Sex in Space: Pollination among Spatially Isolated Plants
Jaboury Ghazoul and R. Uma Shaanker, Guest Editors
(Click for Abstract)
Effects of Forest Fragmentation on Pollinator Activity and Consequences for Plant Reproductive Success and Mating Patterns in Bat-pollinated Bombacaceous Trees
Mauricio Quesada, Kathryn E. Stoner, Jorge A. Lobo, Yvonne Herrerías, Carolina Palacios-Guevara, Miguel A. Munguía-Rosas, Karla A. O.-Salazar, and Víctor Rosas-Guerrero
(Click for Abstract)(Resumen Haga Clic Aquí)
Does Neighbourhood Floral Display Matter? Fruit Set in Carpenter Bee-pollinated Heterophragma quadriloculare and Beetle-pollinated Lasiosiphon eriocephalus
Hema Somanathan, Renee M. Borges, and V. Srinivasa Chakravarthy
(Click for Abstract)
Factors Contributing to Variation in Seed Production among Remnant Populations of the Endangered Daisy Gerbera aurantiaca
Steven D. Johnson, Carine L. Collin, H. Jörgen Wissman, Erika Halvarsson, and Jon Ågren
(Click for Abstract)
Alien Abduction: Disruption of Native Plant-Pollinator Interactions by Invasive Species
Jaboury Ghazoul
(Click for Abstract)
Effects of Animal Pollination on Pollen Dispersal, Selfing, and Effective Population Size of Tropical Trees: A Simulation Study
Bernd Degen and David W. Roubik
(Click for Abstract)(Resumen Haga Clic Aquí)
Sex in Space: A Synthesis
Jaboury Ghazoul and R. Uma Shaanker
(Click for Abstract)
Soil Microbial Dynamics in Costa Rica: Seasonal and Biogeochemical Constraints
Cory C. Cleveland, Alan R. Townsend, Briana C. Constance, Ruth E. Ley, and Steven K. Schmidt
(Click for Abstract)(Resumen Haga Clic Aquí)
Nectar in Hummingbird-pollinated Neotropical Plants I: Patterns of Production and Variability in 12 Species
Lucinda A. McDade and Jennifer A. Weeks
(Click for Abstract)(Resumen Haga Clic Aquí)
Nectar in Hummingbird-pollinated Neotropical Plants II: Interactions with Flower Visitors
Lucinda A. McDade and Jennifer A. Weeks
(Click for Abstract)(Resumen Haga Clic Aquí)
Termite Mounds as Nutrient-Rich Food Patches for Elephants
Ricardo M. Holdo and Lee R. McDowell
(Click for Abstract)
Effects of Hygrothermal Stress, Plant Richness, and Architecture on Mining Insect Diversity
G. Wilson Fernandes, Fabiana M. Caldeira Castro, Maurício L. Faria, Evelyn S. A. Marques, and Magda K. Barcelos Greco
(Click for Abstract)(Resumen Haga Clic Aquí)
Lack of Genetic Structuring among Tropical Brazilian Wood Stork Populations and Low Genetic Differentiation from North American Populations
Cristiano Dosualdo Rocha, Sílvia Nassif Del Lama , and Luciana Correia de Almeida Regitano
(Click for Abstract)(Resumen Haga Clic Aquí)
Aquatic Insect Assemblages in Shrimp-dominated Tropical Streams, Puerto Rico
Alonso Ramírez and Luz Raquel Hernández-Cruz
(Click for Abstract)(Resumen Haga Clic Aquí)
Placing an Omnivore in a Complex Food Web: Dietary Contributions to Adult Biomass of an Ant
Chadwick V. Tillberg and Michael D. Breed
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Co-extinctions of Tropical Butterflies and their Hostplants
Lian Pin Koh, Navjot S. Sodhi, and Barry W. Brook
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Sex in Space: Pollination among Spatially Isolated Plants
Jaboury Ghazoul (j.ghazoul@imperial.ac.uk) and R. Uma Shaanker, Guest Editors
Plant distributions are changing at unprecedented rates, primarily due to habitat clearance and the spread of alien invasive species. Landscape pattern and local density can affect plant sexual processes, particularly those mediated by biotic vectors, by acting on the composition and behavior of pollinators and seed dispersers. Ecologists are now grappling with the likely effects of these altered processes on future forest composition as existing plant reproductive mutualisms break down or adjust to new spatial circumstances. Here, we introduce five papers that address pollinator responses and pollination outcomes in a variety of human-dominated landscapes and emphasize the need to better understand the dynamic nature of plant-pollinator interactions.
