Lardner Björn, Cade Brian S, Savidge Julie A, Rodda Gordon H, Reed Robert N, Yackel Adams Amy A
Department of Fish, Wildlife, and Conservation Biology Colorado State University Fort Collins Colorado USA.
U.S. Geological Survey, Fort Collins Science Center Fort Collins Colorado USA.
Ecol Evol. 2025 Jul 14;15(7):e71695. doi: 10.1002/ece3.71695. eCollection 2025 Jul.
Somatic growth rate is a fundamental trait that influences metabolism, lifespan and reproductive maturity and is critical for understanding population dynamics and informing management actions. Brown Treesnakes () introduced to Guam are highly invasive and can reproduce year-round without discrete cohorts. We compared snake size trajectories described by the conventionally used von Bertalanffy growth function versus the Gompertz model. Using quantile regression with a regularized effect for individual snakes we modeled growth rates of 270 marked, wild snakes as a function of size. The Gompertz model explained more of the variation in growth and rendered more realistic predictions of asymptotic sizes than did the von Bertalanffy model. With the Gompertz model, growth rates were 1.05-1.16× faster in males than in females. Females reached asymptotic sizes at shorter snout-vent lengths than males. Growth rate was positively correlated with amount of precipitation, and modeling wet-dry seasonality on Guam as a sinusoidal function identified a growth peak in September-October. Effects of seasonality and precipitation, however, were minor compared to individual and sex related differences in size-adjusted growth rates. We estimated that the 50th (and 5th, 95th) growth-rate percentile males in our study population become sexually mature at an age of 33 (∞, 15) months, while females mature at 41 (∞, 18) months, where ∞ indicates that the slowest growing snakes never reach maturity. However, 50% of the snakes mature at a size below the median, and age at maturity may be as low as 10.4 (males) and 13.7 (females) months for average-sized hatchlings that grow fast. Our results have implications for the timing of management options for this species and our approach can be broadly applied to animals where repeated growth data are obtained and age is unknown.
体细胞生长率是一种基本特征，它影响新陈代谢、寿命和生殖成熟，对于理解种群动态和指导管理行动至关重要。引入关岛的棕树蛇具有高度入侵性，能够全年繁殖，没有明显的繁殖群体。我们比较了传统使用的冯·贝塔朗菲生长函数与冈珀茨模型所描述的蛇体大小轨迹。通过对个体蛇采用具有正则化效应的分位数回归，我们将270条有标记的野生蛇的生长率建模为大小的函数。与冯·贝塔朗菲模型相比，冈珀茨模型解释了更多的生长变化，并对渐近大小做出了更现实的预测。使用冈珀茨模型，雄性的生长率比雌性快1.05 - 1.16倍。雌性在比雄性更短的吻肛长度时达到渐近大小。生长率与降水量呈正相关，将关岛的干湿季节变化建模为正弦函数，确定了9月至10月的生长高峰。然而，与大小调整后的生长率中个体和性别相关差异相比，季节性和降水量的影响较小。我们估计，在我们的研究种群中，第50百分位（以及第5百分位、第95百分位）的生长率雄性在33（无穷大，15）个月龄时性成熟，而雌性在41（无穷大，18）个月龄时成熟，其中无穷大表示生长最慢的蛇永远不会达到成熟。然而，50%的蛇在低于中位数的大小就成熟了，对于生长快的平均大小的幼体，成熟年龄可能低至10.4（雄性）和13.7（雌性）个月。我们的结果对于该物种管理措施的时机选择具有启示意义，并且我们的方法可以广泛应用于获得重复生长数据且年龄未知的动物。
