COMPETITIVE ABILITY AND THE POTENTIAL FOR LOTTERIES AMONG TERRITORIALREEF FISHES

Stegastes diencaeus and S. dorsopunicans are mutually territorial Cari bbean damselfishes. S. diencaeus is larger, grows faster and fives lon ger than S. dorsopunicans. S. diencaeus is a habitat specialist that s hares its primary habitat mainly with S. dorsopunicans. Field manipula tions show that both S. diencaeus and S. dorsopunicans readily take ov er living space from smaller, but not larger, heterospecific neighbors . Natural changes in the use of living space by both species occur fre quently and adult S. diencaeus often aggressively usurp the living are as of smaller S. dorsopunicans. Lunar and seasonal patterns of juvenil e recruitment by S. diencaeus and S. dorsopunicans are similar. Large size bestows competitive superiority on S. diencaeus by giving its adu lts a superior ability to aggressively acquire living space, and by en abling its juveniles to quickly escape the period when they lack a siz e advantage. Hence they spend much of their lives as competitive domin ants. There is no evidence that competitive advantages arising from la rge size are offset either by other adult attributes or by differences in temporal patterns of recruitment that affect priority of access to space. The lottery hypothesis for species coexistence relies on patte rns of abundance being determined by patterns of recruitment to vacant space because different species have equal space-holding abilities. T hese data show that the existence of such a mechanism is doubtful.