Badger Janelle J, Bowen W Don, den Heyer Cornelia E, Breed Greg A
Department of Biolog y and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, 756100, USA.
Department of Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Dr, Dartmouth, Nova Scotia, Canada.
Ecology. 2020 Jun;101(6):e03024. doi: 10.1002/ecy.3024. Epub 2020 Apr 17.
Individual variation in reproductive ability is a key component of natural selection within populations, driving the evolution of life histories and population responses to changing environmental conditions. Evidence that population density affects individual-level fitness in wild populations is limited, particularly for long-lived animals, which are difficult to observe on a biologically relevant scale. We tested for individual heterogeneity in reproductive performance in female grey seals (Halichoerus grypus) using 35 yr of mark-resighting data at Sable Island, Canada (43.93° N 59.91° W). We used Bayesian generalized linear mixed-effect models and multistate open robust design mark-resight models to investigate whether population size negatively influences individual reproductive performance. We measured reproductive performance in two ways: reproductive frequency (the probability of returning to the island to breed) and annual provisioning performance (the probability of successfully weaning a pup given a female bred). Sighting histories of 1,655 known-aged females with a total of 22,961 pupping events were used for analysis. After accounting for effects of female age, parity, and random year effects, we found that both provisioning performance and reproductive frequency demonstrated a strong, positive correlation with population size. Among-individual variance in reproductive traits and responses to population size indicated considerable heterogeneity in overall reproductive performance. As population size grew, "robust" females increased their reproductive performance more than their more "frail" conspecifics in both reproductive traits, resulting in an amplification of differences among individuals. Consequently, simulations from posterior distributions revealed a large fitness consequence of heterogeneity in this population, with "frail" individuals having 47.1% fewer successful pups than more "robust" females (mean reproductive output ± SD: 9.12 ± 3.77 pups for frail individuals, 16.97 ± 2.94 for robust individuals). Repeatability of overall reproductive performance across environments indicates individual quality may be more influential to lifetime reproductive success than costs associated with reproductive investment. This quantification of relative fitness and its dynamics is crucial to understanding broad evolutionary processes in natural populations.
繁殖能力的个体差异是种群内自然选择的关键组成部分，推动着生活史的进化以及种群对不断变化的环境条件的反应。关于种群密度影响野生种群个体适应性的证据有限，尤其是对于长寿动物而言，因为在生物学相关尺度上对其进行观察很困难。我们利用加拿大黑貂岛（北纬43.93°，西经59.91°）长达35年的标记重捕数据，测试了雌性灰海豹（Halichoerus grypus）繁殖性能的个体异质性。我们使用贝叶斯广义线性混合效应模型和多状态开放稳健设计标记重捕模型，来研究种群规模是否会对个体繁殖性能产生负面影响。我们通过两种方式衡量繁殖性能：繁殖频率（返回该岛繁殖的概率）和年度育幼性能（雌性繁殖后成功哺育幼崽的概率）。分析使用了1655只已知年龄雌性的目击历史记录，这些记录包含总共22961次产仔事件。在考虑了雌性年龄、胎次和随机年份效应后，我们发现育幼性能和繁殖频率都与种群规模呈现出强烈的正相关。繁殖性状的个体间差异以及对种群规模的反应表明，整体繁殖性能存在相当大的异质性。随着种群规模的增长，“强健”的雌性在这两个繁殖性状上的繁殖性能提升幅度超过了“脆弱”的同类个体，导致个体间差异进一步扩大。因此，后验分布的模拟结果显示，这种异质性对该种群的适应性有很大影响，“脆弱”个体成功哺育的幼崽数量比“强健”雌性少47.1%（平均繁殖产出±标准差：脆弱个体为9.12±3.77只幼崽，强健个体为16.97±2.94只）。整体繁殖性能在不同环境下的重复性表明，个体质量对终生繁殖成功的影响可能比繁殖投资成本更大。这种相对适应性及其动态变化的量化对于理解自然种群中的广泛进化过程至关重要。
