Endangered Species Recovery Program
The Wildlife Society, Western Section, 14 Feb. 1998
byDaniel F. Williams
Consideration of how environmental variation affects separate subpopulations of a species is a central task in devising long-term conservation strategies for species and communities in jeopardy. Here we report on preliminary research designed to discover causes of population fluctuations of endangered giant kangaroo rats. We livetrapped animals on 1.44-hectare plots at three sites during annual 6-day censuses from 1993 to 1997. The Carrizo Plain population fluctuated most during the 5-year period, going from 106 individuals in August 1994 to 0 in August 1997. The Elkhorn Plain population fluctuated the least, with a low of 68 in 1994 and high of 115 in 1995. Numbers of kangaroo rats in the Elkhorn population where significantly correlated with the amount of rainfall during the annual growing season (r = 0.92, P = 0.025), while numbers in the other two populations were not correlated with precipitation (Carrizo r = 0.22, P = 0.721; Lokern r = 0.63, P = 0.253). Though the pattern and amount of rainfall had obvious influences on population dynamics, the population responses to rainfall were not uniform across the spatial scale, indicating that other factors were of importance. We discuss the data in reference to some of those factors.