OCR Text |
Show provides some insight into efficacy of conservation programs. The influence of extinction, translocation, and non- native species introductions on current interpretations of Great Basin endemic aquatic fauna are also examined. Temporal and causal patterns of decline were examined by identifying the decade of first population loss, decade of major decline ( ergo loss of either one- half a taxon's distribution or population), and decade of extinction for 205 endemic taxa ( 98 fish, 91 mollusks, 13 insects, 2 amphibians, 1 amphipod). Availability of status information was greatest for fishes ( 84 spp.) and lower for mollusks ( 23 spp.), insects ( 12 spp.), amphibians ( 2 spp.) and amphipods ( 1 sp.). Population loss has affected approximately 54 percent of taxa for which information is available, and 62 percent of taxa have suffered major declines. Temporal differences in rates of population loss, major decline, and extinction were not significant ( ANCOVA, p > 0.05). Declines and extinctions were first recorded in the late 1800s. Rates were comparatively low until the 1940s and increased to their maxima during the 1960s and 1970s. Rates deceased during the 1980s and 1990s, but remain similar to those observed near the turn of the century. We suggest that declines are attributable to anthropogenic activities. Stream diversions had greatest influence ( 67 spp.), followed by competition and predation by non- native species ( 63 spp.), habitat degradation by livestock grazing ( 33 spp.), species introductions for fisheries management ( 31 spp.), ground water use ( 17 spp.), hybridization ( 7 spp.), and urbanization ( 3 spp.). Most species were impacted by more than one anthropogenic factor ( 1 = 20 spp., 2 = 22 spp., 3 = 24 spp., 4= 12 spp., and 5 = 5 spp.). Anthropogenic activities have influenced regional biogeography by introducing non- native species and altering distributions of native species. Introductions of non- native species have reduced the abundance and distribution of many native |