CONVERGENCE AND HISTORICAL EFFECTS IN HARVESTER ANT ASSEMBLAGES OF AUSTRALIA, NORTH-AMERICA, AND SOUTH-AMERICA

In this paper I examine the extent to which contemporary ecological pa tterns in 42 harvester ant assemblages of three continents can be expl ained as a result of present-day environments or from differences in t he history of each ant biota. The contribution of each factor to the o verall variability of six community characters was evaluated by the AN OVA procedure. The method revealed absence of convergence in three-con tinent and pairwise-continent analyses in almost every community attri bute that was measured. Significant convergence was detected only in t he foraging score for the North America-South America comparison. This implies that the foraging mode used by ants for searching seeds is mo re similar within similar environments in the two continents than betw een different environments in the same continent. Significant historic al effects were much more prevalent than convergence both in three-con tinent and pairwise-continent comparisons. Abundance at baits, body si ze, and foraging distance were more variable within similar environmen ts in different continents than between different environments in the same continent. The overall absence of convergence documented in this study suggests that constraints related to the evolutionary history of each species assemblage have inhibited convergent evolution in respon se to local selective pressures.