WESTERN HARVESTER ANTS' FORAGING SUCCESS AND NEST DENSITIES IN RELATION TO GRAZING INTENSITY

Western harvester ants, Pogonomyrmex occidentalis, are seed eaters that occur in short- and mid-grass prairies. Harvester ants are efficient seed predators but they may also be seed dispersers. We examined what ants collect to address that question. We also studied how different cattle grazing intensities affected harvester ant nest densities. Items collected by western harvester ant foragers returning to their nests were categorized as non-seeds, seeds, and nothing. Harvester ants col­ lected large amounts of non-seeds (48%), followed by seeds (33%) and nothing (19%). Western harvester ants tolerate some environmental stress caused by grazing because nest densities were highest in moderately grazed grasslands. Interestingly, other aboveground arthropods in Colo­ rado grasslands are reported to decrease in response to grazing, espe­ cially moderate to heavy grazing regimes. Harvester ants prefer to collect seeds but do not collect them exclusively.

[1]  S. H. Long,et al.  Account of an Expedition from Pittsburgh to the Rocky Mountains , 2009 .

[2]  R. H. Hart,et al.  Plant biodiversity on shortgrass steppe after 55 years of zero, light, moderate, or heavy cattle grazing , 2001, Plant Ecology.

[3]  I. Burke,et al.  Livestock Grazing: Animal and Plant Biodiversity of Shortgrass Steppe and the Relationship to Ecosystem Function , 1998 .

[4]  R. H. Hart,et al.  Grazing intensities, vegetation, and heifer gains: 55 years on shortgrass. , 1998 .

[5]  John A. Wiens,et al.  Scale effects of vegetation on forager movement and seed harvesting by ants , 1994 .

[6]  D. Milchunas,et al.  Quantitative Effects of Grazing on Vegetation and Soils Over a Global Range of Environments , 1993 .

[7]  T. O. Crist,et al.  Harvester Ant Foraging and Shrub‐Steppe Seeds: Interactions of Seed Resources and Seed Use , 1992 .

[8]  James A. MacMahon,et al.  Foraging Patterns of Pogonomyrmex occidentalis (Hymenoptera: Formicidae) in a Shrub–Steppe Ecosystem: The Roles of Temperature, Trunk Trails, and Seed Resources , 1991 .

[9]  R. Nowak,et al.  Prevalence of Oryzopsis hymenoides near harvester ant mounds: indirect facilitation by ants , 1990 .

[10]  W. Lauenroth,et al.  Vegetation associated with nest sites of western harvester ants (Pogonomyrmex occidentalis Cresson) in a semiarid grassland. , 1990 .

[11]  D. Milchunas,et al.  Effects of grazing, topography, and precipitation on the structure of a semiarid grassland , 1989, Vegetatio.

[12]  R. Hobbs.  Harvester ant foraging and plant species distribution in annual grassland , 1985, Oecologia.

[13]  James H. Brown,et al.  EFFECTS OF PREDATION AND COMPETITION ON SURVIVORSHIP, FECUNDITY, AND COMMUNITY STRUCTURE OF DESERT ANNUALS' , 1980 .

[14]  James H. Brown,et al.  An Experimental Study of Competition Between Seed-eating Desert Rodents and Ants , 1979 .

[15]  J. D. Vita.  Mechanisms of Interference and Foraging Among Colonies of the Harvester ant Pogonomyrmex Californicus in the Mojave Desert , 1979 .

[16]  M. Rosenzweig,et al.  GRANIVORY IN NORTH AND SOUTH AMERICAN DESERTS: RODENTS, BIRDS, AND ANTS' , 1978 .

[17]  H. Pulliam,et al.  The Production and Utilization of Seeds in Plains Grassland of Southeastern Arizona , 1975 .

[18]  R. Lavigne,et al.  Environmental Effects of Western Harvester Ants on the Shortgrass Plains Ecosystem , 1974 .

[19]  L. Rogers.  Foraging Activity of the Western Harvester Ant in the Shortgrass Plains Ecosystem , 1974 .

[20]  J. T. Nichols,et al.  Effects of Harvester Ants on Production of a Saltbush Community. , 1966 .

[21]  W. M. Wheeler,et al.  Ants : their structure, development and behavior , 1960 .

[22]  M. Wied,et al.  Travels in the interior of North America during the years 1832-1834 , 2001 .