Abstract. Documenting changes in species distribution is critical to understanding bird diversity... more Abstract. Documenting changes in species distribution is critical to understanding bird diversity, establishing a baseline for comparative studies, quantifying bird turnover rates, and identifying sensitive groups to anthropogenic disturbances. We examine changes in diversity of the avifauna of Carara National Park (Costa Rica), a transitional forest bordered by a busily trafficked road, between the wet and dry seasons of 2007. We established count points in two sectors of the Park (Carara trails, 12 points, and the Meandric Lagoon, 8 points), and did censuses twice a day for five consecutive days in July and August (wet season), and in November (dry season). We measured species similarity among trails and seasons using the Sorensen and Morisita indices, and used principal components to consolidate species numbers, the number of observations, and the Shannon diversity index. The first component (96 % of the variation) served to measure road influence on bird abundance and diversity. We applied these analyses to specialized understory insectivores (Formicariidae, Furnariidae, Troglodytidae and Thamnophylidae), expecting a negative effect of the road on diversity and abundance closer to the road. We observed 178 species (1 690 observations) combining wet and dry season. Species numbers varied little between sites and seasons (estimated number of species = 100). Species similarity between sites was higher during the wet season (Sorensen index = 71.9 %). The trails clustered according to season rather than location. The avifauna was dominated by resident species during wet and dry seasons (94 % and 85 % of observations, respectively). The road affected bird distribution within the first 100 m, showing a significant effect on specialized insectivores. Roads bordering conservation areas will increase in number and traffic in the next decades. It is critical to understand their effects on wildlife to improve management practices and reduce impacts on sensitive species.
ABSTRACT Some understory insectivorous birds manage to persist in tropical forest fragments despi... more ABSTRACT Some understory insectivorous birds manage to persist in tropical forest fragments despite significant habitat loss and forest fragmentation. Their persistence has been related to arthropod biomass. In addition, forest structure has been used as a proxy to estimate prey availability for understory birds and for calculating prey abundance. We used arthropod biomass and forest structural variables (leaf area index [LAI] and aerial leaf litter biomass) to explain the abundance of White-breasted Wood-Wrens (Henicorhina leucosticta), tropical understory insectivorous birds, in six forests in the Caribbean lowlands of Costa Rica. To estimate bird abundance, we performed point counts (100-m radius) in two old-growth forests, two second-growth forests, and two selectively logged forests. Arthropod abundance was the best predictor of wood-wren abundance (wi = 0.75). Wood-wren abundance increased as the number of arthropods increased, and the estimated range of bird abundance obtained from the model varied from 0.51 (0.28 – 0.93 [95%CI]) to 3.70 (1.68 – 5.20 [95%CI]) within sites. LAI was positively correlated to prey abundance (P = 0.01), and explained part of the variation in wood-wren abundance. In forests with high LAI, arthropods have more aerial leaf litter as potential habitat so more potential prey are available for wood-wrens. Forests with a greater abundance of aerial leaf litter arthropods were more likely to sustain higher densities of wood-wrens in a fragmented tropical landscape.RESUMENEfecto de la disponibilidad de presas sobre la abundancia de Henicorhina leucosticta, un ave insectívora de los bosques tropicales de tierras bajasAlgunas aves insectívoras de sotobosque tienen la capacidad de persistir en fragmentos de bosques tropicales a pesar de la perdida significativa de hábitat y fragmentación del bosque. Su persistencia se ha relacionado con la biomasa de artrópodos. Adicionalmente, la estructura del bosque se ha utilizado como una variable para estimar la abundancia de presas disponibles para las aves del sotobosque y para calcular la abundancia de presas. Usamos la biomasa de artrópodos y variables de la estructura del bosque (Índice del Área Foliar [IAF] y biomasa de la hojarasca aérea) para explicar la abundancia de un ave tropical insectívora de sotobosque, Henicorhina leucosticta, en seis bosques en la región de tierras bajas del caribe de Costa Rica. Para estimar la abundancia de aves, realizamos puntos de conteo (radio de 100-m) en dos bosques maduros, dos de crecimiento secundario y dos con tala selectiva. La abundancia de artrópodos fue el mejor predictor de la abundancia de H. leucosticta (wi = 0.75). La abundancia de H. leucosticta incremento a medida que incrementaba el numero de artrópodos, el rango de estimación de la abundancia de aves obtenido a partir del modelo varió entre 0.51 (0.28 – 0.93 [95%CI]) y 3.70 (1.68 – 5.20 [95%CI]) dentro de los sitios. IAF se correlacionó positivamente con la abundancia de presas (P = 0.01), y explicó parte de la variación en la abundancia de H. leucosticta. En bosques con alto IAF, los artrópodos tienen más hojarasca aérea como hábitat potencial, lo cual se traduce en mayores presas potenciales disponibles para H. leucosticta. Bosques con mayor abundancia de artrópodos de hojarasca aérea tuvieron una probabilidad mas alta de sostener una mayor densidad de H. leucosticta en un paisaje tropical fragmentado.
