Not enough niches: non‐equilibrial processes promoting species coexistence in diverse ant communities

Abstract  Explanations for species coexistence in ant communities have traditionally focused on niche partitioning, particularly relating to differences in diet, foraging times and nesting requirements. Although niche separation is undoubtedly important, it seems insufficient to account for the high levels of local species richness that are commonly observed. This paper explores alternative explanations for ant species coexistence, focusing on factors that prevent competitive exclusion in diverse ant communities experiencing high levels of behavioural dominance, such as characteristically occurs in Australia. Very high species densities require two conditions to be met: first, a large number of species must successfully establish; and second, there must be a high rate of species persistence once established. In this context I advance five propositions based around three sets of arguments. First, ant sociality and modularity confers a high level of persistence once colonies are established, so that species coexistence is determined to a significant extent by processes operating at the establishment phase, rather than just by interactions between established colonies. Second, competitive outcomes are highly conditioned by environmental variation, which severely limits competitive exclusion. Finally, dominant species are highly patchy in space, and cannot comprehensively monopolize resources, such that there will usually be room for low densities of subordinate species. These propositions have relevance to neutral theories of community ecology, and to understanding intercontinental differences in local species richness.