Predicting diversity of juvenile neotropical fish communities: patch dynamics versus habitat state in floodplain creeks

The species richness of communities should largely depend on habitat variab ility and/or on habitat state. We evaluated the ability of habitat variabil ity and habitat state to predict the diversity of juvenile neotropical fish communities in creeks of a river floodplain. The young-fish fauna consiste d of 73 taxa, and samples were well distributed over a wide range of releva nt temporal and spatial habitat variability. We were unable to demonstrate clear patterns of richness in relation to temporal and spatial habitat vari ability (if habitat state variables were not included), regardless of the t emporal variability scale, the grouping of sites (up- and downstream sites differed in temporal variability patterns), taxonomic units or life stages considered. Using stepwise multiple regression, 36% of the variance in spec ies richness was explained for all data, and at best 47% was explained for all taxonomic units at upstream sites using temporal and spatial habitat va riability and habitat state (bank length, mean width, mean water level befo re fishing and/or water turbidity). Using Monte Carlo simulations, we blind ly predicted 31% (all data) and at best 37% (all upstream taxa) of the obse rved variance in species richness from these model types. This limited prec ision is probably because rare species produced most of the richness patter ns in our creeks. The prediction of these rare species is generally difficu lt for various reasons, and may be a problem in many ecosystem types.