Realized Ant Assemblages in the Namib, Kalahari and Kara-Kum Deserts
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Ecology of Desert Environments, pp. 301 - 332, 2001 Editor: Ish war Prakash I Publishing Co., Scientific Publishers (India), P.O. Box 91, Jodhpur http://www.scientificpub.com 00 IIivet, P. and Cox, bls., Amsterdam, Wrangel Island. 719 pp. , Paris, France : Realized Ant Assemblages in the Namib, Kalahari and Kara-Kum Deserts . the Biology of .••ca.demic Publs., I the Hengduan era (Col. Chrys.) tnelidae. Biondi, Harold Heatwole 199-309. Department of Zoology, North Carolina State University, ns, China. Acta Raleigh, N C 27695-7617, USA nountains (Col. the Hengduan Abstract of China (Col. Baited transects were used to study the assemblages of ants in the Kalahari and Kara-Kum deserts and across dunes, a plain, and a dry nae. Insects of riverbed in the Namib Desert. Species-richness was related to amount of vegetation, with the shrub desert of the Kalahari having over twice as Iuan Mountain many species as the other, more severe deserts. The point species- rth, D. G. (ed.). richness increased with overall species-richness up to an asymptote of five species. The mean number of species occurring at baits stabilized at slightly more than one species. The assemblages were inequitable, with 11. Chrys.) from one to three species accounting for most of the visits to baits. In the more highly vegetated deserts foraging ants examined virtually the entire 1e in Galeruca desert floor on a daily basis. rth, D. G. (ed.), In the Namib, most species of ants were scavengers or omnivores; no strict granivores were found. In the other deserts only the scavenger guild was studied. In all deserts, ants dominated the scavenger guild, with other taxa coming to sardine baits only infrequently. Foraging took place more often at night and in the morning than in the middle of the day; at most sites it was more intense on the ground than in shrubs. The Kara-Kum differed in that most activity was associated with shrubs. The three most common species in the Namib were partially segregated on the basis of different times of peak activity. No overt combat was observed, and in the less speciose assemblages there was no evidence of interference. With increasing species-richness, however, there was exclusion of some species from baits, and in the Kalahari a dominance hierarchy was observed. 302 Heatwole Ant Introduction ~ assemblages. time can be com This paper represents a continuation of a study of changes in assemblages of ants across environmental gradients and habitat boundaries. The approach is to present Even withir the results from the simplest assemblages first, and then proceed toward more may nest in wac complex ones, eventually providing a general review of a series of habitats ranging Colonies of sot from tundra and desert to tropical rainforest, with examples of each from two or more vicinity, therebj continents. Previous contributions described changes in ant assemblages from tundra, reasons, a given across the treeline to birch, aspen and pine forests in northern Lapland, i.e., near the the realized (J. , distributional limits of ants in a cold region (Heatwole, 1989). That was followed by particular point examination of ant assemblages at the opposite extremes of inhospitability, heat and I· important meas salinity, in two starkly arid habitats, the Atacama Desert in Peru and the Chott El species that ac Djerid in the Tunisian Sahara (Heatwole, 1996). A study of dunes in the Arabian ecologicalimpor Desert (Heatwole, 1991) extended comparison to a somewhat milder dune desert. The In summarj present study expands those comparisons to three additional deserts, each with its /I (1) regional list own combination of climatic and vegetative characteristics. richness, with ti The .structure of desert ant assemblages is highly dynamic and its analysis at any Assemblage one season or year provides an incomplete picture (Whitford, 1978). Dietary niche roles played by breadths may show considerable variation within a species through time, and among the apportionm species at a given time; diet may be opportunistic and shift without apparent pattern omnivores, prec (Marsh, 1985a). Species vary in the rigidity of their activity patterns, some and/or honeyde: maintaining the same cycle at all seasons, others shifting seasonally, especially from ants would be summer nocturnality to winter diurnality (Marsh, 1988; Heatwole & Muir, 1989). qualitative list I Some species close their nests and are not active on the surface for long periods. of one kind of f Such inactivity may be seasonal but does not necessarily show regular patterns and otherwise grani may be opportunistically related to food supply and/or rainfall, with large (Heatwole, 199: year-to-year differences (Marsh, 1985a; Heatwole & Muir, 1991). These species have a the Namib dun pulsed effect on the ecosystem. During active periods their foraging may be intense 1985a, 1990).A and their trophic effect great. When cloistered underground and relying on stored