Effects of Forest Fragmentation on Pollinator Activity and Consequences for Plant Reproductive Success and Mating Patterns in Bat-pollinated Bombacaceous Trees
Mauricio Quesada (mquesada@oikos.unam.mx), Kathryn E. Stoner, Jorge A. Lobo, Yvonne Herrerías, Carolina Palacios-Guevara, Miguel A. Munguía-Rosas, Karla A. O.-Salazar, and Víctor Rosas-Guerrero
Forest fragmentation and the resulting spatial isolation of tree species can modify the activity of pollinators and may have important implications for the reproductive success and mating systems of the plants they pollinate. The objectives of this study were to (1) evaluate the effect of forest fragmentation on pollinator activity of bat-pollinated bombacaceous trees and (2) determine the effects of forest fragmentation on reproductive success and mating systems of bombacaceous trees. We studied these parameters in three bombacaceous tree species in tropical seasonal forest of Chamela, Jalisco, Mexico, and Osa and Guanacaste, Costa Rica. For Ceiba aesculifolia, more visits were observed in fragments by both Glossophaga soricina and Leptonycteris curasoae. For Ceiba grandiflora, Musonycteris harrisoni visited flowers exclusively in forest and G. soricina visited more flowers in forest than in fragments; no difference was shown by L. curasoae. For Ceiba pentandra in Chamela, no differences were found in visitation by G. soricina between forest and fragments; L. curasoae visited significantly more flowers in forest. Ceiba pentandra received more visits by Phyllostomus discolor than G. soricina in Guanacaste, whereas no bat visitors were observed in Osa. Total mean flower production was greater in fragments than forest for C. aesculifolia, whereas no difference was observed for C. grandiflora. Fruit set was greater in forest than in fragments for C. grandiflora, whereas no difference was observed for C. aesculifolia. Outcrossing rates were high for C. aesculifolia, C. grandiflora, and C. pentandra in Guanacaste, independent of tree habitat, while C. pentandra in Osa showed a mixed-mating system. The effects of forest fragmentation on bat pollinators, plant reproductive success, and mating patterns varied depending upon the bombacaceous species. This variability was associated with the effects that forest fragmentation may have on differences in flowering patterns, bat foraging behavior, and plant self-incompatibility systems.
La fragmentación de bosques y el aislamiento especial, producto de este fenómeno, pueden modificar la actividad de los polinizadores y pueden tener implicaciones importantes sobre el éxito reproductivo y los sistemas de apareamiento de las plantas que polinizan. Los objetivos de este estudio consisten en : (1) evaluar los efectos de la fragmentación de bosque sobre la actividad de los polinizadores de árboles de Bombacaceas, y (2) determinar los efectos de la fragmentación sobre el éxito reproductivo y el sistema de apareamiento de árboles de Bombacaceas. Evaluamos estos parámetros en 3 especies de árboles de esta familia en bosques estacionales en Jalisco, México y Guanacaste y Osa, Costa Rica. Las flores de Ceiba aesculifolia fueron mas visitadas en fragmentos por Glossophaga soricina y Leptonycteris curasoae. En Ceiba grandiflora, Musonycteris harrisoni visitó flores exclusivamente en el bosque y G. soricina visitó mas flores en el bosque que en los fragmentos mientras que no hubo diferencias para L. curasoae. En Chamela, no se hubo diferencias en la visitación de flores entre bosque y fragmentos para G. soricina en Ceiba pentandra mientras que L. curasoae visitó más flores en el bosque. En Guanacaste, C. pentandra recibió más visitas de Phyllostomus discolor que de G. soricina mientras que no hubo visitas por murciélagos en Osa. La producción total promedio de flores fué mayor en los fragmentos que en el bosque para C. aesculifolia mientras que no hubo diferencias para C. grandiflora. La probabilidad de que una flor produzca fruto fué mayor en el bosque que en los fragmentos para C. grandiflora pero no hubo diferencias en C. aesculifolia. La tasa de exocruzamiento fue alta para C. aesculifolia, C. grandiflora, and C. pentandra en Guanacaste, independiente del tipo de hábitat, mientras que C. pentandra en Osa mostró un sistema de apareamiento mixto. Los efectos de la fragmentación de bosques sobre la polinización por murciélagos, la reproducción de plantas y sus patrones de apareamiento varía dependiendo de la especie de Bombacaceae. Esta variabilidad está asociada a los efectos que la fragmentación de bosques puede tener sobre diferencias en los patrones de floración, el comportamiento de forrajeo de los polinizadores, y los sistemas de incompatibilidad de las plantas.
