Effects of Highways and Highway Construction Activities on Valley Elderberry Longhorn Beetle Habitat.

摘要

Roads not only divide remnant habitats, they also contribute particulates, mineral nutrients, and noise from traffic and construction activities. Particularly susceptible to these effects of roads are species like the threatened Valley elderberry longhorn beetle (Desmocerus californicus dimorphus) whose habitat has been bisected by roads, and whose relatively short movements may limit its use of this network of isolated habitat fragments. Until now, the effects of proximity to highway and highway construction on the beetle, a subspecies endemic to California's Central Valley, and its host shrub, elderberry (Sambucus mexicana), had not been tested. Field studies revealed that dust accumulated faster with greater distances from highways. Deposits within 200 m of roads, however, had increasing concentrations of elements commonly found in vehicle exhaust as evidenced by increases in concentrations of foliar sulfate and manganese. Shrubs near roads also tended to be more stressed (higher water potentials) and lower nutritive quality (higher C:N) than those farther away. Both site and shrub occupancy rates of the beetle were comparable to those found in non-highway sites across the northern Central Valley. Furthermore, beetle emergence occurred following construction activities in two of three construction sites despite simultaneous increases in foliar sulfate and shrub stress. This illustrates that the beetles life cycle could be completed in the presence of nearby construction. While the availability of sites and occupancy of the beetle were low, power analysis revealed that at least large effects could be detected by these surveys of elderberry. Studies of rare species in urban regions are often hampered by difficulties in obtaining data but are especially important for optimizing remaining impacted habitats.