Sympatric Associations of Three Ants: Iridomyrmex humilis, Pheidole megacephala, and Anoplolepis longipes1 in Hawaii2

Abstract

The ants Pheidole megacephala (F.), Anoplolepis longipes (Jerdon), and Iridomyrmex humilis (Mayr) are mutually exclusive of one another in areas where each ant is dominant. Of the 3 ants, P. megacephala appears to be the most aggressive under normal conditions; however, during the “invasion cycle” of I. humilis, the latter is able to expand its territory into areas previously occupied by P. megacephala. In other regions of the world where I. humilis has become established it has eliminated P. megacephala. Thirty years after I. humilis was first reported in the Hawaiian Islands, however, P. megacephala is still dominant in much of the lowlands and shows no sign of being eliminated. A. longipes appears to be severely limited in its distribution in Hawaii because of its habit of nesting under large rocks or rock-lined irrigation ditches. Movements of I. humilis around the world during the past 100 years indicate it is most successful in areas between 30 and 36° latitude (north or south). This study has shown that of the 3 ant species, I. humilis is best adapted for colonizing areas of Hawaii above 3000 feet. Climatic conditions at these elevations in the Hawaiian Islands correspond to those near sea level at latitudes above 30°.