• Aquatic biomass;
  • community structure;
  • dominant species;
  • energy use;
  • freshwater fish;
  • niche model;
  • resources;
  • species richness;
  • total abundance;
  • Trinidad and Tobago


Aim  To test the hypothesis that communities with higher diversity have more predictable properties by examining patterns of community structure along a species richness gradient.

Location  Trinidad and Tobago (11°00 N, 61°00 W), on the South American continental shelf, opposite the Orinoco River delta, north-east Venezuela.

Methods  We used quantile regressions to investigate how three total abundance, absolute and relative dominance measures – numerical abundance, biomass and energy use, respectively – change across a species richness gradient. We investigated which allocation rule best mimics community assembly in this species richness gradient by examining the abundance of the dominant species and comparing it with predictions of niche apportionment models.

Results  All measures of total abundance increase on average across the gradient, but the upper limit remains constant. On average, absolute dominance is constant, but the distance between the upper and lower limits decreases along the gradient. Relative dominance decreases with species richness. Observed dominance patterns are best described by Tokeshi's random fraction model.

Main conclusions  Our results show that both total abundance and absolute dominance become increasingly variable as biodiversity decreases. Consequently, our study suggests that ecosystem properties are less predictable when biodiversity is lower.