Coexistence of three species of desert scorpions by habitat selection.

Abstract

Coexistence is common in nature. Two fundamental conditions must meet for competitive species to coexist. First, at least one environmental dimension must be heterogeneous enough for various species to exploit it. Second, these species must show a certain degree of intrinsic potential to differentiate along this dimension. Organisms living and partitioning in mosaic habitats are often destined to coexist. Here, I propose that habitat selection is one of the major mechanisms promoting coexistence of desert scorpions. I tested this mechanism in a three-species community (Centruroides exilicauda, Vaejovis spinigerus, and Hadrurus arizonensis) in the Tucson Mountain area. The results show (1) Density-independently selected habitats allowed the scorpions to survive but not to coexist. (2) The dynamic nature of density-dependent habitat selection ensured the scorpions coexistence in various situations. The reckless behavior demonstrated by the subordinate species (i.e. foraging in the face of danger from large species) confirmed this point. (3) Life-history characteristics, especially the body size of the scorpions, play a momentous role in positioning the scorpions on the arena of species interaction. Large scorpions always preempt the best habitats and become the dominant species. And small scorpions have to adjust their habitat preferences in deference to the large. C. exilicauda, the smallest species, is the subordinate. Its habitat use was controlled directly by the density of V. spinigerus and indirectly by the density of H. arizonensis. V. spinigerus, the most abundant species, tolerates many habitats. Its habitat use was molded by the density of H. arizonensis. Being the largest and the dominant species, the habitat use of H. arizonensis depended exclusively on its own density. Thus, the correlation of their selective behavior and density fostered the scorpions' coexistence in an ever changing desert environment.