Dispersal limitation and climate-related environmental gradients structure microcrustacean composition in freshwater lakes, Ellesmere Island, Canada

Dramatic environmental change is expected in the Arctic, yet little is known about the occurrence and community composition of microcrustaceans in Arctic lakes and how this will be influenced by future environmental change. We sampled and calculated relative abundances of microcrustacean species in 54 lakes on Ellesmere Island, Can- ada. New species records on Ellesmere Island included Daphnia umbra, Tachidius discipes, and Artemeopsis stefanssoni. Daphnia middendorffiana/tenebrosa was the most common taxon and often dominated microcrustacean assemblages, likely a result of its pigmentation, which offers resistance to ultraviolet radiation. Species richness was positively associated with nutrients, dissolved organic carbon (DOC), temperature, calcium, and conductivity and negatively affected by elevation. In contrast to most findings in temperate systems, we detected a negative relationship between species richness and surface area. Community composition was influenced by DOC, nutrients, and elevation but was also related to spatial variables, suggesting that spatial gradients in environmental conditions and dispersal are important drivers of differences among sites. Arctic ecosystems are expected to change rapidly in the coming years because of climate change and ozone thinning, and we expect that associated changes in DOC, temperature, and nutrients will affect microcrustacean species richness and distribution throughout the landscape. Resume´ : On s'attend a des changements environnementaux spectaculaires dans l'arctique; on connaoˆt, cependant, assez mal la presence et la composition des communautedes microcrustaces des lacs arctiques et comment elles seront influencees par les futurs changements climatiques. Nous avons echantillonneles especes de microcrustaces dans 54 lacs de l'oˆle d'Ellesmere, Canada, et nous en avons determineles abondances relatives. Daphnia umbra, Tachidius discipes et Artemeopsis stefanssoni sont des especes signalees pour la premiere fois sur l'oˆle d'Ellesmere. Daphnia middendorffiana/ tenebrosa est le taxon le plus commun et il domine souvent les peuplements de microcrustaces, vraisemblablement a cause de sa pigmentation qui lui procure une resistance a la radiation ultraviolette. La richesse specifique est en correlation positive avec les nutriments, le carbone organique dissous (DOC), la temperature, le calcium et la conductiviteet en relation negative avec l'altitude. Contrairement a ce qu'on observe la plupart du temps dans les systemes temperes, nous