The Desert Granivory Experiments at Portal

Abstract

Abstract In 1977 D. W. Davidson, 0. J. Reichman, and I began experimental manipulations in the Chihuahuan Desert near the little town of Portal in southeastern Arizona to study interactions among seed-eating rodents and ants and between these consumers and the annual plants that supply their primary food resources. The study site comprises about 20 ha of relatively homogeneous desert shrub habitat and contains 24 plots, each 0.25 ha in area (50 X 50 m), that were randomly assigned to different treatments: removal of some or all rodent or ant species or addition of supplementary seeds. While the plots initially assigned to seed additions and some of the other treatments were changed to additional replicates of rodent and ant removal treatments in 1988, several plots have had all rodents, just kangaroo rats, or all ants removed continuously and other plots have served as unmanipulated controls for the entire 19-year period. In the nearly two decades that we have been manipulating and monitoring a selected group of organisms on a small patch of ground, we have learned a great deal about how they affect each other and how they respond to natural variation-chiefly in climate-in their environment. Numerous papers describing the responses of the desert community to these longterm “press” experiments (see Bender et al. 1984) have been published, but no major review and synthesis of the experimental research program has been written since Brown, et al.’s chapter in Diamond and Case’s Community Ecology (1986).