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Encyclopedia of Social Insects

Living Edition
| Editors: Christopher K. Starr

Ant Mosaics

  • Nico BlüthgenEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-90306-4_9-1
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Ant mosaics occur when two or more competitively dominant ant species show a nonoverlapping, checkerboard-like spatial distribution pattern within a forest or other habitat. Such a pattern was originally described by Room in 1971 [10] and termed an ant mosaic 2 years later by Leston [7]. Since then, ant mosaics have been studied across different continents and habitats. Among social insects, mosaic-like distribution patterns are not exclusive to ants and have been found for termites as well [6].

Ant colonies commonly vigorously defend their nest sites, and aggression against non-nestmates often extends well beyond the nest entrance, sometimes involving territorial exclusion of other ant species. As a result, competitively superior ant species with relatively large colonies and an aggressive behavioral dominance of other species are expected to mutually exclude each other from their territories. Ant species co-existing within the territories of dominant ants are regarded as non-dominant, submissive, or subdominant. Ant mosaics thus involve both mutually exclusive territories and positive associations (co-occurrence) between species (Fig. 1). Such competition asymmetries and the specific tolerance of a set of subdominant ant species by dominant ants are still not well understood. How ants recognize and discriminate subdominant partners from potential competitors, and whether niche partitioning contributes to a stable co-occurrence of pairs of species, remains unknown in most cases.
Fig. 1

The classic ant mosaic first described on cocoa trees in Ghana [10]. Significant co-occurrence (+) and avoidance (−) between pairs of species are shown by solid and dashed lines, respectively. For example, the dominant ant Crematogaster striatula shared significantly more trees than expected by chance with the subdominant species Atopomyrmex mocquerysi and Camponotus chrysurus, while it co-occurred on significantly fewer trees than expected with at least three other species. From a total of 128 species recorded in Room’s study, only the most frequent ones with significant associations are redrawn here, i.e., those with occurrence on more than 10 trees. Dominant species in bold type, subdominants enclosed by gray circles. Genus abbreviations: Camp. Camponotus, Crem. Crematogaster, Polyrh. Polyrhachis.

The term ant mosaic365体育网站 is mainly applied to arboreal ants in forest canopies, tree plantations, and palm plantations, although territories may occur on the ground as well. On the ground, however, the perimeter of a territory can be more difficult and costlier to defend, whereas a tree trunk or the base of a large branch can be effectively defended by dominant ants, thus monopolizing a relatively large area of the crown.

Two of the most important diets for arboreal ants are honeydew (sugar-rich secretions by plant-sucking insects) and extrafloral nectar (plant nectar secretions outside of flowers). The territorial monopolization of such important, predictable resources, particularly ant-hemipteran associations, can form the basis of an ant mosaic [1, 3]. Consequently, dominant ant species in arboreal ant mosaics often involve certain genera that harvest large amounts of honeydew. In tropical forests, dominant ants often comprise genera from the subfamilies Formicinae (e.g., Oecophylla, some Camponotus) and Dolichoderine (e.g., Azteca and Dolichoderus) [2, 8, 10]. In several cases, their dominance corresponds to modified proventriculi that help to store large liquid loads in their crops, facilitating a particularly effective honeydew feeding [2]. Other tropical ant mosaics involve Myrmicinae such as Crematogaster [1, 2, 8]. Typically, such dominant species have large colonies living in polydomous arboreal nests. In temperate forests, Formica wood ants play a particularly dominant role, and territories of these ground-nesting ants include trees on which they harvest large amounts of honeydew.

Although plant-based liquid diets and honeydew are spatiotemporally more predicable than prey or fruits, temporal changes in honeydew and nectar availability do occur. Such changes coupled with strong competition among co-existing ants suggest that ant mosaics are dynamic rather than static. This holds true for some species that are almost exclusively either diurnal or nocturnal, which may replace each other in their respective territories. In general, an aggressive monopolization of rewarding resources can be quite effective in dominant ant species. The spatial scale of such aggressively defended territories varies depending on such factors as colony size and the degree of competition so that territories do not necessarily extend to entire tree crowns [1, 2].

The complexity of ant mosaics varies across habitats. For instance, ant mosaics in structurally simple plantations are often dominated by a few species [4]. In contrast, ant mosaics in complex, interconnected canopies of tropical forests are more difficult to detect and may not always be as pronounced as in structurally simple habitats [1, 9]. In fact, the statistical power of detecting ant mosaics in communities with numerous species can be low. Moreover, variation in microhabitat preferences or different selection of tree species may blur a clear ant mosaic pattern or provide alternative explanations of a patchy distribution in addition to competition.

Although ant mosaics most likely result from interspecific competition, experimental evidence for competition and for effects of competitive exclusion are rare [5]. For instance, Majer [8365体育网站] showed how ant colonies that have been removed from a tree crown were replaced by others, suggesting a response to competition release.

Since ant species differ in their food and prey spectra and can maintain relatively specific sets of associated organisms such as hemipterans, ant mosaics can have substantial impacts on the distribution of other arthropods [3]. Such changes in communities may translate into variation in processes maintained by ants, such as plant protection against herbivores, deterrence of pollinators, or fruit predators. Hence, ant mosaics potentially represent a key driver in the distribution of arthropods and ecosystem processes in forests, scrublands, and plantations, a factor that merits more attention in ecosystem studies.

References

  1. 1.
    Blüthgen, N., & Stork, N. E. (2007). Ant mosaics in a tropical rainforest in Australia and elsewhere: A critical review. Austral Ecology, 32, 93–104.
  2. 2.
    Davidson, D. W. (1997). The role of resource imbalances in the evolutionary ecology of tropical arboreal ants. Biological Journal of the Linnean Society, 61, 153–181.
  3. 3.
    Dejean, A., Corbara, B., Orivel, J., & Leponce, M. (2007). Rainforest canopy ants: The implications of territoriality and predatory behavior. Functional Ecosystems and Communities, 1, 105–120.
  4. 4.
    Fayle, T. M., Turner, E. C., & Foster, W. A. (2013). Ant mosaics occur in SE Asian oil palm plantation but not rain forest and are influenced by the presence of nest-sites and non-native species. Ecography, 36, 1051–1057.
  5. 5.
    Gibb, H., & Hochuli, D. F. (2004). Removal experiment reveals limited effects of an behaviorally dominant species on ant assemblages. Ecology, 85, 648–657.
  6. 6.
    Leponce, M., Roisin, Y., & Pasteels, J. M. (1997). Structure and dynamics of the arboreal termite community in New Guinean coconut plantations. Biotropica, 29, 193–203.
  7. 7.
    Leston, D. (1973). The ant mosaic – Tropical tree crops and the limiting of pests and diseases. PANS (Pest Articles and News Summaries), 19, 311–341.
  8. 8.
    Majer, J. D. (1976). The ant mosaic in Ghana cocoa farms: Further structural considerations. Journal of Applied Ecology, 13, 145–155.
  9. 9.
    Ribas, C. R., & Schoereder, J. H. (2002). Are all ant mosaics caused by competition? Oecologia, 131, 606–611.
  10. 10.
    Room, P. M. (1971). The relative distributions of ant species in Ghana’s cocoa farms. Journal of Animal Ecology, 40, 735–751.

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Authors and Affiliations

  1. 1.Ecological Networks, Department of BiologyTechnische Universität DarmstadtDarmstadtGermany