Effect of intraspecific and interspecific competition on the facultative and obligatory shredders forage activity in subtropical system

Abstract

Abstract While the significance of competition for resources in shaping the structure of aquatic ecosystems is well recognized, its specific effects on the dynamics of allochthonous matter in streams have received limited attention and remain poorly understood, mainly between interspecific and intraspecific competition. In this study, we investigated the effects of interspecific and intraspecific competition on the shredder organisms Phylloicus and Aegla in leaf litter banks. The impact of competition was assessed through experimental treatments: i - Phylloicus competition-free; ii - Aeglacompetition-free; iii - intraspecific competition within Aegla; iv - intraspecific competition within Phylloicus; v - interspecific competition. In the competition-free treatment, a single organism was placed in a 2-L microcosm, whereas in the competitive pressure treatments, two organisms were placed in a 4-L microcosm, with a 0.05-mm mesh separating them. Our results revealed that interspecific competition had a greater impact on Phylloicus, while intraspecific competition exerted a stronger influence on Aegla. Phylloicusexhibited higher efficiency as a shredder compared to Aegla, which can be attributed to its broader feeding range and unique strategies in leaf litter utilization. The presence of potential competitors led to a reduction in consumption rates in Phylloicus, indicating its sensitivity to competition. Moreover, Aegla's predatory behavior and cannibalism may intensified intraspecific competition within the species. The findings highlight the importance of competition in shaping the feeding activity of shredder organisms in leaf litter banks, which ultimately affects nutrient cycling in aquatic ecosystems.