Effects of freezing and substratum movement on energy flow food webs in Arctic headwater streams: A habitat template analysis

We tested the hypothesis that a three-dimensional habitat template is a major determinant of community structure and function in streams in Arctic Alaska.  Substratum instability, freezing, nutrient supply, and community attributes were assessed in 20 headwater streams representing five pre-determined stream types: mountain spring, tundra spring, mountain, tundra, and glacier.  Thirteen streams froze, with substratum movement ranging from 0-97%, while seven did not.  The latter streams showed substratum movement ranging from 0-75%.  Trophic basis of production and energy flow food webs, based on gut content analyses, showed that mean food chain length was shorter in streams that froze than in perennial streams, and that food web complexity, estimated using linkage density, was greater in streams that had more stable substrata.  Macroinvertebrate production was highest in spring and tundra spring streams, averaging 137-166 mg m^-2 d^-1.  Estimates of consumption showed diatoms to be the most important food type in most streams, accounting for 69-86% of the basal resources.  However, in mountain streams, which had the highest degree of substratum movement, detritus accounted for ~50% of consumption.  This suggests that a single three-dimensional habitat template can be used to predict food web structure and function across Arctic headwater streams.