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Inventory of three beetle species assemblages (Coleoptera: Carabidae, Scarabaeoidea, Tenebrionoidea) from the Chihuahuan Desert of west Texas.

Article Excerpt
Abstract. -- Pitfall traps were used to study the abundance and diversity of three species assemblages of Coleoptera from four proximal sites in the Chihuahuan Desert of the Trans-Pecos region of west Texas. Members of the family Carabidae and superfamilies Scarabaeoidea and Tenebrionoidea were collected from four ecological habitats from September 1999 to September 2000. A total of 994 individuals, representing 53 species of beetles, was collected over the duration of the survey. The tenebrionoids were the dominant assemblage collected, and were only outnumbered by the scarabaeoids at one collecting site (Lower Spring). Carabidae was the least abundant of the three assemblages. The four localities yielded relatively equivalent collections of individuals, yet Camp Site was the least taxonomically diverse and exhibited a beetle fauna consisting primarily of tenebrionoids. Collection sites with water to support a more diverse flora (Sandy Canyon and Upper Spring) also supported a more diverse beetle fauna. This study provides a baseline for continuing arthropod investigations of the desert habitats of the Dalquest Research Site in west Texas.

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The order Coleoptera is the largest and most diverse assemblage of insects (Rieske & Buss 2001). The sheer numbers and taxonomic diversity of beetles commonly dictate that most beetle studies are either restricted geographically or focus on a limited number of families (Arnett & Thomas 2001). Only two works are available that emphasize Chihuahuan Desert beetles of the Trans-Pecos region: a comprehensive study of beetles from a sand dune in Big Bend National Park (Dajoz 2000); and a community assessment of carrion arthropods (Schoenly & Reid 1983). However, beetles comprise an important part of the Chihuahuan Desert arthropod fauna, and have proven to be useful environmental indicators of the region, documenting climatic shifts from the late Pleistocene through Holocene times (Elias & Van Devender 1990).

Pitfall trapping has long been an acceptable method of collecting terrestrial arthropods (Ahearn 1971; Reiske & Buss 2001), in spite of a confounding array of potential biases (Briggs 1960; Thomas & Sleeper 1977; Spence & Niemela 1994; Ward et al. 2001). Nevertheless, this technique provides the opportunity for continuous sampling where the objectives are to generate faunal inventories and to permit assemblage comparisons (Faragalla & Adam 1985).

In 1996, the late Walter W. Dalquest and wife Rose donated 518 ha of land to Midwestern State University for the purpose of fostering biological research. Designated the Dalquest Research Site (DRS), the property straddles the Brewster/Presidio County line and extends along the northern boundary of Big Bend Ranch State Park (Fig. 1). The area is an interface between Bandera Mesa and a rift valley of heavily eroded canyon lands that shelter isolated seeps, springs, and intermittent streams. Vegetation is typical desert scrub, although plant growth is comparatively lush near water sources.

This study stems from an earlier assessment of cursorial spiders at the Dalquest Research Site (Broussard & Horner 2006). This study reports the results of a year of continuous pitfall sampling of beetle diversity from four ecologically diverse sites, emphasizing the three most prominent coleopteran assemblages present: Carabidae (ground beetles and...