Spatial patterns of primary seed dispersal and adult tree distributions: Genipa americana dispersed by Cebus capucinus

The spatial distribution of adult trees is typically not expected to reflect the spatial patterns of primary seed dispersal, due to many factors influencing post-dispersal modification of the seed shadow, such as seed predation, secondary seed dispersal and density-dependent survival. Here, we test the hypothesis that spatial distributions of primary seed shadows and adult trees are concordant by analysing the spatial distributions of adult Genipa americana trees and the seed shadow produced by its key primary disperser, the capuchin monkey (Cebus capucinus) in a tropical dry forest in Costa Rica. We mapped the dispersal of G. americana seeds by the capuchins during focal animal follows (mean = 463 min, n = 50) of all adults in one free-ranging group over two early wet seasons (May–July, 2005 and 2006). We mapped the locations of all G. americana trees within a 60-ha plot that lay within the home range of the capuchin group. We conducted multiple spatial point pattern analyses comparing degrees of clustering of capuchin defecations and G. americana trees. We found that adult tree distributions and primary dispersal patterns are similarly aggregated at multiple spatial scales, despite the modification of the primary dispersal patterns and long dispersal distances.

Seed shadow of Swietenia macrophylla remnant trees in a Mexican rainforest: mplications for forest management

<p>Entender los procesos relacionados con la regeneración y coexistencia de árboles es un tema de gran relevancia en paisajes tropicales perturbados por actividades humanas. En este estudio, se evaluó la sombra de semillas en ocho árboles remanentes de <em>Swietenia macrophylla</em> para determinar las posibles consecuencias de la tala selectiva sobre los primeros estadíos de la regeneración natural de la especie. Se esperaba encontrar una dispersión limitada y una marcada pérdida de semillas debido a las interacciones bióticas. Para probar esto, la sombra de semillas por árbol fue evaluada en cuatro transectos radiales (30 × 1 m) que redundaron en 960 cuadros de 1 m² usados para el muestreo. También se consideró el efecto de la dirección del viento y las características de los árboles, así como el diámetro a la altura del pecho y el área de proyección de la copa, como posibles factores que infl uyen en la sombra de semillas. Además, se registró el número de semillas depredadas y las infectadas por hongos. En total se encontraron 540 semillas de <em>S. macrophylla</em> en los 960 cuadros usados para evaluar la sombra de semillas. Cerca de 86% de estos cuadros mostraron 0 o 1 semilla, mientras que 80% de las semillas se encontraron dentro de los primeros 20 m con respecto a los árboles madre. La regresión entre el número de semillas perdidas por interacciones bióticas y la distancia al árbol madre se ajustó a un modelo cuadrático que explicó el 52.4% de la varianza total. Estos resultados sugieren que los árboles pequeños y remanentes de <em>S. macrophylla</em> muestran una baja capacidad de dispersión causada por una sombra de semillas limitada y una elevada tasa de pérdida de semillas por interacciones bióticas. Los resultados indican que la remoción de los árboles más grandes para su venta podría estar impactando negativamente sobre los primeros estadíos de la regeneración natural de esta especie de alto valor, y que consecuentemente, la extracción selectiva podría amenazar la permanencia local de la caoba en bosques manejados de la zona Maya.</p>

Influence of gibbon ranging patterns on seed dispersal distance and deposition site in a Bornean forest

Frugivores display daily and seasonal behavioural variation, yet the influence of this variability on subsequent seed shadows is rarely considered. We investigated the extent to which three aspects of gibbon (Hylobates muelleri × agilis) foraging and ranging behaviour (revisitation of favoured fruit sources, daily and monthly ranging patterns) influenced seed dispersal distances and deposition sites for two groups in dipterocarp forests at the Barito Ulu research site, Kalimantan, Indonesia. Dispersal distances and sites were estimated using gut retention times and ranging patterns collected over 12 mo. Gibbons dispersed few seeds (0.7%) under parent trees and most seeds (> 90%) were dispersed more than 100 m. Mean dispersal distances differed significantly between groups (339 m and 431 m) and across different months. Deposition site was only influenced by time of day, with all seeds swallowed in the first hour of activity being deposited under sleeping trees used that night. Both groups visited all 0.25-ha quadrats within their home range over the study period, indicating that gibbons potentially disperse seeds throughout their home range. Given the general uniformity of the gibbon seed shadow, the intensity of home range use and large seed dispersal distances, gibbons appear to be consistently effective seed dispersers and are probably one of the most important frugivores in Asian rain forests.

Seed shadow, seedling recruitment, and spatial distribution of Buchenavia capitata (Combretaceae) in a fragment of the Brazilian Atlantic Forest

Here we describe the seed shadow, seedling recruitment, ontogenetic structure and spatial distribution of Buchenavia capitata (an emergent canopy tree) in a 380-ha fragment of the Atlantic forest in northeast Brazil. In particular, we examine seed distribution around 10 parental trees and both seedling recruitment and mortality, during an 18 month period beneath and around parental trees. Moreover, we describe: (1) B. capitata occurrence within treefall gaps; (2) population structure in terms of ontogenetic stages for the whole site; and (3) spatial distribution of adults within an area of 51 hectares. 99% of seeds were found beneath parent crowns (n = 4,236) and seed density reached 14.6 ± 29.9 seeds/m² (0-140 seeds/m²). 49% of all seeds germinated but seedling mortality reached 100% after an 18 month period. In addition, saplings of B. capitata were not found in forest understory and within 30 treefall gaps (94-2,350 m²). The adults showed an average DBH of 69.3 ± 22.1 cm, were 19.2 ± 2.9 m tall and presented a clumped spatial distribution. B. capitata matched some of the features presented by shade intolerant trees or large-gap specialists, and we hypothesize that low rates or even lack of long distance seed dispersal events may be reducing the probability of B. capitata seeds reaching suitable habitats for successful seedling recruitment and growth. Because of that (1) seedlings face high levels of early mortality; (2) there is no sapling recruitment at the study site; and (3) local population faces senility and it is threatened by local extinction.