Impacts of competition on juveniles of two sympatric freshwater prawn species from Pampean ecosystems: Palaemon argentinus and Macrobrachium borellii

Competition is an interaction between individuals, either of the same species (intraspecific) or different species (interspecific), involving the contest for limited resources. This interaction can influence individual growth, reproduction, and survival, playing a critical role in regulating population dynamics and modulating community structures. In this study, we assessed the impact of competition type (intraspecific and interspecific) and competition pressure (low and high) on the coexistence of juvenile individuals of two sympatric prawn species commonly found in freshwater environments of South America: Palaemon argentinus and Macrobrachium borellii. To this end, we developed an experimental design to assess how different competition types and pressures affect the survival and growth rates of juveniles of both species, their frequency of use of the provided substrates and shelters, and their priority in obtaining food. The results showed that both the competition type and pressure influenced how these species coexist in experimental aquaria. High-pressure competition affected the survival of both species, with interspecific competition mainly impacting on the survival of P. argentinus and intraspecific competition mainly impacting on the survival of M. borellii. Macrobrachium borellii proved to be the dominant prawn because, under interspecific competition, this species showed higher survival rate, displaced P. argentinus from the spaces and substrates previously used, and secured food before P. argentinus when competitive pressure was high. However, the growth rate of both species was unaffected by either the competition type or pressure. This study provides insights into how competition can influence the ecological dynamics of these sympatric prawn species.