A demographic comparison of two southern elephant seal populations
A demographic comparison of two southern elephant seal populations
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两个南象海豹种群的人口统计比较
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
M. Bester
中科院分区：
文献类型：
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作者：
C. McMahon;H. Burton;M. Bester
1. 为了估计麦夸里岛和马里恩岛的南象海豹同时的特定年龄存活率，从1993年到1997年，海豹在出生后的前3周被标记，并在返回其出生岛时被重新捕获（1994年至2001年）。这些重新捕获构成了标记-重新捕获程序MARK中生存分析的基础。在每个地点收集断奶肿块。2. 马里恩岛的再捕获概率（x26 = 376.480, P < 0.0001）高于麦格理岛。有两个可能的原因：(1)马里恩岛的海豹数量比麦格理岛小，密度也比麦格理岛低；(2)马里恩岛的海豹被拖出的海岸比麦格理岛小，这：(1)便于发现和识别海豹的个体；(2)增加了被拖出海豹的机会。3. 两个岛的年龄特异性生存估计（经断奶前死亡率和标签丢失校正）不同（x2 = 22.264, P < 0.05），而麦格理岛的年龄特异性生存估计始终较高。麦考瑞岛（X 26 = 34.657, P < 0.0001）和马里恩岛（X 26 = 20.373, P = 0.002）雌雄海豹的存活率存在差异。女性的生存估计高于男性。幼海豹（1-3年）的综合生存估计在岛屿之间存在差异，但老年海豹（4-6年）的生存估计没有差异。在生存模型中纳入性别并没有提高模型的性能，因此男性和女性的估计被联合考虑。4. 1993 ~ 1998年雌、雄海豹平均幼崽质量在各岛屿间差异无统计学意义（T 6837 = 1.169, P = 0.242）。麦考瑞岛的年平均幼崽体重为118.8 kg (SD = 27.2, n = 6504)，而马里恩岛的年平均幼崽体重为120.6 kg （SD = 24.7, n = 335）。5. 两个岛屿种群初次繁殖时的平均年龄不同（P < 0.001）。麦考瑞岛首次繁殖的平均年龄为4.68岁，马里恩岛为3.95岁。3岁雌海豹在马里恩岛繁殖（28.7%）多于在麦格理岛繁殖（1.2%）（X 21 = 67.39, P < 0.0001）， 7岁前至少繁殖过一次的比例在马里恩岛大于麦格理岛。我们得出的结论是，20世纪50年代至90年代在太平洋和印度洋地区观察到的象海豹数量减少主要是由南大洋资源限制造成的。包括虎鲸的本地捕食和种内资源竞争在内的一系列因素被认为是造成岛屿间（区域）种群趋势差异的原因。马里恩岛人口的人均资源似乎比麦夸里岛人口的人均资源要多。
1. To estimate concurrent age-specific survival for southern elephant seals at Macquarie and Marion islands, seals were marked from 1993 to 1997 in the first 3 weeks of life and resighted (recaptured) on return to their natal islands (1994-2001). These recaptures formed the basis for the survival analysis in the mark-recapture program MARK. Weaning masses were collected at each location. 2. Recapture probabilities were (X 2 6 = 376.480, P < 0.0001) higher at Marion Island than at Macquarie Island. There are two possible reasons: (1) the population at Marion Island is smaller and less dense than at Macquarie Island and (2) seals hauled out along a smaller section of the coast at Marion Island than at Macquarie Island, which: (1) facilitates the detection and individual identification of seals and (2) increases access to hauled out seals. 3. Age-specific survival estimates (corrected for preweaning mortality and tag loss) differed (X 2 5 = 22.264, P < 0.05) at the two islands and were consistently higher at Macquarie Island. The survival estimates for male and female seals were different at Macquarie Island (X 2 6 = 34.657, P < 0.0001) and Marion Island (X 2 6 = 20.373, P = 0.002). Female survival estimates were higher than male survival estimates. The combined survival estimates for juvenile seals (1-3 years) differed between islands but survival of older seals (4-6 years) did not. The inclusion of gender in the survival models did not improve model performance and hence male and female estimates were considered jointly. 4. The mean wean masses of male and female seals combined from 1993 to 1998 were not different between islands (T 6837 = 1.169, P = 0.242). At Macquarie Island the mean annual wean mass was 118.8 kg (SD = 27.2, n = 6504) while at Marion Island it was 120.6 kg (SD = 24.7, n = 335). 5. The mean age at first breeding was different (P < 0.001) at the two island populations. At Macquarie Island the mean age of first breeding was 4.68 years, and at Marion Island it was 3.95 years. More (X 2 1 = 67.39, P < 0.0001) 3-year-old females breed at Marion Island (28.7%) than at Macquarie Island (1.2%) and the proportion of seals that had bred at least once by age 7 was greater at Marion Island than at Macquarie Island. 6. We conclude that the observed decreases in elephant seal numbers between the 1950s and 1990s in the Pacific and Indian Ocean sectors were driven principally by resource limitation in the Southern Ocean. A conglomerate of factors including local predation by killer whales and intraspecific resource competition is postulated as a cause for the inter-island (regional) differences in population trends. It appears that more resources are available per capita to the Marion Island population than are available to the Macquarie Island population.