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An Introduction to Ants (Formicidae)
of the Tallgrass Prairie

The Origins and Taxonomy of the Prairie Ant Fauna

The plant life of the tallgrass prairie has a distinctive look, but arguably could be described as the frequent-fire aspect of the temperate forest biome. There are virtually no endemics, and almost all the species occur in lighted openings throughout the eastern woodlands. Tallgrass prairie ants are also largely derived from the fauna of the eastern deciduous forest biome. Incidentally, the mainly eastern origin of prairie plants and ants is paralleled by that of tallgrass prairie reptiles and amphibians (Kucera 1991).

Arboreal, leaf-litter, twig and acorn-inhabiting-inhabiting (i.e., fire-sensitive) species of ants are virtually missing in the prairie. Conversely, soil-nesting ant species, especially those found in drier, more open habitats among the eastern woodlands, come together to form the tallgrass prairie formicifauna. Some ants, e.g. Formica montana and F. incerta attain their greatest abundance in the prairie, giving the tallgrass ant community its distinctive appearance. Characteristic prairie ants and their biogeographic relationships are summarized in Table 1.

Except for a few species which creep in at northeastern edge of the Prairie Peninsula in the Great Lakes States, the tallgrass prairie has little representation of the northern conifer forest/bog ant fauna, with its many Myrmica and Leptothorax species. The ants of southeastern savanna/coastal grassland, rich in Pheidole and other Myrmicinae, are similarly poorly represented in the tallgrass. Rather unexpectedly, Table 1 reveals that the ant fauna of the tallgrass is also rather distinct from that of the mid- and shortgrass prairie of the Great Plains. Some kinds are found in both tallgrass and shortgrass prairie, but these also occur in many other vegetation types from the East Coast to the Rocky Mountains. From the ant perspective, there is no such thing as the North American grassland biome of the textbooks; there are a distinctive Great Plains fauna and a tallgrass/eastern woodland fauna. This fact, in combination to the prairie's floristic and successional features, leads me to the conclusion that the humid and fire-dependent tallgrass, despite its grassy aspect, is a thing quite apart from the edaphic and rainfall-determined grassland biome of the Great Plains, the former constituting instead a subset of the eastern woodland biota.

There may be no absolute tallgrass prairie specialists among the ants. All prairie ants except a few Formica species occur outside the prairie region, and all appear to be found in other natural communities, especially open, oak or pine-dominated woodlands. The lack of endemism among prairie ants may perhaps be attributed to the recent origin of the tallgrass prairie, about 10,000 years ago. Relatively slow-breeding, perennial, highly-outbreeding groups such as ants appear not to have had sufficient opportunity to evolve new species in this span of time.

Striking for their absence or near absence in the tallgrass are species of the dominant woodland genera Camponotus (carpenter ants) and Aphaenogaster. Based on pitfall trap samples and general collecting in prairie tracts in throughout the region, the most abundant ants in tallgrass are certain Formica species, Tapinoma sessile, Lasius neoniger, Monomorium minimum, Leptothorax pergandei and Solenopsis molesta. In northern mesic to wet prairies, Formica montana is a pronounced dominant, while F. subsericea and/or a mix of F. pallidefulva group species (especially F. incerta) dominate in prairies elsewhere.

The ant genus Formica has the highest biomass and species richness of all ants in the tallgrass region. Formica ants are among the most likely to be seen by a casual observer because of their abundance, relatively large size, numerous species, and often-conspicuous mounds. Worldwide, Formica is restricted to the temperate northern hemisphere, and is also dominant in the grasslands of the northern Great Plains and of the Eurasian steppes. Formica becomes far less abundant and less species-rich southward. Lasius, Myrmica and Leptothorax are other genera best developed in the temperate northern hemisphere. The prairie species of these genera are but a small sampling of the totality of North American species. The remaining ant subfamilies and genera in the table (including most Dolichoderus, despite the northerly distribution of the prairie species) are better represented, or even dominant, in warm-temperate and tropical areas. In the southern tallgrass vegetation in Arkansas, Texas and Oklahoma, the Myrmicinae and Forelius pruinosus take on much more importance. There, only few Formica species occur, and they are rarely dominant.

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