Native and exotic ants of the Azores (Hymenoptera: Formicidae)

The Azores, a North Atlantic archipelago, has 14 known ant species. Although some earlier researchers have regarded all ants in the Azores to be exotic, we believe several are native (i.e., predating human arrival). Five ant species found in relatively undisturbed environments and not widely distributed beyond the Azores, neighboring Madeira, and the Mediterranean, we judge to be native to the Azores: Hypoponera eduardi, Lasius grandis, Leptothorax unifasciatus, Monomorium carbonarium, and Plagiolepis schmitzii. In addition, Tetramorium caespitum, though widely distributed, shows variation within the Azores that suggests it is native. Six ant species found only in highly disturbed environments in the Azores and distributed around the world through human commerce, we consider exotic: Hypoponera punctatissima, Linepithema humile, Paratrechina longicornis, Pheidole megacephala, Tetramorium bicarinatum, and Tetramorium caldarium. In addition, Solenopsis (Diplorhoptrum) sp. of unknown taxonomic status, and Aphaenogaster senilis, which is not widely distributed, were restricted to disturbed sites and appear to be exotic. Five of the six native ant species (all except P. schmitzii), but only two of the eight exotic species (A. senilis and L. humile) are common and widespread in the Azores. The Argentine ant, L. humile, is the only exotic ant species that appears to have some impact on native species, but it was abundant only in scattered urban and agricultural areas. Three ant species that are important tropical pests, P. longicornis, P. megacephala, and T. bicarinatum, all have their highest latitude populations in the Azores, probably a reflection of the relatively mild climate due to the warming influence of the Gulf Stream. Relatively natural areas in the Azores have low ant species richness, but usually all the ants present are native. Urban sites often have higher ant species richness due to the presence of both native and exotic species. Thus, the total ant species richness is not a useful indicator of habitat integrity. The presence of exotic ant species, however, is an excellent indicator of disturbance. Twelve of the 14 recorded ant species (all except A. senilis and T. caespitum) in the Azores also occur in Madeira. The Azores have far fewer ant species than Madeira (27 species), no doubt related to the Azores' younger age, higher latitude, and greater distance from continental source populations.