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Energy Relationships of the Mammals of a Desert Shrub (Larrea tridentata) Community

Robert M. Chew and Alice Eastlake Chew
Ecological Monographs
Vol. 40, No. 1 (Winter, 1970), pp. 1-21
Published by: Wiley
DOI: 10.2307/1942439
Stable URL: http://www.jstor.org/stable/1942439
Page Count: 21
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Energy Relationships of the Mammals of a Desert Shrub (Larrea tridentata) Community
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Abstract

A year's study was made of 13 species of mammals in a desert community in southeastern Arizona. Mammal density averaged 17.4/ha: 66% Dipodomys merriami and 10.5% Onychomys torridus. Average biomass was 1130 g/ha: 40% D. merriami and 40% Lepus californicus. Annual energy flow of mammals was 105,950 kcal/ha: 55% by a granivore (D. merriami), 22% by a browser (L. californicus) and 6.5% by an insectivore (O. torridus). 94.6% of the energy flow was spent in maintenance and 5.4% in growth. The secondary productivity of the dominant D. merriami was 1.2% of its energy flow; that of Peromyscus eremicus, the resident species with the lowest and least stable density, was 1.7%. A dominant species may be more important in the cycling of matter in the community, while nondominants may be more important in stabilizing the community and sustaining the higher trophic levels. Since the mammals dissipated only 1.95% of the net annual above ground plant production, their importance must be in their controlling actions on the community rather than in their energy turnover. The mammals got 49.3% of their caloric intake from seeds, destroying about 86.5% of the seed production: 40.9% of their calories were from leaves and stems (1.1% of shoot production). The behavior of D. merriami in shucking and burrying Larrea seeds may enhance the survival of seedlings. The browsing mammals pruned 4% of shrub production (eating only half of this); this pruning may increase productivity of shrubs. The efficiencies with which mammals ate available plant foods were: 2.3% for shrub browse, 2.8% for herbage, 7.4% for cactus, and 86.5% for seeds. Species' efficiencies of ingestion varied from 10.1% for D. merriami to 0.09% for several species. In their secondary production, the mammals directly transferred only 0.016% of the energy of the net above ground plant production to the third trophic level. The amount of plant food available to small mammals in a desert shrub community is about the same as in deciduous forest, but less than in old-field grassland. The percentage of the available food that is used by mammals is about the same in these communities. D. merriami may be adapted to be more efficient in consuming available energy and in utilizing it in growth than are rodents in more productive communities.

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