Interplay between pond size and matrix extent drives odonate diversity patterns in a fragmented landscape

Abstract

Landscape fragmentation impacts freshwater habitats and their quality, affecting aquatic insect assemblages. Adjacent terrestrial areas are important secondary habitats where amphibiotic insects mature, feed, find mates, and move to locate aquatic breeding habitats. Using a factorial design with 27 small and large ponds within small and large natural patches in an exotic tree plantation-fragmented landscape of South Africa, and odonates as model organisms, we investigated (1) how pond size/natural terrestrial patch size interaction affects odonate diversity patterns versus habitat quality variables, and (2) determined whether anisopterans and zygopterans respond differently to landscape fragmentation. Species richness was similar among ponds. However, odonate abundance was highest in large ponds regardless of natural terrestrial patch size. Zygopteran functional richness and diversity was driven by pond and natural patch size, suggesting that zygopterans are sensitive to landscape fragmentation. In contrast, anisopterans were more resilient to fragmentation and more likely to select suitable habitats following water chemistry and vegetation characteristics. Overall, large ponds were occupied by different odonate assemblages compared to small ponds, and occupancy was strongly associated with mobility traits. These findings emphasize that ponds in both small and large natural terrestrial patches have conservation value. A pondscape that represents various pond sizes is important for maintaining regional odonate diversity. Pond conservation needs to be considered in the wider terrestrial context, which host a range of important secondary habitats. Adjacent natural terrestrial habitats also connect nearby aquatic habitats, which enable insects to move across the landscape in response to natural and artificial drivers.