Restriction of Herbivorous Waterbird Distributions in the Middle and Lower Yangtze River Floodplain in View of Hydrological Isolation

Abstract

Effects of hydrological isolation on species distribution is an active research area in biodiversity protection and management. Lakes in the middle and lower Yangtze River floodplains are irreplaceable wintering grounds for waterbirds on the East Asia – Australasian Flyway. However, more and more lakes in this region have become isolated from the main channel of the Yangtze River and the hydrological connectivity between these lakes and the Yangtze River is deteriorating. This study aims to verify whether herbivorous waterbirds abundance is associated with lake connectivity using synchronous survey data in 23 lakes for the period of 2004–2015. The habitat diversity index, the irreplaceability index and waterbird density were used to evaluate the impact of lake connectivity on herbivorous waterbirds distribution. Our results showed that herbivorous waterbirds distribution was restricted to several better connected lakes although the total numbers of herbivorous waterbird in this region increased over this period. The irreplaceability index of herbivorous waterbirds in connected lakes was significantly higher than that in medium-to-highly isolated lakes. The density of herbivorous waterbirds was lower in highly isolated lakes; but there was an increasing gradient towards the well-connected lakes. Our study demonstrated that hydrological isolation had a significantly negative effect on herbivorous waterbirds.