ABSTRACT
The insect stage usually filling the ecological niche of an ambusher in a stream is the larva. Mountain streams give aquatic insects the advantage of low water temperatures, permitting the water to maintain high oxygen concentrations. Many of the conditions that must be controlled in an artificial habitat simulating a mountain stream are difficult to reproduce in a laboratory. The fast-flowing streams have disadvantages that outweigh their advantages for most species. There are far fewer species in headwater streams than there are in lowland water bodies. The chapter discusses large mountain ranges are drained by complex systems of streams, making them important locations for encountering insects in the taxonomic groups. Problems in studying the zoogeography of extant species and ongoing changes in their ranges is being made difficult, if not impossible, by the lack of fundamental information on their distribution and changes in their native ranges throughout the world in historical times.
