Round and round in cycles? Silicon-based plant defences and vole population dynamics
Round and round in cycles? Silicon-based plant defences and vole population dynamics
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循环往复？
DOI：
10.1111/1365-2435.12365
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发表时间：
2015
影响因子：
5.2
通讯作者：
Hartley S
中科院分区：
文献类型：
--
作者：
Hartley S
Elton 首先描述了小型啮齿动物种群丰度的多年周期波动（Elton 1924）；从那时起，生态学家就一直在争论过去人口密度可以调节当前人口密度的机制。早期的假设集中于专门捕食者在驾驶周期中的作用，某些系统得到了很好的支持（例如 Hanski, Hannson & Henttonen 1991；Gilg, Hanski & Sittler 2003），但在其他系统中则不太令人信服（例如 Huitu 等人 2003），包括一些食草田鼠种群：在不同周期阶段的草原地区之间移植的田鼠很快就呈现出其种群的特征。新的环境，表明支撑种群周期的机制源于直接环境内的相互作用（Ergon，Lambin＆Stenseth 2001）。任何这样的机制都需要与田鼠密度具有时滞的倒数关系；尽管放牧引起的植物防御已被认为是一种可能性（Underwood 1999），但传统上认为草相对缺乏这种防御（Vicari & Bazely 1993）。但几十年来，草中的一种诱导防御已经为人所知：硅。 1983 年，McNaughton & Tarrants (1983) 提出草叶硅化作为“针对食草动物的天然诱导防御”。尽管许多关于硅防御的早期研究是相关的或仅涉及人为损伤（例如McNaughton等人，1985年；Brizuela，Dedling＆Cid 1986；Cid等人，1990年），但我们现在知道，硅防御的诱导是草食动物特异性的（对草食动物的反应比对修剪的反应更大），并且与损坏的频率和强度呈非线性关系（需要多次损坏事件和去除相当大比例的生物质）并且它会持续几个月（Massey, Ennos & Hartley 2007；Reynolds et al. 2012）。此外，还观察到田鼠吃草和硅诱导之间可能存在相互负反馈，即田鼠喂食会导致硅含量增加，足以降低成年和幼年田鼠的体重和生长速度（Massey & Hartley 2006；Massey et al. 2008）。尽管田鼠种群密度与田间的硅水平相关（Massey等人，2008年），但迄今为止，尚未发表实验测试来证明田鼠在自然发生的强度下吃草是否足以诱导田间硅防御水平的提高，也不知道这种变化是否有足够的幅度和持续时间来影响野生种群中田鼠的生长和生存。因此，迫切需要测试放牧压力、硅感应和田鼠性能之间的功能联系的操作性田间实验，因此 Wieczorek 等人 (2015) 的论文再及时不过了。最近人们对硅的功能和适应性意义的兴趣增加（例如 Currie & Perry 2007；Cooke & Leishman 2011）至少部分源于硅可以构成干物质的 2-10%。草、莎草和木贼叶的重量，比双子叶植物的典型重量高出许多倍（Hodson 等人，2005 年），并且超过某些常量营养素的水平（Epstein，1999 年）。此外，它以水合无定形二氧化硅的形式沉积在独特的、通常是物种特异性的固体中，称为植硅体（Cooke & Leishman 2011）。如此高水平的积累和独特的沉积模式可能表明硅一定具有某种功能作用（例如，因此重点关注抗草食动物效应）。但在蒸腾流中被动吸收的某些东西一定有其功能吗？硅被植物吸收...
Multi-annual cyclic fluctuations in abundance of small rodent populations were first described by Elton (Elton 1924); ecologists have been debating the mechanisms by which current population densities could be regulated by past ones ever since. Early hypotheses focused on the role of specialist predators in driving cycles, well supported for some systems (eg Hanski, Hannson & Henttonen 1991; Gilg, Hanski & Sittler 2003), but less convincing in others (eg Huitu et al. 2003), including in some grass-feeding vole populations: voles transplanted between grassland areas differing in the phase of their cycle quickly took on the characteristics of populations in their new surroundings, suggesting that mechanisms underpinning population cycles arise from interactions within the immediate environment (Ergon, Lambin & Stenseth 2001). Any such mechanism needed to have a time-lagged reciprocal relationship with vole density; although plant defences induced by grazing had been identified as a possibility (Underwood 1999), grasses were traditionally viewed as relatively lacking in such defences (Vicari & Bazely 1993). But one inducible defence in grasses has been known for decades: silicon. In 1983, McNaughton & Tarrants (1983) proposed grass leaf silication as a ‘natural inducible defence against herbivores’. Although many early studies on silicon defences were correlative or involved only artificial damage (eg McNaughton et al. 1985; Brizuela, Detling & Cid 1986; Cid et al. 1990), we now know that induction of silicon defences is herbivore specific (greater in response to herbivores than to clipping) and nonlinearly related to both the frequency and the intensity of damage (requiring multiple damage events and a significant proportion of biomass removed) and that it persists for several months (Massey, Ennos & Hartley 2007; Reynolds et al. 2012). Furthermore, a possible reciprocal negative feedback between vole grazing and silicon induction has been observed, whereby vole feeding induces increases in silicon content sufficient to reduce the body weight and growth rates of both adult and juvenile voles (Massey & Hartley 2006; Massey et al. 2008). Although vole population densities have been correlated with silicon levels in the field (Massey et al. 2008), as yet there has been no published experimental test of whether vole grazing at naturally occurring intensities is sufficient to induce increased levels of silicon defences in the field, nor is it known whether such changes are of sufficient magnitude and duration to affect the growth and survival of voles in wild populations. Manipulative field experiments, which test for functional links between grazing pressure, silicon induction and vole performance, are thus urgently needed, and hence, the paper by Wieczorek et al.(2015) could not be more timely.The recent increase in interest in the functions and adaptive significance of silicon (eg Currie & Perry 2007; Cooke & Leishman 2011) stems at least in part from the fact that silicon can constitute 2–10% of the dry weight of the leaves of grasses, sedges and horsetails, many times higher than is typical in dicotyledonous plants (Hodson et al. 2005) and more than the levels of some macronutrients (Epstein 1999). Furthermore, it is deposited as hydrated amorphous silica in distinctive, often species-specific solid bodies known as phytoliths (Cooke & Leishman 2011). Such high levels of accumulation and distinctive deposition patterns might suggest that silicon must have some functional role (hence the focus on antiherbivore effects, for example). But must something that is passively taken up in the transpiration stream have a function? Silicon is absorbed by plants …