Post-weaning survival in kangaroos is high and constant until senescence: Implications for population dynamics

Large herbivores typically have consistently high prime-aged adult survival and lower, more variable, juvenile and senescent survival. Many kangaroo populations undergo greater fluctuations in density than other large herbivores, but age- and sex-specific survival of kangaroos and their response to environmental variation remain poorly estimated. We used long-term capture-mark-recapture data on 920 individuals to investigate the survival component of eastern grey kangaroo (Macropus giganteus) population dynamics. Forage availability and population density were monitored quarterly and included as predictors of survival in Bayesian Cormack-Jolly-Seber models. Annual survival probabilities were estimated for 5 age classes: 0 years (juveniles), 1–2 years (sub-adults), 3–6 years (prime-aged adults), 7–9 years (pre-senescent adults), and ≥10 years (senescent adults). Survival of juveniles varied widely during our 12-year study, ranging from 0.07–0.90 for females and 0.05–0.92 for males. Sub-adult survival was 0.80–0.93 for females and 0.75–0.85 for males, while that of prime-aged adults was ≥0.94 for females and ≥0.83 for males, despite large fluctuations in forage and density. The survival of pre-senescent adults spanned 0.86–0.93 for females and 0.60–0.86 for males. Senescent survival was variable, at 0.49–0.90 for females and 0.49–0.80 for males. Male survival was significantly lower than female survival in prime-aged and pre-senescent adults, but not in other age classes. Although most models supported by WAIC selection included one or a combination of environmental covariates, none of these individual covariates had a discernable effect on survival. Temporal variability in overall survival was mostly due to changes in survival of juvenile and senescent kangaroos. Kangaroo survival patterns are similar to those of ungulates, suggesting a strong role of sex-age structure on population dynamics.

大型有蹄类动物通常具有稳定且较高的壮年成体存活率，而幼体与衰老个体的存活率则更低且波动幅度更大。尽管许多袋鼠种群的种群密度波动幅度大于其他大型有蹄类动物，但针对袋鼠的年龄与性别特异性存活率，以及其对环境变化的响应，目前的估算仍较为匮乏。本研究依托920个个体的长期标志重捕（Capture-Mark-Recapture）数据，探究东部灰袋鼠（Macropus giganteus）种群动态中的存活组分。研究按季度监测食物可获得性与种群密度，并将其作为贝叶斯Cormack-Jolly-Seber模型中存活率的预测变量。本研究对5个年龄组的年存活率进行了估算：0龄（幼体）、1~2龄（亚成体）、3~6龄（壮年成体）、7~9龄（预衰老成体）以及≥10龄（衰老成体）。在为期12年的研究周期内，幼体存活率波动幅度极大：雌性幼体存活率介于0.07~0.90之间，雄性则为0.05~0.92。亚成体存活率方面，雌性为0.80~0.93，雄性为0.75~0.85；尽管食物可获得性与种群密度存在大幅波动，壮年成体的雌性存活率仍≥0.94，雄性≥0.83。预衰老成体的存活率，雌性为0.86~0.93，雄性为0.60~0.86。衰老成体存活率同样存在波动，雌性为0.49~0.90，雄性为0.49~0.80。在壮年成体与预衰老成体中，雄性存活率显著低于雌性，但在其他年龄组中未观察到该差异。尽管通过WAIC（Widely Applicable Information Criterion）筛选得到的多数模型均包含一项或多项环境协变量，但所有单独的协变量均未对存活率产生可检测的影响。种群整体存活率的年度波动主要源于幼体与衰老成体的存活率变化。袋鼠的存活模式与有蹄类动物相似，这表明性别-年龄结构对种群动态具有重要调控作用。