Understanding how changing precipitation patterns impact the population dynamics of Amazonian plants is necessary for predicting their long-term survival. Most terrestrial plants are characterized by life cycles intractably slow for evaluating such demographic consequences. Due to the demands of surviving on an ephemeral substrate such as a leaf surface, epiphyllous (leaf-inhabiting) bryophytes have some of the fastest generation times for terrestrial plants. Considering these advantages, we investigated the demographic consequences of seasonality in precipitation during one-year of the epiphyllous bryophyte Radula flaccida Gott. (Radulaceae) in a central Amazonian rain forest. In a 1-ha sized study area, 154 epiphyll colonies from 18 phorophytes of the understory shrub Naucleopsis ulei (Warb.) Ducke (Moraceae) were marked and colony growth, extinction, recolonization, as well as rates of sexual and asexual expression were measured in nine demographic censuses. The probability of survivorship decreased in the dry season due to the synergistic effects of both increased leaf fall (e.g., loss of occupied patches) and colony mortality on persisting leaves. Asexual expression also declined significantly during the driest months; however, sexual expression, as measured by sporophyte density, was not related to seasonality. Logistic regression probabilities also indicate a minimum threshold colony size for optimal sporophyte expression. Lower survivorship and colony growth in the dry season along with reduced sporophyte production in smaller colonies implies that both demographic stability as well as population structure of Amazonian epiphyll species may be compromised whether climate models projecting prolonged droughts for the region are accurate.

Compreender como mudanças na precipitação afetam a dinâmica populacional de plantas amazônicas é necessário para prever suas sobrevivências a longo prazo. A maioria das plantas terrestres são caracterizadas por ciclos de vida consideravelmente lentos para avaliar as suas dinâmicas demográficas. Diferentemente, briófitas epifilas (habitantes da superfície de folhas) em florestas tropicais têm alguns dos tempos de geração mais rápidos entre plantas terrestres, o que as torna úteis para o estudo dos efeitos das secas prolongadas. Durante um ano, investigamos os efeitos da precipitação mensal na demografia da epifila Rádula flaccida Gott. (Radulaceae) em uma floresta de terra-firme da Amazônia central. Em uma área de 1-ha, 154 populações de epifilas de 18 forófitos da espécie arbustiva Naucleopsis ulei Warb. Ducke (Moraceae) foram marcadas e monitoradas. Foram mensurados o crescimento da colônia, taxas de extinção e recolonizarão e taxas de expressão sexual e assexual. A taxa de sobrevivência foi menor nas estações secas devido aos efeitos sinérgicos da queda de folhas e alta mortalidade de colônias em folhas persistentes. A expressão sexual também decresceu durante os meses mais secos. Entretanto, a densidade de esporófitos não esteve relacionada com a sazonalidade. Além disso, as taxas de reprodução indicaram um tamanho mínimo da colônia para condições ideais de produção de esporófito. Menor crescimento e sobrevivência nas estações secas, acompanhados com a redução da produção de esporófitos indicam que tanto a estabilidade demográfica, assim como a estrutura populacional de epifilas da Amazônia podem ser comprometidas caso as projeções de secas prolongadas no futuro se confirmem.

Tadpoles have diverse morphologies and occupy diverse habitats. The morphological differences between tadpoles can be represented by linear and geometric measurements and used to explain the organization of tadpole assemblages. However, the effects of evolutionary history must be isolated from the morphological differences before we can determine which patterns result from the use and sharing of common ecological resources. Here, we aimed to determine how morphological similarities and phylogenetic distances affect microhabitat choice by tadpoles. We analyzed the tadpoles of 101 anuran species and classified them according to ecomorphological guild, habitat use, position in the water column, and floor substrate. We used geometric and traditional morphometric approaches to describe the morphological variation among tadpoles and calculated the patristic distance for each species. Afterwards, we used morphometric and phylogenetic matrices as predictors of the variance in the ecological matrix, using a partial redundancy analysis. When we used traditional morphometric data, phylogeny explained a large amount of the ecological variation. By contrast, when we used geometric morphometric data, morphology and phylogeny explained similar amounts of the ecological variation, showing that the technique used to extract morphological variation affects the results. We provide evidence that both morphology, as a surrogate for contemporary factors, and evolutionary inertia are important in determining the behavior of tadpoles. Thus, niche conservatism can be important in modeling the behavior of tadpoles, but does not explain all the preferences of tadpoles.

