Wintering Population Ecology Of Greater White-fronted Goose And Bean Goose Along The Middle And Lower Yangtze River Floodplain

Due to habitat loss and habitat degradation,biodiversity around the globe has declined dramatically.The phenomenon is particularly serious along the middle and lower Yangtze River floodplain,where lake area has shrunk by c.43%since late 19th century and wintering Anatidae(geese,ducks and swans)together other waterbirds have declined 75%in the last two to three decades.Studies investigating how and why the abundance and distribution of wintering waterbirds have changed along this floodplain are largely lacking,which however is crucial for the conservation of waterbirds and the restoration of wetland system.Such studies are also in line with the nation's strategic positioning of its priority in ecological and sustainable development of the Yangtze River economic zone.Using Greater White-fronted Goose Anser albifrons and Bean Goose Anser fabalis as focal species,in this thesis we firstly studied their wintering population ecology,e.g.abundance and distribution,habitat use,feeding behaviours and diet compositions.We also investigated the potential causes of such changes in the context of hydrological and wetland changes.Next,since Greater White-fronted Goose and Bean Goose are suggested to share similar ecology niche at their wintering grounds,we investigated the potential mechanism of their coexistence.Finally,many species are in decline due to various environmental stressors,but mortality rate is unknown for most species,Greater White-fronted Goose and Bean Goose included.To develop a fast and accurate way to estimate mortality rate,we constructed a statistical model to derive mortality rate from a population's age distribution.Using this model,the accuracy and feasibility of a series of aging techniques were compared when they are used to determine age and further used to estimate mortality rate.The main findings were summarised as below:Between late 1980s/early 1990s and 2010,Greater White-fronted Goose has dramatically changed its abundance and distribution along the middle and lower Yangtze River floodplain.Its abundance has declined up to 90%,from c.140,000 to less than 20,000(the latest survey indicated that its number was c.490,000 in 2011).The number of this species has declined rapidly at Dongting Lake,while it increased dramatically at Shengjing Lake.Wintering Greater White-fronted Goose along the floodplain solely relies on Carex meadow,its abundance and distribution correlated with Carex areas which has been shaped by hydrology changes.This finding demonstrates that hydrology greatly impacts wetland and biodiversity and thus should be taken into consideration with regards to water resource management and restoration of wetland system.In contrast to Greater White-fronted Goose,Bean Goose uses a wide range of foods and feeding behaviours.Besides Carex,it also feeds on foods such as Trapa fruits,rice and underground parts of plants.Especially in mid-winter,when Carex is potentially in shortage and thus competition with Greater White-fronted Goose is likely to occur,Bean Goose feeds on diverse food items.Besides,high proportion of Bean Goose rest during the day and feed at night time.We speculate that such behaviour changes in mid-winter have facilitated Bean Goose to avoid direct competition with Greater White-fronted Goose.Furthermore,the rapid expansion of Trapa at Shengjin Lake potentially explains the increase of Bean Goose.Facing habitat degradation and habitat loss,Greater White-fronted Goose seems more likely to be affected due to its speciality in habitat use;in contrast,Bean Goose could potentially adapt better due to its diverse diet and flexibility in exploiting various habitats.A statistical model was developed to derive mortality rate based on a population's age distribution.Evaluating using this model indicated that most ageing techniques used for this purpose generated mortality rate with a low accuracy and required high sample size.Otolith ring counts,otolithometry and age-length keys used in fishes outperformed all other aging techniques and generated relatively accurate mortality rate with a sample size that can be feasibly obtained.The statistical model could be used to guide future studies estimating mortality based on age structures.This thesis highlights that hydrological changes greatly impact wetland and waterbirds,providing scientific supports for the restoration of wetland system and water resource management.The innovations of this thesis include 1)for the first we studied the changes of abundance and distribution in Greater White-fronted Goose along the middle and lower Yangtze River floodplain;2)we systematically studied the species'wintering ecology such as its diet compositions and feeding behaviours along the floodplain;3)for the first time we explored the potential reasons that caused its changes of abundance and distribution,in the context of hydrological changes and its wintering ecology;5)we studied the potential mechanisms that allow the coexistence of Greater White-fronted Goose and Bean Goose;6)we developed a statistical model to derive mortality rate based on a population's age structure,which could be used as a tool to calculate mortality rate of geese and other vertebrates.