Abstract:

To understand density-dependent processes in a reintroduced free-ranging Milu deer population, we monitored the Milu population in the Hubei Shishou Milu National Nature Reserve (SMNNR) from 1993 to 2013. We collected data on vital rates, including the mortality, survival and birth rate in the population (SMNNRP) using direct divisional counting. We used these data to explore how and if density-dependence regulates the SMNNRP. Our results showed: (1) Based on the annual rate of change of population size, the SMNNRP’s development can be divided into five stages, that is, the stable growth stage (1993-1997), the rapid growth stage (1998-2006), the slow growth stage (2007-2009), the rapidly declining stage (2010) and the population restoration stage (2011-2013). (2) From 1993 to 1997, the population growth rate was 16.60±3.10 (%), and the mortality rate was 4.34±0.93 (%). From 1998 to 2006, the population growth rate was increased to 28.98±3.62 (%), and the mortality rate was 4.35±2.31 (%). From 2007-2009, the population growth rate decreased to 7.36±1.64 (%), and the mortality rate increased to 6.32±2.85 (%). In 2010, an infectious disease caused a significant decrease in population size. From 2011 to 2013, the population growth rate increased to 10.95±4.04 (%), while mortality rate decreased to 5.7±2.03 (%). (3) In SMNNRP, population density was negatively related with population growth rate (r=-0.612, P=0.005<0.01), but was not positively related with the mortality rate (r=0.425, P=0.062>0.05). (4) Throughout all stages, SMNNRP adult and fawn survival rates were relatively stable, except in 2010. In 2010, a disease outbreak caused a spike in deaths, and the survival rates of adults and fawns were 65.05% and 0 respectively. Before and after the disease in 2010, adult survival was 95.40±1.56 (%) and 96.67±0.92 (%) respectively, and fawn survival was 95.79±1.80 (%) and 94.04±2.20 (%) respectively. Survival rates before 2010 did not differ from those after 2010 for either life stage (adult: t=-0.503, df=8, P=0.628>0.05; fawn: t=0.558, df=8, P=0.592>0.05). (5) Neither adult nor fawn survival rates were related to population density in SMNNRP (adult: r= -0.493, P= 0.124>0.05; fawn: r= -0.411, P=0.209>0.05). But there was a negative relationship between the population density and the birth rate (r=-0.902, P=0.000<0.01). Our results implied that density dependence had affected SMNNRP through decreasing birth rates since 2003. The factors regulating this population were classified into density-dependent and environment factors, including flood, disease and human interference. Our study provides information that is useful for the protection and management of free-ranging Milu populations.

Key words: Milu, mortality rate, survival rate, birth rate, species reintroduction, Hubei Shishou Milu National Nature Reserve (SMNNR)