Xiao Zhishu, Zhang Zhibin
State Key Laboratory of Integrated Management of Pest Insects and Rodents in Agriculture, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing, 100101, China.
J Anim Ecol. 2016 Sep;85(5):1370-7. doi: 10.1111/1365-2656.12542. Epub 2016 May 31.
It is well known that direct effects of seed predators or dispersers can have strong effects on seedling establishment. However, we have limited knowledge about the indirect species interactions between seeds of different species that are mediated by shared seed predators and/or dispersers and their consequences for plant demography and diversity. Because scatter-hoarding rodents as seed dispersers may leave some hoarded seeds uneaten, scatter hoarding may serve to increase seed survival and dispersal. Consequently, the presence of heterospecific seeds could alter whether the indirect interactions mediated by scatter-hoarding rodents have a net positive effect, creating apparent mutualism between seed species, or a net negative effect, creating apparent competition between seed species. We present a testable framework to measure short-term indirect effects between co-occurring plant species mediated by seed scatter-hoarding rodents. We tested this framework in a subtropical forest in south-west China using a replacement design and tracked the fate of individually tagged seeds in experimental patches. We manipulated the benefits to rodents by using low-tannin dormant chestnuts as palatable food and high-tannin non-dormant acorns as unpalatable food. We found that seed palatability changed the amount of scatter hoarding that occurred when seeds co-occurred either among or within patches. Consistent with our predictions, scatter-hoarding rodents created apparent mutualism through increasing seed removal and seed caching, and enhancing survival, of both plant species in mixed patches compared with monospecific patches. However, if we ignore scatter hoarding and treat all seed harvest as seed predation (and not dispersal), then apparent competition between palatable chestnuts and unpalatable acorns was also observed. This study is the first to demonstrate that foraging decisions by scatter-hoarding animals to scatter hoard seeds for later consumption (or loss) or consume them can influence indirect effects among co-occurring seeds, and rodent-mediated indirect effects vary depending on whether the harvested seeds are hoarded or eaten.
众所周知，种子捕食者或传播者的直接作用会对幼苗的建立产生强烈影响。然而，对于由共享的种子捕食者和/或传播者介导的不同物种种子之间的间接物种相互作用及其对植物种群统计学和多样性的影响，我们了解有限。由于作为种子传播者的分散贮藏啮齿动物可能会留下一些未被食用的贮藏种子，分散贮藏可能有助于提高种子的存活率和传播。因此，异种种子的存在可能会改变由分散贮藏啮齿动物介导的间接相互作用是产生净正效应（在种子物种之间形成明显的互利共生）还是净负效应（在种子物种之间形成明显的竞争）。我们提出了一个可测试的框架，用于衡量由种子分散贮藏啮齿动物介导的共存植物物种之间的短期间接效应。我们在中国西南部的一个亚热带森林中使用替代设计对这个框架进行了测试，并追踪了实验地块中单个标记种子的命运。我们通过使用低单宁休眠板栗作为可口食物和高单宁非休眠橡子作为不可口食物来操纵对啮齿动物的益处。我们发现，种子的适口性改变了种子在地块间或地块内共存时发生的分散贮藏量。与我们的预测一致，与单物种地块相比，分散贮藏啮齿动物通过增加种子移除、种子贮藏以及提高混合地块中两种植物物种的存活率，从而形成了明显的互利共生。然而，如果我们忽略分散贮藏，将所有种子收获都视为种子捕食（而非传播），那么也会观察到可口的板栗和不可口的橡子之间存在明显的竞争。这项研究首次证明，分散贮藏动物为以后食用（或丢失）而分散贮藏种子或食用种子的觅食决策会影响共存种子之间的间接效应，并且啮齿动物介导的间接效应会因收获的种子是被贮藏还是被食用而有所不同。
