Fruits and Frugivory

Interactions between a large community of vertebrate frugivore-granivores (including 7 species of large canopy birds, 19 species of rodents, 7 species of ruminants, and 6 species of monkeys), and 122 fruit species they consume, were studied for a year in a tropical rainforest in Gabon.

The results show how morphological characters of fruits are involved in the choice and partitioning of the available fruit spectrum among consumer taxa. Despite an outstanding lack of specificity between fruit and consumer species, consideration of simple morphological traits of fruits reveals broad character syndromes associated with different consumer taxa. Competition between distantly related taxa that feed at the same height is far more important than has been previously supposed. The results also suggest how fruit characters could have evolved under consumer pressure as a result of consumer roles as dispersers or seed predators. Our analyses of dispersal syndromes show that fruit species partitioning occurs more between mammal taxa than between mammals and birds. There is thus a bird-monkey syndrome and a ruminant-rodent-elephant syndrome. The bird-monkey syndrome includes fruit species on which there is no pre-dispersal seed predation. These fruits (berries and drupes) are brightly colored, have a succulent pulp or arillate seeds, and no protective seed cover. The ruminant-rodent-elephant syndrome includes species for which there is pre-dispersal predation. These fruits (all drupes) are large, dull-colored, and have a dry fibrous flesh and well-protected seeds.

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Fruit characters as a basis of fruit choice and seed dispersal in a tropical forest vertebrate community.

The disabilities experienced by colour-blind people show us the biological advantages of colour vision in detecting targets, in segregating the visual field and in identifying particular objects or states. Human dichromats have especial difficulty in detecting coloured fruit against dappled foliage that varies randomly in luminosity; it is suggested that yellow and orange tropical fruits have co-evolved with the trichromatic colour vision of Old World monkeys. It is argued that the colour vision of man and of the Old World monkeys depends on two subsystems that remain parallel and independent at early stages of the visual pathway. The primordial subsystem, which is shared with most mammals, depends on a comparison of the rates of quantum catch in the short- and middle-wave cones; this system exists almost exclusively for colour vision, although the chromatic signals carry with them a local sign that allows them to sustain several of the functions of spatiochromatic vision. The second subsystem arose from the phylogenetically recent duplication of a gene on the X-chromosome, and depends on a comparison of the rates of quantum catch in the long- and middle-wave receptors. At the early stages of the visual pathway, this chromatic information is carried by a channel that is also sensitive to spatial contrast. The New World monkeys have taken a different route to trichromacy: in species that are basically dichromatic, heterozygous females gain trichromacy as a result of X-chromosome inactivation, which ensures that different photopigments are expressed in two subsets of retinal photoreceptor.

“Tho' she kneel'd in that place where they grew…” The uses and origins of primate colour vision

Primates are apparently unique amongst the mammals in possessing trichromatic colour vision. However, not all primates are trichromatic. Amongst the haplorhine (higher) primates, the catarrhines possess uniformly trichromatic colour vision, whereas most of the platyrrhine species exhibit polymorphic colour vision, with a variety of dichromatic and trichromatic phenotypes within the population. It has been suggested that trichromacy in primates and the reflectance functions of certain tropical fruits are aspects of a coevolved seed-dispersal system: primate colour vision has been shaped by the need to find coloured fruits amongst foliage, and the fruits themselves have evolved to be salient to primates and so secure dissemination of their seeds. We review the evidence for and against this hypothesis and we report an empirical test: we show that the spectral positioning of the cone pigments found in trichromatic South American primates is well matched to the task of detecting fruits against a background of leaves. We further report that particular trichromatic platyrrhine phenotypes may be better suited than others to foraging for particular fruits under particular conditions of illumination; and we discuss possible explanations for the maintenance of polymorphic colour vision amongst the platyrrhines.

Fruits, foliage and the evolution of primate colour vision

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.

Fig-eating by vertebrate frugivores: a global review.

(1) Fruit, leaves and animal matter form the main part of the diets of the three Cercopithecus monkeys studied. Cercopithecus nictitans eats less fruit and insects and more leaves; C. pogonias more fruit and insects and fewer leaves; C. cephus is intermediate. (2) Sex-related differences occur: males eat more fruit than females who eat more leaves and animal matter, especially when these foods are abundant. (3) Interspecific differences in food items taken are small for fruit (68% of the species are taken by the three monkeys), obvious for animal matter. Cercopithecus nictitans preys mainly on sedentary prey (caterpillars, ants), C. pogonias on mobile ones (orthoptera) while C. cephus captures both types. Sex-related differences occur in C. cephus and C. pogonias. (4) Interspecific overlap in diets is great during the main part of the year. Species diets change and overlap less when fruit, young leaves and animal matter production are short (main dry season). This suggests that interspecific competition is important in determining resource partitioning. A second decrease in diet overlap occurs at the end of the long rainy season while foods are abundant. Females are either pregnant or lactating and select protein-richer foods such as young leaves and/or insects while males eat more fruit. At this time, intraspecific competition could be the selective force in food sharing. However increasing protein-requirements could account for the reorientation in food choice of the females. (5) The intermediate trophic position of C. cephus rests upon sex-related differences. The cephus male behaves like nictitans while the cephus female behaves like pogonias. (6) Interspecific differences are related to search strategies which depend on body weight, forest levels used, social roles, etc. Differences in spatial and temporal feeding patterns are small.

Seasonal Variations of Diet Related to Species and Sex in a Community of Cercopithecus Monkeys

(1) This paper analyses the frugivorous diet of Cercopithecus cephus through one annual cycle in comparison with variations in fruit species availability, fruit morphology and nutrient and mineral content of fruit. (2) Among the whole spectrum of fruiting species available, a small fraction (termed edible species) is included in the monkeys' diet. (3) Among these edible species, some are more frequently sampled by monkeys than expected by their density, whereas several abundant species are only occasionally eaten. Overall, twenty species (35% of those sampled) contribute to 85% of the diet; among them, only three are included in the list of the twenty most abundant plant species in the study site. (4) According to their selection ratio (percentage sampled/percentage abundance), fruit species have been classified into three categories: preferred, neutral and avoided species. These three categories differ by their nature, their colour and their chemical composition. (5) Brightly coloured fruits possessing either a succulent pulp or arillated seeds are largely eaten: they possess either a high water content and a high sugar content (succulent pulp) or a high protein content and a high fatty acid content (arils). (6) Dull-coloured fleshy fruits are avoided: they possess a relatively low nutritive value and a high concentration of fibres. (7) The most preferred species exhibit a high acidity content. (8) We discuss the different levels of selection exerted by monkeys and underline the difficulties involved in the assumption that fruits constitute a superabundant food resource or alternatively are a limiting resource in tropical rain fore

Annie Gautier-Hion

Papers

Seasonal Variations of Diet Related to Species and Sex in a Community of Cercopithecus Monkeys

Fruit Selection by a Forest Guenon