Microcrustaceans (Cladocera and Copepoda) of the Boreal/Tropical Transition Zone in the Russian Far East: A Case Study of Species Associations in Three Large Lakes

The Far East of Russia is a region where boreal and tropical faunas mix; it is also a zone of cladoceran endemism. The present study aimed to compare a set of microcrustacean (Cladocera and Copepoda) associations in three large lakes of the Russian Far East: Khanka, Bolon, and Chukchagir. The associations of the microcrustaceans were identified based on the function of the discrete hypergeometric distribution. Many of the 108 taxa found here were unaffiliated with an association. Interestingly, the portion of taxa involved and "not involved" in species associations differed among geographic faunistic complexes. The rate of endemism was significantly higher among the taxa incorporated into the associations as compared to the "not involved" taxa. In all the lakes, there were large clusters of phytophilous species characteristic of the macrophyte zone (and its margins) and clusters characteristic of pelagic and sublittoral plankton. We found that in the three lakes, the microcrustaceans formed a set of functionally similar associations, but the taxonomic composition of each functional association was specific to each lake. We hypothesize that the composition of functional clusters reflects the history of colonization for each water body. That is, the founder effects and subsequent "monopolization" of habitats have affected species associations.