Temporal partitioning: An experiment with two species of spiny mice

We studied temporal partitioning between two spiny mouse species that coexist in hot rocky deserts in the Middle East: nocturnal common spiny mice (Acomys cahirinus) and diurnally active golden spiny mice (A. russatus). Although A. russatus is diurnally active, it retains the physical activity and body temperature rhythms of nocturnal mammals. We studied the two species in four 1000-m(2) enclosures at Ein Gedi, Israel: two experimental enclosures with A. russatus kept alone, and two controls with individuals of both species kept together. We monitored activity with Sherman traps and by studying foraging microhabitat use and efficiency using giving-up densities (GUDs) in food trays. The trays contained broken sunflower seeds mixed in local soil and placed in three microhabitats: under boulders, between boulders, and in the open. Trapping revealed that, in the absence of A. cahirinus, the usually diurnal A. russatus was active both day and night. However, during the day A. russatus still foraged in significantly more patches and to significantly lower GUDs than during the night. Both species, but in particular A. russatus, preferred to forage in the boulder habitat. Spiny mice foraged in the same number of trays in the under- and between-boulder microhabitats, but to lower GUDs in the under-boulder microhabitat, both during the day (A. russatus) and during the night (both species). The nocturnal A. cahirinus exploited more patches with greater efficiency than did A. russatus either during the day or during the night. This result suggests that foraging trade-offs that give each species a competitive advantage along some portion of the resource axis cannot be a mechanism of nocturnal coexistence between the two species. Perhaps this is why A. russatus resorts to diurnal activity in this hot rocky desert and why the otherwise rare mechanism of temporal partitioning occurs for these species.