|The Ants of
Chapter 5 - More on Niches
|Chapter 5 - Diverse Habitats|
A synthesis of the mosiac as a combination of dominants and associated species was referred to in the "Mosaics" conclusion and can be seen in the summary diagram. In cocoa farms an absence of big trees means no colonies of Crematogaster africana or Crematogaster depressa. These have very large single nests built of carton requiring broad areas of trunk to which to adhere the nest. When present, however, both species will forage on and defend ground areas within their territories. They tend Homoptera on leaf flushes, aphids, and Pseudococcids on flower cushions - the latter are a peculiarity of cocoa and its relatives, a condition known as cauliflory, or flowers on the trunk as well as on branches.
In contrast, the closely related Crematogaster clariventris readily builds its carton nests on narrower trunks, and those of cocoa fit the requirements. The species also contrasts in tending Stictococcids, a fact which leads it into direct competition with Oecophylla longinoda.
Two major dominants actually dwell in the canopy using leaves as nest sites or components of the nest and having colonies made up of numerous nests. These are Tetramorium aculeatum, which builds felt nests on the under side of large soft leaves, and Oecophylla longinoda, which binds leaves together using larval silk. The first does not descend below the lowest jorquette or branch junction and is not found on the ground. Interestingly it is a carnivorous species which does not utilise plant or insect secreted sugars as an energy source. Oecophylla longinoda, however, will forage on the ground, especially if food resources on the tree become limited, as remarked above the favourite sugar secretors are Stictococcids, indeed, other Homoptera are used for food.
The foregoing are basically arboreal species nesting solely on trees, but another dominant, Pheidole megacephala, has the capacity to nest in or among dead wood and debris in crevices on the trees or on the ground. It is omnivorous, avidly tending Homoptera of most types, and feeding on smaller invertebrates.
A purely ground dweller, restricted, however, to areas where the ground is exposed to sunlight, is Camponotus acvapimenis. This is an aggressive species which has a soldier morph and will take on almost any other ant. Its range of dominance moreover includes Guinea savannah where it appears to be one of the few species to hold true surface territories. Its success must lie in its omnivorous habits, tending any sugar secretor and devouring anything that can be overcome.
Returning to the trees, dominants with more precise requirements for nest sites are Crematogaster zavattarii and Crematogaster striatula. The first has a colony made up of several nests which are constructed of carton but under and around flaky bark. In cocoa such bark is found only on trees which have been attacked by disease, such as canker caused by Phytophthora. The latter species nests within dead wood on trees and in well managed cocoa such nest sites are not to be found.
The remaining dominants, at least as determined by their abundance and capacity to occupy obvious territories are Lepisiota guineensis & L. cacozela (formerly denoted as capensis and Lepisota cacozela/T²), and Odontomachus troglodytes, which controls the bases of trees otherwise occupied by Tetramorium aculeatum. The Lepisiota could be described as vacancy-fillers, exploiting the absence of the more usual dominants.
The earlier Chapter on the ant mosaic presented evidence on how each of the dominants has been found to have both positive and negative associations with other ant species. Such associations tend to be the end result of competition for resources, both food and nest sites. More perhaps is known of the latter.
Thus, Camponotus vividus is associated with Crematogaster africana but nests only within large rot holes on standing trees, both species need large trees. A key factor in this instance is the specialist diet of Camponotus vividus, in which (perhaps uniquely for ants) almost 80% of its sugar needs are obtained from tree gums (Lévieux & Louis, 1975).
The small Crematogaster species found with Oecophylla longinoda nest in dead small branches and twigs on the trees. What their main diet is remains unknown, although, as with other smaller species, they are known to tend the lesser Homoptera, such as aphids and fulgorids, which do not attract the major dominants. To protect their "cattle" from the carnivorous Oecophylla these small Crematogaster species build tents, usually of vegetable debris.
A few species seem to simply be co-existors, for example Cataulacus guineensis with Oecophylla longinoda; and Myrmicaria fumata with Camponotus acvapimensis.
Some such as the large armoured Polyrhachis militaris and Polyrhachis laboriosa have small colonies, build small specialist silk and debris nests among branches, and simply go about their business unaffected by dominants. They, however, remain relatively low in terms of abundance.
Then there are what can be termed "avoiders". On trees these include the hollow dry twigs nesters such as the fast-moving and very alert Tetraponera anthracina. Others are very small, live in small dead wood nests and perhaps are most active at night - examples include Plagiolepis brunni, various Technomyrmex species, some small Cataulacus species, and some Tetramorium species.
A brief outline of some of the habitats of West Africa is given in Chapter 5 - Examples of Diverse Habitats.
©1998, 2012 - Brian Taylor CBiol FSB FRES
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