BIOGEOGRAPHY ANDCOMMUNITYSTRUCTURE OFNORTHAMERICANSEED-HARVESTERANTS

Abstract

Seed-harvester ants are a dominant and conspicuous insect group throughout arid portions of the southwestern United States and northern Mexico, and they include approximately 75 species. Intense study in the late 1970s and early 1980s led to the paradigm that interspecific competition for limited seed resources is the primary factor that structures seed-harvester ant communities. This review attempts to adjust this paradigm, suggesting that interspecific competition for food is probably less important than previously thought, whereas intraspecific competition is common and strong. Abiotic-habitat factors also have important effects on local species composition and attributes. This review also emphasizes several aspects of seed-harvester ants that have been poorly studied, including historical factors, adaptive radiation, and biogeography, to provide a more detailed evolutionary background for understanding existing species assemblages.

Rapid shifts in Atta cephalotes fungus-garden enzyme activity after a change in fungal substrate (Attini, Formicidae)

“…obs.). This is remarkable, as other ant genera such as Pogonomyrmex, Messor and Pheidole have specialized in seed harvesting (Johnson, 2001). This suggests that grass seeds, as exemplified by rice grains in our study, are unlikely to be a long-term sustainable substrate for the clades of fungi that are domesticated by attine ants, possibly because they lack a full complement of nutrients to sustain garden growth (Champagne et al, 2004).…”

Digging beneath the surface: incipient nest characteristics across three species of harvester ant that differ in colony founding strategy

“…Time could be valuable during founding in that it can be traded off on either nest construction or raising brood (foraging and oviposition). Colonies that get a head start on the latter may have a competitive advantage (Hölldobler and Wilson, 1990;Johnson, 2001;Tschinkel and Howard, 1983), reach reproductive size faster (Vargo, 1988), or be in better condition before a time of dormancy (e.g., winter). Energy and time spent foraging in semi-claustral and facultative species thus may put a constraint on nest construction.…”

“…In more mesic eastern areas (e.g., southeastern Arizona, western Texas and eastern Mexico (Cole, 1968;Johnson, 2000b)), P. rugosus inhabits drier soils with less clay content and is replaced by P. barbatus in wetter areas (Johnson, 2000a, b). Their large size (smaller surface area to volume ratio) allows them to retain more water and serves as an explanation for why they live in soils with more sand (Johnson, 2000a(Johnson, , 2001). Yet, foundresses of this species dig the deepest nests, which seems counterintuitive.…”

“…Thus, reproductive success is solely dependent upon the success of the foundress at initiating a nest. Harvester ant foundresses are subject to predation and desiccation risks (Hölldobler and Wilson, 1990), resulting in a high mortality rate (Hölldobler and Wilson, 1990;Wiernasz and Cole, 2003) that may reach 99% (Gordon and Kulig, 1996;Johnson, 2001;Pfennig, 1995). This indicates that there is likely high selective pressure on foundresses during colony initiation.…”

Mites (Acari) Associated with the Desert Seed Harvester Ant,Messor pergandei(Mayr)

“…This species forms populous, long-lived colonies with an estimated 30,000 to 50,000 workers [7,8]. Its nests have been estimated to span 15.5 m in underground diameter, and extending to a depth of 4 m [2].…”