simplest cases an impervious body wall protects the 

 internal fluids, and excess water and salts obtained 

 with the food are excreted (most adult beetles and 

 bugs). Wigglesworth (1938) showed that there is a 

 correlation in mosquito larvae between salt concen- 

 tration of the surrounding medium and degree of devel- 

 opment of the anal papillae (intro. fig. 10). Larvae 

 reared in distilled water had well-developed papillae 

 (functional hypertrophy for chloride uptake), whereas 

 larvae reared in a medium with 0.90 per cent NaCl had 

 greatly reduced papillae. This same phenomenon is 

 observed in nature where salt-marsh mosquitoes are 

 able to adapt to varying degrees of salinity. 



Aquatic Habitats in California 



Probably no area of equal extent in the world can 

 claim a greater variety of aquatic habitats than Cali- 

 fornia. Spanning ten degrees of latitude and nearly 

 15 thousand feet in altitude, the state offers practi- 

 cally every kind of aquatic situation except the arctic 

 tundra and tropical jungle. The average annual precip- 

 itation ranges from 109 inches or more in parts of 

 Del Norte County on the north coast to less than 

 2 inches in Death Valley, and the climate varies 

 from cool and uniform along the coast to extremes of 

 heat and cold in the interior mountains and deserts. 

 To understand the present climate and topography 

 it is necessary to know something of the geological 

 history of the state. 



Evidence from fossils (Camp, 1952) shows that 

 moist climates prevailed throughout most of the 

 Tertiary (70 million years) and that the present period 

 is one of relative aridity. In the Miocene and Pliocene, 

 inland seas occupied such present-day depressions 

 as the Central Valley, the Great Basin, and the south- 

 ern California deserts. In keeping with this kind of 

 climate redwoods were widely distributed over the 

 western United States, and a broad-leaved deciduous 

 forest occurred in many places. More recently the 

 Pleistocene glacial and pluvial periods (the last as 

 recent as 10 thousand years) resulted in a southward 

 extension of boreal faunas and floras and retreat of 

 the southern biotas. Unlike the great ice sheet of the 

 northeastern states, Sierran glaciers were local, 

 cutting cirques and gouging U-shaped valleys with 

 terminal or lateral moraines. These processes, which 

 are still going on to a limited extent, set the stage 

 for the great variety of lakes and streams that are 

 now so characteristic of the Sierra Nevada. Relict 

 glaciers and ice caves now serve as refuges for more 

 northern plants and animals, most of which retreated 

 with the advent of warmer, more arid conditions. 



During this same period "pluvial" lakes extended 

 over wide areas in the Southwest (Hubbs and Miller, 

 1948). Lake Lahontan (including present-day lakes 

 such as Pyramid and Walker in Nevada and arms extend- 

 ing into California and Oregon) and Lake Manly 

 (including Death Valley and parts of Inyo and San 

 Bernardino counties) are examples. These fluctuated 

 from large inland lakes to dry playas. Most of the 

 pluvial lakes are now gone, but a few like Mono Lake 



Utinger: Introduction 



still persii i an. I other i, like Owi tod 



go, depending <>n surface and ground water flui I 



One of the besl known of die deserl ba in I 

 is the Salton Sea. Ii certain thai at one 



the Gulf of California extended northward over 



of the Imperial and Coachella valley- (intTO. fig. I la). 

 Subsequently the Colorado River built up a -ill 



(intro. fig. 11/0, creating an ancient salt-water I 

 This lake had no outlet and, like man) other inland 

 waters of the West, eventually dried up. Mill later, 



possibly during a pluvial period, the Colorado River 



changed its course, emptying into the dry basin rather 

 than into tho Gulf, thus creating prehistoric 1 

 Cahuilla (or Lake LeConte as it i- -ore; lied) 



(intro. fig. lie). This maj have persisted until the 

 time of the early Cahuilla Indians, jud^inr; bj a Legend 

 handed down to the present (Blake, fide, Ilubb- and 

 Miller, 1948). In the last stage but one in the story, 

 the Colorado River again shifted its course and 1 

 Cahuilla dried up. Then, in 1905, the n\er poured 

 water into the basin for a two-year period, forming 

 the Salton Sea which was 17 by IS miles in extent, 

 84 feet in maximum depth, and well below sea level. 

 Since 1907 its area at first slowly decreased by evap- 

 oration and its salinity increased (intro. fig. lid). Now 

 irrigation water is reversing the process. 



Since the last pluvial period geological processes 

 throughout the stale continued as in the past, includ- 

 ing upfaulting and subsidence of Large area-, erosion, 

 and volcanic action. As a result water courses were 

 formed, dammed at various points by moraines, lava 

 flows, or alluvium, and finally reached the sea or 

 disappeared into the underground water table or were 

 lost through evaporation. This happened repeatedly 

 through time, the processes being continuous, so that 

 our present aquatic habitats and the insects that 

 inhabit them are but a momentary stage in physio- 

 graphic and biotic evolution. 



Stream and Lake Classifications 



There have been several attempts by limnologists 

 to classify streams, lakes, and other aquatic habitats 

 for purposes of ecological analysis. Such classifica- 

 tions are doomed from the start because they attempt 

 to fit continuously variable and endlessly diverse 

 situations into stereotyped systems. Nevertheless, 

 the urge to classify runs deep in human nature, and 

 useful generalizations and clearer understanding 

 have resulted from certain broadly based ecological 

 classifications. 



In California the streams and lakes are profoundly 

 influenced in form and distribution by the topography 

 of the land. This is of course a truism, but it is 

 especially striking in regions of high relief. For 

 purposes of analysis Meyer (1951) has divided the 

 state into seven major hydrographic areas and numer- 

 ous drainage basins, subbasins, and stream groups. 

 The biota, too, is determined to a large extent by 

 topography which has largely influenced the migration 

 of floras and faunas. Therefore any stream or lake 

 classification must take into account both physical 



