Diet overlap and consumption patterns suggest seasonal flux in the likelihood for exploitative competition among piscivorous fishes

• Published in: Ecology of freshwater fish 2004-12, Vol.13 (4), p.276-284
• Main Authors: Raborn, S.W., Miranda, L.E., Driscoll, M.T.
• Format: Article
• Language: English
• Subjects: bioenergetics; diet overlap; exploitative competition; fish; Freshwater; predator; prey; reservoir
• ISSN: 0906-6691; 1600-0633
• DOI: 10.1111/j.1600-0633.2004.00066.x

–  Competition, both intraspecific and interspecific, among piscivorous fishes (predators) may be more pronounced in reservoirs because of the artificial nature of these systems and the continuous anthropogenic influences that may not allow natural processes to regulate their densities. Most studies attempting to measure the extent of competition are based on predator–prey balance indices that are annual snapshots and do not account for seasonal changes. We sought to identify times during the year when intra‐ and interspecific exploitative competition for prey was most likely among dominant predators in a large reservoir of the south‐eastern United States. The possibility of interspecific competition was measured by examining the seasonal extent of diet overlap based on samples of stomach contents. The likelihood or severity of this competition was indexed by how well predators met their energy needs. We found predators were realising less of their energy requirements during spring and autumn, and diet analyses showed predators overlapped substantially in their use of prey during those seasons. Thus, exploitative competition was most likely or severe during spring and autumn; furthermore, this competition had the potential to be interspecific as evidenced by resource overlap. Resumen 1. La competición intra‐ e inter‐específica entre peces piscívoros (i.e., predadores) puede ser más pronunciada en embalses dada la naturaleza artificial de estos sistemas y la continua influencia antropogénica que pueden no permitir que los procesos naturales regulen sus densidades. La mayor parte de los estudios que han intentado medir esta competición se basan en índices de balance predador‐presa que solo representan imágenes anuales y no incluyen cambios estacionales. Buscamos identificar los momentos del año en los que la competición intra‐ e inter‐específica por las presas es más probable entre los predadores dominantes de un embalse de grandes dimensiones del sur‐este de los Estados Unidos. La posibilidad de competición inter‐específica fue medida examinando el solapamiento alimenticio estacional basado en muestreos de contenidos estomacales. La probabilidad o severidad de esta competición fue cuantificada sobre el nivel en el que los predadores satisficieron sus demandas energéticas. 2. Encontramos que los predadores realizaron menos sus demandas energéticas durante la primavera y el otoño y los análisis de las dietas mostraron que los predadores solaparon substancialm