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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #173144



Submitted to: Journal of Animal and Veterinary Advances
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2004
Publication Date: 9/1/2004
Citation: Nash, M.S., Whitford, W.G. 2004. Understanding an ecological system: an example of temporal and spatial variability of Dorymyrmex (Conomyrma) insana in a stressed system. Journal of Animal and Veterinary Advances. 3(9):631-637.

Interpretive Summary: To understand the behavior of biota, it is necessary to study that biota in the context of space and time variability. If some species or group of species is to be used as ecological indicators, their responses to environmental stress must be examined both spatially and temporally. Biological indicators may respond directly or indirectly to environmental stress. Indirect responses may include behavioral changes or numerical changes. Numerical responses are typically examined by classical statistics where mean values are used to test for differences between treatments. However, behavioral responses may best be examined by the theory of regionalized variables using a geostatistical method (Matheron, 1963, 1971) in order to obtain an explicit solution for spatial variability. During the last decade, the need for biological indicators to assess the condition of an ecological system was introduced (NRC, 1994). These indicators needed to be sensitive to disturbance (e.g., livestock grazing) and to be consistently applied across large areas. In arid rangelands,ants were used as a biological indicator, because ants affect ecosystem processes such as water infiltration, soil nutrient distributions, and compositions of the soil seed bank. Ant species can differ with respect to the physical characteristics of the sites chosen for the construction of nests (Holldobler and Wilson, 1990;Lobry de Bruynand Conacher, 1990; Whitford and DiMarco, 1995). For some species, the distribution and characteristics of the vegetation may be of less importance than soil characteristics such as depth and texture. For other species, the presence of tall plants that provide shade may determine where nests are being constructed (Burbidge et al., 1992; Roth et al., 1994; Perfecto and Snelling,1995). Species respond, therefore, differently to ecosystem structural changes by relocating their colonies or by modifying their foraging behavior (Nash and Whitford, 2001). In this paper, results from a multiyear spatial analysis of pyramid ants (Formicidae: Dorymyrmex insana Buckley) communities exposed to intensive, short-term grazing by cattle and to vegetation restructuring resulting from the removal of honey mesquite, a woody shrub (Fabaceae:Prosopis glandulosa Torrey) in a shrub grass land mosaic will be discussed. D. insana is a small, liquid-feeding ants that is abundant and widely distributed in most habitats on the Jornada Experimental Range. The honey mesquite Shrubs not only provide a reliable food source for liquid-feeding ants, their shade also modifies the soil microclimate (Chew, 1995). An analysis of spatial patterns may provide information that could be used in interpreting the effects of stressors on ecosystem function. Results from the analysis will be used to test a hypothesis that the nest distribution of D. insana is not independent of the honey mesquite shrub cover.

Technical Abstract: The responses of pyramid ants Dorymyrmex (Conomyrma) insana (Buckley) to structural change (removal of an invasive shrub species) and to an environmental stress (short-term, intense grazing by cattle) are presented from an experiment study in Chihuahuan Desert grassland. Spatial and temporal responses of D. insana were examined by analysis of variances, kriging maps, and regression analyses. There were no significant responses of D. insana to grazing. The numerical and spatial responses of ants recorded from pitfall trap data were the same as those recorded from mapping ant nests. The spatial distribution of D. insana nests was a function of the canopy cover of the invasive, woody shrub, honey mesquite (Fabaceae: Prosopis glandulosa Torrey) (r = 0.82) and explained 68% of the variability in nest distribution. The dominant, liquid-feeding ant species (D. insana) responded numerically and spatially to structural change and environmental stress. Spatially referenced data are as important or more important for monitoring ecosystem change than are numerical data.