Identifying demographic and environmental drivers of recruitment and population growth in a cavity nesting sea duck population

Traits with the greatest proportional effects on fitness are typically conserved (Stearns 1992), and traits with larger temporal variation frequently play a dominant role in population dynamics (Cooch et al. 2001). We examined recruitment patterns and population growth in Common Goldeneyes (Bucephala clangula; hereafter goldeneye), using Pradel mark-recapture models from a long-term nest box study (1997-2010). Our objectives were to estimate recruitment (f) and population growth (λ) relative to recruitment origin group (in-situ or unknown), investigate environmental and density dependent effects on these parameters, and evaluate potential immigration patterns. We detected group-specific differences for f (in-situ: 0.47± 0.13 SE, unknown: 0.31 ± 0.04), and the proportion of boxes occupied by goldeneyes the year prior to recruitment had a significant negative effect on recruitment for the in-situ group (β = -1.04; 85% CI -1.29, -0.78), and a positive effect for the unknown group (β = 0.45; 85% CI 0.30, 0.61). The negative box occupancy effect in the year prior to recruitment, when in-situ yearling goldeneyes prospect for potential nest sites, suggests that local nesting densities may limit recruitment of locally hatched females. We identified two competitive models for λ, which averaged 1.04 ± 0.03 and included interactions between recruitment origin group and a linear temporal trend, and the proportion of ducklings marked two years prior. By evaluating all levels of marking effort on λ, we determined that even if all hatched ducklings were marked in a given year, the resulting in-situ λ was consistently lower than all observed population-level λs during the study, indicating that individuals produced outside of study area nest boxes contributed to λ. Though female goldeneyes are considered highly philopatric, our results suggest that female natal and breeding dispersal may be more prevalent than previously thought, and the spatial scale at which these processes occur requires further investigation.

对适合度（fitness）影响占比最高的性状通常具有进化保守性（Stearns 1992），而时间变异度更高的性状往往在种群动态中占据主导地位（Cooch et al. 2001）。我们基于1997-2010年的长期巢箱监测研究数据，采用普拉德尔标记-重捕模型（Pradel mark-recapture models），对普通鹊鸭（Bucephala clangula；下文简称鹊鸭）的补充招募模式与种群增长情况展开研究。本研究的目标为：估算不同补充招募起源组（本地出生组与未知起源组）对应的补充招募率（f）与种群有限增长率（λ）；探究环境因子与密度依赖效应对上述参数的影响；评估潜在的迁入模式。我们检测到不同起源组的补充招募率存在显著组间差异：本地出生组为0.47±0.13 标准误（SE），未知起源组为0.31±0.04。在补充招募发生的前一年，巢箱占用率对本地出生组的补充招募率存在显著负向影响（β=-1.04；85%置信区间CI：-1.29~-0.78），而对未知起源组则存在显著正向影响（β=0.45；85%CI：0.30~0.61）。当本地出生的1龄鹊鸭探查潜在营巢位点时，招募前一年的巢箱占用率所产生的负向影响，暗示当地营巢密度可能会限制本地孵化雌鸭的补充招募。我们针对种群增长率λ筛选出两个最优竞争候选模型，其模型平均估计值为1.04±0.03，模型中包含补充招募起源组与线性时间趋势的交互项，以及两年前标记的雏鸭比例这一协变量。通过评估不同标记强度对种群增长率λ的影响，我们发现：即便在某一年对所有孵化出的雏鸭都进行标记，由此计算得到的本地出生组种群增长率仍始终低于研究期间观测到的所有种群水平增长率，这表明研究区域巢箱之外产出的个体对种群增长存在显著贡献。尽管鹊鸭被认为具有高度恋巢性（philopatric），但本研究结果显示，雌性个体的出生扩散与繁殖扩散可能比此前认知的更为普遍，而这些过程发生的空间尺度仍需进一步研究。