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Title: Ecological energetics of the desert tortoise (Gopherus Agassizii): Effects of rainfall and drought

Abstract

To elucidate ecological effects of variation in the temporal distribution of a limiting resource (water in the Mojave Desert), energetics of two free-living populations of desert tortoises (Gopherus [=Xerobates] agassizii) were studied concurrently over 18 mo with use of doubly-labeled water. Field metabolic rates (FMR) and feeding rates were highly variable. This variability was manifested at several levels, including seasonal changes within populations, year-to-year differences within populations, and differences between populations. Underlying observed patterns and contrasts was considerable variation among individuals. Much of the variation in energetic variables was associated with a single climatic variable, rainfall. Seasonal, annual, and interpopulation differences in FMR and foraging rates corresponded to differences in availability of free-standing water from rainstorms. Some differences among individuals were apparently due to differences in proclivity or ability to drink. Tortoises had very low FMRs relative to other reptiles, allowed them to tolerate long periods of chronic energy shortage during a drought. Calculations suggested that tortoises experienced a net loss of energy shortage during a drought and tortoises experienced a net loss of energy on their spring diet of succulent annual plants. If so, tortoises require drier forage to accrue an energy profit, emphasizing reliance on drinking rainwater. Further,more » it suggests that growth (as protein deposition) and net acquisition of energy may be temporally decoupled in desert tortoises, with potential consequences for geographic variation in life history. Energy acquisition and expenditure in desert tortoises are strongly constrained by the contingencies of rainfall, both indirectly through effects on availability and quality of food, and directly through reliance on free-standing water for drinking, which is apparently necessary for achieving a net annual energy profit. 61 refs., 5 figs., 5 tabs.« less

Authors:
 [1]
  1. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
513388
Resource Type:
Journal Article
Journal Name:
Ecology
Additional Journal Information:
Journal Volume: 77; Journal Issue: 6; Other Information: PBD: Sep 1996
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 55 BIOLOGY AND MEDICINE, BASIC STUDIES; POPULATION DYNAMICS; RESPONSE MODIFYING FACTORS; TURTLES; ARID LANDS; ATMOSPHERIC PRECIPITATIONS

Citation Formats

Peterson, C.C. Ecological energetics of the desert tortoise (Gopherus Agassizii): Effects of rainfall and drought. United States: N. p., 1996. Web. doi:10.2307/2265787.
Peterson, C.C. Ecological energetics of the desert tortoise (Gopherus Agassizii): Effects of rainfall and drought. United States. doi:10.2307/2265787.
Peterson, C.C. Sun . "Ecological energetics of the desert tortoise (Gopherus Agassizii): Effects of rainfall and drought". United States. doi:10.2307/2265787.
@article{osti_513388,
title = {Ecological energetics of the desert tortoise (Gopherus Agassizii): Effects of rainfall and drought},
author = {Peterson, C.C.},
abstractNote = {To elucidate ecological effects of variation in the temporal distribution of a limiting resource (water in the Mojave Desert), energetics of two free-living populations of desert tortoises (Gopherus [=Xerobates] agassizii) were studied concurrently over 18 mo with use of doubly-labeled water. Field metabolic rates (FMR) and feeding rates were highly variable. This variability was manifested at several levels, including seasonal changes within populations, year-to-year differences within populations, and differences between populations. Underlying observed patterns and contrasts was considerable variation among individuals. Much of the variation in energetic variables was associated with a single climatic variable, rainfall. Seasonal, annual, and interpopulation differences in FMR and foraging rates corresponded to differences in availability of free-standing water from rainstorms. Some differences among individuals were apparently due to differences in proclivity or ability to drink. Tortoises had very low FMRs relative to other reptiles, allowed them to tolerate long periods of chronic energy shortage during a drought. Calculations suggested that tortoises experienced a net loss of energy shortage during a drought and tortoises experienced a net loss of energy on their spring diet of succulent annual plants. If so, tortoises require drier forage to accrue an energy profit, emphasizing reliance on drinking rainwater. Further, it suggests that growth (as protein deposition) and net acquisition of energy may be temporally decoupled in desert tortoises, with potential consequences for geographic variation in life history. Energy acquisition and expenditure in desert tortoises are strongly constrained by the contingencies of rainfall, both indirectly through effects on availability and quality of food, and directly through reliance on free-standing water for drinking, which is apparently necessary for achieving a net annual energy profit. 61 refs., 5 figs., 5 tabs.},
doi = {10.2307/2265787},
journal = {Ecology},
number = 6,
volume = 77,
place = {United States},
year = {1996},
month = {9}
}