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Abstract
Wright fishhook cactus (Sclerocactus wrightiae Benson) is a small barrel cactus endemic to the San Rafael Swell in south-central Utah. It was listed as an endangered species in 1979 due to its small population size, threats of over-collecting, and development associated with oil and gas. Demographic monitoring was initiated in 1993 with the following objectives: to establish permanent plots to monitor growth, fecundity, recruitment, and mortality for at least 10 years; to identify habitat factors positively associated with cacti presence; and to identify important insect visitors and predators. Three permanent plots were located throughout the range of S. wrightiae, and 93 individuals were followed from 1993 to 2000. In general, diameter size class was significantly different (P c 0.001) for all three plots. Size classes 3 and 4 (adults) produced the greatest number of flowers and fruits. Size class 3 produced more flowers and fruits by virtue of its higher density, whereas size class 4 produced more flowers and fruits because of its larger diameter. Mortality exceeded recruitment by a 2.5:l ratio for all plots. At Hanksville, 21 cacti (68%) were recorded dead in 1994, and the remaining 10 individuals and 5 recruits were recorded dead in 1995. No new recruits have been recorded since 1995 at Hanksville. Ord's kangaroo rats and white-tailed antelope ground squirrels were primary mortality sources at Hanksville, and the cactus-borer beetle was the primary mortality source at Giles and Mesa Butte.
Parent Publication
Citation
Kass, Ronald J. 2001. Demographic monitoring of Wright fishhook cactus. In: Maschinski, Joyce; Holter, Louella, tech. eds. Southwestern rare and endangered plants: Proceedings of the Third Conference; 2000 September 25-28; Flagstaff, AZ. Proceedings RMRS-P-23. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 51-58.
