| Milu (Elaphurus davidianus) is classified into Artiodactyla, Cervidae, Elaphurus. It is only one species living of the genus, a large ungulate species, and inhabitating the wetland.In past, Milu distributed widely in the area of middle and downstream of Yangtze River. Milu disappeared in China at the end of 19th century by some causes, such as the change of environment, human disturbing and personal causes. Last a breeding herd of milu, introduced from China, lived in England. The deer was reintroduced to China in 1985 and lived in enclosure. The work of rewilding milu was started in 1998. At present, two rewild populations have been established, Dongting Lake natural rewild population and Dafeng rewild population. The study works mainly were devoted to the populations in enclosure, relatively little to rewild ones.The founder of natural rewild milu population in Dongting Lake area is some deers escaping from Hubei Shishou Milu National Nature Reserve (SMNNR) by big flood in 1998. The population size had increased to about 500 in 2009, and the distribution area also have extended. In the study, we explore the dispersal mechanism and the dynamics for the population to reveal the characteristics of dispersal behaviour and the factors regulating the population. Our results are significant to the protection and management for rewild milu.The escaped Milu found "stepping stones" for further dispersal and established "refuge" populations in the Dongting Lake region south of the Yangtze River. Process of naturally re-wide of Milu is continuing. We recorded 122 dispersals of the re-wild Milu from 1995 to 2012. Milu normally disperse in March, July and November. Peaks of dispersals occurred in 1998,2003,2006 and 2010, respectively. Started from the SMNNR, the Milu dispersed southward along the route "SMNNR-Sanheyuan-Shenfengxiang-Eastern Dongting Lake area-Southern Dongting Lake-Western Dongting Lake". After more than 10 years, the Milu have dispersed to six counties and cities in Hubei and Hunan Provinces. The most north location of the dispersed Milu recorded was 14km from SMNNR while the most south location of dispersed Milu recorded was 49.69km. Average dispersal distance was 14.08 ± 9.03km, with 91.41% of dispersal distances shorter than 25km. Dispersal of Milu could be divided into exploring phase, settle down phase and fast expanding phase. During the exploring phase, Milu actively searched for available remnant habitat patches in anthropogenic landscape as "stepping stones" or "refuges". Milu stayed in a "stepping stone" for a short period whereas established a breeding population in a "refuge"; then population of Milu increased until its population density reached a threshold then the Milu in the population started next dispersal. We found the population density is the ultimate cause for Milu dispersal while floods, human disturbance and seasonal changes of habitat quality are proximate causes. Significance of the study is that an extinct species like Milu can naturally re-wild by searching "stepping stones" and "refuges" to establish metapopulation.In most species of the Cervidae, Male usually is more than female in dispersal rate and longer in dispersal distance. In the study, dispersal behavior of the naturally re-wild milu was investigated to reveal whether the above-mentioned phenomenons exist. From 1995 to 2012, the released population in the area of Dongting Lake, which was released in 1998, had been monitored with focusing on the dispersal behavior by interview survey, followed by fieldwork for confirmation and data acquisition. By sex ratio, the dispersal group is divided into male, female and mixed group.The counts of 122 dispersals by milu were recorded, but only 65 of them can be determined which type of group they belong to (Mixed=26, Female=3, Male=36),60 of them have accurate structure of group with sex ratio (Mixed=23, Female=3, Male=34). Milu is an ungulate with female-defence polygyny, so we test the two hypothesis that:(1) male is more inclined to dispersal than female, (2) the dispersal distance by male is longer than female. the article mainly explores the group structure’s effect on dispersal.The result shows:The dispersal frequency of male group is more than female group and mixed group.50% of male groups in dispersal only include one individual. Dispersal distance by male group is 13.73±8.74 km, female is 8.95±2.16 km, the mixed is 11.05±4.16 km. Despite there is no statistically significant difference in dispersal distance for three types of group (x2=1.896,df=2,P=0.387), Dispersal distances by female groups are shorter than 15 km, so are 89.28% of dispersal by mixed group (others< 25km), and 5.88% by male group are longer than 25km. The three type of dispersal group are different in group size. Mixed group usually have 26.39±15.97 individuals, female is 2.33±1.15, male is 2.74±2.86. The mixed group size is significant greater than female and male (F:F=48.085, df=55, P=0.00<0.05; M:F=5.324, df=24, P=0.00<0.05). Male group dispersal has three peak times every year, individually in March, June and November. Mixed group have four peak times, individually in January, March, July and November. Female have two peak times, individually in March and November.Our data suggests that male is more than female in dispersal tendency and ability. More frequency and longer dispersal distance of male group, especially dispersal of one individual, imply that male is more suitable for dispersal than female. Female group seldom dipersal, but they seemingly do it more with male together. The result of principle component analysis for 7 factors shows that group size and sex ratio affect dispersal distance.By SMNNR’s daily records and our survey records, we obtained a set of population dynamics data about SMNNR population and Sanheyuan subpopulation (SHS) from 2003 to 2012, including adult/calf survival rate, mortality rate and adult female production rate. We make a comparison of some vital rates between both populations to explore how the populations change with population density. Our result reveals the development of SMNNR population can be classified into four stages and the three stages in SHS. There were no significant different in adult/calf survival rate, mortality rate and production rate between SMNNR and SHS. Both populations are regulated by density-dependent factors. There are significantly negative relationships between population sizes and growth rate in the both populations (SMNNR:r=-0.612, P=0.005<0.05; SSP:r=-0.749, P=0.001<0.05), significantly positive relationships between population size and mortality rate (SMNNR: r=0.489, P=0.033<0.05, SSP:r=0.661,P=0.027<0.05). SHS’s population density always are lower than SMNNR in every year. The phenomenon is in accordance with "density compensation theory", that is, the enclosed environment has higher capacity for grazing than open one.The datum of death occuoring during 2003-2013 in SMNNRP and Naturally re-wild Milu population were analyzed. We mainly answer the three questions:what are the factors causing Milu to die? What are the roles of these factors in Milu deer? Do there has a difference in the strength of these factors in both populations? Disease is the most important factor causing Milu to die in SMNNRP and naturally re-wild population,237(43.81%) individuals died in SMNNRP and 76(53.90%) individuals in naturally re-wild population caused by disease. The secondary factor causing death is Anthropogenic. Wire fence of SMNNR threats free-ranging Milu population and caused 7 individuals to die. Fishing net is also a threat to both populations, but the role of fishing net in naturally re-wild population is more important than free-ranging population.The article’s results are useful for the management and protection of naturally re-wild Milu. The study to the mechanism of dispersal not only recruit our kownledge about Milu, and is helpful to the future success of Milu rewild plans and the development of living naturally rewild population by providing some valuable data. The study to the population dynamics can be used in the management rewild and free-ranging population. |
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