|The Ants of
CHAPTER 3 - Mosaics - Evidence from Zaïre - Dejean
Locations in the area between Kinshasa (Leopoldville) and Kikwit, shown on Map (mainly west or northwest of Kikwit).
Alain Dejean, who had earlier worked in Cameroun, combined with D. Masens, K. Kanika, M. Nsudi and R. Gunumina to report studies of the soil populations of different groups of invertebrates in a range of forest and grassland habitats in Zaïre (Dejean et al., 1986).
The habitats were Grassland savannah (at Kimwenza), Grassy fallow (at Kasamba), Shrubby fallow - 15 years old (at Kimwenza), Wooded savannah (at Kumbi), Palm-grove (at Mumekant Embe), Bamboo-grove (at Kinzambi), Secondary forest (at Kinzambi), Secondary forest - ridge top (at Kimwenza) and Secondary forest - lake side (at Kimwenza). Essentially all were derived from primary forest, in the humid tropical regions of Kinshasa and Bandunu. The amount remaining of gallery forest, however, has declined very quickly, with most areas modified by fire, due to human activities, and thus converted to savannah.
Dejean and his colleagues aimed to examine the impact of this human activity and to see if it could be reversed, restoring something of the lost soil quality. Six or 9 evaluations were made at each site, in the period March-April 1984, which was in the rainy season. They combined quadrat and random sampling; a strip 10 m wide was demarcated into 100 quadrats each of 1 m² from each quadrat a 20 cm³ sample was taken made up of leaf litter, humus and top soil. these samples were sorted by hand, removing larger organisms with forceps, followed by floatation in warm water. The forest zone samples were subjected to a correction, by counting the societies (colonies) on the surface of 400 to 600 m² and determining the mean of those societies. For the ants (following Lévieux, 1971) an 800 m² area was felt necessary to obtain a good evaluation. In the form which I have seen, the usefulness of their report is limited for those interested in ants because of a lack of information below genus level for all but a few instances.
Ants and termites were the most prolific groups in all habitats - except palm groves where earthworms were the most important, and bamboo groves where Collembola were the most important group.
To deal specifically with ants, first, it was noted that these were most abundant in wooded savannah, but their biomass was the greatest in the shrubby fallow. The latter was due to the prevalence of species with large individuals - Pachycondyla tarsata (as Paltothyreus tarsatus), Camponotus maculatus and Polyrhachis species. In total the biomass in each habitat was (kg/ha):
Grassland savannah, 32.7 kg; Grassy fallow, 37.1 kg; Shrubby fallow, 119 kg; Wooded savannah, 62.3 kg; Palm-grove, 38.1 kg; Bamboo-grove, 3.3 kg; Secondary forest (Kinzambi), 5 kg; Secondary forest - ridge top (Kimwenza), 32.5 kg; and Secondary forest - lake side (Kimwenza), 45.9 kg.
In terms of numbers of individuals the results from each habitat was (per m²):
Grassland savannah, 1576; Grassy fallow, 3452; Shrubby fallow, 3400; Wooded savannah, 5745; Palm-grove, 4493; Bamboo-grove, 166 (only foragers); Secondary forest (Kinzambi), 257 (only foragers); Secondary forest - ridge top (Kimwenza), 1493; and Secondary forest - lake side (Kimwenza), 2095.
In grassy fallow, savannah or prairie the Ponerines were poorly represented - Odontomachus troglodytes was found where there were trees, and Pachycondyla senaarensis (as Brachyponera senaarensis) in areas fully exposed to the sun. In the copse edges there were colonies of Pachycondyla tarsata. Foraging columns of Dorylines were several times encountered. Pseudomyrmicines living on the trees were rarely found on the ground. Myrmicines were well represented, notably Pheidole, Crematogaster and Myrmicaria species, mainly exploiting the trees and shrubs, provided that was that the trees were not dominated by Monomorium. Also found were Cataulacus in grass leaf axil nests with certain Crematogaster species, also Tetramorium and Leptothorax. Among the Dolichoderines the genus Tapinoma was well represented. Finally, the Formicines included several terrestrial Camponotus, also Polyrhachis and Phasmomyrmex species. Where there were citrus trees Oecophylla longinoda could be found foraging on the soil.
In secondary forests, in contrast, there were many Ponerines nesting especially in rotting wood on the ground. Relatively few were from Amblyopone, Plectroctena, Leptogenys, Phrynoponera or Pachycondyla (as Mesoponera); abundant, however, were other Pachycondyla and Odontomachus and Anochetus abounded in fallen trunks attacked by Nasutitermes. Again Doryline columns were encountered. The only Pseudomyrmicine species was Tetraponera anthracina descending from its host tree (Barberia nigricans). Among the Myrmicines, Crematogaster and Pheidole were predominant, Myrmicaria occupied the edges of paths and Cataulacus abandoned termitariums (Cubitermes). Occasionally encountered were Oligomyrmex, Tetramorium, Calyptomyrmex and Pyramica (Serrastruma) species. Dolichoderines were restricted to Tapinoma. The most common Formicine was Camponotus maculatus and Polyrhachis and Oecophylla species descended from the trees.
In the poorer habitat of shrubby fallow only seven species of ants were found. Ponerines were Odontomachus troglodytes and Pachycondyla tarsata. No Dorylines, Pseudomyrmicines or Dolichoderines were found. Pheidole species were very abundant and Crematogaster species were well represented but no other Myrmicines. Camponotus maculatus again abounded and Polyrhachis species (both terrestrial and abroreal) were found.
In the bamboo groves few ants were found - Odontomachus troglodytes, Tetramorium species, Pyramica (Serrastruma) lujae and Pheidole species were found in small numbers.
Palm groves also were species-poor, with Odontomachus troglodytes, some Pheidole and Crematogaster, rarely Cataulacus, Myrmicaria, Monomorum and Camponotus maculatus.
Ants were undoubtedly the major predators among the invertebrates, and the secondary forest had the greatest panoply of genera and species, with many specialising in predation. Although not really a true source of information on ant mosaics the brief report does fit with observations in West African countries as to the overall pattern of species numbers and types.
©1998, 2001, 2003 - Brian Taylor CBiol FSB FRES
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