The flowering phenology and flower predation of Cullenia exarillata, a canopy tree at Kakachi in the southern Western Ghats, India, was studied from 1991 to 1993 in relation to general phenological patterns at the community level. Flowering was monitored from 30 marked trees and flower predation estimated from fallen flowers in 40, 1 m2 nets placed under the trees. Flowering occurs in the dry season and coincides with the period of fruit scarcity in the forest. Flowering is synchronous in the population and each tree produces a mean of c. 8730 flowers per tree over a period of c. 47 d. Flowers produced little nectar but the edible fleshy sepals compensated for this. Six species of arboreal mammals and seven species of birds ate the flowers. These consumed 57% of the flower crop of which 37% were completely destroyed. Flower predators could be important in flower fertilization. The overabundance of the flower crop and the timing of flowering, may have evolved as a strategy to satiate predators and enable the flowers to be pollinated during the annual period of fruit scarcity in the forest. This in turn makes Cullenia exarillata a possible keystone species in this forest.

For many tropical forests a tendency for fruit production to fluctuate seasonally has been established, with pronounced peaks of abundance and periods of fruit scarcity during which a few important resources maintain frugivore communities. However, there is a lack of studies in subtropical forests on community phenology and on the identification of important resources. In this study, community-wide fruit availability and its use by the local frugivore community was investigated in the subtropical coastal dry forest of Oribi Gorge Nature Reserve, South Africa over 13 mo from July 1997 to July 1998. Along 19.5 km of phenology trails, 940 individuals of 96 plant species bearing fleshy fruits were monitored twice per month and fruit-eating animals observed. Although some fruit was available all year round richness of both fruiting species and fruit abundance showed a seasonal pattern with peaks at the end of August to beginning of October (i.e. before the rainy season) and March to May (i.e. after the rainy season). Periods of fruit scarcity were found in July and August (i.e. during the long dry season) and in November and December (i.e. during the rainy season). Fruits of 23 plant species were observed being eaten by 18 species of bird and two of monkey. Highest animal numbers were attracted by Ficus thonningii, a species that fruited asynchronously during most of the year and during periods of fruit scarcity, and provided high overall fruit biomass. The importance of this species as a potential keystone resource for the frugivore community is discussed.

The consumption of figs (the fruit of Ficus spp.; Moraceae) by vertebrates is reviewed using data from the literature, unpublished accounts and new field data from Borneo and Hong Kong. Records of frugivory from over 75 countries are presented for 260 Ficus species (approximately 30% of described species). Explanations are presented for geographical and taxonomic gaps in the otherwise extensive literature. In addition to a small number of reptiles and fishes, 1274 bird and mammal species in 523 genera and 92 families are known to eat figs. In terms of the number of species and genera of fig-eaters and the number of fig species eaten we identify the avian families interacting most with Ficus to be Columbidae, Psittacidae, Pycnonotidae, Bucerotidae, Sturnidae and Lybiidae. Among mammals, the major fig-eating families are Pteropodidae, Cercopithecidae, Sciuridae, Phyllostomidae and Cebidae. We assess the role these and other frugivores play in Ficus seed dispersal and identify fig-specialists. In most, but not all, cases fig specialists provide effective seed dispersal services to the Ficus species on which they feed. The diversity of fig-eaters is explained with respect to fig design and nutrient content, phenology of fig ripening and the diversity of fig presentation. Whilst at a gross level there exists considerable overlap between birds, arboreal mammals and fruit bats with regard to the fig species they consume, closer analysis, based on evidence from across the tropics, suggests that discrete guilds of Ficus species differentially attract subsets of sympatric frugivore communities. This dispersal guild structure is determined by interspecific differences in fig design and presentation. Throughout our examination of the fig-frugivore interaction we consider phylogenetic factors and make comparisons between large-scale biogeographical regions. Our dataset supports previous claims that Ficus is the most important plant genus for tropical frugivores. We explore the concept of figs as keystone resources and suggest criteria for future investigations of their dietary importance. Finally, fully referenced lists of frugivores recorded at each Ficus species and of Ficus species in the diet of each frugivore are presented as online appendices. In situations where ecological information is incomplete or its retrieval is impractical, this valuable resource will assist conservationists in evaluating the role of figs or their frugivores in tropical forest sites.

Keystone plants that produce seasonally critical trophic resources comprise one of the main classes of keystone species, yet no studies have attempted to examine the ecological attributes that might help us recognize them and evaluate their importance in species-rich plant assemblages. In this paper the concept of keystone plant resources is reviewed using potential candidates proposed in the literature for neotropical forest sites. A poorly known example of a potential keystone resource—the gums produced by mature pods of two emergent tree species (Parkia nitida and P. pendula, Leguminosae: Mimosoideae)—is described for primates and other arboreal vertebrates in Amazonian forests. In particular, the fruiting phenology, tree density, patterns of vertebrate consumption, and nutritional quality of Parkia gums in Amazonian terra firme forests are considered. Putative neotropical keystone resources are then divided into four intersecting ecological attributes defining their community-wide importance to vertebrate frugivores: (1) temporal redundancy, (2) degree of consumer specificity, (3) reliability, and (4) abundance. From a vertebrate perspective, keystone plants are here defined as those producing reliable, low-redundancy resources that are consumed by a large proportion of the bird and mammal assemblage with which they coexist. Plant populations proposed to date as keystone species range widely across two of these four variables, which may disqualify most putative taxa (including Parkia spp.) from a more formal definition of keystone resources. Other importance attributes, the context-dependent role, the taxonomic refinement, and removal effects of the keystone plant resource concept as applied to tropical forests are also discussed.