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首页> 外文期刊>Conservation Biology >Using age structure to detect impacts on threatened populations: A case study with steller sea lions
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Using age structure to detect impacts on threatened populations: A case study with steller sea lions

机译：利用年龄结构检测对受威胁种群的影响：以斯特勒海狮为例

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A delayed response to change is often a characteristic of long-lived species and presents a major challenge to monitoring their status. However, rapid shifts in age structure can occur even while population size remains relatively static. We used time-varying matrix models to study age-structure information as a tool for improving detection of survivorship and fecundity change and status. We applied the methods to Steller sea lions (Eumetopias jubatus), a long-lived endangered marine mammal found throughout the North Pacific Rim. Population and newborn counts were supplemented with information on the fraction of the population that was juvenile, obtained by measuring animals in aerial photographs taken during range-wide censuses. By fitting the model to 1976-1998 data, we obtained maximum-likelihood estimates and 95% confidence intervals for juvenile survivorship, adult survivorship, and adult fecundity in the mid-1980s, late 1980s, and 1990s. We used a series of nested models to test whether the data were best fit by a model with one, two, or three temporal changes in demographic rates, and we fit the models to different lengths of data to test the number of years of data needed to detect a demographic change. The declines in the early 1980s were associated with severely low juvenile survivorship, whereas declines in the 1990s were associated with disproportionately low fecundity. We repeated these analyses, fitting only to the count data without the juvenile-fraction information, to determine whether the age-structure information changed the conclusions and/or changed the certainty and speed with which demographic-rate changes could be detected. The juvenile-fraction data substantially improved the degree to which estimates from the model were consistent with field data and significantly improved the speed and certainty with which changes in demographic rates were detected. [References: 40]
机译：对变化的反应迟钝通常是长寿命物种的特征，并且对监测其状况提出了重大挑战。但是，即使人口规模保持相对不变，年龄结构也会发生快速变化。我们使用时变矩阵模型来研究年龄结构信息，以此作为提高对生存率，生育力变化和状态的检测的工具。我们将这些方法应用于斯特勒海狮（Eumetopias jubatus），这是一种在北太平洋沿岸发现的长寿濒危海洋哺乳动物。人口和新生儿计数补充了青少年人口比例的信息，这些信息是通过在范围普查期间拍摄的航空照片中测量动物而获得的。通过将模型拟合到1976-1998年的数据，我们获得了1980年代中期，1980年代末期和1990年代的青少年生存率，成年生存率和成年生育力的最大似然估计和95％置信区间。我们使用了一系列嵌套模型来测试数据是否最适合人口统计学上具有一个，两个或三个时间变化的模型，然后将模型拟合到不同的数据长度以测试所需数据的年限检测人口变化。 1980年代初期的下降与少年生存率严重降低有关，而1990年代的下降与成年率过低有关。我们重复了这些分析，只适合没有青少年分数信息的计数数据，以确定年龄结构信息是否改变了结论和/或改变了人口统计学变化的确定性和速度。少年分数数据大大提高了模型估计与实地数据的一致程度，并显着提高了人口统计率变化的检测速度和确定性。 [参考：40]

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