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The Effect Of Diet On Distribution, Energy And Nitrogen Budget, And Behavior Of Wintering Lesser White-fronted Geese

Posted on:2014-01-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:X WangFull Text:PDF
GTID:1220330398464000Subject:Ecology
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The globally threatened Lesser White-fronted Goose Anser erythropus underwent a rapid decline in abundance and contraction in distribution. Little is known about the status and changes of this species in Yangtze wetlands, the biggest wintering ground in the world. Another unsolved question about this species is its extraordinarily localized distribution, comparing with other species such as the Bean Goose Anser fabalis serrirostris and Greater White-fronted Goose Anser albifrons which widespread within Yangtze River wetlands. In addition, the foraging behavior of wintering Lesser White-fronted Geese is poorly understood. In order to answer these questions, I conducted five studies in this thesis:1. Changes in distribution and abundance of wintering Lesser White-fronted Geese in eastern ChinaThe global population of Lesser White-fronted Geese has decreased rapidly in recent decades. Before this study, the world population estimate of this population was25000to28000, among which c.20000individuals wintered in East Dongting Lake, China. By analyzing published and unpublished data, we present the first distribution, abundance and population changes in recent two decades. After a rapid historical population decline, the geese now highly concentrate at a few sites within East Dongting Lake. The relatively stable numbers at these sites suggest the population is not currently threatened, but the localized distribution makes the species vulnerable. In order for effective conservation, factors contributing to the unique distribution of this species need to be investigated.2. Energy budgets of Lesser White-fronted Geese at different habitat typesAmong factors influencing distribution, food is most likely to determine the distribution of wintering geese. By using the endogenous indigestible marker in plants, we estimated the energy budgets of Lesser White-fronted Geese foraging on two types of habitats. The results show the Alopecurus, Cynodon and Eleocharis, patchily distributed within East Dongting Lake, could provide the geese with overall positive energy budgets through the entire wintering period, while geese failed to maintain the energetic balance by feeding on Carex, the dominant species along Yangtze River wetlands. Our finding explains why Lesser White-fronted Geese are not widely distributed. However, this study also sets two new questions:why the geese foraged on energy-poor Carex, and whether the wide distribution of Greater White-fronted Geese and Bean Geese can be explained from the same perspective.3. Nitrogen budgets of Lesser White-fronted Geese at different habitat typesWhen the main diet is short of some necessary element (for herbivorous geese this element is often nitrogen), consumers may temporarily shift to a rare diet to supplement this nutrient. This may explain species abnormal distributions. Under this hypothesis, we examined the nitrogen budgets of Lesser White-fronted Geese foraging on energy-rich and-poor diets, by using the endogenous indigestible marker in plants. The results show that the energy-rich diet could provide the geese with positive nitrogen budget all through the wintering period, but the energy-poor diet failed to support the geese with nitrogen balance. In conclusion, Lesser White-fronted Geese did not feed on Carex for nitrogen intake, but probably did so as a result of the anthropogenic disturbance.4. The energy budgets of wintering Greater White-fronted Geese and Bean Geese feeding on Carex at Shengjin LakeIf the localized distribution pattern of Lesser White-fronted Geese could be explained by its failure by grazing Carex, the widespread Greater White-fronted Geese and Bean Geese through Yangtze River wetlands should also result from the benefit from grazing Carex. We estimated energy budgets of these two species foraging on Carex at Shengjin Lake, through the entire wintering period. Our results show that both species could gain overall positive energy budgets by grazing Carex through the wintering period. This result explains the wide distribution of both species.5. The unexpected time-activity budgets of Lesser White-fronted Geese on two habitat typesElevated investment in foraging time is usually associated with low food availability or low metabolizable energy intake. But this may not always be the case. Comparing full-day activity budgets through the course of the winter, we found an unexpected difference in activity budgets of wintering Lesser White-fronted Geese Anser erythropus at two sites in close proximity, which differed in vegetation, within East Dongting Lake, China. Counter to expectations, geese fed for significantly more of the time and spent significantly less time resting at the site which provided energy-rich food than the energy-poor one. Given the little time invested in vigilance and aggression, and the absence of other factors influencing activity budgets, we argue that the unexpected differences in investment in feeding activity were primarily shaped by the high quality but low quantity of the food at one site (causing a constraint intake rates that elevated harvest time) and high quantity low quality at the other, where the lower investment in feeding resulted from limits on digestion rate. Our finding urges caution regarding drawing conclusions on energy budgets and food preferences based on activity budgets alone.The five studies provide the first overview of the status and history of Lesser White-fronted Geese, explain the distribution of the Lesser White-fronted Goose and its neighboring Greater White-fronted Geese and Bean Geese from the energetic and nutrient perspectives, find the effect of diet type on behavior and present the first time-activity budgets of Lesser White-fronted Geese on natural habitats during the entire wintering period.
Keywords/Search Tags:Anser albifrons, Anser erythropus, Anser fabalis serrirostris, EastDongting Lake, energy budget, food availability, foraging, nitrogenbudget, Shengjin Lake, time-activity budget, Yangtze wetlands
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