LTREB: Collaborative Research: Experimental Manipulation and Monitoring of the Chihuahuan Desert Ecosystem at Portal

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The PIs request LTREB support to continue experimental studies in the Chihuahuan Desertnear Portal, Arizona. The 20-ha study site contains 24 fenced plots, each 0.25 ha inarea. They have maintained the removal of some or all species of rodents and/or ants from10 plots continuously since 1977 and from an additional 4 plots since 1988. Standardizedcensuses of rodents, ants, and plants provide invaluable data on responses of individuals,populations, and communities both to experimental perturbations and to background temporaland spatial variation in the environment.Results to date demonstrate: 1) complex interannual and seasonal dynamics of rodent, ant,and plant populations; 2) direct effects of seed predation by rodents, birds, and ants onwinter annual plants; 3) direct effects of competition by kangaroo rats on populationdensities and species diversity of other seed-eating rodent species; 4) indirect effectsof kangaroo rats on vegetation, other rodents, birds, and lizards; 5) reorganization ofthe entire ecosystem, including large increases in woody vegetation and extinctions,colonizations, or shifts in abundance of many animal species, apparently caused by achange in climate since the late 1970's; 6) regulation of emergent properties, such asspecies diversity, biomass, and energy use of rodents and plants, within narrow boundsdespite large shifts in species composition in response to environmental change. The proposed research for the next five years includes: 1) continuation of experimentalmanipulations and standardized censuses of rodents, ants, and plants; 2) focus on spatialpatterns and processes over a wide range of scales; 3) investigation of the experimentalmanipulations and functional groups of organisms on ecosystem processes; 4) examination ofthe dynamics of the ant community; and 5) assessment of the interacting influences ofclimate, livestock grazing, and fire on the transition between desert shrubland and aridgrassland.