Niche breadth and trophic diversity:: feeding behaviour of the red swamp crayfish (Procambarus clarkii) towards environmental availability of aquatic macroinvertebrates in a rice field (Portugal)

The red swamp crayfish, Procambarus clarkii (Girard 1852), an alien species in Portugal, may have dramatic effects on aquatic communities by depleting all food resources available, just after its introduction. The purpose of this study was to evaluate, through the concept of niche breadth, whether the diet of this species reflected the temporal changes of aquatic macroinvertebrate availability once it is acclimated. Petraitis' index of niche breadth and Herrera's trophic diversity index were used to evaluate the trophic behaviour of P. clarkii towards available resources over time and intraspecifically (size classes and sex) in a rice field in Portugal. Results from this study showed that the consumption of aquatic macroinvertebrates by P. clarkii reflected their seasonal availability. The high values of niche breadth and trophic diversity indicated resource use according to trophic availability, diversified diets and different individual exploitation of resources regardless of size or sex. These findings suggest that in habitats where P. clarkii is already acclimated, it adjusted its trophic behaviour to the seasonal availability of aquatic macroinvertebrates. The large niche breadth and high trophic diversity presented by P. clarkii enables it to successfully expand its range to new areas, when other environmental conditions are favourable, as has been observed in Portugal and worldwide. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.