Does Neighbourhood Floral Display Matter? Fruit Set in Carpenter Bee-pollinated Heterophragma quadriloculare and Beetle-pollinated Lasiosiphon eriocephalus
Hema Somanathan, Renee M. Borges (renee@ces.iisc.ernet.in), and V. Srinivasa Chakravarthy
Fruit set is pollen-limited in the self-incompatible tree Heterophragma quadriloculare (Bignoniaceae), pollinated by long-distance flying carpenter bees, and in the self-compatible shrub Lasiosiphon eriocephalus (Thymeleaceae), pollinated by weak-flying, sedentary beetles. We studied a single H. quadriloculare population over high and low flowering years and found no difference in bee visitation rates between these years. For H. quadriloculare, neighborhood floral display did not make a significant contribution to reproductive success. We investigated dense and sparse L. eriocephalus populations in the same year. In the low density L. eriocephalus population, individual floral displays were higher than in the dense population, yet reproductive success was low, indicating that plant isolation was a major factor influencing fruit set. This result was due to the extremely low number of beetles per plant and per flower in this population. In the dense L. eriocephalus population, although the displays of individual neighbors were smaller and plants were closer, neighborhood floral display did not contribute significantly to reproductive success, whereas the effect of individual floral display was ambiguous. Species with self-incompatible rather than self-compatible breeding systems are expected to experience neighborhood effects on reproductive success; however, at the spatial scale and floral display levels of plants in this study, only individual floral display affected fruit set in H. quadriloculare, whereas neither individual nor neighborhood display influenced fruit set in L. eriocephalus. Therefore, pollinator type, pollinator behavior, and plant and population isolation, rather than breeding system alone, will determine if neighborhood floral display affects fruit set.
Factors Contributing to Variation in Seed Production among Remnant Populations of the Endangered Daisy Gerbera aurantiaca
Steven D. Johnson (Johnsonsd@nu.ac.za), Carine L. Collin, H. Jörgen Wissman, Erika Halvarsson, and Jon Ågren
The species-rich mist-belt grasslands of southern Africa have been severely reduced in extent as a result of commercial afforestation, thus confining many endemic plants and animals to small populations in habitat fragments. We investigated the influence of various environmental factors on seed production and seedling recruitment in remnant populations of the endangered grassland herb Gerbera aurantiaca (Asteraceae). Experiments with color traps showed that Eriesthis beetles, which appear to be the primary pollinators of G. aurantiaca, were most abundant in the two largest extant populations. Seeds are produced in a very small proportion (typically <10%) of the ca 80 female florets in a capitulum. The mean number of seeds produced in undamaged capitula was found to be significantly lower in small than in large populations. Pollen limitation was evident from a significant overall increase in seed set after supplemental pollination in three populations over two seasons. The proportion of capitula containing seed predators did not differ markedly among populations or years, but lepidopteran larvae, which destroy all of the seeds in a capitulum, were most abundant in the two largest populations in 2003. The presence of juvenile plants varied markedly among populations, but this could not be linked firmly to estimates of seed production. Clonal growth is likely to contribute to the persistence of small isolated populations of G. aurantiaca, even when seed production is severely compromised by pollen limitation and predation.
Alien Abduction: Disruption of Native Plant-Pollinator Interactions by Invasive Species
Jaboury Ghazoul (j.ghazoul@imperial.ac.uk)
The indirect impacts of Shorea siamensis -logging on the reproductive ecology of Dipterocarpus obtusifolius, a self-incompatible butterfly-, moth-, and bird-pollinated tree, was studied in tropical dry forest in Thailand. Pollinator activity at D. obtusifolius trees and subsequent seed production were recorded in three forest areas subject to differing intensities of S. siamensis extraction. The pollinator and plant understory communities in these areas were also noted. Forest areas subject to high S. siamensis extraction intensities had very high understory flowering plant cover, dominated by the exotic invader Chromolaena odorata. Activity of butterfly pollinators at D. obtusifolius trees decreased in these disturbed areas, although their abundance remained comparable to other forest areas subject to only moderate or no extraction. For sphingid moth pollinators, there was no difference across differentially disturbed forest areas in either abundance or in the proportion bearing pollen. Pollinator activity by birds increased at highly disturbed locations but was not sufficient to offset a decline in overall pollinator activity at D. obtusifolius canopies in areas of heavy S. siamensis extraction. Thus, extraction of S. siamensis indirectly affected the pollination of D. obtusifolius, primarily by causing changes in the foraging behavior of butterfly pollinators rather than their abundance. A shift in the relative abundance of floral nectar resources from the canopy to the understory, a consequence of S. siamensis extraction, led to a parallel shift in foraging location of the principal diurnal pollinators, the butterflies, toward the understory. Despite reduced pollination at disturbed sites, behavioral changes did not translate into a D. obtusifolius seed set effect, possibly because pollination by birds (or moths) at the disturbed site compensated for reduced butterfly pollination.