multiple guilds food they exert little immediate influence and can be considered as functionally seeds, but occas "absent" from the assemblage. For these reasons it is necessary to distinguish guild, but plaj between the "total assemblage" (comprising both active and inactive components) and participation in the "realized assemblage" (that part of it playing an immediate role in community to baits of diffe dynamics). than one guild. Not only does composition of the realized assemblage change temporally, but it The present also does so spatially, even to the extent of differing between north-facing and . assemblage stn south-facing slopes in the same habitat (Donnelly & Giliomee 1985). Often ants show assemblages ac mosaic distributions, with the species composition of a given patch being controlled by structure. a particularly dominant species (Majer, 1972). Different patches may have different mixes of species, although having some species in common. The assemblage of a given patch or habitat can be designated an ex assemblage, with its number of species being the ex species-richness. As one adds new patches or different habitats in the same The investi general area, the number of species increases and the larger assemblage can be Kalahari, and t considered as the ~ assemblage and its number of species as the ~ species-richness. Heatwole (199E One can ascertain the realized ex and ~ assemblages for a particular season or time, from below the and over a prolonged period accumulation of data can lead to estimates of total ex and abutting eastw: cold Benguela c Ant Assemblages in the Namib, Kalahari and Kara-Kurn. deserts 303, P assemblages. Finally, the total list of species from all patches in all habitats over time can be considered the regional assemblage. [ages of ants s to present Even within a patch, species may not be uniformly distributed. Particular ones oward more may nest in wood or under rocks and only forage within a certain radius of such sites. .ats ranging Colonies of some species may inhibit establishment of founder queens in their two or more vicinity, thereby denying access to rival species. For these and possibly many other rom tundra, reasons, a given point in the habitat may not be visited by all ofthe species present in .e., near the the realized 0: assemblage. The number occurring and potentially interacting at a followed by particular point is the "point species-richness". Biologically, this is probably the most ;y, heat and important measure of biodiversity. In terms of community dynamics, the number of e Chott EI species that actually make contact and interact at a specific point is of greater he Arabian ecologicalimportance than the overall species-count. desert. The In summary, the various measures of species-richness, in descending order, are: ch with its (1) regional list, (2) ~ species-richness, (3) 0: species-richness, and (4) point species- richness, with the last three being divided into a total and realized richnesses ysis at any Assemblages are composed of different guilds, as defined by the various ecological !tary niche roles played by component species. The trophic structure of an assemblage indicates and among the apportionment of species among the various guilds. Major guilds among ants are mt pattern omnivores, predator-scavengers, granivores, and feeders on sweet substances (nectar rns, some and/or honeydew), although other minor trophic specialists also exist. Most species of cially from ants would be considered omnivores if trophic designation were based solely on a 1989). qualitative list of their known foods. However, many species feed on a preponderance 19 periods. of one kind of food and take only small amounts of other items. For example, many tterns and otherwise granivorous species include small amounts of animal matter in their diet rith large (Heatwole, 1991). Similarly, Camponotus detritus, mainly a consumer of honeydew in :ies have a the Namib dunes (Curtis & Seely, 1987), is also an opportunistic scavenger (Curtis, )e intense 1985a, 1990). An assemblage structure should take into account such participation in on stored multiple guilds. For example, an abundant omnivorous ant, primarily feeding on nctionally seeds, but occasionally taking carrion, would be a major participant in the granivore istinguish guild, but play a relatively minor role in the scavenger guild. The extent of rents) and participation in particular ones may vary in time or space. The relative attractiveness Immunity to baits of different types permits assessment of the extent of membership in more than one guild. Iy, but it The present study employs the above definitions. It depicts differences in realized cing and assemblage structure among different deserts; in one desert, the Namib, it compares mts show assemblages across habitat boundaries at a particular time, and examines guild .rollsd by structure. differcnt )f a given Study Areas ies being .he same The investigation was carried out in three different deserts, the Namib, the e can be Kalahari, and the Kara-Kum.