The Ants of Africa
CHAPTER 3 - Mosaics - Evidence from Ivory Coast - Lévieux and colleagues

Locations shown on Map 8

{Savannah at Lamto}Jean Lévieux has led a series of studies of ants in the forest edge savannah and in the neighbouring evergreen rain forest (commencing in 1962 and continuing until 1969, and 1974-1978), but mainly on ground-dwelling species (Lévieux, 1971, 1973, 1982, 1983b). The work was based at two locations. One was the Lamto Field station of the University of Abidjan, 200 km north-east of Abidjan (6°13' N-5°2' W, location 7 on the map), and off the main highway 50 km south of Toumodi. The other was Ferkéssédougou, in the north of the country (9°30' N-5°10' W, location 8 on the map). Lamto is interesting because it is a location where the primarily coastal rainforest penetrates alongside the River Bandama into the Guinea savannah (Delage-Darchen, 1972). Thus useful comparisons could be made between the ant fauna of the two ecosystems. Ferkéssédougou in contrast is in the much drier Sudan savannah, with a pronounced dry season from November to May, and no more than 1100 mm annual rainfall (Lévieux & Diomande, 1978).

Myrmicaria nitida is primarily a species of the Sudan savannah according to Lévieux (1983a), who made extensive studies of its behaviour (as Myrmicaria eumenoides) at Lamto and Ferkéssédougou. He described it as more common than Myrmicaria striata, with a surface-foraging habit and nests with distinct crater openings. Nests tend to be clumped. The colony size was 18,000-22,000 individuals, the latter being in a colony more than three years old. Foraging in the Guinea savannah was over some 12-15 m² and in the Sudan savannah over a much larger 110 m², up to 11 m from the nest. The diet consists of 95% arthropods (insects 60-80%, especially other ants and termites, both adults and larvae. It collects honeydew from Aleyrodoidea, whiteflies, living on grasses or on trees. The nests were surrounded by nests of other species including Polyrhachis schistacea, Camponotus acvapimensis, Pheidole sculpturata, Strumigenys species and various Tetramorium. Whereas Camponotus acvapimensis defended a given area Myrmicaria nitidans appeared not to do so. One can conjecture that a territory has less merit for a largely predatory species, which requires other species to enter its foraging area. At any one point in time, however, both Camponotus and Myrmicaria were thought to being effectively foraging in about 10% of the total ground area potentially utilisable from the nest. This was thought to be the case also for other essentially predatory ants.

Lévieux & Diomande (1978) in their description of the activity of Pachycondyla sennaarensis at Ferkéssédougou, also mentioned that it appeared to show a marked indifference to the activities of other ants occupying the same milieu, for instance Camponotus acvapimensis, Camponotus maculatus and Camponotus sericeus (or a close relative); plus two unnamed Pheidole species and a Tetramorium species. Tetramorium sericeiventre, however, was a different case as it was an active predator on other ants, and they had seen it transporting Pachycondyla sennarensis workers to its nest.

In a study of Camponotus vividus, which they described as a forest species, one of the most common arboreal species of the region, and also able to live in degraded zones, Lévieux & Louis (1975) gave some information on its part in the mosaic. The research was carried out at an unnamed location in a degraded forest near the coast at Abidjan. The biology of a nest from apparently the same area had earlier been studied by Soulié (1967). It often nests at up to 50m above ground, with some 6,000 individuals in a colony of some three years of age. For such a population to inhabit a single nest would require a cavity of considerable size within a tree and, hence, the more common situation is that of polycaly, with some five or six nests per colony. These small nests are constructed within dead branches, often by reusing the galleries excavated by other insects, with instances of utilisation of termite nests (Soulié reported actual elimination of a termite colony). There may be 1-3 nests on any one tree but no preference for any one tree species was reported. A typical colony appreared to occupy an area of some 25 to 35 metres hoizontally and up to 60 meres vertically. The large area was thought to account for the relatively low density of the species as a whole. Mapping of an area of mixed cocoa, cashew and forest trees showed its colonies on separate trees from Oecophylla longinoda and some apparent displacement of the latter by the vividus colony. Most of the Camponotus vividus activity was at the beginning and end of the daylight hours, but heavy rain causing leaf wetting inhibited activity. Writing on the source of food, they described how the bulk (79%) of its sugar needs are obtained from dried tree gums, especially from Sterculia traegacantha (Gum Tragacanth, 34% of food) and Anacardium occidentalis (Cashew, 28% of food), apparently highly unusual if not unique among ants. Of the remaining diet, 17% was of undetermined vegetable origin and 21% of animal origin, almost all insects and of no particular kind. Some sugars came also from Homoptera which were tended and over which tents of vegetable material, such as bark fragments from Terminalia callapa, glued to give a rigid domed structure, with access only through a hole just sufficient to permit the ant to enter.

©1998, 2001 - Brian Taylor CBiol FSB FRES
11, Grazingfield, Wilford, Nottingham, NG11 7FN, U.K.