Determinants of Macroinvertebrate Diversity in Karst Springs

The amphipod Gammarus minus is a dominant member of karst springs. It suffers from size-selective predation from sculpin predators; individuals are smaller where sculpins are present. This study aims to identify the relationship between G. minus size and the diversity of benthic macroinvertebrates in karst springs. Samples were collected over four seasons from three springs where sculpins were present, with small G. minus, and three springs where sculpins were absent, with large G. minus. Morphospecies richness was significantly higher in springs with sculpin predators and larger G. minus individuals, and order Insecta was the most diverse taxon observed in both groups. Both Shannon’s and Margalef’s diversity were significantly higher in springs with fish than in springs without, while there was not a significant difference in Simpson’s diversity. Similarly, there was stronger community similarity between springs of the same type (fish present/absent) than between groups, indicating that predator presence, and secondarily G. minus size, is an influencing factor in the diversity of karst springs. This implies that larger G. minus may act as stronger competitors against other macroinvertebrates, decreasing diversity in springs where larger G. minus are present and sculpins are absent.