INTERFERENCE COMPETITION AND TEMPORAL AND HABITAT PARTITIONING IN 2 GERBIL SPECIES

We have tested two hypotheses which may explain two different patterns which underlie coexistence in two species of desert gerbils (Gerbillus allenbyi and G. pyramidum). The two patterns are temporal partitioning of foraging activity and shared preference habitat selection. When sympatric, G. pyramidum uses the early part of the night most heavily while G. allenbyi is most active in the late part of the night. Although both species prefer the same habitat type (semistabilized sand dune), in the presence of G. pyramidum, G. allenbyi utilizes mainly the secondary habitat type (stabilized sand dune). The hypotheses are 1) one species is dominant (G. pyramidum) while the other (G. allenbyi) is an energetically more efficient forager, and 2) one species has the ability to quickly harvest seeds in dense resource patches and the other species can harvest seeds profitable at lower resource densities. We tested the hypotheses in an experiment conducted in four enclosed plots. Two additional unfenced plots served as controls. Two of the enclosed plots contained mixed populations of both species while the other two fenced plots contained G. allenbyi only. In contrast to patterns of activity of G. allenbyi with G. pyramidum present, G. allenbyi is also very active early in the night even on the semistabilized dunes when G. pyramidum is absent. The results of the experiment supported the hypothesis that interference is the key factor to understanding the coexistence of the two species. Both the temporal and spatial patterns are the result of the dominant G. pyramidum species excluding the energetically efficient G. allenbyi from the preferred time of activity and habitat type.