Climate‐driven range retraction of an Arctic freshwater crustacean

1. Species responses to global warming are predicted to be manifest as poleward and upward extension of species ranges, whereas cold‐adapted species experience range retractions. We report on recent range retraction of a freshwater crustacean, the Arctic fairy shrimp Branchinecta paludosa (Branchiopoda, Anostraca) from alpine ponds of southern Norway, a southernmost extension of its otherwise arctic range. 2. The species was mapped during two separate surveys, in 1970 and 2011. In 1970, it occurred in numerous ponds from the tree line at 900 m altitude to high alpine sites at 1500 m. Re‐sampling of the same ponds 41 years later revealed extinction of populations from ponds along the lowest 200 m of its altitudinal range. 3. Reconstruction of summer temperatures for the periods 1965–70 and 2005–10 revealed a thermal increase for the period, corresponding to a c. 200‐m upward shift of the local isotherms. More specifically, the number of warm summer days had doubled in the lowest 200 m of the region, which might be particularly detrimental for the species. 4. The extinctions at lower altitudes were not compensated for by corresponding upward colonisations. The range retraction of B. paludosa is possibly associated with oxygen stress and hypoxia, induced by increased water temperatures.     

How many species of arthropods? Erwin's estimate revised

Erwin's much debated estimate of 30 million species of arthropods is revised. The original estimate is based on the evaluation of host specificity of guilds in beetle samples, and subsequent hierarchical ratio extrapolations. The growing number of studies including mass sampling of arthropods have provided several data sets suitable for obtaining an empirical basis of this estimate. The structure in this modified version is somewhat changed compared to the original estimate in order to make each hierarchical step more easily testable. Plant species are separated into different growth forms, and host specificity measures are based only on phytophagous species. Effective specialization is applied as a measure of host specificity to correct for the fauna shared between plant species. A between community correction factor is applied to correct for differences in host specificity at different spatial scales. There are still great uncertainties attended with such estimates. The largest problems refer to the between community correction factor and the proportion of canopy species to total species. Further work on host specificity and the least known hyperdiverse groups are also needed. The revised version of the estimate does not support hyperestimates of 30 100 million species. Rather, it compares nicely with estimates derived from other estimation methods, indicating a global arthropod species richness of 5–10 million species.