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

Saint Louis University, Saint Louis MO

Investigators

Abstract

The PIs request LTREB support to continue experimental studies in the Chihuahuan Desert near Portal, Arizona. The 20-ha study site contains 24 fenced plots, each 0.25 ha in area. They have maintained the removal of some or all species of rodents and/or ants from 10 plots continuously since 1977 and from an additional 4 plots since 1988. Standardized censuses of rodents, ants, and plants provide invaluable data on responses of individuals, populations, and communities both to experimental perturbations and to background temporal and 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 on winter annual plants; 3) direct effects of competition by kangaroo rats on population densities and species diversity of other seed-eating rodent species; 4) indirect effects of kangaroo rats on vegetation, other rodents, birds, and lizards; 5) reorganization of the entire ecosystem, including large increases in woody vegetation and extinctions, colonizations, or shifts in abundance of many animal species, apparently caused by a change in climate since the late 1970's; 6) regulation of emergent properties, such as species diversity, biomass, and energy use of rodents and plants, within narrow bounds despite large shifts in species composition in response to environmental change. The proposed research for the next five years includes: 1) continuation of experimental manipulations and standardized censuses of rodents, ants, and plants; 2) focus on spatial patterns and processes over a wide range of scales; 3) investigation of the experimental manipulations and functional groups of organisms on ecosystem processes; 4) examination of the dynamics of the ant community; and 5) assessment of the interacting influences of climate, livestock grazing, and fire on the transition between desert shrubland and arid grassland.