Population dynamics of kit foxes

We evaluated data from field studies of kit foxes to identify factors that strongly influence or regulate their population dynamics. Two density-depen dent relating mechanisms were detected. First, the rate of juvenile recruit ment was inversely related to the density of adult foxes because a higher p roportion of juveniles were killed by coyotes at higher fox densities. The mortality rates of adult foxes were independent of population density. Seco nd, populations of kit foxes are bounded by their territorial spacing behav ior, which limits recruitment at high densities. These regulatory factors m ay operate in concert to curtail population growth at high densities, where as decreased juvenile mortality by coyotes can operate independently to inc rease population growth at low densities. Despite the presence of these str ong regulating factors, density-independent variations in reproductive rate s often result in population crashes or irruptions that are the fundamental causes of instability in populations of kit foxes. Desert systems are char acterized by unpredictable fluctuations in precipitation, which contribute to high-frequency, high-amplitude fluctuations in the abundance of mammalia n prey (leporids, rodents) for kit foxes. These fluctuations subsequently c ontribute to density-independent variations in fox reproductive rates, whic h are strongly influenced by food supply. Projection models of a kit fox po pulation showed that unpredictable, short-term fluctuations in precipitatio n and, in turn, prey abundance could generate longer term, aperiodic fluctu ations in the density of foxes. Consequently, high amplitude fluctuations i n the abundance of kit foxes may be intrinsic to the desert systems that th ey inhabit and need not reflect special or persistent causes such as predat ion or disease.