SOME CALANOID COPEPODS FROM ARIZONA WITH NOTES ON CONGENERIC OCCURRENCES OF DIAPTOMUS SPECIES

Abstract

Seven species of Diaptomus are reported from Arizona, including 4 new to the state. D. shoshone, D. nudus, and D. leptopus occur on the Colorado Plateau; D. clavipes and D. siciloides are abundant in the mountainous area below the Mogollon Rim; D. albuquerquensis occurs rarely in turbid ponds on the Plateau and in the Sonoran Desert; D. dorsalis lives in permanent, oligohaline ponds near Phoenix.Thirty‐four examples of congeneric coexistence are presented, including 3 from Arizona. In 24 instances, coexistence involved species of different subgenera. Differences in length of co‐occurring species are common and are particularly marked in temporary ponds and saline lakes. Genetic changes in the nature of character displacement may modify dimensions of coexisting species, although environmental factors other than congeneric competition also play a part. Adult diaptomids from Arizona tanks may be larger when early instars are passed during summer rather than winter. Extrinsic factors thus tend to blur morphological character displacement. Modified life cycles and ecological displacement are further intrinsic mechanisms whereby habitats are partitioned, although not revealed by ordinary sampling techniques.