Data from: Species richness of trophic guilds increases with discharge and decreases with variability in tropical river fish communities

Species Area Relationships (SARs) are one of the most well-established
conservation biogeography patterns, and in rivers habitat area is mediated
by discharge. Species richness and river discharge have a well-established
positive relationship, but how discharge affects trophic diversity is less
clear. Free-flowing tropical river ecosystems are hotspots of global
biodiversity, but they are under increasing threat from water resource
developments which alter river discharge regimes. Here we investigate
relationships between river discharge metrics and the species richness of
freshwater fish trophic guilds in tropical rivers of northern Australia,
using data collated from 40 catchments. We analysed relationships between
the species richness of freshwater fish trophic guilds and discharge
metrics including mean annual discharge (Q), mean daily dry and wet season
discharge and the coefficient of variation (CVQ) of Q. Invertivores and
omnivores were the most species rich trophic guilds. Our results show that
the species richness of trophic guilds in north Australian freshwater
fishes was correlated with multiple components of wet-dry tropical river
discharge regimes. The species richness of predators, invertivores and
herbivore-detritivores increased with Q and wet season discharge, whereas
omnivore and invertivore richness increased with dry season discharge.
Increasing variability in discharge had a negative effect on the species
richness of invertivores and omnivores suggesting adverse effects of low
discharge periods. We found no statistical support for the hypothesis that
the slope of SARs increases with trophic level as predicted by the Trophic
Island Biogeography Theory. These findings suggest that decreases in wet
and dry season discharge, or increases in flow variability due to water
resource development or climate change, may result in the loss of trophic
diversity from tropical rivers. Our results suggest that the conservation
of both wet and dry season natural flow regimes in tropical rivers will be
needed to protect freshwater fish trophic diversity.