Effects of Animal Pollination on Pollen Dispersal, Selfing, and Effective Population Size of Tropical Trees: A Simulation Study
Bernd Degen (degen_b@kourou.cirad.fr), and David W. Roubik
Animals, especially insects, are principal pollen vectors of tropical trees and have behavior patterns that affect gene dispersal. Here, we explore complex pollination systems using a new simulation model Eco-Gene and considering, among other factors, flowering synchrony, spatial distribution of trees, degree of selfing, population densities, pollinator flight distances, pollen deposition, and pollinator response to floral display size. Sensitivity analyses using two contrasting tree data sets (Jacaranda copaia and Dipteryx odorata) determined the importance of each parameter on three response variables: the proportion of seeds from self-pollination, effective population size, and pollen dispersal. Spatial considerations and attractiveness of floral displays were prominent features determining the population genetic result of pollinators, and some biological implications of the results are discussed.
Animales, insectos en particular, son los vectores principales del polen de los arboles tropicales y como consecuencia su comportamiento afecta dispersión genética. Aquí se examina sistemas de la polenización en su totalidad, aplicando un nuevo programa de simulacro Eco-Gene, que se toma en cuenta, entre otros factores, sincronicidad de floración, distrubución de arboles, grado de auto-fecundación, densidad poblacional, distancia de vuelo, polen deposición, y respuesta comportamiental de polenizadores al tamaño del anuncio floral. Sensitivity análisis con datos contrastantes de dos arboles (Jacaranda copaia y Dipteryx odorata) evaluó la importancia de cada parámetro y su resultado respeto a: la proporción de semillas producidas por autofecundación, tamaño poblacional efectivo, y distancia de dispersión del polen. Las cualidades espaciales de poblaciones, y la atractividad del anuncio floral determinaban fuertemente las consecuencias de polinizacion, y se considera implicaciones biológicas y genéticas de los resultados.
Sex in Space: A Synthesis
Jaboury Ghazoul (j.ghazoul@imperial.ac.uk) and R. Uma Shaanker
The five papers in this Special Section illustrate that pollination processes are often disrupted by changing plant distributions. They further demonstrate that plant pollination and seed production outcomes are highly complex due to multidimensional spatial effects and numerous interactive biological responses of both plants and pollinators at individual and population scales. Nevertheless, these studies also lend support to some emerging generalities that (through modeling) begin to provide a coherent framework by which further research, and ultimately management planning, could proceed.
Soil Microbial Dynamics in Costa Rica: Seasonal and Biogeochemical Constraints
Cory C. Cleveland (cory.cleveland@colorado.edu), Alan R. Townsend, Briana C. Constance, Ruth E. Ley, and Steven K. Schmidt
The soil microbial biomass is largely responsible for the transformation of organic matter and the associated mineralization of important nutrients that regulate plant productivity. While the controls on soil microbial biomass and activity in temperate ecosystems have been well investigated, there is a paucity of such information from tropical rain forest ecosystems. Hence, we used a natural soil gradient (nutrient-poor oxisols and nutrient-rich mollisols) to investigate seasonal changes in the size and activity of the soil microbial community in two primary tropical rain forest sites in southwestern Costa Rica. In a nutrient-poor oxisol, microbial biomass ranged from 952 μg/g in the dry season (February) to 1967 μg/g in the wet season (June). The greater microbial biomass estimates corresponded to greater rates of microbial activity in the oxisol forest; however, the active fraction of the soil microbial biomass remained consistently low, regardless of soil C availability. In addition, while there was very little seasonal variability in microbial C:N ratios, we found extreme variations in seasonal microbial C:P ratios, with the highest microbial C:P ratio occurring when microbial biomass C was at a maximum. Our results suggest the importance of P availability in regulating soil microbial processes and that decomposition during the wet season (of litter accumulated in the previous dry season) may play an important role in driving seasonal changes in microbial biomass and activity.
Las comunidades microbianas del suelo influencian en gran medida la descomposición de materia orgánica y la mineralización de los nutrientes necesarios para la producción primaria de plantas. Aunque los factores que gobiernan la actividad microbiana de suelos en la zona templada han sido investigados extensamente, carecemos de información sobre bosques tropicales húmedos. En este estudio, usamos sitios de fertilidades variables con el fin de investigar efectos estacionales en el tamaño y la actividad de las comunidades microbianas del suelo en dos bosques tropicales húmedos en el sudoeste de Costa Rica (Península de Osa). En los suelos infértiles (oxisoles), el tamaño de la comunidad microbiana se extendió de 952 μg/g en la estación seca (febrero) a 1967 μg/g en la estación lluviosa (junio). Además, las mayores estimaciones de la comunidad microbiana correspondieron a mayores tazas de cambio de la actividad microbiana. Sin embargo, la fracción microbiana activa se mantuvo siempre baja independientemente de la cantidad de carbono en el suelo. Además, aunque no hubo mucha variabilidad en las proporciones de carbono (C) y nitrógeno (N) en la masa microbiana con la estación del año, encontramos grandes cambios en las proporciones de C y de fósforo (P). En particular, observamos una proporción mas grande de C (sobre P) cuando el tamaño de la comunidad microbiana fue máximo. Nuestros resultados sugieren que la disponibilidad de P regula el tamaño y la actividad microbiana en este ecosistema, y que la descomposición de hojascara en la estación lluviosa (de hojas que se cayeron en la estación seca anterior) influencia en gran medida el tamaño y la actividad microbiana entre las estaciones del año.
