Population Dynamics of Colonies of Three Species of Ants in Desertified Grassland, Southeastern Arizona, 1958-1981

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Abstract
The demography and temporal and spatial dynamics of colonies were followed over 23 years for the three largest ant species in a desert scrub community: Myrmecocystus depilis (diurnal), M. mexicanus (nocturnal) and Novomessor cockerelli. There is evidence for interactions within and between these species that affect density and longevity, and for a negative association of M. mexicanus and shrubs. All species were conspecifically evenly spaced; M. depilis and N. cockerelli were also evenly spaced from M. mexicanus. The frequency of establishment of new Myrmecocystus nests was inversely related to previously existing densities of colonies within quadrats. Mean life span of Mymecocystus colonies was directly related to the census age of the cohort of colonies. During the 23 years, density of M. depilis varied only .+-. 17% around an overall mean, whereas density of M. mexicanus increased 11-fold and that of N. cockerelli declined 56%. Entrances to M. mexicanus nests were never found under shrub canopies, whereas M. depilis was independent of cover.