Small mammal granivory as a biotic filter for tree establishment beyond elevation range boundaries

Trees often experience migration lags in their response to rapidly changing climate. Preferential granivory by nocturnal small mammals has the potential to create lags by reducing germination success beyond range edges. To determine how granivory may limit establishment of trees beyond their range margins, we conducted a seed choice experiment which offered seeds of five regionally dominant tree species to small mammals within distinct forest communities across a 400m elevational gradient on four mountains in the northeastern United States. Multinomial logistic mixed effects models were used to (a) quantify seed preference of each species across the elevational gradient and (b) assess relationships between seed preference and abiotic variables. A separate seed dispersal experiment was used to compare the probability of seed consumption versus seed caching. The low-elevation temperate tree species Fagus grandifolia and Acer saccharum had an equally high probability of granivory within an..., Seed Selection Experiment
Seeds of five regionally dominant tree species were offered in a cafeteria-style experiment in the fall of 2020 (mid-September through mid-October), coinciding with the timing of natural seed release and dispersal of our focal tree species (Burns and Honkala, 1990). The focal tree species included American beech (Fagus grandifoila), sugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), balsam fir (Abies balsamea), and red spruce (Picea rubens). All seeds were purchased from either Sheffield’s Seed Company (Locke, NY) or F.W. Schumacher Seed Company (Sandwich, MA). Seed species were offered in equal amounts by mass (3 g per station) in order to standardize across species with various seed sizes (Boone & Mortelliti, 2019). Seeds were offered to mammals as they would naturally be found post-dispersal on the forest floor (conifer seeds removed from cones and sugar maple wings attached).
At each seed selection station, five Petri dishes (6 cm diame...,

树木在响应快速变化的气候时，往往存在迁移滞后（migration lags）现象。夜行性小型哺乳动物的选择性食谷（granivory）行为，有可能通过降低分布范围边缘以外区域的种子萌发成功率，加剧这种滞后效应。为明确食谷行为如何限制树木在分布范围边缘外的定居过程，我们开展了一项种子选择实验：在美国东北部4座山地的400米海拔梯度上的不同森林群落中，为小型哺乳动物提供5种区域优势树种的种子。我们采用多项式逻辑混合效应模型（multinomial logistic mixed effects models），(a)量化各树种在海拔梯度上的种子偏好性，(b)评估种子偏好与非生物变量之间的关联。此外，我们还通过另一项种子扩散实验（seed dispersal experiment），比较了种子被取食与被贮藏的概率。低海拔温带树种美洲山毛榉（*Fagus grandifolia*）和糖槭（*Acer saccharum*）在……内的食谷概率同样较高。

种子选择实验
本实验于2020年秋季（9月中旬至10月中旬）开展，采用自助餐式（cafeteria-style）实验设计，投放5种目标树种的种子，该时段与目标树种的自然种子释放和扩散周期一致（Burns & Honkala, 1990）。目标树种包括美洲山毛榉（*Fagus grandifolia*）、糖槭（*Acer saccharum*）、黄桦（*Betula alleghaniensis*）、香脂冷杉（*Abies balsamea*）以及红云杉（*Picea rubens*）。所有种子均购自Sheffield’s Seed Company（美国纽约州洛克市）或F.W. Schumacher Seed Company（美国马萨诸塞州桑威奇市）。为统一不同种子大小的实验标准，各树种种子按质量等量投放（每个实验点3克），参考Boone & Mortelliti, 2019的方法。种子按照自然扩散后在林地上的存在形式进行投放：针叶树种子去除球果，糖槭种子保留果翅。
每个种子选择实验点设置5个直径6厘米的培养皿（Petri dish）……