Global meta-analysis reveals that invertebrate diversity is higher in permanent than in temporary lentic water bodies

One of the main constraints affecting invertebrate diversity in many freshwater lentic habitats is the presence of a dry phase which forces aquatic organisms to avoid this period through the migration to other water bodies or the production of resting stages. Field studies show contradictory results when comparing invertebrate diversity in permanent (PW) and temporary lentic waters (TW). Our objective was to test how diversity is influenced by the permanence of water in lentic habitats, and which factors affect the magnitude and direction of this difference, including sampling design. Through a systematic review, 66 publications were selected and classified according to the sampling design (spatial, temporal, and spatio-temporal datasets). Meta-analysis of the spatial dataset, which included 70% of the studies, revealed that diversity in PW was higher than in TW, and this difference was not influenced by annual precipitation, dispersal mode, habitat type or level of anthropogenic impact (proximity to urban or agricultural areas). We found a significantly higher effect size (PW greater than TW) when considering species richness rather than cumulative richness or Shannon diversity index, disconnected water bodies (hindering the exchange of individuals through water connection), organisms with passive dispersal (which cannot actively avoid the dry period), and study sites with high anthropogenic impact (where temporary habitats could undergo impacts; e.g. concentration of pollutants and eutrophication). We also found that the differences in diversity between PW and TW may decrease with increasing sampling effort. This result may be attributable to high species turnover due to the higher temporal environmental variation in TW relative to PW. Also, it indicates that sampling effort should be comparatively higher in TW to properly characterize the biodiversity in these environments in order to compare with PW. As global climate continues to change, our results suggest that loss in aquatic invertebrate diversity of TW will be likely to occur in regions where the frequency of drying events increases.