9420254 HAMRICK The columnar cacti of the North American Sonoran Desert offer an excellent opportunity to analyze how plants interact with their pollinators to produce the patterns of matings that characterize their populations. Each of the four species of cactus to be studied has large, open flowers visited by a shared set of pollinators (i.e. bats, birds, insects). We will establish exclusion treatments to insure that individual flowers are pollinated by a single pollinator type. Genetic analyses at multiple gene locations will then be used to describe the breeding structure of each pollinator-cactus species combination. These analyses will allow us to determine how the different pollinators distribute the pollen of an individual cactus species and will lead to a basic understanding of the relative importance of each pollinator to the overall breeding structure of each cactus species. Knowledge of the roles that different pollinators play in the reproduction of these dominant plant species will allow more effective and efficient management of desert reserves. For example, the determination that bats may disperse pollen long distances leads to the conclusion that the preservation of bat roosts which may be outside of the reserve is an essential component for the maintenance of genetic diversity in the cactus populations. If we find that a large proportion of the effective pollinations are performed by a single pollinator species for each of the cactus species, .the maintenance of this pollinator would be essential to the reproduction of an individual cactus species and to the overall integrity of the Sonoran Desert community.