Larvas de anuros apresentam uma grande diversidade morfológica e de hábitat. Essas diferenças morfológicas entre girinos podem ser representadas por medidas lineares e geométricas e usadas para explicar a organização de assembleias de larvas de anuros. Porém, é necessário isolar os efeitos da história evolutiva dessas diferenças morfológicas antes de determinar quais os padrões são resultantes do uso e compartilhamento de recursos ecológicos em comum. Nós pretendemos determinar como a similaridade morfológica e a distância filogenética entre espécies afeta o comportamento de escolha de microhábitat de girinos. Analisamos larvas de 101 espécies de anuros e classificamos de acordo com a guilda ecomorfológica, uso do hábitat, posição na coluna d’água e substrato do solo. Nós usamos duas técnicas para descrever a variação morfológica entre as larvas de anuros: morfometria geométrica e morfometria tradicional. Nós calculamos a distância patrística para cada espécie. Posteriormente, usamos as matrizes de morfometria e filogenia como preditoras da variância encontrada na matriz ecológica, usando uma análise de redundância parcial. Quando usamos os dados de morfometria tradicional, a filogenia explica uma grande parte da variação ecológica. Em contraste, quando usamos os dados da morfometria geométrica, a morfologia é mais informativa do que a filogenia, mostrando que a técnica utilizada para extrair a variação morfológica afeta o resultado. De todo modo, nós somos capazes de fornecer evidencias de que a morfologia, como um substituto para fatores contemporâneos, e a inercia evolutiva são importantes para determinar o comportamento de larvas de anuros. Portanto, conservatismo de nicho pode ser importante para modelar o comportamento de larvas de anuros, mas não explica todas as preferências dos girinos.

Amazonian floodplain forests have remarkable variation in tree diversity and structure related to flood duration. We assessed how floodplain forests respond to the continuum flooding gradient and found that Fisher's α values vary up to seven times across the landscape.

Florestas de várzea da Amazônia apresenta uma variação expressiva na diversidade de árvores e na estrutura florestal relacionada com a duração da inundação. Nós medimos como as florestas de várzea do Purus respondem a variação continua e gradual na inundação e encontramos que apenas atributos de diversidade responderam significativamente, sendo que os valores de Fisher's α variaram até sete vezes ao longo da paisagem.

Communities of invertebrate animals in lower canopy and saxicolous tank bromeliads, originally studied in 1993–1997, were resampled along an elevational gradient in tabonuco, palo colorado, and dwarf or cloud forest in Puerto Rico in 2010. These Puerto Rican montane rain forests were impacted strongly by hurricanes in 1989 and 1998, so the surveys in the 1990s represented 4–8 yr of post-hurricane recovery, whereas our recent survey represents 12 yr of post-hurricane recovery. At most elevations, species diversity, both within individual bromeliads and at the forest scale, declined between the 1990s and 2010. This decline in diversity between decades is associated with reductions in bromeliad density as the canopy progressively closed during recovery from hurricane damage. The observed decline in alpha and gamma diversity appears to have involved the loss of rarer species, as might be expected from standard metapopulation theory. By contrast, the most common species were remarkably stable in abundance, composition, and frequency of occurrence over the two decades. In the lowermost tabonuco forest, two endemic bromeliad specialists, restricted to bromeliads for their entire life cycle, were not found on resampling. This study also demonstrates that, at least in Puerto Rico, sets of ten plants from each forest were sufficient to monitor bromeliad invertebrate populations and their diversity over time.

