ABSTRACT

High seasonality of semiarid aquatic ecosystems may be due to large-amplitude water level fluctuations. The 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 semiarid 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 underground 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 tended 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 semiarid 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.

摘要

半干旱水生生态系统的高季节性可能是由于大幅度的水位波动造成的。由于物种替代或丧失，所造成的栖息地变化影响了水生社区和食物网结构。为了研究水位波动对浮游食物网结构的影响，我们比较了不同季节的食物网描述符。我们研究了在干热（HDS），湿热（WS）和冷干季节（CDS）期间，在津巴布韦万基国家公园采样的与半干旱天然和人造水坑相关的浮游食物网。天然水坑被雨水充满，而地下水被泵入人工水坑，以在干旱季节为野生生物提供饮用水。我们计算了66个食物网的描述符。WS食物网往往比HDS和CDS复杂。基础物种的百分比较低，而食物网的连通性，中间物种的百分比，杂食性指数，平均营养水平和最大营养高度则较高。在干旱季节抽水维持平底锅对食物网的性能没有影响。半干旱环境中水坑的干燥简化了浮游食物网。与其他研究相比，小轮虫的优势可能解释了在HDS中观察到的低杂食动物指数和食物网连接性。半干旱环境中水坑的干燥简化了浮游食物网。与其他研究相比，小轮虫的优势可能解释了在HDS中观察到的低杂食动物指数和食物网连接性。半干旱环境中水坑的干燥简化了浮游食物网。与其他研究相比，小轮虫的优势可能解释了在HDS中观察到的低杂食动物指数和食物网连接性。