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Supplement to Arid Lands Resource Information Paper No. 5: Jojoba: A Wax-Producing Shrub of the Sonoran Desert; Literature Review and Annotated Bibliography (1974)

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This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Although reptiles are well known for their low energy requirements and high efficiencies of biomass conversion, few studies have addressed the ecology and energetics of species with very low activity levels. I investigated the ecology and energetics of two such reptilian groups: helodermatid lizards, and viperid snakes. I radiotracked Mexican beaded lizards and three rattlesnake species in their natural environments to determine their activity patterns, the time and energy they invest in activity, home ranges, thermal biology, habitat and other resource use, and behavior. I measured metabolic rates in the laboratory to determine rates of energy use. Beaded lizards had a mean home range of 21.6 ha, an activity peak at 1800 hrs and traveled, on average, 25.3 km during approximately 121 h of surface activity over the year. They had very low metabolic rates during rest. However, helodermatids had maximal rates of oxygen consumption that were among the highest of any lizard measured, a trait that may be adaptive during their intensive male-male agonistic behaviors. Males had significantly higher capacities for aerobic activity than did females. Heloderma horridum can fulfill its annual maintenance energy requirements with a quantity of prey equivalent to approximately 1.4 times its body mass. Rattlesnakes had a mean home range size of 4.6 hectares and traveled, on average, 12.4 km over approximately 95 hours of annual surface activity. Rattlesnakes spent considerable time inactive on the surface, whereas Heloderma spent the vast majority of their time resting in shelters. Heloderma and Crotalus had similar body temperature preferences for activity (around 30 C). Like Heloderma, Crotalus had very low rates of metabolism during rest. A 300-g rattlesnake had a standard metabolic rate only 40% that of other squamate reptiles of similar mass, and could fulfill its yearly maintenance energy requirements with a prey quantity equivalent to 0.93 x its body mass, which could be met with 2-3 large meals. After feeding, free-ranging rattlesnakes exhibited thermophilic responses that varied, in part, due to their reclusive behavior, and thermal constraints in the environment. The temperatures selected for digesting and activity are apparently similar in rattlesnakes.

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An evaluation was made of soil solarization to control Macrophomina phaseolina and Sclerotium rolfsii under the climatic conditions of the Sonoran Desert region of Arizona. Tarping of moist soil with clear polyethylene in the summer was most effective in raising soil temperatures, while tarping during the fall and spring were less efficient. In one summer trial, the maximum temperatures achieved were 7-8 C higher than control plots at 1, 15, and 30 cm depths. In none of the tests was the application of tarp effective in reducing M. phaseolina populations to non-detectable levels. After a six-week summer solarization treatment, S. rolfsii was controlled at the 15-cm but not the 30-cm depth. During a fall treatment control of S. rolfsii was achieved only at the 1-cm depth. After solarization, seeds of Euphorbia lathyris were planted in solarized and control plots. The incidence of M. phaseolina-associated mortality among seedlings planted in solarized plots was always the same as the control plot with the highest disease incidence. The utility of this technique may be limited by the heat tolerance of the target organisms. Studies of bacterial antagonists were initiated to determine their utility in enhancing pathogen control after the solarization treatment. Screening 43 bacterial isolates showed that seven of Pseudomonas fluorescens and one of Serratia marcescens exhibited some form of antagonism toward M. phaseolina, S. rolfsii and Verticillium dahliae in vitro. Antagonism was manifested as a complete inhibition of fungal development or reduced hyphal development coupled with suppression of sclerotial development. The action of the antagonists was found to be fungitoxic or fungistatic rather than fungicidal. None of the four P. fluorescens isolates tested were effective in preventing M. phaseolina infection of E. lathyris seedlings. The ability of these bacteria to prevent sclerotial formation while still permitting hyphal growth may be a useful technique for studying the two phases of the fungal life cycle separately.