Las comunidades de animales invertebrados en el dosel menor y las bromelias tanque saxícolas, estudiadas originalmente entre los años 1993–1997, fueron re-muestreadas a lo largo de un gradiente altitudinal en Tabonuco, Palo Colorado, y en bosque enano o nublado en Puerto Rico en el año 2010. Estos bosques húmedos montanos de Puerto Rico se vieron muy afectados por los huracanes en los años 1989 y 1998, por lo que los estudios realizados en la década del 1990 representaron 4.8 años de recuperación post- huracán, mientras que nuestro reciente inventario representa doce años de la recuperación posterior a los huracanes. La diversidad de especies, tanto dentro de individuos de bromelias, y a nivel del bosque, disminuyó entre los años 1990 y 2010 en la mayoría de las elevaciones. Esta disminución de la diversidad entre décadas, se asocia con reducciones en la densidad de bromelias, mientras el dosel se cierra de forma progresiva durante el proceso de recuperación de daños ocasionados por huracanes. El descenso observado en la diversidad alfa y gamma parece implicar la pérdida de especies raras, como era de esperarse según la teoría estándar de la meta-población. Por el contrario, las especies más comunes fueron notablemente estables en abundancia, composición, y en la frecuencia de ocurrencia en más de dos décadas. En las partes más bajas del bosque Tabonuco, dos bromelias endémicas especializadas, restringidas a las bromelias durante todo su ciclo de vida, no se encontraron en el re-muestreo. Este estudio también demuestra que, al menos en Puerto Rico, series de diez plantas de cada bosque fueron suficientes para monitorear las poblaciones de invertebrados de bromelias y su diversidad a través del tiempo.

Five sets of herbivore exclosures situated in mesic and semi-arid savannas in Hluhluwe-iMfolozi Park, South Africa were used to investigate the effects of mammal browsers and savanna type on plant traits relating to leaf nutrient content, defense, and growth in seven Acacia species. Mostly, browsing did not significantly affect leaf nutrient content but for a few species (i.e., increasing foliar N and P, decreasing C/N, and total polyphenols). Browser effects on structural defenses tended to be more pronounced than for leaf nutrient content and chemical defenses, particularly for semi-arid species, resulting in longer, thicker, and denser spines, and a lower bite size index on browsed plants for most semi-arid species. Browsing had no significant effect on growth rates for all species. Secondly, we investigated the effect of savanna type (mesic vs. semi-arid) on the same set of plant traits and growth rates. A trade-off in defense strategy was evident where mesic species had lower quality leaves and invested more heavily in growth and chemical defenses, while semi-arid species generally had higher nutrient content leaves and invested more in structural defenses and higher levels of ramification. These findings suggest that the previously documented trade-off in plant growth, resprouting ability and architecture between herbivore versus fire-adapted savanna woody species can possibly be extended to include browse quality and defense type.

Studies of biodiversity and terrestrial ecosystem functioning have concentrated almost exclusively on temperate grasslands. To broaden the reach of biodiversity-functioning research, five fast growing species, comprising three eudicot trees and two congeneric palms (none symbiotic with nitrogen-fixing microorganisms), were grown for 13 yr in a replacement-series mixture and monocultures on a fertile soil in a high-rainfall area of lowland Costa Rica. The mixture accrued more biomass and had greater net productivity than the average, but not the most productive, monoculture. Relative Land Output (a measure of comparative yield) increased steeply. The combined evidence points to an increase in resource partitioning or facilitation among species over time. Spatial partitioning of aboveground space (for light capture) and soil (possibly for retrieval of deep nitrogen), and facilitation of phosphorus availability by one species, are mechanisms that may account for the inferred complementarity. Extending the generalized findings on biodiversity–productivity relationships from well-studied grasslands to tropical forests is warranted. Mixtures of fast growing trees can out-perform the average of their component monocultures, whether the metric is biomass accrual or productivity. The modular growth of long-lived structure enables arborescent species to retain crown space previously captured and may lead to increased spatial partitioning and facilitation of resources over time.

