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Southwestern USA, Mexico, Costa Rica. Costa Rica: Cordillera de Tilar‡n, Cordillera Volcanica Central.
In Costa Rica, this species is a strict cloud forest specialist. In the Monteverde area, it is one of the most abundant ants in the cloud forest on the ridge crest, at 1400-1800m elevation. Most Winkler samples from the forest floor contain workers, and baits placed on the forest floor will attract workers. The species decreases in abundance as one descends into the Pe–as Blancas Valley east of Monteverde. It is present at El Aleman, a site at 900m elevation. Just a few kilometers away at Refugio Eladio, at 800m elevation, I have never collected it, in spite of abundant Winkler sampling at the site.
Sampling by Project ALAS along the Barva transect in Braulio Carrillo National Park reveals a similar pattern. The species is abundant in the leaf litter at sites between 1000-1500m. It is absent from the 2000m site and the 500m site.
Although my sampling in the Cordillera de Talamanca is limited, I have taken a few Winkler samples from montane forest sites such as Wilson Botanical Garden and Estacion Biologica Pittier, and I have not found P. austroccidua. The Cordillera Volcanica Central may be the southern limit of this northern element in the Costa Rican fauna.
At the northern end of the range, in the United States, this species inhabits the tops of mountains, often island-like forested habitats surrounded by lowland deserts. In douglas fir forests and pine forests in the Huachuca Mountains and similar areas it nests under stones and dead wood (Trager 1984).
Trager, J. C. 1984. A revision of the genus Paratrechina (Hymenoptera: Formicidae) of the continental United States. Sociobiology 9:49-162.
Found most commonly in these habitats: 141 times found in montane wet forest, 109 times found in cloud forest, 71 times found in cloud forest, mature but probably disturbed, some big trees, bordering road on steep slope, 12 times found in riparian forest, cloud forest along stream, near dairy farm pasture, 2nd growth or disturbed primary, 6 times found in wet forest, 5 times found in oak-juniper woodland, 4 times found in moist forest, 3 times found in mature wet forest, 2 times found in riparian mesophytic forest, 4 times found in cloud forest edge, near dairy farm pasture, some big trees in rocky areas, probably disturbed primary or old second growth, on a steep slope, ...
Found most commonly in these microhabitats: 117 times ex sifted leaf litter, 85 times hojarasca, 81 times ex sifted litter from forest floor, 8 times forest litter, 11 times at bait, 8 times Hojarasca, mature forest, dropping, 10 times ex sifted leaf litter on ground, 6 times Hojarasca, second growth, vegetation only about 4m high, climbing steeply, 4 times Camino casa de Serrano, 2 times Hojarasca, second growth, dropping, 1 times wet for. leaf litter, ...
Collected most commonly using these methods: 112 times Winkler, 106 times Mini Winkler, 90 times miniWinkler, 33 times Berlese, 9 times search, 6 times hand collecting, 10 times baiting, 9 times maxiWinkler, 5 times Malaise, 1 times bait, 2 times fogging, ...
Elevations: collected from 960 - 2280 meters, 1488 meters average