Stephen G. Compton

Fig-eating by vertebrate frugivores: a global review

The consumption of figs (the fruit of Ficus spp.; Moraceae) by vertebrates is reviewed using data from the literature, unpublished accounts and new field data from Borneo and Hong Kong.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.

Phylogenetic relationships, historical biogeography and character evolution of fig-pollinating wasps

Nucleotide sequences from the cytochrome oxidase I (COI) gene were used to reconstruct phylogenetic relationships among 15 genera of fig–pollinating wasps. We present evidence supporting broad–level cocladogenesis with respect to most but not all of the corresponding groups of figs. Using fossil evidence for calibrating a molecular clock for these data, we estimated the origin of the fig–wasp mutualism to have occurred ca. 90 million years ago. The estimated divergence times among the pollinator genera and their current geographical distributions corresponded well with several features of the break–up of the southern continents during the Late Cretaceous period. We then explored the evolutionary trajectories of two characteristics that hold profound consequences for both partners in the mutualism: the breeding system of the host (monoecious or dioecious) and pollination behaviour of the wasp (passive or active). The fig–wasp mutualism exhibits extraordinarily long–term evolutionary stability despite clearly identifiable conflicts of interest between the interactors, which are reflected by the very distinct variations found on the basic mutualistic theme.

Old World fruit bats can be long–distance seed dispersers through extended retention of viable seeds in the gut

Seed dispersal and pollination by animals play a crucial role in the maintenance of forest ecosystems worldwide. Frugivorous bats are important pollen and seed dispersers in both the Palaeo– and Neotropics, and at least 300 plant species are known to rely on Old World fruit bats (Megachiroptera, Pteropodidae) for their propagation. However, rapid food transit times (generally less than 30 minutes) in frugivorous bats have been thought to limit their ability to disperse seeds to just a few tens of kilometres. Here we demonstrate regular daytime (>12 hours) retention of food and viable fig seeds (Ficus, Moraceae) in the gut of the Old World fruit bat Cynopterus sphinx: a behaviour not previously reported for any frugivorous bat. Field observations indicate that this behaviour also occurs in other genera. Old World fruit bats are highly mobile and many species undertake considerable foraging and migration flights. Our findings indicate that Old World fruit bats have the potential to disperse small seeds hundreds of kilometres. This necessitates a reappraisal of their importance in transporting zoochorous seeds to remote areas and facilitating gene flow between isolated populations of plants, both within mainlands and across ocean barriers.

Wind-borne insects mediate directional pollen transfer between desert fig trees 160 kilometers apart

The question of how far pollen can move between plants has implications for topics as diverse as habitat fragmentation, conservation management, and the containment of genetically modified crops. The monoecious African fig tree Ficus sycomorus L. relies on the small, short-lived, night-flying, host-specific fig wasp Ceratosolen arabicus Mayr for pollination. We used microsatellite markers to characterize a geographically isolated riparian population of F. sycomorus growing along the Ugab River in the Namib Desert, Namibia, together with paternity analysis of seedlings from known mothers, to map pollen movement within this population. In this way we tracked insect movements between individually recognizable trees by means of their pollen cargo and documented the movement of C. arabicus between known trees separated by more than 160 km, with a mean distance for confirmed successful pollination events of 88.6 km. The predominant observed movement of pollinators was in a westerly direction, toward the sea, reflecting seasonal nighttime wind direction and the wind-borne dispersal of fig wasps. Our results suggest the existence of an extensive panmictic population of trees that are well suited to overcome the effects of geographical isolation.

Ant‐Herbivore Interactions: Reasons for the Absence of Benefits to a Fern with Foliar Nectaries Vanessa K. Rashbrook

We tested the hypothesis that ants, attracted to the foliar nectaries of bracken fern (Pteridium aquilinum) confer protection to the plant in South Africa. Using ant—exclusion experiments with unmanipulated and artificially augmented ant densities, we were unable to detect a positive effect of ants on bracken, as neither the number of herbivores nor the level of herbivory was significantly greater on ant—free fronds. We then examined possible explanations for these results by performing a number of laboratory experiments using the ant Cremtogaster peringueyi and two lepidopteran species, the major bracken—feeding herbivores. We showed that their eggs were susceptible to ant predation, but gained protection from their oviposition sites. We also demonstrated that bracken can benefit when densities of ants are high, such as when fronds are infested with honeydew—producing homopterans, as the lepidopteran larvae were more vulnerable to attack under these conditions. We propose that low ant density on the fronds is the primary factor limiting the occurrence of mutualism between bracken and ants in nature.

