Community dynamics of tropical reef fishes: Local patterns between latitudes

Latitudinal variation in the dynamics of biological communities is among the least addressed and understood topics of modern ecology. Here, I examine the dynamics of coral-reef fish communities inhabiting small rubble patches at 2 locations separated by approximately 9 degrees of latitude (One Tree Island and Lizard Island) on Australia's Great Barrier Reef. This sampling program ran simultaneously at the 2 locations using identical. census methods, sampled over 16 mo and included 2 summer recruitment seasons. Total abundance of all fish species pooled fluctuated seasonally, peaking in summer. Total abundance at sites within locations differed, but sites at different locations overlapped in abundance. The dynamics of these communities were apparently unrelated to family membership among species, intraspecific abundances or diet. Rank abundances of species present at both locations did not differ, and only a single negative correlation of abundances between species was detected. Changes in abundance, however, were density dependent. Maximum abundance of fishes observed in the first summer explained between 42 and 93% of the variation in subsequent per capita declines in abundance by the following winter and before recruitment had commenced in the second year. These density-dependent effects were observed across families and across widely separated locations. These results suggest that the dynamics of these communities were not structured by strong pairwise interspecific interactions, but, instead, may have been structured by some density-dependent process(es) that affected a broad cross section of species and that operated irrespective of locality.