Aumento en la diferencia de crecimiento a través del tiempo entre una mezcla y monocultivos de árboles tropicales

Los estudios de biodiversidad y funcionamiento de ecosistemas terrestres se han concentrado casi exclusivamente en pastizales templados. A fin de ampliar el alcance de la investigación biodiversidad-funcionamiento, durante 13 años se estudió en el trópico húmedo de Costa Rica el comportamiento de cinco especies de crecimiento rápido en monocultivos y en una mezcla donde se mantuvo la misma densidad de individuos que en los monocultivos. Las especies fueron tres árboles eudicotas y dos palmeras del mismo género (ninguna en simbiosis con microorganismos fijadores de N), y el experimento se condujo en un sitio fértil de alta pluviometría. La mezcla de especies acumuló más biomasa y tuvo mayor productividad neta que el promedio de los monocultivos, pero no mayor que la especie más productiva. El RLO (una medida de rendimiento comparativo en base al área representada por cada especie) se incrementó marcadamente. Los resultados apuntan a un aumento en el tiempo de la partición de recursos o la facilitación entre especies. Los mecanismos que podrían explicar la complementariedad que se infiere son la partición del espacio aéreo (para captar luz) y del suelo (posiblemente para recuperar N de los horizontes más profundos), y la facilitación de la disponibilidad de P por una de las especies. Por lo tanto, estos resultados justificarían la extrapolación a bosques tropicales de las relaciones biodiversidad-productividad comúnmente encontradas en estudios de pastizales. Las mezclas de árboles de crecimiento rápido pueden superar al promedio de sus respectivos monocultivos, ya sea como biomasa acumulada o productividad. El crecimiento modular de las estructuras longevas le permite a las especies arborescentes retener el espacio ocupado previamente por la copa, lo que puede conducir al aumento con el tiempo de la partición espacial y de la facilitación de recursos.

Amazonian Dark Earths (ADE) are the result of human modification of the Amazonian landscape since pre-Columbian times. ADE are characterized by increased soil fertility compared to natural soils. In the Amazonian forest, soil fertility influences understory herb and fern species composition. However, little research has been done to evaluate the effect of ADE on the composition of the understory community. We evaluated the effects of ADE and soil in 36 plots (150 m × 4 m) established in a Bolivian moist forest (La Chonta). For each plot, we determined soil nutrients, and the composition, richness, and abundance of terrestrial fern, angiosperm herb, and understory palm species. We found that the presence of ADE created a gradient in soil nutrients and pH that affected the understory species composition especially of ferns and palms. Additionally, the higher nutrient concentration and more neutral soil pH on ADE soils caused a decrease of ferns species richness. We therefore conclude that the current composition of the understory community in this particular Bolivian forest is a reflection of past human modifications of the soil.

Los suelos negros amazónicos (ADE por su siglas en Inglés) son parte del legado de las modificaciones en el paisaje amazónico realizadas por el hombre desde tiempos precolombinos. Los ADE se caracterizan por presentar mayor fertilidad en comparación con los suelos naturales de la Amazonía. En el bosque amazónico, la fertilidad del suelo determina la composición de especies de hierbas y helechos en el sotobosque. Sin embargo, pocos estudios han evaluado el efecto de la presencia de ADE en la composición de la comunidad del sotobosque. En el presente artículo, evaluamos este efecto en 36 parcelas (150 × 4 m) establecidas en un bosque húmedo boliviano (La Chonta). En cada parcela, determinamos los nutrientes del suelo y la composición, diversidad y abundancia de especies de helechos, hierbas y palmas del sotobosque. Encontramos que la presencia de ADE crea un gradiente de nutrientes y pH en el suelo que afecto la composición de las especies del sotobosque, particularmente las palmas y helechos. Adicionalmente, una mayor cantidad de nutrientes y un pH más neutral como el que caracteriza los ADE causó una disminución de la riqueza de especies de helechos. Concluimos que en este particular bosque boliviano, la composición de la comunidad de plantas del sotobosque es un reflejo de las modificaciones en el suelo realizadas por los humanos en tiempos pasados.

Abstract in Spanish is available in the online version of this article.