Fig volatiles: Their role in attracting pollinators and maintaining pollinator specificity

Each fig tree species (Ficus) is totally dependent on a specific species of wasp for pollination and the larvae of these wasps only develop in the ovules of their specificFicus host. Because the fig crop on any particular tree is generally highly synchronized, the shortlived female wasps must leave their natal tree in order to find figs which are suitable for oviposition. Chemical volatiles produced by figs when they are ready for pollination are thought to be the means by which the wasps detect a suitable host. Gas chromatograms of the fig volatiles of 7 species ofFicus showed them to be species specific. Age related changes in the volatile profiles were noted as extra volatiles are produced when the figs were ready for pollination.

Determinants of species richness in southern African fig wasp assemblages

SummaryWe investigated the species richness of 24 fig wasp (Hymenoptera) assemblages associated with southern African fig trees (Ficus species, Moraceae). Assemblage sizes ranged between 3 and 30 species on different host tree species, with parasitoids slightly outnumbering gall-forming phytophages. Ten potential taxonomic, geographic and ecological determinants of assemblage richness were examined. Galler richness differed significantly between taxonomic sub-groups of Ficus and was significantly correlated with several ecological characteristics of the host trees, but there was no species-area effect. Parasitoid richness was strongly correlated with galler richness. We conclude that both ecological and historical factors have combined to determine the numbers of species that form fig wasp assemblages.

Responses of fig wasps to host plant volatile cues

Fig wasps (Chalcidoidea; Agaonidae) are intimately associated with the 750 or so species of fig trees (Ficus, Moraceae). Each tree species is usually pollinated by a single species of wasp belonging to the subfamily Agaoninae, while other wasps of the family are parasitoids or seed predators. Previous experiments have shown that the wasps are attracted to the trees by volatiles emanating from the figs. Using fig-bearing trees and arrays of sticky traps baited with figs, we investigated the specificity of wasp attraction and its timing. The pollinators of two closely relatedFicus species were specifically attracted to figs of their host species and only at the time when figs were ready to be pollinated. Some nonpollinating fig wasps appear to respond to the same volatile cues.

Breakdown of Pollinator Specificity in an African Fig Tree

A single giant-leafed fig tree (Ficus litea) is planted on the Rhodes University campus in Grahamstown, South Africa, some 500 km outside its normal distribution range. Small numbers of fig wasps (Hymenoptera, Agaonidae) which normally pollinate two other Ficus species entered and successfully pollinated the figs of this tree. One of the wasp species reproduced successfully. Monitoring of adult fig wasps arriving at the tree established that these alien species were not attracted to F. I/tea. However, from laboratory studies it appears that once having landed on F. lutea figs, these wasps were stimulated to search for the ostiole, through which they gained entrance to the fig cavity. Females of a third pollinator species were also present on the tree, but they failed to initiate ostiole searching behavior when on the figs. Hybrid seeds resulting from the entry of the alien wasps germinated successfully, but did not progress past the cotyledon stage, indicating postgermination deficiencies in the hybrids.

Foraging, food selection and worker size in the seed harvesting ant Messor bouvieri

Abstract Interactions among granivores and seeds depend on the foraging behaviour and morphology of the granivores and on the attributes and availability of seeds. We investigated seed selection by the seed harvesting ant Messor bouvieri in three adjacent plant communities in Spain by relating the harvested seeds to those in the seed rain. Preference was positively correlated with seed size and abundance which accounted for 43% and 20% of the variance respectively. Contrary to predictions of central place foraging theory, the size of seeds harvested did not increase with distance from the nest. Inclusion of a less-preferred item in the diet was more strongly related to the abundance of more-preferred items (60% of the variance) than the abundance of the less-preferred item (14% of the variance). Worker size accounted for 20–30% of the variance in the size of harvested seeds, although small workers did not appear to be constrained by load size for the range of seeds available. The body size of ants was significantly larger in the community with the greatest proportion of large seeds, although this was not due to their ability to carry larger loads or due to the greater force required to crush these seeds. The strong preference of M. bouvieri for large seeds may have important consequences for the plant communities in which they forage.