Vertical stratification and caloric content of the standing fruit crop in a tropical lowland forest

Abstract

Fruit abundance in tropical forests thus far has been studied in relation to consumer populations. Area-based surveys that focus on the quantity and quality of the standing fruit crop of an entire plant community, however, are lacking. This paper presents the results of a four-month study on the seasonality and vertical distribution of the standing fruit crop within a tropical forest during the dry season in southern Venezuela. Fruit numbers ranged from 262,000 to 424,000 fruits/ha. The standing crop was between 39 and 92 kg/ha, yielding 67,000 to 126,000 kJ. Fruits were not evenly distributed in different forest layers. They were most abundant in the canopy above 16 m and scarce between 4 and 12 m above the ground. Despite a scarcity of fruits in the mid-strata, the caloric value of the total fruit supply peaked within a narrow layer of subcanopy at 12 to 16 m above ground due to a high amount of energy per fruit. Palms fruited mostly in this layer, their fruits contributing 59 percent of the energy supplied by all fruits. Above 12 m, we found a broader range of fruit sizes than in the forest below 12 m. Small-sized fruits were distributed in the understory and in the canopy but were nearly absent from the mid-story. Corresponding to the abundance of small-sized fruits in the canopy, small frugivorous species, such as members of the Thraupidae, limited their foraging to the canopy strata whereas larger avian frugivores foraged mainly in the mid-story.