mayor dispersión en las medidas corporales de los estadios tardíos. La mejor correlación para la determinación de estadios fue largo del estuche-ancho de cabeza (Pearson= 0.90, P= 2.2e-16, N= 120). Phylloicus pulchrus tiene un ciclo de vida multivoltino con desarrollo larval asíncrono. La abundancia de adultos fue baja. Los primeros tres estadios larvales fueron influenciados significativamente por la lluvia y la estacionalidad de la lluvia tuvo un efecto significativo en la abundancia del segundo estadio larval (ANOVA= 7.45, P= 0.02). Las masas de huevo complejas fueron probablemente ovipositadas por diferentes hembras que se reunieron para oviponer. Phylloicus pulchrus mantiene la característica de desarrollo predominante en Trichoptera de tener cinco estadios larvales. Los tiempos de desarrollo fueron mayores a lo esperado (los más largos para una especie de Phylloicus) y puede ser un efecto de la crianza en el laboratorio. El ciclo de vida multivoltino asíncrono observado es el esperado en un entorno tropical debido a las temperaturas más cálidas del agua, la disponibilidad constante de recursos y la baja estacionalidad. La causa de la poca abundancia de adultos permanece incierta, aunque puede estar relacionada con bajas tasas de emergencia y la eficiencia de la trampa de luz. La influencia de la lluvia (y su estacionalidad) en diferentes estadios larvales evidencian la importancia de esta variable en el desarrollo larval temprano.