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Nutritional Bottleneck in a Herbivore, the Desert Wood Rat (Neotoma lepida)

William H. Karasov
Physiological Zoology
Vol. 62, No. 6 (Nov. - Dec., 1989), pp. 1351-1382
Stable URL: http://www.jstor.org/stable/30156217
Page Count: 32
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Nutritional Bottleneck in a Herbivore, the Desert Wood Rat (Neotoma lepida)
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Abstract

The nutritional ecology of desert wood rats (Neotoma lepida) was studied at a site in the Mojave Desert that lacked succulents such as cactus, yucca, and agave. During the late fall and early winter, before winter rains, wood rats ate primarily mature leaves and stems ofcreosote bush (Larrea tridentata), whereas after winter rains they ate newly germinating annuals. Wood rats lost body mass during the prerain period and some were visibly emaciated, whereas they suffered no significant mass loss at other times. In a laboratory feeding trial wood rats would not eat a diet of 100% Larrea but were in energy and N balance when the diet was supplemented with alfalfa pellets (average 74% Larrea, 26% pellets). Because of its H₂O content, Larrea should be marginally adequate in satisfying the wood rat's H₂O requirement. In spite of this, the H₂O flux offree-living wood rats was slightly less the minimum H₂O flux in the laboratory. This suggests that wood rats ate too little of a diet that contained adequate H₂O. Wood rats were apparently deterred from eating enough Larrea to satisfy energy requirements by Larrea's high resin content, but their need to maintain H₂O balanceprobably precluded them from relying heavily on other plant species, all of which contain less H₂O. Thus, until the winter rains and the germination ofannuals, wood rats suffered mass decreases and someprobably died.

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