Sumerged aquatic plants limit the suitability for trout management of many shallow lakes in the Southwest. Control of these weeds has been achieved by the introduced crayfish Orconectes causeyi. The life history, ecology, and weed-control activities of the crayfish are discussed. Abundant crayfish populations occur over a wide range of elevations in permanent well-oxygenated ponds, lakes and streams where predaceous warm-water fishes are scarce. Weed control is proportional to the crayfish population and proximity of a rocky substrate which is preferred habitat. This crayfish is a tertiary burrower establishing relatively shallow burrows for hibernation and egg hatching periods. It has not damaged dams or irrigation ditches and has been compatible with local agriculture.

Hybrid zones--geographical areas in which the hybrids of two races are found--have attracted the attention of evolutionary biologists for many years, both because they are windows on the evolutionary process and because the patterns of animals and plant variation seen in hybrid zones do notfit the traditional classification schemes of taxonomists. Hybrid zones provide insights into the nature of the species, the way barriers to gene exchange function, the genetic basis of those barriers, the dynamics of the speciation process. Hybrid Zones and the Evolutionary Process synthesizes theextensive research literature in this field and points to new directions in research. It will be read with interest by evolutionary biologists, geneticists, and biogeographers.