Perspectives in Conservation Biology in Southern California: I. Current Extinction Rates and Causes

Perspectives in Conservation Biology in Southern California I. Current Extinction Rates and Causes Tracy Tennant, Michael F. Allen, Fred Edwards Center for Conservation Biology University of California, Riverside July 12, 2001 The state of California houses some of the highest levels of species richness in the world. The California floristic province is considered one of the 18 global biodiversity hot-spots (Wilson 1992). More than one quarter of all plant species found north of Mexico are native to California and about half of these are found only in California. Further, it is estimated that there may be as much as 700 endemic 1 species in the Southern California area and several entire endemic families of invertebrates, vertebrates, and Anniellidae (legless lizards) (Scott, T.A. 2 , personal communication). Based simply on the numbers of species in California, many are likely at risk to becoming threatened, endangered, or extinct. County population (X 1000) Riverside San Bernardino Figure 1. Human population changes and projections in Riverside and San Bernardino Counties. California remains also among the fastest growing states. The human population has been growing rapidly since the gold rush of the 1850’s and, at the decadal time scale, shows no signs of slowing down. The 1998 data from the California Department of Finance suggests the state population of 29.9 million in 1990 will nearly double to 58.7 million by 2040. In Riverside and San Bernardino counties alone, the population is expected to increase by 3.5 to 4-fold (Fig 1). The high number of endemic species with small and Reported no. of extinct species restricted distributions in California means that species Predicted no. of extinct species extinctions will likely be more severe in this state before the rest of the continental U.S. For example, as a result of the reduced number of year-round flowing streams in Southern California, most native freshwater Date fish are now extinct, rare or endangered (Swift et al. Figure 2. Rate of animal species extinctions in California over the 1993). To estimate the rate of animal species past 200 years. extinctions in California, we plotted the cumulative number of extinct animal species against time (Fig 2) using a database compiled by the California State Fish and Game. The data set covers the last 200 years, but it is possible that Native Americans had an Populations native and restricted to a specific region - Not naturally occurring outside a particular region. Scott, T.A., University of California, Riverside, Department of Earth Sciences. ExtinctionFinal2.doc Number of animal species extinct/extirpated Given the unique biological richness and human population pressures in California, the rate of species extinctions in the state may serve as a useful indicator of where species conservation is headed in the rest of the continental U.S. To evaluate this, we examined the rate of animal extinctions in California using data compiled by the California Department of Fish and Game (Wildlife and Habitat Data Analysis Branch), and the rate at which plant and animal species in Regression Equation: California were listed as threatened or endangered y = 57.6942/(1 + e (-(x-1954.9934)/23.4023)) (using U.S. Fish and Wildlife Service data). R^2 = 0.992 Understanding these trends and the underlying causes will help us begin to put extinction and policy into perspective.