REEF-FISH COMMUNITY STRUCTURE AND DYNAMICS - AN INTERACTION BETWEEN LOCAL AND LARGER-SCALE PROCESSES

Studies of coexistence in biotic communities have focused largely on l ocal ecological processes. As a result, effects of regionally varying processes on community structure and their interactions with other pro cesses operating locally have received considerably less attention. He re I investigate variation in predator abundance and species richness at a large spatial scale and associated community-wide patterns of spe cies richness and abundance of tropical fishes on Australia's Great Ba rrier Reef. I constructed reefs from natural substrata to standardize their structure, isolation and history, which could otherwise be confo unded between locations. Recruitment, both total abundance and species richness of recruits, to these reefs was greater at the northern loca tion than at the southern one. In contrast, communities of resident fi shes that developed on these reefs showed the opposite pattern; specie s richness and abundance were greater on the southern reefs. Piscivoro us fishes were proportionately more abundant on the northern reefs. Th erefore, predators were more abundant at the location with greater rec ruitment but lower abundance and species richness of resident fishes. Also, the declines in species richness and abundance of fishes from th e observed maximum in one year to the following observed minimum were related to average predator densities among reefs. These results sugge st that one ecological process that varies between distant locations, in this case predation estimated by predator abundance, may override t he effects of other ecological processes, in this case recruitment, in determining local patterns of coexistence. Furthermore, they suggest that understanding causes of local patterns of species richness and ab undance may require information about processes that determine regiona l variation in ecological interactions.