Functional traits are morphological and physiological characteristics that determine growth, repr... more Functional traits are morphological and physiological characteristics that determine growth, reproduction, and survival strategies. The leaf economics spectrum proposes two opposing life history strategies: species with an "acquisitive" strategy grow fast and exploit high-resource environments, while species with a "conservative" strategy emphasize survival and slow growth under low resource conditions. We analyzed interspecific variation in nine functional traits related to biomass allocation and tissue quality in seven Neotropical palm species from three forest strata (understory, subcanopy, and canopy). We expected that the level of resources of a stratum that a species typically exploits would determine the dominance of either the exploitative or conservative strategy, as well as the similarity in functional traits between species. If this is correct, then canopy and subcanopy species will show an acquisitive strategy emphasizing traits targeting a larger siz...
In the dry forest of Santa Rosa National Park, Costa Rica, the understory shrub Jacquinia nervosa... more In the dry forest of Santa Rosa National Park, Costa Rica, the understory shrub Jacquinia nervosa presents an inverse pattern of phenology that concentrates vegetative growth and reproduction during the dry season. In this study, we tested the “escape from herbivory” hypothesis as a potential explanation for the inverse phenological pattern of J. nervosa. We monitored leaf, flower and fruit production in 36 adult plants from October 2000 to August 2001. Leaves of six randomly selected branches per plant were marked and monitored every two weeks to measure the cumulative loss in leaf area. To analyze pre-dispersal seed predation we collected 15 fruits per plant and counted the total number of healthy and damaged seeds, as well as the number and type of seed predators found within the fruits. Leaf, flower, and fruit production occurred during the first part of the dry season (end of November to February). The cumulative herbivory levels were similar tothose observed in other tropical ...
Abstract. Documenting changes in species distribution is critical to understanding bird diversity... more Abstract. Documenting changes in species distribution is critical to understanding bird diversity, establishing a baseline for comparative studies, quantifying bird turnover rates, and identifying sensitive groups to anthropogenic disturbances. We examine changes in diversity of the avifauna of Carara National Park (Costa Rica), a transitional forest bordered by a busily trafficked road, between the wet and dry seasons of 2007. We established count points in two sectors of the Park (Carara trails, 12 points, and the Meandric Lagoon, 8 points), and did censuses twice a day for five consecutive days in July and August (wet season), and in November (dry season). We measured species similarity among trails and seasons using the Sorensen and Morisita indices, and used principal components to consolidate species numbers, the number of observations, and the Shannon diversity index. The first component (96 % of the variation) served to measure road influence on bird abundance and diversity. We applied these analyses to specialized understory insectivores (Formicariidae, Furnariidae, Troglodytidae and Thamnophylidae), expecting a negative effect of the road on diversity and abundance closer to the road. We observed 178 species (1 690 observations) combining wet and dry season. Species numbers varied little between sites and seasons (estimated number of species = 100). Species similarity between sites was higher during the wet season (Sorensen index = 71.9 %). The trails clustered according to season rather than location. The avifauna was dominated by resident species during wet and dry seasons (94 % and 85 % of observations, respectively). The road affected bird distribution within the first 100 m, showing a significant effect on specialized insectivores. Roads bordering conservation areas will increase in number and traffic in the next decades. It is critical to understand their effects on wildlife to improve management practices and reduce impacts on sensitive species.
