JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Wiley-Blackwell and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos. Savolainen, R. and Vepsalainen, K. 1988. A competition hierarchy among boreal ants: impact on resource partitioning and community structure. -Oikos 51: 135-155.Differences in social organization and behaviour rank ant species into a competition hierarchy (starting with superior competitors): territorials (e.g., the Formica rufa -group red wood ants), encounterers (e.g. Camponotus, Lasius niger), and submissives (e.g., Formica fusca). Territorials and encounterers behave aggressively against individuals of alien colonies; these species are not expected to cooccur. Submissives behave recessively and may coexist with stronger species, but their forager numbers and nest densities should decrease. If such small-scale behavioural processes structure the ant community, predictable larger-scale nest-distribution pattern of the species is expected. We tested the expectations with bait experiments and nest mapping, and modelled the results by multiway contingency tables. Submissives showed complementary abundances with territorials in terms of forager numbers on the baits, and their nest densities within the territory increased toward its periphery. Pressure by territorial and encounter species on the baits caused the submissive species to shift from protein to carbohydrate. Territorials and encounterers had complementary occurrences on the baits. The nests of territorials were far apart, with only occasional nests of encounter species at the outskirts of the territory. In the late successional habitats of the boreal taiga biome superior territorial competitors, especially the polycalic red wood ant species, assume the role of organizing centers of ant species assemblages.

Sympatric speciation through intraspecific social parasitism has been proposed for the evolution of Hymenopteran workerless parasites. Such inquilines exploit related host taxa to produce their own sexual offspring. The relatedness of inquilines to their hosts has been generalized in Emery's rule, suggesting that social parasites are close or the closest relatives to their host species. If the closest relative of each parasite is its host, then multiple independent origins of the parasite species are implied even within a single genus, probably through sympatric speciation. To test the plausibility of sympatric speciation in inquilines, we conducted a mitochondrial DNA phylogenetic analysis in three inquiline-host pairs of Myrmica ant species. We show that congeneric inquilines have originated independently several times. We also show that two of the inqulines are more closely related to their hosts than to any other species. Our results suggest sympatric speciation of Myrmica inquilines. Sympatric speciation is probably facilitated by the social biology and ecology of Myrmica, with polygyny as a prerequisite for the evolution of intraspecific parasitism.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Wiley-Blackwell and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos. Savolainen, R. and Vepsalainen, K. 1989. Niche differentiation of ant species within territories of the wood ant Formica polyctena. -Oikos 56: 3-16.The question if dominant ant species affect habitat use of other ant species was studied around two mounds of the territorial Formica polyctena. We sampled foraging ants at 10, 30 and 60 m from the mounds in four vertical layers on rocky outcrop interspersed with small vegetation patches and in neighbouring forest. We tested expected interactions among ant species on the basis of a linear competition hierarchy concept consisting of three levels: territorial (top competitors), encounter (aggressive but nonterritorial) and submissive (nonaggressive) species. We focussed on resource partitioning by space (not by food) and shifts in use of vertical layers of the habitat in presence of the territorial species. F polyctena was present everywhere except in the litter. Its numbers decreased with distance from its mound, although its activity was substantially patchy within each distance zone. The encounter species occurred occasionally in places where F. polyctena was scarce. The submissive F. fusca, morphologically similar to the top dominant, did not respond by layer shifts; but its numbers decreased toward the mound of F polyctena. The submissive Myrmica shifted from surface of ground to litter and shrub layers at high densities of the dominant. Small colonies and short foraging distances of the submissive species allow coexistence within the territory in lowdensity patches of F polyctena. Our ant community consists of three functional guilds corresponding to taxonomic and morphological guilds: the larger above-ground Formicinae, the smaller and compacter Formicinae, and the small litter-inhabiting Myrmicinae. Interference competition is stronger and more effective among the Formicinae than among the Myrmicinae or between the subfamilies, but the top dominant affects all ant species of the community. Coexistence between the submissives and the top dominant is facilitated by niche differentiation and behavioural responses in the presence of the top dominant.

Widely distributed Palearctic insects are ideal to study phylogeographic patterns owing to their high potential to survive in many Pleistocene refugia and—after the glaciation—to recolonize vast, continuous areas. Nevertheless, such species have received little phylogeographic attention. Here, we investigated the Pleistocene refugia and subsequent postglacial colonization of the common, abundant, and widely distributed ant Myrmica rubra over most of its Palearctic area, using mitochondrial DNA (mtDNA). The western and eastern populations of M. rubra belonged predominantly to separate haplogroups, which formed a broad secondary contact zone in Central Europe. The distribution of genetic diversity and haplogroups implied that M. rubra survived the last glaciation in multiple refugia located over an extensive area from Iberia in the west to Siberia in the east, and colonized its present areas of distribution along several routes. The matrilineal genetic structure of M. rubra was probably formed during the last glaciation and subsequent postglacial expansion. Additionally, because M. rubra has two queen morphs, the obligately socially parasitic microgyne and its macrogyne host, we tested the suggested speciation of the parasite. Locally, the parasite and host usually belonged to the same haplogroup but differed in haplotype frequencies. This indicates that genetic differentiation between the morphs is a universal pattern and thus incipient, sympatric speciation of the parasite from its host is possible. If speciation is taking place, however, it is not yet visible as lineage sorting of the mtDNA between the morphs.

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Ants were collected with sets of pitfall traps in four coniferous-forest habitats in southern Finland. A three-level competition hierarchy concept was used to generate predictions on ant community structure. The levels of the hierarchy, and the respective predictions, from top to bottom were: (1) The dominant territorial wood ants (Formica rufa-group species), expected to exclude each other. (2) The other aggressive species, likely to be excluded by the F. rufa-group. (3) The submissive species, non-aggressive and defending only their nest, and thus likely to coexist with the dominants but in reduced numbers. As expected, the species of the F. rufa-group excluded each other, and the species number of the other aggressive ants was significantly cut down in the presence of the F. rufa-group. The aggressive species F. sanguinea and Camponotus herculeanus showed complementary occurrences with the F. rufa-group, and Lasius niger reduced occurrences. The number of the submissive species was not significantly affected by the F. rufa-group. However, pairwise correlation coefficients were significantly more often negative than positive between presence of the F. rufa-group and average proportion of pitfalls per set with a submissive species, each analyzed in turn. The result indicates that the F. rufa-group also reduced the colony densities of the submissive species. We conclude that in the taiga biome territorial wood ants are, after adjusting for physical vicissitudes of the environment, the major structuring force of ant species assemblages.