Abstract
Seed dispersal is a key process that determines the spatial structure and dynamics of populations of plants, establishes the potential area of recruitment and in this way, the basis for subsequent processes such as predation, germination, competition and growth. The purpose of this research was to identify the guild of frugivores of the Oenocapus bataua palm in fragments of Andean forest, determine the effective dispersers and relate the spatial distribution of palm populations with the dispersion of seeds. To this end, between August 2005-June 2006, observations of the removal of fruits from eight clusters were done, and counting of consumption of fruits beneath 78 palms with mature fruits was undertaken; focal observations of 13 individuals during 90 hours; registration of frugivory with photographic traps during 165 days/nights for a total of 195 photographs and 144 consumption events; experiments with dispersion using 751 perforated fruits/seeds attached to strings and finally, plots to determine spatial distribution all were carried out. In the study area at least five species of mammals ate, dispersed, buried (Sciurus granatensis, Microsciurus mimulus, Dasyprocta punctata y Proechimys sp.), cover (Marmosa robinsoni) and carried the fruits of O. bataua off to caves (Marmosa robinsoni y Proechimys sp.) without damaging the seed. A 21.7% of the fruits were dispersed, 13.2 gnawed or peeled, 5.6% covered, buried and carried to caves. The average distance of removal of seeds and fruits was 3.1m although in a lesser proportion, dispersion events of >50m were recorded. The abundant production of fruits, their size and weight, their intense removal by frugivores, the short dispersion distances, the absence of large size frugivores (reduced by hunting and fragmentation), that might perform long-distance dispersion, and the increase of rodents, especially squirrels, that strongly pressure the fruit resource, generate a spatially restricted seed rain of seeds responsible for the aggregate patterns of distribution of seeds, seedlings and subsequently of juveniles and sub-adults. However the short time and high percentage of seed germination and the robustness of seeds and seedlings give O. bataua the capacity to survive in dense aggregations. Therefore, despite the limitations on dispersion, this is a dominant species in the study area. Populations of O. bataua have been reduced by intense exploitation and by the transformation and reduction of their natural habitat. The over-exploitation of the fruits or the juvenile phases of this palm can affect the age structure and population dynamics. Therefore, the management and exploitation of this palm in the future will depend to large degree on the conservation of forest habitats.
Highlights
La dispersión de semillas se considera un proceso clave que determina la estructura espacial y la dinámica de las poblaciones de plantas (Nathan & Muller-Landau 2000); establece el área potencial de reclutamiento y de esta forma, la base para procesos subsecuentes tales como depredación, germinación, competencia y crecimiento (Barot et al 1999, Nathan & MullerLandau 2000, Wang & Smith 2002)
Igualmente colocamos las cámaras apuntando a montones de frutos en el suelo, en palmas con frutos maduros cayendo o con evidencias de que previamente estaban siendo visitadas por los frugívoros
En O. bataua la abundante producción de frutos (Rojas & Stiles 2009), el tamaño, peso, la intensa remoción de frutos del racimo, las cortas distancias de dispersión por frugívoros y posiblemente la ausencia de frugívoros de gran porte encargados de la dispersión de más larga distancia, generan una sombra de semillas espacialmente restringida responsable de los patrones de distribución agregados en plántulas y posteriormente en juveniles y sub-adultos (Rojas et al 2008)
Summary
Área de estudio: La investigación se llevó a cabo en un área de bosque subandino o bosque húmedo premontano (bh-PM) (Holdridge 1996), en la cuenca media del río Porce (6°45’37’’ N - 75°06’28’’ W), sobre la Cordillera Central andina de Colombia. Cada mes se contó el número de frutos en las raquilas, hasta que el racimo maduro quedó sin frutos por la remoción de los frugívoros. Igualmente colocamos las cámaras apuntando a montones de frutos en el suelo, en palmas con frutos maduros cayendo o con evidencias de que previamente estaban siendo visitadas por los frugívoros. Utilizamos la prueba de chi-cuadrado para: comparar frugivoría en el suelo y en el racimo; diferencias en la dispersión de frutos con relación a semillas; diferencias entre semillas y frutos tapados, enterrado y llevado a las cuevas y para comparar dispersión de semillas y frutos entre los fragmentos de bosque muestreados. Como los valores de las distancias de semillas y plántulas al vecino reproductivo más cercano no presentaron una distribución normal, ni al realizar transformación logarítmica, se uso la prueba no paramétrica de Kruskal-Wallis (H) para comparar el comportamiento de las distancias al vecino más cercano en los fragmentos muestreados.
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