Fruit-frugivore interactions in a Malagasy littoral forest: a community-wide approach of seed dispersal

From January 2000 through December 2002 phenological transects were carried out to assess monthly leaf, flower and (ripe) fruit presence for 423 individual plants (95 plant species, 43 families) within the littoral forest of Sainte Luce. Fruit-on-trail-counts were conducted additionally in the year 2000 to allow comparison between both methods. Despite low climatic seasonality and absence of a dry season in the littoral forest, interannual phenological patterns were seasonal at our site. Within-year variability was present with clear periods of abundance and scarcity. All phenophases were highly intercorrelated and peak from November through February. This was found in other humid Malagasy forests as well, while in dry Malagasy forests phenophases seemed to be more spaced in time due to the more seasonal climate. Day length seems to have the strongest impact on all phenophases, while rainfall is associated with flushing only and temperature with fruiting and ‘ripe fruiting’. Differences in presence of ripe fruits when comparing between both sampling methods can be explained by the differential contribution of several life forms in both methods, which influence overall fruiting patterns. INTRODUCTION Phenological studies address the timing of reproductive events in plants such as bud formation, flowering and fruiting along with vegetative processes like leaf flushing and shedding. Tropical trees display an enormous variety in temporal patterns of flowering and fruiting. Both flowers and fruits are patchily distributed in time and space and are relatively scarce food items compared to leaves and insects (Howe 1984). Therefore it is critical to study food availability and distribution in order to understand the behavioural ecology of tropical wildlife. In the tropics, many animal species are frugivorous to a lesser or greater degree and in terms of biomass, frugivores are the dominant trophic group in most tropical forest mammalian communities (Terborgh 1983). This is further reflected by the dominance (60-90%) of zoochorous plant species producing fleshy fruits (Howe and Smallwood 1982). Quantifying fruit availability has been a primary objective in many studies, which focus on the ecology of tropical fruiting trees and their consumers (Chapman et al. 1992a; Janson and Chapman 1999). During the alternation of seasons and years in rain forests, the availability of vegetative and reproductive plant parts is irregular and induces periods of abundance and scarcity of food for consumers (Brugiere et al. 2002). These temporal