Nectar in Hummingbird-pollinated Neotropical Plants I: Patterns of Production and Variability in 12 Species
Lucinda A. McDade (mcdade@acnatsci.org) and Jennifer A. Weeks
We studied nectar characteristics in 12 species of Neotropical hummingbird-pollinated plants: Aphelandra golfodulcensis, A. sinclairiana, A. storkii, Justicia aurea (Acanthaceae); Heliconia irrasa, H. latispatha, H. mathiasii (Heliconiaceae); Pavonia dasypetala (Malvaceae); Isertia haenkeana, Palicourea guianense, Pentagonia macrophylla (Rubiaceae); and Renealmia cernua (Zingiberaceae). The diurnal patterns in sugar content and cumulative volume of nectar were documented in flowers that were protected from flower visitors. Sugar content in these species (mean of all flowers sampled per species ranged from 16 to 28%) was comparable to those reported for other hummingbird-pollinated species. Mean nectar volume per flower spanned an order of magnitude (i.e., 8.8 [Palicourea] -72.7 μl [H. latispatha]), indicating that hummingbirds visited flowers with a wide range of reward. We observed low intraspecific variation in sugar content but high variation in nectar volume. Among species, 10-50 percent of the variation in nectar volume was explained by time of day. For a subset of four species (A. sinclairiana, Isertia, Palicourea, and Pentagonia), we studied variation among individuals in nectar volume. With time of day controlled, individual explained as much as 70 percent of the variation in nectar volume (A. sinclairiana) and as little as 20 percent (Pentagonia). We suggest that nectar volume likely has a genetic component in these species, but also that variation may itself be a trait, especially in Palicourea and Pentagonia. In three of the four species for which we had data from individuals, mean nectar volume and standard deviation were not correlated, suggesting that these traits may vary independently (Pentagonia was the exception with mean and standard deviation positively correlated). For two species (Isertia and Palicourea), we found evidence of seasonal variation in nectar production, with more nectar per flower produced early in the flowering season than later.
Estudiamos las características del néctar de 12 especies de plantas neotropicales polinizadas por colibríes: Aphelandra golfodulcensis, A. sinclairiana, A. storkii, Justicia aurea (Acanthaceae); Heliconia irrasa, H. latispatha, H. mathiasii (Heliconiaceae); Pavonia dasypetala (Malvaceae); Isertia haenkeana, Palicourea guianense, Pentagonia macrophylla (Rubiaceae); y Renealmia cernua (Zingiberaceae). Documentamos los patrones diurnos de contenido de azúcares y volumen acumulado de néctar en flores protegidas de visitantes florales. El contenido de azúcares de estas especies (promedio para todas las flores muestreadas por especies = 16-28%) es similar al reportado para otras especies polinizadas por colibríes. Los volúmenes de néctar promedio por flor variaron en un orden de magnitud (8.8 [Palicourea] -72.7 μl [Heliconia latispatha]; valores tomados de las horas de muestreo con volúmenes máximos) indicando que los colibríes visitan flores en un amplio rango de producción de recompensa. Nuestros resultados también indican que hay poca variación intraespecifica en contenido de azúcares, pero una gran variación en volumen de néctar producido. Entre especies, entre 10-50 por ciento de la variación en volumen de néctar es explicada por la hora del día. Estudiamos la variación de volumen de néctar entre individuos en cuatro especies (A. sinclairiana, Isertia, Palicourea, y Pentagonia). Controlando por hora del día (con todos los muestreos llevados a cabo a mediodía), los individuos explicaron entre el 70 (A. sinclairiana) y el 20 por ciento (Pentagonia) de la variación en volumen de néctar. Sugerimos que el volumen de néctar en estas especies posiblemente tenga un componente genético, pero también que la variación puede ser considerada un carácter por si misma, especialmente en Palicourea y Pentagonia. Para tres de las cuatro especies de las cuales tenemos datos a nivel de individuo, los promedios y las desviaciones estándar del volumen de néctar no están correlacionados, sugiriendo que estos caracteres pueden variar independientemente (Pentagonia fue la excepción teniendo su promedio y desviación estándar correlacionados positivamente). Para dos especies (Isertia y Palicourea), encontramos evidencia de variación estaciónal en producción de néctar, con más néctar siendo producido por flor al principio de la temporada de floración.
