Multiple Regulation States in Populations of the California Vole, Microtus Californicus

E-ISSN： 1557-7015|56|2|161-181

ISSN： 0012-9615

Source： Ecological Monographs, Vol.56, Iss.2, 1986-02, pp. : 161-181

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Abstract

Two experiments were designed to test which hypothesis of population regulation provided the most consistent explanation of population fluctuations in the California vole. The first experiment tested the effects of spacing behavior and of initial breeding—season density on population regulation. The second experiment tested the effects of resource level, of population history, and of population substructure. A factorial design was used for each experiment. The first experiment was analyzed as two separate factors. The second experiment was analyzed with a 2 × 2 × 2 factorial analysis of variance. The results indicate that naturally occurring populations appear to be regulated by two separate but equally important mechanisms. When habitat occupation is patchy, spacing behavior dominates and densities are regulated below 200 individuals/ha. Individuals from these populations can be characterized as coming from low or early—increase phases. Survival is low due to very high dispersal losses and a moderate mortality rate. Individuals have a greater tendency to be reproductive. Males have lower masses. When habitat occupancy is more uniform, increasing overall density reduces the dispersal rate and, as a result, densities increase further. In this situation, resource limitation dominates the regulation process. Peak densities of these populations range from 500 to 800 individuals/ha. Individuals from these populations can be characterized as coming from the peak phase. Survival is high due to low dispersal losses and a moderate mortality rate. Individuals tend less to be reproductive, and males are heavier.