To design feasible conservation and management policies for wild species, it is critical to understand the effects of periodic disturbances, be they natural or anthropogenic. The Caribbean Basin is characterized by high cyclonic activity that has a strong impact on the demography and population dynamics of many taxa, including epiphytic orchids. We conducted a 5-yr study of rare ghost orchid demography, Dendrophylax lindenii, to assess the stability of a protected population of this species in Cuba. Using both stochastic and deterministic integral projection models, we found that mean annual population growth rates are negative (λ = 0.975). However, we found both population growth rate and extinction risk are highly sensitive to survival rates and reproduction, a difficult to quantify rate for many orchids including our study species. While this species is fairly long-lived, its relatively slow increase in annual survival with increasing size may reflect the lack of a protected (i.e., subterranean) storage organ—a life-history trait that may typify other epiphytic species and increase susceptibility to disturbance events. Hurricanes, which are predicted to increase in frequency as a result of climate change, dramatically increase adult mortality. Simulations of these effects indicate that hurricanes and similar disturbances could result in near certain extinction in short time horizons (25 yr) if their annual probability of occurrence exceeds 14 percent. These results suggest a need to better quantify recruitment rates, as well as the sensitivity of population dynamics of this and other orchid species to hurricanes and other periodic disturbances.

Para un diseño de políticas de conservación y de gestión viables en especies silvestres es fundamental tener en cuenta los efectos de las perturbaciones periódicas, ya sean naturales o antropogénicas. La Cuenca del Caribe se caracteriza por una alta actividad ciclónica que tiene un fuerte impacto en la demografía y dinámica poblacional de muchos taxones, incluyendo las orquídeas epífitas. Hemos llevado a cabo un estudio de cinco años de la demografía de la orquídea fantasma rara, Dendrophylax lindenii, para evaluar la estabilidad de una población protegida de esta especie en Cuba. Usando tanto modelos de proyección integrales deterministas como estocásticos, encontramos una tasa media anual de crecimiento poblacional negativa (λ = 0,975). Sin embargo, encontramos que tanto la tasa de crecimiento de la población como el riesgo de extinción son muy sensibles a las tasas de supervivencia y reproducción. Este último un parámetro muy difícil cuantificar en muchas orquídeas incluyendo nuestra especie. Si bien esta especie es bastante longeva, su relativo lento aumento de la supervivencia anual con el aumento de tamaño, pueden reflejar la falta de un órgano de subterráneo que le brinde protección—un rasgo típico de la historia de vida de las epífitas especies que aumentar la susceptibilidad a las perturbaciones. Los huracanes, que se prevé que aumente en frecuencia como resultado del cambio climático, aumentan drásticamente la mortalidad de adultos. Las simulaciones de estos efectos indican que los huracanes y disturbios similares podrían producir una muy probable extinción en horizontes a corto tiempo (25 años) si su probabilidad anual de ocurrencia supera el 14%. Estos resultados sugieren la necesidad de cuantificar mejor las tasas de reclutamiento, así como la sensibilidad de la dinámica poblacional de esta y otras especies de orquídeas a los huracanes y otras perturbaciones periódicas.

Migration is a common life-history strategy that includes traits such as directed flight, increased wing size, seasonal lipid deposition and reproductive arrest. The degree of investment in these traits ultimately determines the life-history strategy of individuals. Partial migration is a common mixed life-history strategy where species or populations consist of both migrant and resident individuals. While this phenomenon is widespread across taxa, the ecological factors that select for and maintain partial migration are poorly understood, especially among insects. Here, we investigate regional life-history traits associated with migration in the southern monarch, Danaus erippus, and describe a mixed life-history strategy in this butterfly. Individuals from the Bolivian lowlands were observed throughout the year exhibiting mate- and milkweed-directed behaviors. These butterflies had smaller wings, lower wing loads and maintained constant lipid and egg loads across summer and autumn months. Danaus erippus in the highlands of the Bolivian Andes were observed only in the summer and autumn months, during which they also showed mate- and milkweed-directed behaviors. These individuals possessed similar-sized wings and maintained similar lipid and egg loads as the lowland butterflies. In contrast, individuals from northwest Argentina showed persistent, directed, southwesterly flight during the autumn (March–May), larger wing size, higher wing loads, and increased autumn lipid deposition along with decreased egg production. These data indicate that D. erippus utilizes a mixed life-history strategy with a combination of residents and migrants in the Bolivian lowlands, elevational migrants in the Bolivian Andes, and latitudinal migrants in northwestern Argentina.

