The Ants of Africa CHAPTER 3 - Mosaics - Introduction

Definition

The origin of the term ant mosaic is attributed usually to Dennis Leston and his succinct definition is worth quoting

"The humid tropics fauna includes certain dominant ants. Where they occur these are more numerous than other ants and to the exclusion of other dominants, i.e., those ants which elsewhere are more abundant. Dominants are usually non-nomadic, arboreal, multi-nested, saccarophilic and predatory, practicing mutualism with Homoptera: they have a potential for rapid population growth. Optimally dominants are spaced out in a three-dimensional mosaic with few lacunae but forest degradation leads to a two-dimensional structure. Three mosaic patterns are recognised: (1) the forest canopy mosaic, occurring too but simplified in the crowns of cocoa, coffee, coconut and oilpalm, etc.; (2) the forest understorey pattern; (3) theCrematogaster striatula pattern, peculiar to West Africa" (Leston, 1973-1974).

The attribution of the "ant mosaic" concept to Dennis Leston, at least among anglophones, may not be strictly correct. For instance, T.C. Schneirla writing before his death in 1968, noted - "Actually, any tropical forest is a mosaic of zonal patterns in which adjacent sites may differ greatly as living nooks for any animal. As a result, colonies of any species of ant (or other potential doryline booty) are likely to be distributed unevenly through the forest (Wilson, 1958)" (Schneirla, 1971). Wilson (1976) described how he had examined the question of diversity and consequent prevalence of the various ant genera. This was largely by drawing on the results of his own surveys in Papua New Guinea, various South Pacific Islands, Sri Lanka and Mexico and is summarised at the end of this Chapter. The assemblage of ant species which he surveyed differs, however, in many ways from that of West Africa.

An earlier use of the term "dominant" can be found in the work of F. Bernard (1952). In his extensive report of the Mt. Nimba ant surveys in Guinea, Table II - "Distribution of Ants at Mt. Nimba" has the categories - Dominantes (dominants), Communes (common), Assez communes ou infrequentes (fairly common or infrequent) and Raretés or nouveautés les plus notables (the most notable rarities or new species); with each category divided according to habitat Ubiquistes (ubiquitous); Savane (savanna, 500-900 m); Forêt dense (dense forest, 452-1250 m); Prairie (montane grass land, 1200-1600 m). Bernard, however, probably used "dominant" to denote high numerical abundance and not necessarily territorial control (as used by the later mosaic investigators). Strickland (1951b) also used the term in noting that Oecophylla longinoda was "the dominant ant species inhabiting cacao in the Eastern province of the Gold Coast".

In Journey to the Ants, Bert Hölldobler described his fascination for the Weaver ants, Oecophylla longinoda from Africa and O. smaragdina from Asia and further east (Hölldobler & Wilson, 1994). Unfortunately, the reader is misled, perhaps as a result of Bert's non-reporting of work from outside East Africa. For instance, one finds that "They destroy workers of most other ant species" and "Battles between neighboring weaver ant colonies are so severe that they create narrow, unoccupied borders between the territories, a kind of 'no ant's land'". Now, in West Africa, as will be seen below, O. longinoda is but one of the dominant ants of the forest trees. Given a true forest situation, with large trees available as nest sites, there are equally, if not more, successful species of Crematogaster ants. Indeed it has been argued that O. longinoda fits the lacunae between Crematogaster dominants. Moreover, to find a "no ant's land" is highly unusual. In Nigeria, we examined "non-dominated situations" and found several other species which were regular occupiers of such lacunae. Another African species, Pheidole megacephala, which Bert and Ed mention as a global menace because of its ability to destroy local species in places where it has been accidentally introduced, also seems to be more than able to compete with O. longinoda. A further fascinating truth is that there are distinct cohorts of ant species which live within the territories of dominants; several researchers having discovered patterns of positive and negative associations with specific dominants.

Lastly, subsequent evidence has shown that Leston's assertion regarding Crematogaster striatula may well be unsound.

href="mosaics1.htm"