Nectar in Hummingbird-pollinated Neotropical Plants II: Interactions with Flower Visitors
Lucinda A. McDade (mcdade@acnatsci.org) and Jennifer A. Weeks
We documented the diurnal pattern of nectar volumes in flowers of seven Neotropical hummingbird-pollinated plant species that were open to flower visitors and compared these standing crop data to nectar volumes in flowers protected from visitors. Standing crop of nectar bore little relationship to nectar in bagged flowers either in terms of volume or temporal pattern of availability. There was almost no nectar in open flowers except in those collected at dawn and those of Aphelandra sinclairiana; these were apparently too abundant to be depleted by visitors. Nectar volumes in open flowers were even more variable than in bagged flowers. We argue that understanding the evolution of plant-pollinator interactions requires understanding the relationship between nectar production and standing crop, as well as the impact of high variability on decisions by foraging animals. We conducted experiments to determine the effect of nectar removal on nectar production. Nectar removal via simulated legitimate visits had no impact on total production in flowers of Pavonia, Isertia, and Palicourea. For A. sinclairiana and Pentagonia, total nectar production in visited flowers was reduced compared to unvisited flowers. Data from individuals of these last two species indicated that the population-level pattern was assembled from individuals that responded differently to nectar removal; clearly, understanding the evolution of nectar traits demands data from individuals. We argue that detecting patterns of plant responses to nectar removal requires the context of floral characteristics (e.g., longevity, ovule number, or pollinators). Nectar removal via simulated nectar-robbing visits had no impact on total nectar production in A. sinclairiana but reduced total production in Isertia. Nectar robbing did not cause plants to invest more energy in nectar than they would have the absence of robbing. Finally, we found no difference in seed set by robbed and unrobbed flowers of A. sinclairiana. Our results add to a growing body of literature suggesting that nectar robbers are not always detrimental to plant fitness.
Documentamos los patrones diurnos de volúmenes de néctar en flores que estaban disponibles para sus visitantes florales y los comparamos con los volúmenes de néctar de flores protegidas de visitantes, en siete especies de plantas neotropicales polinizadas por colibríes. Los volúmenes de néctar disponibles (standing crop) tuvieron poca relación con los volúmenes de néctar y sus patrones de disponibilidad en flores embolsadas. Las flores abiertas casi no presentaron néctar, con la excepción de las flores colectadas al amanecer y las flores de Aphelandra sinclariana; las cuales aparentemente eran demasiado abundantes para ser vaciadas por visitantes. Los volúmenes de néctar fueron aun más variables en las flores abiertas que en las flores embolsadas. Argumentamos que para entender la evolución de las interacciones planta-polinizador requiere tanto entender la relación entre producción de néctar y volúmenes de néctar disponibles, como el impacto que la alta variabilidad de producción de néctar tiene sobre las decisiones de forrajeo de los animales. Por lo tanto, llevamos a cabo experimentos para determinar el efecto que la remoción de néctar tiene sobre sus patrones de producción. La remoción de néctar, por medios que simulan las visitas legítimas, no tuvo impacto en la producción total de néctar de las flores de Pavonia, Isertia, y Palicourea. En A. sinclariana y Pentagonia, la producción total de néctar en flores visitadas fue menor que en las que no lo fueron. Datos de diferentes individuos de estas dos especies indican que el patrón a nivel poblacional esta formado por individuos que responden de manera diferente a la remoción de néctar; claramente, el entender la evolución de las características del néctar requiere datos a nivel de individuos. Argumentamos que detectar patrones de respuesta de las plantas a la remoción de néctar requiere conocer las características florales (e.g., longevidad, número de óvulos, polinizadores). La remoción de néctar, por medios que simular visitas de robadores de néctar, no afectó la producción de néctar de A. sinclairiana, pero redujo la producción total en Isertia. El robo de néctar no provocó que las plantas invirtieran más energía en néctar que la que hubieran utilizado en ausencia de robo. Finalmente, no encontramos diferencias en la producción de semillas de flores robadas o no robadas de A. sinclairiana. Nuestros resultados se suman a los de otros trabajos que sugieren que los robadores florales no siempre tienen efectos negativos sobre la adecuación de las plantas.
