气候变化领域集成服务门户

The River Continuum Concept (RCC) predicts that food webs (and, in particular, invertebrates) of rivers in temperate, forested drainages should exhibit a longitudinal gradient from reliance on terrestrially derived organic matter (e.g., seasonally shed leaves) in the headwaters to autochthonous sources (e.g., algae) in the mid-orders, to suspended material in larger rivers. This prediction has been evaluated by longitudinal comparisons of macroinvertebrate communities in terms of functional feeding groups (FFGs), but such an approach yields only indirect evidence regarding actual food use. To retest this prediction, we investigated invertebrate diets from the Salmon River, Idaho, by examining the gut contents of archived specimens from the longitudinal set of sites sampled in the original 1976 RCC study and by collecting invertebrates from these same sites in 2009. We detected no apparent shifts in diets over the similar to 30-y time span. The importance of allochthonous materials in invertebrate diets differed significantly among sites along the longitudinal gradient. As predicted, it was greatest at the 2nd-order headwater site (30-42% of gut contents, on average) and decreased longitudinally to 10 to 20% at the most downstream site. However, invertebrates at the 2nd-order site also consumed large percentages of autochthonous materials (35-45%), and diets contained from 35 to 75% autochthonous resources across all sites. The shredder (Yoraperla) with the highest density at the most upstream 2nd-order site had gut contents composed of 52 to 81% diatoms depending on season, illustrating the importance of autochthonous resources in the headwaters. Our findings show that measuring shifts in FFG alone without examining actual food resources present in macroinvertebrate diets may lead to erroneous inferences regarding patterns of resource use by macro invertebrates in food webs.