François Feer

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

SummaryInteractions 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.

Effects of dung beetles (Scarabaeidae) on seeds dispersed by howler monkeys ( Alouatta seniculus ) in the French Guianan rain forest

The dispersal of seeds by howler monkeys (Alouatta seniculus) and the role of dung beetles in determining the fate of the dispersed seeds were studied at Nouragues Station, French Guiana, during three 2-mo periods (April-May, 1995-97). Howler monkeys were observed to disperse seeds of 47 plant species. Monkey dung attracted 57 species of dung beetles (Scarabaeidae), including tunnellers (maximum size 37 mm) and ball rollers (12.6 mm). The rate of seed burial was negatively correlated with seed size (10 plant species) and positively correlated with dung beetle size (six species of tunnellers). More than 80% of small seeds (< 5 mm) and 30% of large seeds (22 mm), were buried by the largest tunnellers. Dung beetles buried 13 to 23% of seeds ranging 8-13 mm in width. The maximum average depth of burial was 28 cm and varied according to the species of dung beetle. The rate of disappearance of large dung clumps varied during the day and was completed by nocturnal dung beetles. Seeds of Chrysophyllum lucentifolium (Sapotaceae) buried at 5 and 10 cm depths did not suffer predation, but showed low germination success compared to seeds left at the soil surface. Dung beetles affected the survival and distribution of a portion of the seeds dispersed by monkeys, and their relative importance in shaping seed fate depended on seed and beetle size.

Diel flight activity and ecological segregation within an assemblage of tropical forest dung and carrion beetles

Temporal variation in activity of dung and carrion beetles in tropical forest is considered as a mechanism of ecological segregation between potentially competing species. We describe the diel flight activity of Scarabaeidae collected with baited pitfall traps at Les Nouragues field station in French Guiana. A total of 2663 individuals of 63 species was recorded, from the subfamilies Coprinae, Scarabaeinae and Aphodinae. Temporal guilds of diurnal, nocturnal and crepuscular species were identified. Diurnal species were about twice as numerous and abundant as either nocturnal or crepuscular species. Two main activity patterns characterize the diurnal species while nocturnal and crepuscular species show overlapping activity. The association of activity rhythm with the other niche variables, food selection, functional group, body size and relative abundance, was analysed using multiple correspondence analysis. Small diurnal coprophagous species were opposed to large crepuscular necrophagous species. Species packing is suggested but further analysis showed that the variables were independent of one another. The temporal differentiation of species combined with separation along multiple niche dimensions and resource gradients may facilitate the coexistence of species assumed to be strongly affected by interspecific competition.

Seed fate of two Sapotaceae species in a Guianan rain forest in the context of escape and satiation hypotheses

Seed removal by rodents was investigated for Manilkara huberi and Chrysophyllum lucentifolium in a French Guianan forest. According to the escape hypothesis, seed survival was expected to be greate ...

The latrine effect: impact of howler monkeys on the distribution of small seeds in a tropical rain-forest soil

We studied the impact of dung deposition by the red howler monkey (Alouatta seniculus), and subsequent burial by dung beetles and other biotic and abiotic processes, on the distribution of small seeds in the soil seed bank (Nouragues Reserve, French Guiana). Seeds were collected from 54 soil samples taken under three sleeping sites and adjoining control sites, at three positions according to afixed grid and at threedifferent depths (0-2, 2-4 and 4-6 cm). Despite large differences between the three sites, defecation areas (latrines) were found to contain more seeds and higher seed diversity than control areas. Seed density decreased with depth in the top 6 cm in two sites but not in the third. Shannon diversity decreased with depth in both defecation and control areas. Differences in the distribution of seedsofdifferentspecieswerefoundaccordingtosizeandgrowthhabits(pioneervsnon-pioneerspecies).Theviability of seeds, ascertained from toughness and integrity of the seed coat, varied according to depth, site and defecation. Seed viability was on average higher in defecation areas compared with control areas.

Topsoil as Affected by Dung Deposition Under Resting Places of Red Howler Monkey (Alouatta seniculus)

The short-term influence of dung deposition and the further redistribution of dung by dung beetles were studied under a resting place of the red howler monkey (Alouatta seniculus) living in tropical rainforests of South America. Monkey dung was experimentally clumped on the field in a place used by troops of howler monkeys for resting in the Nouragues Reserve Station, French Guiana. Dung-treated plots were sampled serially over three weeks and compared with controls located in their immediate vicinity. The composition of the soil matrix (top 10 cm) was studied in successive microlayers using an optical method. Under the influence of dung beetle activity, the topsoil became more homogeneous by losing its litter, its content in earthworm faeces increased in the course of time, and surface mineral deposits were penetrated by roots. The results were interpreted in the light of present knowledge on the effects of soil animal activity on plant growth and survival of seedlings.

