Shredders play an important role in leaf decomposition in headwater streams; however, their activities can be affected by irregular leaf availability, shredder density, and interactions between species. We performed two experiments to evaluate the effects of interspecific (InterComp) and intraspecific (IntraComp) competition and food availability on survival and leaf consumption of two shredder species, Triplectides egleri and Phylloicus elektoros, of an Amazonian stream. We hypothesized that: (i) shredder density (InterComp and IntraComp experiments) has a negative effect on shredder survival and leaf consumption due to increase in interactions between individuals (e.g. direct encounters) that will lead to competition; and (ii) low food availability (IntraComp experiment) will increase competition among individuals, decreasing shredder survival and leaf consumption. In both experiments, high densities of shredders caused direct encounters between individuals and led to a decrease in survival and leaf consumption. Moreover, In the IntraComp experiment, lower survival and leaf consumption were observed in treatments with low food availability, probably associated with competitive interactions for limited resources. Our results indicate that decreased food availability, increased shredder density, and inter-and intraspecific interactions lead to competition for food and space, resulting in direct encounters between shredders and the occurrence of events such as cannibalism, and/or can inhibit feeding activities (e.g., avoiding conspecifics), thereby decreasing survival and leaf consumption.

碎纸机在源头溪流中的叶子分解中起着重要作用；然而，它们的活动可能会受到不规则的叶片可用性、碎纸机密度和物种之间的相互作用的影响。我们进行了两个实验来评估种间 (InterComp) 和种内 (IntraComp) 竞争和食物可用性对两种切碎机物种Triplectides egleri和Phylloicus elektoros生存和叶片消耗的影响，亚马逊流。我们假设： (i) 切碎机密度（InterComp 和 IntraComp 实验）对切碎机存活率和叶片消耗量有负面影响，因为个体之间的互动增加（例如直接接触）会导致竞争；(ii) 食物供应量低（IntraComp 实验）将增加个体之间的竞争，降低切碎机的存活率和叶片消耗量。在这两个实验中，高密度的碎纸机导致个体之间的直接接触，并导致存活率和叶片消耗量下降。此外，在 IntraComp 实验中，在食物可用性低的处理中观察到较低的存活率和叶片消耗，这可能与有限资源的竞争性相互作用有关。我们的结果表明，食物供应减少，