ABSTRACT Some understory insectivorous birds manage to persist in tropical forest fragments despi... more ABSTRACT Some understory insectivorous birds manage to persist in tropical forest fragments despite significant habitat loss and forest fragmentation. Their persistence has been related to arthropod biomass. In addition, forest structure has been used as a proxy to estimate prey availability for understory birds and for calculating prey abundance. We used arthropod biomass and forest structural variables (leaf area index [LAI] and aerial leaf litter biomass) to explain the abundance of White-breasted Wood-Wrens (Henicorhina leucosticta), tropical understory insectivorous birds, in six forests in the Caribbean lowlands of Costa Rica. To estimate bird abundance, we performed point counts (100-m radius) in two old-growth forests, two second-growth forests, and two selectively logged forests. Arthropod abundance was the best predictor of wood-wren abundance (wi = 0.75). Wood-wren abundance increased as the number of arthropods increased, and the estimated range of bird abundance obtained from the model varied from 0.51 (0.28 – 0.93 [95%CI]) to 3.70 (1.68 – 5.20 [95%CI]) within sites. LAI was positively correlated to prey abundance (P = 0.01), and explained part of the variation in wood-wren abundance. In forests with high LAI, arthropods have more aerial leaf litter as potential habitat so more potential prey are available for wood-wrens. Forests with a greater abundance of aerial leaf litter arthropods were more likely to sustain higher densities of wood-wrens in a fragmented tropical landscape.RESUMENEfecto de la disponibilidad de presas sobre la abundancia de Henicorhina leucosticta, un ave insectívora de los bosques tropicales de tierras bajasAlgunas aves insectívoras de sotobosque tienen la capacidad de persistir en fragmentos de bosques tropicales a pesar de la perdida significativa de hábitat y fragmentación del bosque. Su persistencia se ha relacionado con la biomasa de artrópodos. Adicionalmente, la estructura del bosque se ha utilizado como una variable para estimar la abundancia de presas disponibles para las aves del sotobosque y para calcular la abundancia de presas. Usamos la biomasa de artrópodos y variables de la estructura del bosque (Índice del Área Foliar [IAF] y biomasa de la hojarasca aérea) para explicar la abundancia de un ave tropical insectívora de sotobosque, Henicorhina leucosticta, en seis bosques en la región de tierras bajas del caribe de Costa Rica. Para estimar la abundancia de aves, realizamos puntos de conteo (radio de 100-m) en dos bosques maduros, dos de crecimiento secundario y dos con tala selectiva. La abundancia de artrópodos fue el mejor predictor de la abundancia de H. leucosticta (wi = 0.75). La abundancia de H. leucosticta incremento a medida que incrementaba el numero de artrópodos, el rango de estimación de la abundancia de aves obtenido a partir del modelo varió entre 0.51 (0.28 – 0.93 [95%CI]) y 3.70 (1.68 – 5.20 [95%CI]) dentro de los sitios. IAF se correlacionó positivamente con la abundancia de presas (P = 0.01), y explicó parte de la variación en la abundancia de H. leucosticta. En bosques con alto IAF, los artrópodos tienen más hojarasca aérea como hábitat potencial, lo cual se traduce en mayores presas potenciales disponibles para H. leucosticta. Bosques con mayor abundancia de artrópodos de hojarasca aérea tuvieron una probabilidad mas alta de sostener una mayor densidad de H. leucosticta en un paisaje tropical fragmentado.
Functional traits are morphological and physiological characteristics that determine growth, repr... more Functional traits are morphological and physiological characteristics that determine growth, reproduction, and survival strategies. The leaf economics spectrum proposes two opposing life history strategies: species with an "acquisitive" strategy grow fast and exploit high-resource environments, while species with a "conservative" strategy emphasize survival and slow growth under low resource conditions. We analyzed interspecific variation in nine functional traits related to biomass allocation and tissue quality in seven Neotropical palm species from three forest strata (understory, subcanopy, and canopy). We expected that the level of resources of a stratum that a species typically exploits would determine the dominance of either the exploitative or conservative strategy, as well as the similarity in functional traits between species. If this is correct, then canopy and subcanopy species will show an acquisitive strategy emphasizing traits targeting a larger siz...
In the dry forest of Santa Rosa National Park, Costa Rica, the understory shrub Jacquinia nervosa... more In the dry forest of Santa Rosa National Park, Costa Rica, the understory shrub Jacquinia nervosa presents an inverse pattern of phenology that concentrates vegetative growth and reproduction during the dry season. In this study, we tested the “escape from herbivory” hypothesis as a potential explanation for the inverse phenological pattern of J. nervosa. We monitored leaf, flower and fruit production in 36 adult plants from October 2000 to August 2001. Leaves of six randomly selected branches per plant were marked and monitored every two weeks to measure the cumulative loss in leaf area. To analyze pre-dispersal seed predation we collected 15 fruits per plant and counted the total number of healthy and damaged seeds, as well as the number and type of seed predators found within the fruits. Leaf, flower, and fruit production occurred during the first part of the dry season (end of November to February). The cumulative herbivory levels were similar tothose observed in other tropical ...
Uploads
Papers by Gerardo Avalos