Temperature-related distributions of Metadiaptomus and Tropodiaptomus (Copepoda: Calanoida), particularly in southern Africa

Updated locality records of species of Metadiaptomus and Tropodiaptomus on the African continent confirm the generally disjunct distribution of these two taxa as recognised by Dumont (1980) in North Africa. Distributional data for southern Africa reveal little range overlap between these two genera. Apart from two south western Cape taxa, species of Metadiaptomus are largely confined to upland, higher latitude, semi-arid or arid warm subtemperate regions, while species of Tropodiaptomus generally occupy moist, lower-lying, lower latitude subtropical regions. Separation along latitudinal and/or altitudinal axes implicates temperature as a controlling factor, while separation on the precipitation axis suggests the importance of habitat permanence. Using a multiple regression equation derived for African waters to predict water temperature from latitude and altitude, it is shown that the two genera tend to separate around the 20 °C mean annual temperature isotherm. Additional factors influencing distribution (habitat permanence, water quality, competition and predation) are discussed.