COEXISTING POPULATIONS OF ACOMYS-CAHIRINUS AND A-RUSSATUS - A PRELIMINARY-REPORT

Two species of the genus Acomys, cahirinus and russatus, co-occur in E n Gedi. A. cahirinus is nocturnal, whereas A. russatus is diumal. This pattern of temporal partitioning has been ascribed to competitive exc lusion of A. russatus by A. cahirinus. Study of the ecological basis f or this phenomenon and its mechanisms, however, is still required. Her e we report preliminary results of longterm research that we undertook in order to establish precise activity patterns, body temperature rhy thms, spatial distribution, food habits, and population dynamics of th e two species. Population densities of both species are quite row, and much lower than those found in agricultural areas. A. russatus was; f ound mainly in a creek bed strewn with boulders, and also on the hills ide among boulders. A. cahirinus appeared to be more evenly distribute d, and was found also among smaller rocks; determination of precise sp atial distribution patterns, however, requires more thorough study. Wh ile A. cahirinus was active almost only during the night, A, russatus was active during the entire day during the winter months. Both specie s exhibit body temperature rhythms that conform to those expected of a nocturnal rodent; however, A. russatus body temperatures rise earlier (several hours before sunset) and drop later than those of A. cahirin us, and only reach their minimal level several hours after sunrise. Th is difference may reflect an adaptation to a diurnal activity pattern.