Prey Refuges in Emergent Vegetation Enhance Diving Beetle (Coleoptera: Dytiscidae) Diversity in Urban Ponds in the Presence of Predatory Fish

Abstract

\n Aquatic plants are important prey refugia for aquatic organisms, and their species richness is positively related with aquatic invertebrate species richness. Yet, little is known about how the quantity of refugia, i.e. aquatic vegetation cover, affect aquatic invertebrate assemblages and their habitat use in different levels of predation risks. Here, we investigated how provision of refugia affects diving beetle (Dytiscidae) species richness and abundance in the presence and absence of fish predators. We found that plant cover affected dytiscid populations differently: (1) At the pond level, dytiscid presence was positively correlated with increasing plant cover, both with and without fish, indicating the importance of emergent plants for aquatic biodiversity. (2) At the microhabitat level, dytiscid species richness and abundance responded positively to increasing plant cover in ponds with fish, but there was no such relationship in fishless ponds, emphasizing that the level of predation risks can alter prey species’ use of prey refugia. Our findings provide evidence that the availability of both vegetated and non-vegetated microhabitats can benefit a diversity of aquatic invertebrates. We suggest maintaining variation in provision of emergent plant cover to retain high habitat heterogeneity in urban ponds to enhance freshwater biodiversity.