Behaviours of collared and white-lipped peccaries (Tayassu tajacu andT. pecari) in relation to sexual receptivity of the female

Changes in behaviours of the two peccary species,Tayassu tajacu Linnaeus, 1758 andT. pecari Link, 1795 between non-receptive and receptive periods were followed by presenting females to males daily for 15 minutes. InT. tajacu, the rank order of behaviours, similar in both sexes during the non-receptive period, differs during receptivity. Contact behaviours decrease in males, whereas sexual ones progress. The same tendency appears in females. Inhibited bites replace markings of partner as the most common behaviour in both sexes. InT. pecari, the rank order of behaviours always differs between sexes. When females become receptive, the differences from the non-receptive period are neither numerous nor significant. The most common behaviour of males, previously markings of partner, becomes mounts, whereas in females agonistic behaviours reinforce their dominance. In this species, the only behaviours that increase are those leading directly to copulation or those of an agonistic nature. In both species, females show more agonistic behaviours than males (mainly inhibited bites inT. tajacu, truly aggressive ones inT. pecari). When females are receptive, males ofT. pecari become less active, contrary toT. tajacu where both sexes double their activity. InT. tajacu, most behaviours vary significantly in relation to the progesterone level, contrary to the other species. These pecularities appear correlated to herd composition and organisation.

Monkey and dung beetle activities influence soil seed bank structure

In Neotropical forests, dung beetles act as efficient secondary dispersers of seeds that are dispersed primarily by red howler monkeys. Here, we investigated the origins of soil seed bank variability in relation to monkey and dung beetle activity, to assess the impact of dung beetles on seed fate, and their adaptability to resource availability. This question is important to better understand the process of tree regeneration, and is especially timely in the current context of threat to primates. We characterized soil seed bank structures in sites differing in monkey frequentation, and conducted field experiments with artificial beads to monitor bead fate. We also conducted experiments on specific roller and tunneller beetle species to examine bead processing behavior and its variability among and within species. We found that seed number and diversity increased with monkey frequentation, but seed viability was optimal under moderate monkey frequentation. We showed for the first time that dung provisioning yielded higher beetle activity in sites more often visited by monkeys, which calls for further investigation to understand the mechanisms of attraction to resource and potential spatial structuration of beetle populations. Although all beetle species involved in the experiments actively excluded beads from dung reserves, selectivity was higher for small than large beetle species, and for large compared to small bead sizes. It also increased when per-capita dung resource decreased, suggesting that intraspecific competition could alter seed fate. Altogether, our results support a major role of dung beetles in soil seed bank structure and dynamics. They reveal interesting interspecific variability within the dung beetle community and a complex interplay with primary dispersal.

Frugivory and Seed Dispersal by Terrestrial Mammals

Fruit is a major food resource for vertebrates inhabiting Neotropical rainforests (Terborgh 1986, Dubost 1987, Janson & Emmons 1990). Once on the ground after natural fall, or having been dropped by flying or arboreal vertebrates beneath fruiting trees as well as away, fruits and seeds are also dispersed and eaten by ground-dwelling vertebrates. Terrestrial mammalian frugivores comprise some of the most species-rich vertebrate groups (e.g. rodents) and one of the most important groups in term of biomass (e.g. ungulates) in this bioregion. These mammalian groups contain many species typical of the tropical lowland forest of South America.

Post-Dispersal Seed Removal in Four Frugivore-Dispersed Tree Species

In Neotropical forests, a majority of plant species relies upon arboreal and flying frugivores for the dispersal of their seeds (Howe 1986, Howe & Smallwood 1982, Charles-Dominique Chapter 17). Once the fruits are consumed and the pulp or arillote digested, seeds are either regurgitated or dropped into faeces below the parent tree or a conspecific tree, a nearby perch tree or along canopy routes frequently used by animals (Howe 1989, Howe 1993, Julliot 1996, Julliot 1997, Schupp et al. 1989). As animals move along pathways in the canopy or fly over trees within their home range seeking other fruit sources, they may forage into forest areas where the previously consumed tree species is at low density or absent (van Roosmalen 1985). Given the retention time in the stomach and gut, and habit of frugivores, seeds may thus be dropped below the parent tree crown, in the parent neighbourhood, or farther away from any conspecific tree (Julliot 1997). Consequently, seeds may be deposited in areas varying in the density of the dispersed tree species (Schupp 1992).