Food matters: trophodynamics and the role of diet in the invasion success of Procambarus clarkii in an Atlantic Forest conservation area.
Procambarus clarkii is an important invasive freshwater species whose ecological plasticity allows for its establishment in different kinds of environments; such plasticity is also reflected in its diet with two main consequences: invasion success and impact on native biota. In order to investigate P. clarkii's feeding habits, examine how its diet varies both seasonally and among different demographic groups (reproductive males, non-reproductive males and females) and explore the two consequences mentioned above, we investigated the trophic role of this species in an Atlantic Forest conservation area in the city of São Paulo (Brazil). A total of 540 specimens collected monthly over a year were measured and weighed. Their stomachs were weighed and classified according to the degree of stomach fullness. Stomach contents were examined, and animal and plant matter weighed. Food items were identified to the lowest possible taxonomic level and the percentage of occurrence of each item was calculated, as well as the diet diversity. Collected data were compared according to seasons and demographic groups through the Analysis of Similarity and Similarity Percentage Analysis. The percentage of animal weight attributed to stomach weight and the degree of fullness of stomachs did not vary significantly among seasons; however, non-reproductive males had significantly less full stomachs. Diet composition was evenly balanced between plant and animal material for both reproductive males and females, while non-reproductive males consumed a lower proportion of animal matter. The diversity in diet composition was high in all seasons and for all demographic groups, although always slightly lower for non-reproductive males. The percentage of occurrence of food items evidenced high consumption of algae and macrophytes throughout the year. It also reflected the seasonal variation of consumed prey, with a shift in consumption of insects and microcrustaceans in spring and summer to decapods and amphibians in fall and winter. The dissimilarity in diet composition was more pronounced among demographic groups than among seasons, being non-reproductive males the most different, with higher ingesting of less evasive prey. Nonetheless, winter differed from other seasons and was the season with least different food composition among demographic groups, indicating a homogenization in diet composition, which might be due to restricted availability of resources. Procambarus clarkii at Jaraguá State Park demonstrated conspicuous dietary variability and flexibility. The occurrence of filled stomachs indicates that food resources are not a constriction for this population. The species presented a diversified and adaptable diet, foraging on algae and macrophytes, and preying on different vertebrate and invertebrate taxa. Its trophic plasticity favors successful establishment in invaded areas and summed to its notable voracity, P. clarkii offers a wide, variable and significant interaction in food webs, being able to generate major impacts on native species by its feeding habits.