Variation in annual estimates of effective population size for San Joaquin kit foxes

We used a demographic model to calculate a series of annual N-e/N estimates ((Ne/N)(S)) for a population of the endangered San Joaquin kit fox (Vulpes macrotis mutica) and to identify the demographic parameters explaining significant portions of the variation in (N-e/N)(S) estimates. Demographic data were collected between 1981 and 1995 from adult kit foxes located on the Naval Petroleum Reserves in California. Demographic parameters were estimated by determining the sex of captured adult foxes and monitoring the survival and reproduction of adult foxes fitted with radiocollars. Individual demographic parameters explaining significant portions (P < 0.10) of the variation in (N-e/N)(S) estimates was determined using forward stepwise multiple regression. Estimates of ((Ne/N)(S) were highly variable, ranging from 0.22 to 1.15, (<(x)over bar> = 0.67, SEM = 0.07, n = 14), with a harmonic mean of 0.55. Forward stepwise multiple regression analysis indicated that mean annual female survival ( P = 0.002) and mean annual female reproductive success (P = 0.004) explained significant portions of the variation in estimates of (N-e/N)(S), while mean annual sex ratio (P = 0.159), mean annual litter size (P = 0.406) and mean annual male survival (P = 0.922) did not. Long-term kit fox conservation strategies will probably have to account for wide variation in (N-e/N)(S) ratios and focus on maintaining or expanding the size and connectivity of populations.