Respnse Of Large Anatidae And Waterbird Communities To Environmental Factors In The Middle And Lower Yangtze River

Abundance and distribution of animal is affected by various environmental factors at different scales.Due to human activities,environmental changes have caused many species extinct at local or global scales.It is necessary for us to understand population changes of certain species as well as how environmental factors contribute to it.The middle and lower Yangtze River floodplaine is the most important wintering area in Eastern China.However,most waterbird populations have been decreasing in recent years.Large-bodied Anatidae,including swans and geese,is the most dominant waterbird group in this area.During the last decades,the number of wintering Anatidae in Eastern China has dropped 75%.Previous studies suggested that the bigger the migratory birds are,the more sensitive to environmental changes.Thus,it should be our first priority to learn how and why their population and distribution changed before we make protection strategies or plans.In this paper,1)we firstly compiled survey data for five large-bodied Anatidae in the middle and lower Yangtze River floodplain during 1990s-2016 to evaluate their population trends and distribution changes,2)then we conducted different analyses on their response to environmental factors at multiple tempo-spatial scales(from lake to basin,from single year to long-term),3)further we deducted our conclusion to the whole waterbird community;and 4)finally we described how environmental factors changed in 21 key wetlands in this region and how much risk wintering waterbird would take from such changes.Also,we exemplified the effect of environmental changes on wetland with a true case.Please find our main conclusions in the following text:i.We compiled the long-term survey data of two swans(Whooper Swan and Tundra Swan)and four geese(Swan Goose,Bean Goose,Greater and Lesser white-fronted Goose)in three countries(South Korea,Japan and China)of East Asia during 1990s-2011.Based on these data,we made new population estimates for these species in East Asia Flyway.Also,we found different population trends in South Korea,Japan and China:basically,population in South Korea and Japan has been increasing or stable while fluctuating greatly or decreasing in China.Key sites maps demonstrated the northerner distribution of Whooper Swan,the wider distribution of Bean Goose and the restricted distribution of Swan Goose and Lesser white-fronted Goose in China.ii.Based on our experiment in Shengjin Lake,we found that Individual-area relationship best explained abundance and distribution of two grazing geese(Bean Goose and Greater White-fronted Goose)at lake scale.Food resource and disturbance hypotheses were not supported according to our result.Besides,buffalo grazing would change the food structure as well as nutrient contents,thus to facilitate Greater White-fronted Goose.Abundance and distribution of five large-bodied Anatidae(Tundra Swan,Swan Goose,Bean Goose,Greater and Lesser White-fronted Goose)were best modelled with slope and climate related factors in wetlands of Yangtze River floodplain in 2005.Other factors,such as patch area,food abundance and habitat heterogeneity had minor effects simultaneously.Moreover,we found that National Nature Reserve plays an important role in species conservation while it cannot alter the generally decreasing trends.Accorfing to survey data of five waterbirds(Tundra Swan,Swan Goose,Bean Goose,Greater and Lesser White-fronted Goose)in four key wintering wetlands of Yangtze during 2000-2016,we found that tuber-feeders decreased faster than grazers.Beside,we found habitat quality(i.e.food abundance)was more important than patch area in defining abundance and distribution of grazing waterbirds on larger scales.iii.Based on waterbird survey in the Yangtze of 2005 and 2016,we explored the relationship between abundance and diversity of waterbird community and environmental factors.Comparing with 2005,we found decreased abundance and diversity of waterbird in 2016.Furthermore,we found inundation area(defined by geomorphological feature and water level fluctuation)and water quality(total nitrogen,as the surrogate of nutrient level)were the most important factors determining waterbird abundance and diversity in the Yangtze.vi.We extracted changes of environmental factors in key wetlands in the Yangtze during 1985-2010 and found that:inundation area of most wetlands were fluctuating and no general trends were detected;nutrient level were increasing in more than half of the key wetlands;the trends of climatic factors were clear and general.Thus,these key wetlands,even National Nature Reserves,might suffer habitat degradation and capacity decrease if no further measures are to be taken.Biodiversity conservation,especially conservation of wintering waterbird need to be cared urgently.Our case study emphasized that wetland ecosystem health could be achieved through scientific and appropriate managements thus to benefit both local economy and ecology.We found that different mechanism dominated at different scales.Thus we need to deal with each scales when making conservation plans.The most innovatie contribution of this paper is that we found that inundation area and nutriend level are the most important factors in determining waterbird abundance and diversity.We need to adjust and improve current conservation strategies as well as reserve management based on this finding.