Usinger: Introduction 



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CALIFORNIA 



Lake Cahuilla 

 \ "*■ " 



Silt deposited by 

 Colorado River 



Colorado River 



Salton Sea 241 feet below level of Gulf 



\ ■» < Colorado River wun/iuuw .mvoi Colorado River 



^^■^^^" SiltDam^*^B| ^^^--5- Silt Oepositr^^lH 



8 probable history of the Salton Sea 

 copyright Lane Publishing Company). 



The distinctions between these faunas (and floras) 

 are striking to the field naturalist but are only evident 

 to the taxonomist after careful analysis of distribu- 

 tional patterns in particular groups. Such analyses 

 must be based on extensive collections from all parts 

 of the state, and it is unfortunate that such collec- 

 tions of aquatic insects have not yet been made, 

 except in a few groups like the mosquitoes. 



Streams 



General faunistic relations apply equally to streams, 

 lakes, and other aquatic situations, but many other 

 features are distinctive for each type of water. Streams 

 are especially susceptible to outside influences and 

 hence are infinitely variable. As a result, our knowl- 

 edge of streams has lagged far behind that of lakes. 

 Nevertheless, certain generalizations have emerged 

 from extensive field investigations, and it may be 

 useful to summarize these and see if they apply to 

 California streams. 



Stream habitats. — Ricker (1934) speaks of the 



"overwhelming variety of habitats presented in streams 

 and rivers." At the same time, certain habitats occur 

 repeatedly within any short section of a stream. For 

 example, there are falls, riffles, runs, and pools in 

 nearly every stream in the world, and bottom habitats 

 including boulders, rubble, gravel, sand, and mud. 

 Also there are endless microhabitats, where each 

 aquatic organism occupies a unique ecological niche 

 with preference for a particular side of a rock, for 

 example, or finds other special conditions different 

 for each stage in its life cycle. The accompany ing 

 figure (intro. fig. 14) shows an assemblage of stream 

 organisms as they might appear on a submerged rock in 

 any stream. The species would be different for each 

 part of the world, but the main groups or their ecolog- 

 ical equivalents would be the same. 



Stream habitats for Yellowstone National Park and 

 other regions of the northwest were classified by 

 Muttkowski (1929) as follows: 



1. Permanent habitats, with native (endemic) biota 



a. White water habitats — falls, cascades, white 

 rapids 



b. Clear rapids and stone bottoms — on and under 

 rocks 