Termite Mounds as Nutrient-Rich Food Patches for Elephants
Ricardo M. Holdo (rholdo@Princeton.EDU) and Lee R. McDowell
This study examined elephant use of woody vegetation on termite mounds with surrounding woodlands in western Zimbabwe. Twelve sites consisting of paired plots on termite mounds and in woodlands were selected. At each site, soil and vegetation samples (leaf and stem) were collected for chemical analysis. Both soil and plant samples were analyzed for calcium, magnesium, potassium, sodium, and phosphorus, and plant samples were also analyzed for crude protein concentration. Two indices of elephant feeding damage were computed: the median number of stems and branches removed per plant, and the mass of stems and branches removed by elephants per unit area. Termite mound soils had higher concentrations of all elements tested than soils from woodlands, and termite mounds differed from woodland plots in terms of plant species composition. Trees growing on termite mounds had higher concentrations of all nutrients except sodium and crude protein, and were subjected to more intense feeding by elephants than trees from the surrounding vegetation matrix. Termite mounds may play an important role in determining food availability and spatial feeding patterns by elephants and other herbivores.
Effects of Hygrothermal Stress, Plant Richness, and Architecture on Mining Insect Diversity
G. Wilson Fernandes (gwilson@mono.icb.ufmg.br), Fabiana M. Caldeira Castro, Maurício L. Faria, Evelyn S. A. Marques, and Magda K. Barcelos Greco
We investigated the distribution patterns of leaf mining insects along an elevational gradient in cerrado vegetation of southeastern Brazil. We tested four hypotheses related to the distribution of mining insects: (1) the "altitudinal gradient hypothesis," which predicts that mining insect species richness will decrease with altitude or elevation; (2) the "habitat-mediated richness hypothesis," which predicts that mining insect species richness will be higher in mesic habitats than in xeric habitats; (3) the "plant species richness hypothesis," which predicts that mining insect species richness will be positively correlated with plant species richness; and (4) the "plant architecture hypothesis," which predicts a positive correlation between mining insect species richness and plant structural complexity. A total of 33,000 herbs, 3520 shrubs, and 1760 trees were sampled at 44 sites across an elevational gradient of 700 m. Mining insect species richness and plant species richness showed a negative correlation with elevation in xeric habitats, while in mesic habitats mining insect species and plant species richness did not show any statistically significant relationship with elevation. The differential distribution of mining insect species between xeric and mesic habitats supported the habitat-mediated richness hypothesis, which states that miners would be more speciose in mesic, more favorable habitats. Mining species richness also increased with increasing plant structural complexity. The results suggest that the mining habit may not represent a strong adaptive strategy in protecting mining insects against desiccation.
Nós investigamos os padrões de distribuição de insetos minadores ao longo de um gradiente altiudinal no cerrado, no sudeste do Brasil. Testamos quatro hipóteses relacionadas à distribuição de insetos minadores: (1) a "hipótese do gradiente altitudinal" que prediz que a riqueza de espécies de minadores aumenta com o decréscimo da altitude; (2) a "hipótese da riqueza mediada pelo habitat" que prediz que a riqueza de espécies de minadores deve ser maior em habitats mésicos que em habitats xéricos; (3) a "hipótese da riqueza de espécies de plantas" que prediz que a riqueza de espécies de minas deve ser positivamente correlacionada com a riqueza de espécies de plantas; e (4) a "hipótese da arquitetura da planta" que prediz uma correlação positiva entre riqueza de espécies de minas e complexidade estrutural das plantas. Foram amostradas 33,000 ervas, 3520 arbustos, e 1760 árvores, em 44 sítios ao longo de um gradiente de 700 m: A riqueza de espécies de minadores e de plantas apresentou uma correlação negativa com a altitude em habitats xéricos. Entretanto, em habitats mésicos as espécies de minadores e a riqueza de espécies de plantas não apresentaram nenhuma relação estatisticamente significativa com a altitude. A distribuição diferencial de espécies de minadores entre habitats xéricos e mésicos corroborou a hipótese da riqueza mediada pelo habitat, segundo a qual a riqueza de minas deve ser maior em habitats mésicos, que são mais favoráveis. A riqueza de espécies de minadores aumentou com o aumento da complexidade estrutural da planta. Estes resultados sugerem que o hábito minador não deve representar uma forte estratégia adaptativa para fornecer aos minadores proteção contra dessecação.
Lack of Genetic Structuring among Tropical Brazilian Wood Stork Populations and Low Genetic Differentiation from North American Populations
Cristiano Dosualdo Rocha, Sílvia Nassif Del Lama (dsdl@power.ufscar.br), and Luciana Correia de Almeida Regitano
The Wood Stork (Mycteria americana) is a wading bird inhabiting subtropical and tropical regions of the American continent. This species is considered endangered in the United States. We compared variability and genetic structuring of nine Brazilian Pantanal subpopulations with an North American population using eight allozyme loci data (MPI, ICD, NSP, EST-D, LDH, PGM, 6PGD,and PEP-A) and four microsatellite loci data (WS1, WS2, WS4, and WS6). Average expected heterozygosity of Pantanal population was similar (0.198 ± 0.065) to that expected for the North American population (0.231 ± 0.066). No significant genetic differentiation was found among Pantanal subpopulations (F st = 0.012) and low differentiation was detected between Pantanal and North American populations (F st = 0.023). Lack of differentiation among Pantanal subpopulations may have been due to high gene flow level among birds of neighbor breeding colonies and low natal philopatry. We propose that low differentiation between North and South American populations has arisen either because these populations occupied neighboring regions during late glaciation or because there is a continuous gene flow between them, via Central American or northern South American populations.
