Faunal diversity and ecology of a Sonoran Desert cave - Arkenstone Cave, Colossal Cave Mountain Park, Pima County, Arizona, USA

Arizona has a significant cave resource with approximately 1,500 known caves, but our knowledge of the fauna inhabiting these caves remains mostly unknown. This ongoing, long-term study is one of only two such comprehensive efforts to document the faunal diversity and ecology of Arizona caves. Arkenstone Cave is located in the southern foothills of the Rincon Mountains within Colossal Cave Mountain Park, 37 kilometres southeast of Tucson, Arizona, USA. The cave is situated within the eastern and upper elevational limits of the Arizona Upland Subdivision of the Sonoran Desertscrub biome. Caves in the Sonoran Desert region serve as important refugia for relictual arthropod populations of earlier, more mesic times. The long-term study of Arkenstone Cave has revealed a species-rich biota consisting of 72 animals, primarily arthropods, which are ecologically associated with the cave. The species are apportioned to ecological groups as follows: four troglobionts, nine eutroglophiles, 15 subtroglophiles and 44 trogloxenes. There are 66 additional animal species recorded from the cave, consisting of four fossil vertebrate taxa and 62 incidental occurrences. The biology and ecology of each associated species are discussed. The cave food web is supported by allochthonous organic input, primarily the guano of an undescribed cave cricket (Rhaphidophoridae: Ceuthophilus aff. pinalensis Hubbell 1936). Unusual ecological associations include confirmed nesting of three ectoparasitoid Hymenoptera: Ageniella evansi Townes 1957, Auplopus mexicanus Cresson 1867 (Pompilidae) and Liris beatus Cameron 1889 (Crabronidae) in the cave. A fourth parasitoid hymenopteran, Meringopus fasciatus Townes 1962 (Ichneumonidae), a repeat visitor to the cave, is suspected to have a host that lives in the cave. Colossal Cave Mountain Park is the only place in the world currently known to support deep cave-nesting pompilid wasps. Based on current knowledge, Arkenstone Cave is the third most species-rich cave in Arizona.