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<br />. <br /> <br />. <br /> <br />Colorado River drainage is attributed to persistent winter winds. <br />Slope and valley winds can disperse food resources, such as seeds <br />and aerially dispersing adult Diptera. <br /> <br />Climatic Change through Time <br /> <br />Biotic parameters in riparian habitats are strongly <br />influenced by changing climatic conditions on circadian, seasonal, <br />annual, long-term (ecological) and geolo~ic (evolutionary) <br />intervals, as demonstrated by the followlng examples of p1ant- <br />herbivore relationships from the Grand Canyon. Stevens (1985) <br />showed that invertebrate herbivore species diversity on Salix <br />exigua changed between diurnal and nocturnal hours in the Grand <br />Canyon. Beaver foraging behavior changed seasonally from <br />predominant browsing on herbs and roots during spring and summer <br />months to predominantly shrub/tree feeding in fall and winter in <br />the Grand Canyon (Ruffner and Clark 1981, unpublished); and <br />Stevens (1985) documented shifts between seasons in invertebrate <br />communities associated with Salix and Tamarix. Drought years <br />(e.g., 1981) changed invertebrate communities on Salix exigua in <br />the Colorado River corridor the Grand Canyon, shifting from <br />predominance of phloem-feeding Homoptera to leaf-chewing Acrididae <br />and Lepidoptera (Stevens 1985). Holocene desiccation has been <br />responsible for the upslope retreat of boreal plant species to the <br />more mesic Canyon rims, altering plant/herbivore interactions. <br />Cenozoic changes in climate resulted in changes in species <br />composition the vertebrate herbivore fauna, as discussed in the <br />previous chapter. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />20 <br /> <br />. <br />