In this highly informative post Paul Humphries explains the concepts behind different stream order systems such as Horton’s, Strahler’s and Shreve’s scheme which are widely used in river ecology. Myself, I have applied especially the latter two and incorporated them in our fish dispersal model studies: Strahler’s stream order provides a valuable proxy for stream size when explaining dispersal distances of riverine fish (Radinger and Wolter, 2013). Shreve’s method respectively a modification is applied in the GIS fish dispersal model FIDIMO (Radinger et. al 2013) to split modeled probabilities of upstream fish movement at confluences (like decision points where to go) of rivers.
Here it is also worth to mention a recent publication on the importance of viewing rivers as networks (Attermatt F., 2013, Diversity in riverine metacommunities: a network perspective. Aquatic Ecology, 47:365–377). Attermatt also showed exemplarily the strong relationship between Strahler stream order and catchment size for 3 large European river systems (Rhine, Rhone, Inn).
All animals and plants live within the constraints of their physical environment. But the physical form of the flowing water environment is unique. In the sea, there are, of course, vast distances between one ocean and another and these are typically separated by landmasses. And in terrestrial environments, mountain ranges and large waterbodies like lakes, can separate geographic regions. But if you are a whale, fish, jellyfish, seastar, wildebeast, elk, bear or whatever, moving reasonable distances between one location and another is, generally speaking, pretty straightforward. In streams, things are very, very different. And that is one reason why river scientists have come up with a way of classifying stream channels that tells us in a simple way how large a channel is and something about its location in a drainage basin.
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