O Cabeça-seca (Mycteria americana) é uma ave aquática habitante das regiões tropicais e subtropicais do continente americano. Essa espécie está ameaçada de extinção nos Estados Unidos. Nós comparamos a variabilidade e a estruturação genética de nove subpopulações brasileiras do Pantanal com as da população norte americana, baseando-se em dados de oito locos alozímicos (MPI, ICD, NSP, EST-D, LDH, PGM, 6PGD, e PEP-A) e em dados de quatro locos de microssatélites (WS1, WS2, WS4, e WS6). A heterozigosidade média esperada para a população do Pantanal (0.198 ± 0.065) foi semelhante à esperada para a população norte americana (0.231 ± 0.066). Não foi encontrada diferenciação genética significativa entre as subpopulações do Pantanal (F st = 0.012) e baixa diferenciação genética foi detectada entre as populações do Pantanal e a norte americana ( F st = 0.023). A não diferenciação entre subpopulações do Pantanal pode ser resultante de um alto nível do fluxo gênico entre aves de colônias reprodutivas vizinhas e da baixa filopatria natal. Nós propomos que a baixa diferenciação entre as populações norte e sul americanas seja decorrente da ocupação de regiões vizinhas por essas populações durante a última glaciação ou devido há existência de fluxo contínuo entre elas, via populações da América Central ou do norte da América do Sul.
Aquatic Insect Assemblages in Shrimp-dominated Tropical Streams, Puerto Rico
Alonso Ramírez (aramirez@ sunites.upr.clu.edu) and Luz Raquel Hernández-Cruz
We examined the effects of shrimp on insects in Puerto Rico by assessing insect assemblages in streams relative to varying shrimp densities and also by manipulating shrimp presence. Insect assemblages were typical of tropical island streams and insects were found in all stream habitats. Shrimp impacted insects directly via predation and competition and indirectly through removing particles from the water column. Variation in shrimp distribution is likely to be an important factor determining insect-assemblage structure in tropical streams.
Examinamos los efectos de los camarones sobre los insectos en Puerto Rico, para ello estudiamos quebradas con densidades contrastantes de camarones y manipulamos su presencia. Los ensamblajes de insectos fueron típicos de quebradas de islas tropicales y usaron todos los hábitats. Los camarones impactaron directamente a los insectos vía depredación y competencia e indirectamente al remover partículas del agua. Variación en la distribución de camarones es un factor importante en determinar la estructura de los ensamblajes de insectos en las quebradas tropicales.
Placing an Omnivore in a Complex Food Web: Dietary Contributions to Adult Biomass of an Ant
Chadwick V. Tillberg and Michael D. Breed (michael.breed@colorado.edu)
Workers of Paraponera clavata, a common Neotropical ant, collect both nectar and insect prey. Previous reports show that nectar accounts for up to 90 percent of the ants' food loads, while calculations suggest that nectar contributes only 10 percent of colonies' energy supply. We assessed the trophic source of carbon and nitrogen in adult workers using stable isotope analysis. Carbon in adult workers was largely derived from plant sources. Worker nitrogen isotopic ratios varied significantly among colonies and were enriched compared to prey. Prey nitrogen isotope ratios suggest considerable intercolonial variation in diet, with some colonies collecting prey from lower trophic levels than other colonies. The importance of nectar as a source of metabolic carbon in adult worker biomass, coupled with the high frequency of nectar collection, supports the conclusion that omnivory is a key to supporting this species' biomass in Neotropical wet forests.
Co-extinctions of Tropical Butterflies and their Hostplants
Lian Pin Koh, Navjot S. Sodhi (dbsns@nus.edu.sg), and Barry W. Brook
The co-extinction of interdependent species in relation to massive, long-term habitat disturbance has not been thoroughly investigated. Using logistic regression analyses, we examined the relationship between the loss of butterflies and their specific hostplants from the tropical island of Singapore and report the probable occurrence of their co-extinctions at the community level. Our simulation shows that the number of extinct butterfly species is expected to increase exponentially with that of extinct hostplants. The close association between butterflies and their hostplants suggests that the preservation of whole habitats is urgently needed if we are to avoid the possible cascading effects of species (co-)extinctions.