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

Chew, Robert; Chew, Alice

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 the energy flow; that of Peromyscus eremicus, the resident species with the lowest and 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 burying Larrea seeds may enhance 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 abou

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

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