Disponibilités et utilisation des ressources par le Magot Macaca sylvanus dans différents milieux en Algérie

Résumé En

A quantitative study of the vegetation structure, and of the seasonal variations of resource availability, was carried out from February 1983 to January 1987 in a deciduous Oak forest (Akfadou) and in an evergreen Cedar-Oak forest (Djurdjura). The diet of the two troops of Barbary macaques living in the same areas was studied at the same time. The results of these two simultaneous investigations are here compared. The tree and shrub cover were found to be less important, and the food resources more varied, in Djurdjura than in Akfadou. Great seasonal variations in resource availability were found in both habitats. However, food production was more evenly spread over the whole year in Djurdjura than in Akfadou. The most critical period of the year, in terms of food availability, took place in summer (mostly in June) in Akfadou. The mature Cedar leaves became an important item in the monkeys’ diet during the winter in Djurdjura, when snow covers the ground. The spring outbreaks of geometrid caterpillars were more frequent in Akfadou than in Djurdjura ; their major consequence was to induce a lower acorn production the following autumn. By and large, the Cedar-Oak forest appears to be a more favourable habitat for the Barbary macaque than the deciduous Oak forest. Great seasonal variations in diet were noticeable, the macaques successively shifting from a mostly insectivorous diet to a granivorous, and finally to a folivorous diet, as the season advanced. These seasonal variations were dependent on the spring caterpillar’s outbreaks. The Barbary macaques of Djurdjura fed more on plants of the herbaceous layer (58.4 %) than those of Akfadou (37.1 %) ; they also ate more leaves (48.1 % and 26.7 % respectively), and less seeds, particularly acorns (26.7 % and 32.1 % respectively). The Barbary macaque is generally considered as an eclectic feeder. This is true. However, they definitively select their food items. Only 47 % (Akfadou) and 48 % (Djurdjura) of the available plant species were included in their diet, and available plants could be easily allocated to three distinct categories : those which were preferred, those which were avoided, and the « neutral » ones, according to their « selection ratio ». The herbaceous species were favourites in both habitats throughbout the year. The Djurdjura Barbary macaques avoided a smaller proportion of the available plant species (8 %) than those of Akfadou (11 %), and a larger number of species were selectively searched for (9 % and 7 % respectively). The leaves of herbaceous plants made up 18 % of the annual diet of monkeys in Akfadou. Within the species pool, the leaves of 10 % of the species were avoided (i.e. 82 % of the plant resources available). On the contrary, the same leaves made up 35 % of the annual diet in Djurdjura, 6 % only of the species being avoided (i.e. 61 % of the available species). There was also a definite selection of certain plant parts. The macaques’ food choices obviously depend as much on the availability and nature of the existing food items as on the animals nutritional requirements at various times of the year. Moreover, any environmental change furthering the growth of avoided plant species in a given area can influence the Barbary macaque populations. This is well in agreement with our previous findings on the population dynamics of our monkeys showing that their reproductive success is higher in the Cedar forest troop than in the others (Ménard et al., 1985, 1986). We therefore agree with Taub (1977) who considers the Cedar forest as the habitat most suitable for Macaca sylvanus.