湖北石首散养麋鹿种群的调控机制：密度制约下种群产仔率下降

Regulation of free-ranging Milu population in Shishou, Hubei, China:a density-dependent decrease in birth rate

为了探讨散养麋鹿(Elaphurus davidianus)种群密度制约的调控机制,1993–2013年,我们以湖北石首麋鹿国家级自然保护区围栏内的散养麋鹿种群为研究对象,采用分区直接计数法统计麋鹿种群数量,计算种群增长率、死亡率、存活率和产仔率等参数,对麋鹿种群的发展是否受到密度制约影响以及作用于哪些种群参数进行了研究。结果表明:石首麋鹿保护区散养麋鹿种群的发展过程可分为5个阶段,分别为稳定增长阶段(1993–1997年)、快速增长阶段(1998–2006年)、缓慢增长阶段(2007–2009年)、迅速下降阶段(2010年)和种群恢复阶段(2011–2013年)。1993–1997年,种群增长率为16.60±3.10(%),而死亡率为4.34±0.93(%);1998–2006年,种群增长率增加为28.98±3.62(%),死亡率为4.35±2.31(%);2007–2009年,种群的增长率下降为7.36±1.64(%),而死亡率增加为6.32±2.85(%);2010年种群暴发传染性疾病,数量急剧下降;2011–2013年,种群增长率增加为10.95±4.04(%),而死亡率下降为5.70±2.03(%)。Pearson相关性检验结果显示:种群密度与增长率呈极显著负相关(r=–0.612,P=0.005<0.01),与产仔率也呈极显著的负相关(r=–0.902,P=0.000<0.01),与死亡率的相关性不显著(r=0.425,P=0.062>0.05)。独立样本t检验结果显示,2010年之前(1993–2009年)和之后(2011–2013年)的成、幼体存活率分别为95.40±1.56(%)、95.79±1.80(%)和96.67±0.92(%)、94.04±2.20(%),两者差异不显著(成体:t=–0.503,df=8,P=0.628>0.05;幼体:t=0.558,df=8,P=0.592>0.05),这说明密度制约因素未对石首麋鹿保护区散放麋鹿种群的存活率产生明显影响。从2003年起,种群受到密度制约机制的调控,主要表现为产仔率下降,同时也受到了洪水、疾病和人类干扰等环境因素的影响。针对目前石首麋鹿保护区散养麋鹿种群面临的密度制约和环境容纳量等问题,我们提出了应对策略。

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.