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Keywords:

  • Autotrophs;
  • freshwater;
  • heterotrophs;
  • log-logistic regression;
  • relative species richness;
  • species sensitivity;
  • total phosphorus

Abstract

Aim

We investigated the patterns of autotrophic and heterotrophic relative species richness along a total phosphorus (TP) concentration gradient. The relative species richness–TP relationships were calculated separately for four different regions [(sub)tropical, xeric, temperate and cold] and two types of water bodies (lakes and streams).

Location

Global

Methods

Using data from peer-reviewed articles reporting the occurrence of freshwater species at specific TP concentrations, we determined the species richness along a TP gradient. Using log-logistic regressions, we then estimated the TP concentration at which the potential decrease of relative species richness (RSR) equals 0.5 and the slope at which the decrease occurs (β). The RSR is given as the ratio of species richness to maximized species richness along a TP gradient.

Results

The RSR of streams generally decreased more rapidly than that of lakes with increasing P, as illustrated by the steeper slope of the log-logistic functions for streams (βlakes < βstreams). Although there was no consistent trend between autotrophs and heterotrophs in the different regions, we found that the TP concentration at which the RSR equals 0.5 was lower in cold regions (0.04–0.22 mg P/L) than in warmer regions (0.28–1.29 mg P/L).

Main Conclusions

The log-logistic relationships between RSR and TP concentration vary considerably among regions of the world, between freshwater types (lakes and streams) and between species groups (autotrophs and heterotrophs). This variability may be attributed to differences between the two freshwater types in respect to their species groups and evolutionary patterns, nutrient demand, biogeochemical and hydrological processes. We were not able to derive log-logistic regressions for all combinations of freshwater type or species type and region [e.g. (sub)tropical lakes]. For other areas, our results can be used to assess the potential impact of phosphorus eutrophication on freshwater biota.