Department of Biological Sciences, East Tennessee State University, Johnson City, Tennessee, USA.
Natural Resources and the Environment, University of New Hampshire, Durham, New Hampshire, USA.
J Anim Ecol. 2024 Sep;93(9):1303-1315. doi: 10.1111/1365-2656.14148. Epub 2024 Jul 28.
Following a resource pulse, animals may finance reproduction by consuming concurrently available resources (income breeding) or by storing resources for future reproduction (capital breeding). Understanding how these reproductive strategies are used is important for determining the ecological mechanisms that structure timing of reproduction and that drive interannual population fluctuations in animals. We gathered a reproductive dataset for five small mammal species over a 12-year period in Northeastern USA during which six masting events of American beech (Fagus grandifolia) and eastern hemlock (Tsuga canadensis) occurred. Masting created alternate years where seeds were either available late (masting year) or early (cached from the previous year) in the breeding season. The small mammal species differed in reliance on seeds and overwintering strategies. We quantified the diet using stable isotopes and recorded reproduction timing, proportion breeding and litter size in females and testes size in males. Timing of seed availability minimally affected litter size but strongly affected proportion breeding and timing of reproduction. During masting years (late seed availability), a higher proportion of females reproduced, with breeding taking place later in the season (lactation timed with peak seed availability), although the delay was restricted in Napaeozapus insignis, an obligate hibernator. After a fall mast, cached seeds were used as capital in the following spring (early seed availability) to support a litter that, depending on the species, occurred 24-79 days sooner than a mast year. No late-season reproduction occurred in years with early seed availability except for Myodes gapperi which produced a second litter, likely financed by fungal consumption. Males also showed strong responses to seed availability, mirroring female reproduction with testes size staying constant in years with late seed availability and sharply decreasing over the breeding season in years with early seed availability. Our results highlight that although photoperiod and temperature broadly set bounds of the breeding season in temperate environments, resource availability influences the reproductive strategies that species use, which in turn alters reproductive timing and can drive large inter-annual population fluctuations. Differences in overwintering strategies and diet may further modulate reproductive timing and output relative to resource pulses.
在资源脉冲之后，动物可以通过消耗同时可用的资源（收入繁殖）或储存资源以备未来繁殖（资本繁殖）来为繁殖提供资金。了解这些繁殖策略是如何被利用的，对于确定控制繁殖时间的生态机制以及驱动动物年际种群波动的因素非常重要。我们收集了美国东北部 5 种小型哺乳动物在 12 年期间的繁殖数据集，在此期间，发生了 6 次美洲山毛榉（Fagus grandifolia）和东部铁杉（Tsuga canadensis）的结实事件。结实导致种子在繁殖季节要么在当年晚些时候（结实年）供应，要么在当年早些时候（从前一年储存）供应。这些小型哺乳动物物种在对种子的依赖程度和越冬策略上存在差异。我们使用稳定同位素量化了饮食，并记录了雌性的繁殖时间、繁殖比例和窝仔数以及雄性的睾丸大小。种子供应时间的变化对窝仔数的影响最小，但对繁殖比例和繁殖时间的影响最大。在结实年（种子供应较晚），更多的雌性繁殖，繁殖时间更晚（哺乳期与峰值种子供应时间相匹配），尽管这一延迟在必须冬眠的 Napaeozapus insignis 中受到限制。秋季结实后，储存的种子被用作次年春季（种子供应较早）的资本，以支持一窝仔，根据物种的不同，这一窝仔比结实年早 24-79 天出生。除了 Myodes gapperi 外，在种子供应较早的年份中没有晚季繁殖，后者可能通过消耗真菌来产生第二窝仔。雄性也对种子供应有强烈的反应，与雌性繁殖相对应，睾丸大小在种子供应较晚的年份中保持不变，而在种子供应较早的年份中，睾丸大小在繁殖季节急剧下降。我们的研究结果表明，尽管光周期和温度在温带环境中广泛设定了繁殖季节的范围，但资源供应影响了物种所使用的繁殖策略，这反过来又改变了繁殖时间，并可能导致年际间的大规模种群波动。越冬策略和饮食的差异可能进一步调节繁殖时间和对资源脉冲的反应。
