A Competition Hierarchy among Boreal Ants: Impact on Resource Partitioning and Community Structure

Abstract

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.