Dominance relationships in captive male bare-tailed woolly Opossum (Caluromys philander, Marsupialia : Didelphidae)

In this study, we test the hypothesis that body size is a key factor in determining dominance relationships during agonistic encounters between captive males Caluromys philander, and male-male competition was experimentally tested. Physiological and behavioural parameters were investigated during 18 experimental trials including two males alone (6), and two males with a female (12). A dominance-submission relationship exists even with no female, although competition is stronger when a female is present. Dominance is based on age and body mass in C. philander under experimental conditions. When dominance was settled, dominance rank was clear cut and consistent during all the experimentation. Stable dominance-subordination relationships may benefit both dominants and subordinates by minimizing the incidence of serious wounds. Males show typical signs of social stress: both body weight and hematocrit rate decrease, but subordinates are more stressed than dominants. Dominant males exhibit a lower decrease in hematocrit rate and a higher decrease in testosterone concentration in blood. They display most of the "aggressive" behaviours, scan more actively the experimental cages and engage in fewer aggressive interactions with females in comparison with subordinate malesAu cours de ce travail nous avons voulu tester en captivité l'importance du poids corporel dans l'établissement de relations de dominance chez les mâles Caluromys philander, chez qui des compétitions inter-mâles ont été étudiées. Les comportements et l'évolution de différents paramètres physiologiques ont été observés durant 18 expérimentations effectuées respectivement sur 6 groupes de deux mâles et sur 12 groupes de deux mâles et une femelle. Des relations de dominance-subordination se mettent en place même en l'absence de femelle, mais la compétition est plus forte dans les groupes comprenant une femelle. Dans ces conditions expérimentales, le rang social est basé principalement sur le poids et l'âge. Lorsque la relation de dominance est mise en place, le rang social des mâles est bien défini et il reste stable jusqu'à la fin de l'expérimentation. Ces relations de dominance stables pourraient profiter aux dominants et aux dominés en minimisant les risques de blessures sérieuses. Les mâles montrent des signes typiques caractérisant un stress social : une baisse du poids et de l'hématocrite, les dominés étant plus stressés que les dominants. Chez les mâles dominants, la baisse de l'hématocrite est plus faible que chez les dominés, et la concentration de testostérone dans le sang diminue plus que chez les dominés. Au niveau comportemental, les dominants effectuent la plupart des interactions agonistiques "offensives" et plus d'investigations olfactives de leur environnement (flairage-léchage) que les dominés. De plus, leurs interactions avec les femelles sont plus nombreuses et moins agressives que celles des dominés

Les mammifères frugivores arboricoles nocturnes d'une forêt guyanaise : inter-relations plantes-animaux

The relationships between a community of nine nocturnal frugivorous mammal species and the plants on which they feed were studied during 14 consecutive months in a secondary forest near Cayenne, French Guiana. Two major trophic groups can be defined : 1. - The seed eaters, which open unripe fruits to eat their seeds. All are rodents : Coendou prehensilis (average adult weight 4 000 g), Echimys armatus (400 g) and Oryzomys concolor (35 g). 2. - The pulp eaters, which specialize in ripe fruits. They eat the pulp and swallow most of the seeds which are disseminated with their feces. Five of them are marsupials : Didelphis marsupialis (1 000 g), Philander opossum (400 g), Caluromys philander (300 g), Marmosa cinerea (80 g) and Marmosa murina (45 g). The sixth species is a Procyonid Carnivore : Potos flavus (3 000 g). These differing types of feeding strategies are discussed in relation to the morphology of the teeth and digestive tract of the species. Species with a similar diet and comparable body size generally live in different forest layers. The population density and biomass of these nocturnal frugivorous mammals were estimated on the basis of direct counts along forest trails at night, trapping results and radio-tracking. Out of the 127 plant species listed, 26 play a major role as a food source for the mammals studied. The trunk diameter (DBH) of the 13 most common species was measured, and the distribution of these trees mapped in the 8.5 ha study area. These 13 tree species account for approximately half of the total basal area, which is considered here as an index of standing crop biomass. The same 13 species account for 25 % of the total number of individual trees. Fruit production was measured during 13 months by weighing all fallen fruits along 1 200 m of trails. Fruit production and consumption of the same species were also estimated by the use of fruit collectors located under fruiting trees. Special attention was given to the phenological cycles of trees. Three types of fruiting cycles could thus be related to three different foraging strategies of the sympatric frugivorous mammals : 1. - Species with a low fruit production spread over an extended time period. Only a few fruit ripen at the same time, but fruiting takes place almost all year long. Such trees are early - or late - pionneer species ; their fruits have tiny seeds which are mainly eaten by small vertebrates which scatter them more or less homogeneously. 2. - Species with synchronous, but irregular cycles of fruit production. Such trees have rather large seeds which are very attractive to seed-eating rodents. These animals even destroy part of the fruit crop before ripening. The massive, irregular, and unpredictable fruiting cycles of these species may reduce seed predation by rodents . The few trees belonging to this category which do not bear fruit synchronously with their conspecifics may have their crop totally destroyed by rodents. 3. - Species with synchronous and regular cycles of fruit production. Such trees have rather large seeds, which are ingested by large frugivorous vertebrates and spread through their feces. Chemical or physical deterrents are generally present in such fruits before ripening. The tree species belonging to this category have successive and partly overlapping periods of fruit production. In this way, food is made available for pulp-eaters during most of the year. This pattern of fructification is presumably the end-result of a long lasting mutual interaction between plants and seed-scattering vertebrales. Frugivorous mammals apparently need two different kinds of fruit in their diet, sorne rich in sugar and others rich in fat. Trees producing these two categories of fruit produce their crop successively, so that the necess ary nutrients are made available throughout the year. A definite decrease in fruit production takes place in our study are ajust before the beginning of the dry season. The marsupial pulp-eaters have adapted to this temporary food shortage by storing fat during the season of plenty. However, their production of young is strongly affected by this seasonal food shortage, as shawn by an increased mortality rate of pouch young

The opportunistic frugivory of three Diphelphid marsupials of French Guiana

The diet of three sympatric species of Didelphid Marsupials from French Guiana bas been investigated . AH these animais have a mixed diet (frugivorous and insectivorous), a difference in the proportion of fruits between the arboreal species Coluromys philonder (75 %) and the two terrestrial-arboreal species . Philonder opossum and Didelphis morsupiolis (50 %), being however noticeable. These Didelphids eat a wide variety of fruit species, which share few common characteristics , except that all of them have a fleshy pulp, with a high percentage of water, completely unprotected or protected in a way easy to overcome . The species consumed may have small or large fruits , with a bright or dull (cryptic) color . The shape of the fruit does not seem to be of great importance . The pulp may be rich in sugars or lipids, but is rather poor in total nitrogen, a nutrient these marsupials find in the animal prey the consume . These Didelphids have an opportunistic frugivorous diet , without any obvious mutualistic relation with vegetation. Nevertheless fruits are essential for them during lactation, the sugars they contain helping the females to cover their increased energy needs during this perio