Biodiversity analyses: are aquatic ecologists doing any better and differently than terrestrial ecologists?

Species richness is a key variable in biodiversity analyses, being often analyzed as either a response or an explanatory variable. We addressed whether biodiversity studies conducted in aquatic habitats (including both freshwater and marine habitats) differed substantially from those conducted in terrestrial habitats. Using a systematic literature search, we show that aquatic and terrestrial ecologists use species richness predominantly as a response variable. However, the number of studies in terrestrial systems was greater than the number of studies in aquatic habitats. The amount of variance in species richness explained by the statistical models was similar--around 59%. The frequency of citation was also similar between terrestrial and aquatic studies. The sample sizes of studies conducted in aquatic habitats were significantly lower than those of studies conducted in terrestrial habitats. Both aquatic and terrestrial ecologists tend to use a large number of explanatory variables to model species richness. We conclude that the differences between the ways aquatic and terrestrial ecologists conduct biodiversity studies were not substantial; their impacts on the scientific community were similar; and there is a need to increase the focus on theory-driven analyses. We recommend that research efforts on the mechanisms underlying species richness variation in aquatic systems should be intensified.