Temporal changes in food web structure in semiarid waterholes

Abstract

Semi-arid climate aquatic ecosystems may be highly seasonal due to large-amplitude waterlevel fluctuations. These resulting habitat changes impact aquatic communities and food web structures as a result of species replacement or loss. To study the impact of water-level fluctuations on planktonic food web structure, we compared food web descriptors in contrasting seasons. We examined the planktonic food webs associated with semi-arid natural and artificial waterholes sampled in Hwange National Pak, Zimbabwe, during the hot dry (HDS), wet (WS), and cold dry seasons (CDS). Natural waterholes are filled by rainwater, while water is pumped into artificial waterholes to provide drinking water to wildlife during the dry season. We computed the descriptors of 66 food webs. WS food webs tend to be more complex than those of HDS and CDS; the percentage of basal species was lower, whereas the food web connectance, percentage of intermediate species, omnivory index, mean trophic level, and maximum trophic height of species were higher. Pumping water to maintain pans in the dry season had no effect on food web properties. The drying up of waterholes in semi-arid environments simplifies planktonic food webs. The dominance of small rotifers may explain the observed low omnivory index and food web connectance in HDS compared to those observed in other studies.

Advances in limnological research in Earth's drylands

“…This synergy of drivers may be a great challenge to the management and sustainable use of saline lakes in that region. Hulot et al (2020) analyzed 30 salt pans in Zimbabwe to show how water level fluctuations can influence the aquatic communities and food web structure by the replacement or loss of species. They found seasonal changes in the food webs associated with the simplification of networks during the dry period.…”