Scorpions are not an exceptionally diverse group of arthropods and, consequently, their communities tend to be simpler than that of many other taxonomic groups of the same rank. For example, a given habitat will typically support an extremely diverse assemblage of spiders or beetles, but at most might support about a dozen scorpion species. Thirteen species have been reported in the immediate vicinity of Loreto in Baja California del Sur, Mexico (Due & Polis 1986); nine species occur sympatrically at the Sauceda Ranch at Big Bend Ranch State Park in Texas (Sissom, unpublished data); eight species are known from the vicinity of South Mountain near Phoenix, Arizona (Williams 1970); four at a site that was extensively studied for 10 years near Palm Springs, California (Polis 2001), and only three in the vicinity of Albuquerque, New Mexico (Bradley and Brody 1984). The farther north on the North American continent (and in Eurasia as well), the less diverse the scorpion fauna. Over most of its range, which includes much of northwestern USA and parts of southern Canada, Paruroctonus boreus is the only scorpion to be found.
At most locations, scorpion diversity is not uniform. What appears to be the main cause of scorpion diversity is habitat diversity, in particular, the nature of the substrate. For example, in much of the Chihuahuan Desert, loose sandy areas are necessary for Paruroctonus utahensis, more consolidated sands for P. gracilior, and rocky outcrops for Vaejovis waueri, Pseudouroctonus apacheanus, and Vaejovis intermedius. Some species, such as Centruroides vittatus, may be more generalized and found in a variety of habitats. If a given area is diverse in landforms and substrates, it will likely hold higher numbers of scorpion species. In some cases, the presence of a species may be linked to the availability of surface cover. For example, higher scorpion diversity and abundance occurs in grassland habitats with rocks, fallen yuccas, and other surface debris than in grassland habitats without these luxuries.
Among the more interesting community interactions are those which involve scorpions of different species, solpugids, and spiders (Polis & McCormick 1986). These insectivorous animals exhibit complex feeding relationships where they prey on each other as well as their usual insect prey, a phenomenon referred to as intraguild predation. Evidence suggests that predation by scorpions, which are often extremely abundant in their communities, is a major factor in determining the population size and structure of their intraguild competitors, in particular spiders (Polis 1993, Polis & McCormick 1986).
Bradley, R. and A. Brody. 1984. Relative abundance of three vaejovid scorpions across a habitat gradient. Journal of Arachnology, 11: 437-440.
Due, A. D. and G. A. Polis. 1986. Trends in scorpion diversity along the Baja California peninsula. American Naturalist, 128: 460-468.
Polis, G. A. 1993. Scorpions as model vehicles to advance theories of population and community ecology: The role of scorpions in desert communities. Memoirs of the Queensland Museum 33(2): 401-410.
Polis, G. A. 2001. Population and community ecology of Desert Scorpions. In: P. Brownell and G. Polis (Eds.), Scorpion Biology and Research. Oxford University Press, New York, 302-316.
Polis, G. A. & S. J. McCormick. 1986. Scorpions, spiders and solpugids: predation and competition among distantly related taxa. Oecologia, 71: 111-116.
Williams, S. C. 1970. Coexistence of desert scorpions by differential habitat preferences. Pan-Pacific Entomologist, 46(4): 254-267.