動物所發(fā)現(xiàn)種子與動物的相對豐度影響森林種子存活與擴散
在自然界,，許多植物結(jié)實存在明顯的大小年現(xiàn)象（mast seeding),。大小年結(jié)實現(xiàn)象對以植物種子為食的動物（包括種子捕食者和種子擴散者）和植物種群本身均產(chǎn)生重要的生態(tài)和進化影響,。目前,，針對植物大小年結(jié)實現(xiàn)象已提出了多個假說,，其中捕食者飽和假說（predator satiation hypothesis）被廣為接受,。捕食者飽和假說是指在結(jié)實歉年時,，種子捕食者的可利用食物有限,，不利于其種群繁殖增長，因而其種群數(shù)量回落至較低水平,，而接下來的豐年結(jié)實,，由于種子捕食者種群有限而不足以消耗所有的種子產(chǎn)量，從而保證有部分種子能夠存活,，促進植物的種群更新,。以往支持捕食者飽和假說的證據(jù)多來自專食性的昆蟲種子捕食者，但很少有證據(jù)來自廣食性的脊椎動物捕食者（如鼠類）,。
大小年結(jié)實現(xiàn)象在許多堅果類植物（如櫟類）中十分普遍,，但這些堅果植物主要依賴以其種子為食的鼠類和鳥類通過分散貯藏的方式來傳播其種子。因此分散貯藏的動物既是種子捕食者，也是種子擴散者,。為此,，一些學(xué)者提出了捕食者擴散假說（predator dispersal hypothesis）。該假說認(rèn)為豐年結(jié)實將促進動物來擴散其種子,，并預(yù)測種子擴散率在豐年高于歉年,，或者種子擴散距離在豐年遠(yuǎn)于歉年。但鮮有證據(jù)支持捕食者擴散假說,。
由于持續(xù)跟蹤動物對種子命運的影響難度大,，以往種子命運的數(shù)據(jù)多為1-3年，而且相關(guān)研究很少同時提供種子產(chǎn)量和動物種群數(shù)據(jù),。這些情況也是論證上述2個假說證據(jù)不足的的重要原因,。事實上，捕食者飽和效應(yīng)或影響種子命運的關(guān)鍵因子不僅與種子產(chǎn)量多寡有關(guān),，而且與動物種群數(shù)量有極大關(guān)系,。為此，中科院動物研究所肖治術(shù)副研究員等科研人員在四川都江堰常綠闊葉林對油茶種子產(chǎn)量,、鼠類密度和種子命運等進行了長達8年的調(diào)查研究,，并對上述2個假說進行了深入論證分析。他們首次提出了由種子產(chǎn)量和捕食者密度（基于能量代謝）來決定種子與鼠類的相對豐度,，并且發(fā)現(xiàn)種子存活與種子擴散之間存在權(quán)衡,，取決于種子與動物的相對豐度。發(fā)現(xiàn)在種子歉收年份,，更多種子為鼠類所貯藏,，擴散距離更遠(yuǎn)，并有更多貯藏的種子存活到種子萌發(fā)和幼苗建成,。但隨著種子產(chǎn)量或種子相對豐度增加,，種子的搬運速率減慢，貯藏種子的比例降低,，擴散距離更近,，且二次貯藏的比例也降低，并有更多種子在原地存活,，但被貯藏種子的存活率也較低,。這一研究結(jié)果顯然支持捕食者飽和假說，但不支持有關(guān)大年比小年更有利于種子擴散的觀點（即捕食者擴散假說）,。
該研究近期在線發(fā)表在國際生態(tài)學(xué)期刊Journal of Ecology上,。論文得到了審稿專家和編輯的高度肯定。他們認(rèn)為該研究對揭示植物結(jié)實策略以及種子存活與種子擴散策略有明顯新的貢獻,。
該研究得到了國家自然科學(xué)基金和中國科學(xué)院知識創(chuàng)新重要方向項目等的資助,。（生物谷 Bioon.com）
生物谷推薦的英文摘要
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.
