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Invertebrates <br />This group includes insects, spiders and other arthropods that are <br />extremely abundant in the vegetation types of the South Platte River <br />basin. One insect species, the Pawnee montane skipper butterfly, is rare <br />and the only known population of this species occurs in a 12 -mile section <br />of canyon bottom of the South Platte River between Douglas and Jefferson <br />Counties, Colorado (Figure 1). <br />Human Population <br />The combination of climate and abundant natural resources is responsible in <br />part for the rapid growth of human population within the South Platte River <br />basin. Much of the population growth of the last 2 decades has occurred in <br />the foothills and suburban areas around Denver. On the other hand, several <br />rural communities, particularly in the eastern Plains zone of the basin, <br />have lost population between 1960 and 1970 (Toups Corporation, 1975). <br />Preliminary population figures from the 1980 population census showed that <br />the basin's growth increased from nearly 1.48 million in 1970 to <br />1.96 million in 1980 (Colorado Division of Planning, 1980). For counties <br />in the basin, the average percentage population increase for the period <br />from 1970 to 1980 was 32.3 percent, compared to the entire state's <br />population growth of 30.2 percent during the same period. The population <br />of many suburban and foothills communities increased substantially during <br />this period; whereas, the City and County of Denver actually lost <br />population. Eastern rural counties in the basin also recorded small <br />population gains from 1970 to 1980 compared to population losses in several <br />cases from 1960 to 1970 (Table 1). <br />-16- <br />r_ <br />I <br />n <br />