66 
Psyche 
[Vol. 88 
invest about equally in the production of males and females. 
Evidence presented suggests that the sex ratio may be ecologically 
determined and that there may be a yearly change in the sex ratio. 
Acknowledgements 
I would like to thank Clay Sassaman, Rodolfo Ruibal, Robert 
Luck and Bert Holldobler for the critical review of the manuscript. 
Walter Whitford provided unpublished information on several 
Pogonomvrmex spp., Charles Kugler provided unpublished data on 
Pogonomyrmex mayri. Jessie Halverson, Cecil Hoff and the U.S. 
Forest Service generously granted permission to conduct the 
investigation on property under their jurisdiction. I am especially 
grateful to Emma MacKay, who assisted in all aspects of the field 
and laboratory work, prepared the figures and made important 
contributions to the manuscript. Kenneth Cooper, Fred Andrews, 
Gary Alpert, David Kistner, and Stewart Peck kindly identified the 
beetles found in the ant nests, and provided much stimulating 
information on the ecologies of the beetles. Oscar Clarke identified 
the plant seeds. 
The research was supported by the Theodore Roosevelt Memori- 
al Fund of the American Museum of Natural History, three Grants- 
in-Aid of Research from Sigma Xi, The Scientific Research Society 
of North America, the Chancellor’s Patent Fund of the University 
of California, and the Irwin Newell Award of the Department of 
Biology of the University of California at Riverside. The Depart- 
ment of Entomology of the Colegio de Graduados of Ciudad 
Juarez, Mexico, paid the costs of publication. 
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