动物所发现种子与动物的相对丰度影响森林种子存活与扩散
在自然界，许多植物结实存在明显的大小年现象（mast seeding)。大小年结实现象对以植物种子为食的动物（包括种子捕食者和种子扩散者）和植物种群本身均产生重要的生态和进化影响。目前，针对植物大小年结实现象已提出了多个假说，其中捕食者饱和假说（predator satiation hypothesis）被广为接受。捕食者饱和假说是指在结实歉年时，种子捕食者的可利用食物有限，不利于其种群繁殖增长，因而其种群数量回落至较低水平，而接下来的丰年结实，由于种子捕食者种群有限而不足以消耗所有的种子产量，从而保证有部分种子能够存活，促进植物的种群更新。以往支持捕食者饱和假说的证据多来自专食性的昆虫种子捕食者，但很少有证据来自广食性的脊椎动物捕食者（如鼠类）。
大小年结实现象在许多坚果类植物（如栎类）中十分普遍，但这些坚果植物主要依赖以其种子为食的鼠类和鸟类通过分散贮藏的方式来传播其种子。因此分散贮藏的动物既是种子捕食者，也是种子扩散者。为此，一些学者提出了捕食者扩散假说（predator dispersal hypothesis）。该假说认为丰年结实将促进动物来扩散其种子，并预测种子扩散率在丰年高于歉年，或者种子扩散距离在丰年远于歉年。但鲜有证据支持捕食者扩散假说。
由于持续跟踪动物对种子命运的影响难度大，以往种子命运的数据多为1-3年，而且相关研究很少同时提供种子产量和动物种群数据。这些情况也是论证上述2个假说证据不足的的重要原因。事实上，捕食者饱和效应或影响种子命运的关键因子不仅与种子产量多寡有关，而且与动物种群数量有极大关系。为此，中科院动物研究所肖治术副研究员等科研人员在四川都江堰常绿阔叶林对油茶种子产量、鼠类密度和种子命运等进行了长达8年的调查研究，并对上述2个假说进行了深入论证分析。他们首次提出了由种子产量和捕食者密度（基于能量代谢）来决定种子与鼠类的相对丰度，并且发现种子存活与种子扩散之间存在权衡，取决于种子与动物的相对丰度。发现在种子歉收年份，更多种子为鼠类所贮藏，扩散距离更远，并有更多贮藏的种子存活到种子萌发和幼苗建成。但随着种子产量或种子相对丰度增加，种子的搬运速率减慢，贮藏种子的比例降低，扩散距离更近，且二次贮藏的比例也降低，并有更多种子在原地存活，但被贮藏种子的存活率也较低。这一研究结果显然支持捕食者饱和假说，但不支持有关大年比小年更有利于种子扩散的观点（即捕食者扩散假说）。
该研究近期在线发表在国际生态学期刊Journal of Ecology上。论文得到了审稿专家和编辑的高度肯定。他们认为该研究对揭示植物结实策略以及种子存活与种子扩散策略有明显新的贡献。
该研究得到了国家自然科学基金和中国科学院知识创新重要方向项目等的资助。（生物谷 Bioon.com）
生物谷推荐的英文摘要
Journal of Ecology doi: 10.1111/1365-2745.12113
Xiao Z-S, Zhang Z-B, Krebs CJ
Long-term seed survival and dispersal dynamics in a rodent-dispersed tree: Testing the predator satiation hypothesis and the predator dispersal hypothesis
1. Mast seeding in animal-dispersed plants has previously been accounted for by two main hypotheses: the predator satiation hypothesis (that it increases seed survival and establishment before dispersal) and the predator dispersal hypothesis (that it increases seed dispersal or dispersal distance). However, neither hypothesis has been rigorously tested with simultaneous data on seed production, seed predation and seed dispersal by vertebrate seed predators.
2. We studied oil tea Camellia oleifera (Theaceae) seed production for eight years (2002–2009) in a subtropical forest in south-west China, and investigated how annual seed and rodent abundance determined per capita seed availability for rodent seed predators and seed dispersers and how seed and rodent abundance were related to seed dispersal and seed survival via scatter-hoarding. We predicted the patterns of seed dispersal and survival to test the two hypotheses about mast seeding. Edward's long-tailed rat Leopoldamys edwardsi acted as the principal seed disperser of oil tea seeds because of scatter-hoarding, while other sympatric rodent species acted only as seed predators.
3. We first provided a reasonable method to estimate per capita seed availability based on annual seed abundance and annual metabolic rodent abundance (corrected for metabolic-scaling body mass of each rodent species). We found that annual seed abundance, annual metabolic rodent abundance and per capita seed availability all had some significant effects on different estimators of seed fates (including dispersal distances) across each stage from seedfall to seedling establishment. Both annual seed abundance and per capita seed availability were positively correlated with pre-dispersal seed survival, but negatively correlated with scatter-hoarding (and recaching), seed survival after dispersal and dispersal distances. However, annual metabolic rodent abundance had a positive effect on scatter-hoarding, but had a negative effect on the time to cache recovery.
4. Synthesis. Since greater seed production was associated with improvement in pre-dispersal survival of oil tea seeds but a reduction in dispersal (including secondary dispersal and dispersal distance), our long-term study indicates that, compared with the predator dispersal hypothesis, the predator satiation hypothesis provides a better mechanism predicting seed dispersal and seed survival in animal-dispersed plants by integrating seed abundance and animal abundance.
