Ecological scaling of aerobiological dispersal processes

A variety of organisms change their geographic locations during their life history, and many use the atmosphere to accomplish this shift. Biota that h ow in the atmosphere range from very small (viruses, bacteria, pollen, and spores) to quite large (weed seeds, aphids, butterflies and moths, songbird s, and waterfowl). As these organisms move, they experience meteorological and ecological conditions that occur at a wide range of spatial and tempora l scales. We present an ecological scaling approach that integrates concept s and elements of spatial and temporal scaling to understanding aerobiology and provide examples of the ecological scales important to the long-distan ce aerial movement of organisms and associated biological events and proces ses. An operational framework for ecological scaling of long distance biota move ment is achieved by linking spatially-static ecoregion classification syste ms with temporally-dynamic measures of vegetation phenology. The ecoregions provide ecological boundaries for the phenological dynamics of plants. Ope rationally, this approach integrates the bi-weekly vegetation greening indi ces (NDVI) derived from AVHRR or TM satellite data (representing temporal s caling) with the less dynamic land cover-land use classification (IGBP) and the relatively static ecoregion boundaries (representing the spatial scali ng). We argue that the correlation of the life histories of species, especi ally the timing of take-off to ecosystem phenology through meteorological-b ased variables and indices (e.g., degree days and moisture indices), allows for dynamic characterization of source ecosystems and can be used to param eterize atmospheric models to forecast the flow of biota in the air. The scale of these processes, the diversity of the types of biota involved in long-distance movement, and the complexity of the processes require syst ems thinking. We anticipate that this paper will stimulate studies to enhan ce our understanding of the flow of organisms in the biosphere. (C) 1999 Pu blished by Elsevier Science B.V. All rights reserved.