CRUSTACEAN ZOOPLANKTON SPECIES RICHNESS AND ASSOCIATIONS IN RESERVOIRS AND PONDS OF AGUASCALIENTES STATE, MEXICO

We report the species of crustacean zooplankton found in 19 resevoirs and ponds that were sampled at on at least two occasions in Aguascalie ntes State, Mexico, at a latitude of about 21 degrees 30' North Latitu de. We collected a total of 33 cladoceran taxa, 15 calanoid and cyclop oid copepods, an Ergasilus copepod, 2 anostracans, one notostracan spe cies and an amphipod. All these taxa had previously been reported in M exico. As in more temperate areas, there was a significant correlation between the species richness and lake size. The species-area relation ship for Aguascalientes was indistinguishable from that of more northe rly lakes. The two most common associations of zooplankton species wer e (1) those small species that occurred with fish: Daphnia parvula, Di aphanosoma birgei, Leptodiaptomus siciloides, Mastigodiaptomus albuque rquensis, and Thermocyclops inversus, and (2) the large Daphnia schodl eri that occurred with the predator Notonecta, in the absence of fish. With minor variations, these two associations also occur throughout t emperate North America.