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  • Springer  (6)
  • American Association for the Advancement of Science  (1)
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  • 1
    ISSN: 1432-1939
    Keywords: Key words Physiological ecology ; El Niño (ENSO) effect ; Geographic variation ; Gopherus agassizii ; Resource availability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We used the doubly labeled water method to measure the field metabolic rates (FMRs, in kJ kg−1 day−1) and water flux rates (WIRs, in ml H2O kg−1 day−1) of adult desert tortoises (Gopherus agassizii) in three parts of the Mojave Desert in California over a 3.5-year period, in order to develop insights into the physiological responses of this threatened species to climate variation among sites and years. FMR, WIR, and the water economy index (WEI, in ml H2O kJ−1, an indicator of drinking of free water) differed extensively among seasons, among study sites, between sexes, and among years. In high-rainfall years, males had higher FMRs than females. Average daily rates of energy and water use by desert tortoises were extraordinarily variable: 28-fold differences in FMR and 237-fold differences in WIR were measured. Some of this variation was due to seasonal conditions, with rates being low during cold winter months and higher in the warm seasons. However, much of the variation was due to responses to year-to-year variation in rainfall. Annual spring peaks in FMR and WIR were higher in wet years than in drought years. Site differences in seasonal patterns were apparently due to geographic differences in rainfall patterns (more summer rain at eastern Mojave sites). In spring 1992, during an El Niño (ENSO) event, the WEI was greater than the maximal value obtainable from consuming succulent vegetation, indicating copious drinking of rainwater at that time. The physiological and behavioral flexibility of desert tortoises, evident in individuals living at all three study sites, appears central to their ability to survive droughts and benefit from periods of resource abundance. The strong effects of the El Niño (ENSO) weather pattern on tortoise physiology, reproduction, and survival elucidated in this and other studies suggest that local manifestations of global climate events could have a long-term influence on the tortoise populations in the Mojave Desert.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Wild howler monkeys were fed natural fruit and leaf diets in order to determine their ability to assimilate minerals (Ca, P, Mg, Si, Sr, Ba, Fe, Al, Mn, B, Cu, Li, V), and to assess their water and electrolyte budgets by the balance method. Results were extrapolated to the field situation so that the nutritional status of free-living monkeys could be examined in relation to their diet. The figs and young leaves of Ficus insipida and F. yoponensis trees (the most important foods in the dry season) provide adequate amounts of most required minerals, and an abundance of water. However, the copper requirement would not be met by this diet, which also provides only marginal amounts of sodium and phosphorus. These deficiencies may be corrected by consuming other available food items that are rich in Cu, Na or P. These results help explain the diversity that has been observed in the diet of wild howler monkeys, and suggest that these herbivores should feed selectively in order to obtain a nutritionally adequate diet.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 79 (1972), S. 39-62 
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Seasonal water metabolism in the herbivorous desert lizardSauromalus obesus (chuckwalla) was measured with tritiated water (HTO). Electrolyte budgets were obtained from field and laboratory measurements. These data describe the roles of various excretory organs in maintaining balance and permit evaluation of some aspects of the physiological ecology of these lizards. 2. When vegetation was succulent, chuckwallas obtained more than enough water from their food to meet their needs (Table 5). The excess was excreted rather than being stored (Table 1). 3. Although water requirements of chuckwallas maintaining constant weights are low in comparison to some other desert vertebrates, metabolic water production is insufficient to balance losses. These lizards must eat succulent vegetation to maintain water balance. 4. When vegetation was dry (summer), chuckwallas remained in crevices most of the day and did not eat. This behavior resulted in a considerable reduction in water loss. 5. These lizards did not drink rain water. 6. During drought, chuckwallas became dehydrated (Fig. 2), but fractional fluid volumes were maintained at normal levels (Table 1), as were plasma electrolyte concentrations (Table 2). 7. Chuckwallas entered winter dens in October weighing only two-thirds as much as in April (Fig. 1). They did not grow in length during 1970. 8. The diet was always hyperosmotic with K+ predominating, but this load was excreted by the nasal salt glands and as precipitated potassium urate (Table 7). These avenues of electrolyte loss require little water (Table 6), resulting in effective separation of water excretion from electrolyte excretion.
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  • 4
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 °C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O2/g·h, or 24 J/g·h. Total thermal conductance below the TNZ. was 1.8 mW/g·°C, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 °C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1998-12-07
    Print ISSN: 0029-8549
    Electronic ISSN: 1432-1939
    Topics: Biology
    Published by Springer
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  • 6
    Publication Date: 1979-01-01
    Print ISSN: 0029-8549
    Electronic ISSN: 1432-1939
    Topics: Biology
    Published by Springer
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  • 7
    Publication Date: 1972-12-15
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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