Factors Related to Populations Fluctuations in Two Sympatric Lagomorphs in the Mojave Desert

Sosa-Burgos, Lucy

Relative effects of biotic and abiotic factors on two populations of desert lagomorphs are evaluated during a three year period. The Audubon cottontail rabbit (Sylvilagus audubonii), and the black-tailed jackrabbit (I&pus californicus) have very similar patterns of population fluctuations at a site in the Granite Mountains of the Mojave Desert. Their populations were estimated from censuses made every four weeks from June 1987 to June 1990. Perennial and annual cover was evaluated, and coyote density was estimated from the relative abundance of the scats. Time series analysis is used to establish the temporal sequence of each of the variables involved. Both lagomorphs reach high densities during spring and crash to almost zero in late fall. Results indicate that precipitation is followed by a peak in annual plant cover 40 days later, and almost simultaneously, rabbits and hares reach maxima in their populations about 185 days after rainfall. By the time lagomorph populations are at their highest, their main forage species have also attained their highest water content. Simple correlation and multiple regression analysis were used to investigate the best predictors of lagomorph population fluctuations. For the rabbit the best multiple regression model was the one that included: precipitation, annual plants, and Sphaeralcea ambigua, its main food item; and for the jackrabbit: coyote activity, and a combination its six main forage species. A linear stochastic model is proposed in order to explain the fluctuations in the lagomorph populations.

Factors Related to Populations Fluctuations in Two Sympatric Lagomorphs in the Mojave Desert

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