EDWARDS, J.S.; univ of Washinton: Sustenance of arthropod populations at high altitude

The high alpine habitat occupies a small fraction of Earth’s total land area. About 20% lies above 1 kilometer, and relatively little of this entails steep altitudinal gradients that bring lowland and alpine environments into proximity. On a broad scale the habitat is rare but it is inhabited by arthropods at all but extreme latitudes. Primary productivity is low or lacking at high altitude, as it is in the ocean depths and yet communities thrive at both extremes in what G.E.Hutchinson termed the Allobiosphere, where transported biomass provides energy and nutrients. The aeolian zone, defined as the name implies in terms of wind-transported materials, is populated by diverse arthropods. The evolutionary success of terrestrial arthropods is due, at least in part, to their capacity for dispersal by active or passive means but one consequence is the deposition at altitude of the derelicts of dispersal; lowland species that ended up on the wrong place. This material provides sustenance for resident and transient predatory and scavenging arthropods. Measurement of the arthropod flux at alpine and subalpine sites in the Pacific Northwest and elsewhere exemplify the taxonomic diversity and significant biomass that sustains bird populations by day and diverse arthropods such as carabid beetles, grylloblattids, spiders and harvestmen by night. The massive transport of lowland species to islands of alpine habitat raise questions concerning the evolution of adaptation to the physiological demands of high altitude where there is continual introduction of lowland genomes.