La migración es una estrategia de historia de vida utilizada frecuentemente que incluye características tales como el vuelo dirigido, el aumento del tamaño del ala, el aumento de lípidos y el paro de la actividad reproductiva por temporadas. La estrategia de historia de vida de los individuos está determinada por el grado de inversión de los mismos con cada una de estas características. La migración parcial es una estrategia de historia de vida mixta muy común en la cual las especies o poblaciones están conformadas por algunos individuos migratorios y otros residentes. A pesar de que este fenómeno es común entre los taxa, los factores ecológicos que seleccionan y mantienen la migración parcial no han sido propiamente estudiados, especialmente en los insectos. Este ensayo investiga las características regionales de la historia de vida asociadas con la migración de la monarca del sur, Danaus erippus, y describe una estrategia de historia de vida mixta en esta mariposa. Se observaron individuos de la zona baja de Bolivia a lo largo del año, y éstos exhibieron comportamientos característicos del apareamiento –vuelo irregular– y de la cercanía a las hierbas de leche (Asclepias spp.). Estas mariposas tenían alas más cortas y mantuvieron cargas constantes de lípidos y óvulos durante los meses de verano y otoño. Las D. erippus de los terrenos altos de los Andes bolivianos fueron observadas sólo en los meses de verano y otoño, durante los cuales también demostraron comportamientos característicos del apareamiento –vuelo irregular– y de la cercanía a las hierbas de leche. Estos individuos tenían tamaños de alasy cargas de lípidos y óvulos similares a los de las mariposas de las zonas bajas. Por el contrario, los individuos del noroeste argentino presentaron un vuelo dirigido y persistente, hacia el sur-oeste, durante el otoño (marzo-mayo), así como también alas de mayor tamaño, y un aumento en la cantidad de lípidos durante el otoño conjuntamente con una disminución de la producción de óvulos. Estos datos indican que D. erippus utiliza una estrategia de historia de vida mixta con una combinación de individuos residentes y migratorios en las zonas bajas de Bolivia, migratorios en las elevaciones de los Andes bolivianos y migratorios latitudinales en el noroeste de Argentina.

River damming has created fragmented landscapes in parts of the Amazon basin. The resulting decrease in forest area could directly affect amphibian species if large areas of habitat are required to guarantee the presence of specific types of breeding sites. Here, we describe the anuran assemblages on islands created by damming of the Tocantins River twenty years ago in the eastern Amazon basin. We surveyed 10 undisturbed islands varying in size from 3 to 2140 ha and located at distances of up to 6.7 km from the margin of the reservoir. We identified 32 frog species, of which 15, 14, and 3 have aquatic, semiaquatic, and terrestrial development, respectively. The number of frog species increased significantly with island area but was not affected by island distance from the margin. Species with aquatic or semiaquatic development tended to be absent from the smaller islands, regardless of the degree of isolation from the mainland. These findings emphasize the need to preserve specific microhabitats on smaller land-bridge islands to maintain amphibian diversity in reservoir environments.

O represamento de rios para a instalação de hidrelétricas tem contribuído significativamente para a redução de áreas florestadas da Bacia Amazônica. Assim, se grandes áreas de florestas são fundamentais para a manutenção de específicos sítios reprodutivos, então a fragmentação causada pelo represamento de rios afetará diretamente as comunidades de anfíbios remanescentes. Neste estudo avaliamos as assembleias de anuros remanescentes em ilhas de florestas originadas após o represamento do Rio Tocantins, Amazônia Oriental. Nós amostramos 10 ilhas que variaram de três a 2140 ha de área, e localizadas até 6.7 km de distância da margem do reservatório. Nós encontramos 32 espécies de anuros, 15 com desenvolvimento direto, 14 com desenvolvimento semi-aquático e três com desenvolvimento terrestre. O número de espécies aumentou significativamente com a área da ilha, mas não foi influenciado pela distância da margem do reservatório. As espécies com desenvolvimento aquático ou semi-aquático tenderam a não ocorrer nas ilhas menores, independente delas estarem perto ou longe da margem do reservatório. Estes resultados têm importante implicação para a conservação e restauração de ilhas formadas pelo represamento de rios para a construção de hidrelétricas, enfatizando a necessidade de se preservar ilhas menores que tenham específicos habitats ou ilhas grandes o suficiente para manter sítios reprodutivos que contribuam para a manutenção da diversidade de anfíbios nestes ambientes remanescentes.