Effects of plant traits and the relative abundance of common woody species on seedling herbivory in the Thousand Island Lake region
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植食性动物对植物的植食作用(herbivory)是生态系统中动植物之间重要的相互关系(Tilman et al., 2012), 植食活动对植物种群、群落和食物网结构都有较大的影响(Bagchi et al., 2014), 是生物多样性和生态系统功能研究的核心问题(曾凡勇和孙志强, 2014)。其中, 植物功能性状对植食作用的影响受到了广泛的关注(王小菲等, 2015; 禹海鑫等, 2015)。
植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(Awmack & Leather, 2002; Poorter et al., 2004)。形态性状包括叶厚度、叶干物质含量和比叶质量等, 主要影响植物的纤维素含量和适口性(Poorter et al., 2009)。叶干物质含量和比叶质量越高的叶片含有越高的组织密度, 通常可以防御植食性动物从而较少受到植食侵害。化学成分表征植物化学组成包括碳水化合物、含氮化合物和防御性代谢产物等, 这些化合物能够直接影响植物的营养性和防御性成分组成。碳水化合物中,纤维素含量影响植食性动物的消化,高浓度可溶性糖能稀释其他营养物质而产生对虫食的负作用(Awmack & Leather, 2002)。含氮化合物(如氨基酸等)一般是植食性动物的直接营养来源, 部分含氮化合物(如生物碱)也可以防御动物取食(Carmona et al., 2011)。防御性代谢产物(如酚类、萜类)多对植食性动物有害, 显著影响虫食率(谢辉等, 2012; Wetzel et al., 2016)。
植物的其他特征, 如相对多度等被认为可能是影响虫食率的因素(Coley, 1980; Haukioja & Koricheva, 2000; Farji‐Brener, 2001)。一方面, 物种相对多度通常能够代表该物种在群落中的适合度, 而植物性状对适合度有强烈影响(Shipley et al., 2016)。植物整个生活史阶段的若干个功能性状的共同作用在很大程度上决定了植物的适合度。适合度高的物种通常多度也高, 具有较高的个体生存、繁殖和生长率, 可反映为受到较低的虫食影响等(Shipley et al., 2016)。另一方面, 相对多度高的物种密度通常较高, 密度制约(negative density dependence)相关的研究结果提示密度或多度高的植物更易受到专一性植食动物的取食, 从而影响个体的生长生存(Comita et al., 2010)。
以往大部分研究集中在植物功能性状对植食性动物取食的影响及其机制上, 少有研究综合植物群落结构特征, 探讨不同植物功能性状和多度特征对于植物种间虫食特征差异的重要性。本研究以千岛湖岛屿上16种常见木本被子植物的幼苗为调研对象, 调查植物功能性状和物种相对多度等因素及幼苗叶片受植食性动物(本研究主要为昆虫)损伤的强度, 并提出以下两个假设: (1)叶片的营养和防御性状共同影响虫食率, 其中的碳氮比和叶干物质含量是相对重要的性状; (2)群落中相对多度高的物种叶片受虫食损伤低。本研究旨在进一步研究植物性状对种间虫食率差异的相对重要性, 并探讨虫食特征能否反映物种适合度, 为生态系统中动植物相互作用和森林生态系统功能等研究提供资料。
1 材料和方法
1.1 研究地区概况
千岛湖(29.37°-29.83° N, 118.57°-119.25° E)位于浙江省西南部, 是1959年建成的新安江水电站截新安江而成的大型人工湖泊, 水域面积约为 573 km2。在最高水位海拔108 m时, 水库拥有1 078个0.25 hm2以上的岛屿。该地区属亚热带季风气候, 年平均气温约17.0 ℃, 1月份最低气温-7.6 ℃, 7月份最高气温41.8 ℃; 年降水量1 430 mm, 降雨集中在4月到6月的雨季。本研究位于千岛湖中心湖区, 选取29个面积跨度0.08-1 158.00 hm2的岛屿(据最新的GIS计算结果), 每个岛屿的植被以次生马尾松(Pinus massoniana)林为主, 种类组成高度相似(Hu et al., 2016)。1.2 数据采集
本研究调查16个植物物种幼苗(胸径< 1 cm, 高度50-200 cm), 以植食性昆虫造成的叶片损伤百分比作为虫食率(图1)。16个物种包括9种灌木和7种乔木(表1), 是该地区植物群落的主要组分。于2015年9-10月, 在29个岛屿的样地随机选择每个岛屿每个物种最多10株幼苗, 16个物种的幼苗在研究岛屿上都有足够的样本。
显示原图|下载原图ZIP|生成PPT图116种常见木本植物幼苗受虫食损伤的平均叶片面积百分比(平均值±标准误差)。
-->Fig. 1Percentages of leaf damage by insect herbivores for seedlings of 16 common woody species (mean ± SE).
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Table 1
表1
表1选取虫食调查的16种木本植物的相关信息, 包括种名, 叶生活周期(落叶/常绿), 生长型(乔木/灌木), 光耐受性(耐阴/阳性), 分布的岛屿数, 幼苗样本量
Table 1Information on the 16 woody species for insect herbivory survey, including species, leaf lifespan (deciduous/evergreen), growth form (tree/shrub), light tolerance (shade tolerance/shade intolerance), number of sampling island, and number of seedling sample
| 种名 Species | 叶生活周期 Leaf lifespan | 生长型 Growth form | 光耐受性 Light tolerance | 分布岛屿数 No. of sampling island | 幼苗样本量 No. of seedling samples |
|---|---|---|---|---|---|
| 野柿 Diospyros kaki var. silvestris | 落叶 Deciduous | 乔木 Tree | 耐阴 Tolerance | 8 | 32 |
| 白花龙 Styrax faberi | 落叶 Deciduous | 灌木 Shrub | 耐阴 Tolerance | 9 | 55 |
| 白檀 Symplocos paniculata | 落叶 Deciduous | 灌木 Shrub | 不耐阴 Intolerance | 20 | 97 |
| 苦槠 Castanopsis sclerophylla | 常绿 Evergreen | 乔木 Tree | 耐阴 Tolerance | 9 | 32 |
| 石栎 Lithocarpus glaber | 常绿 Evergreen | 乔木 Tree | 耐阴 Tolerance | 8 | 45 |
| 冬青 Ilex chinensis | 常绿 Evergreen | 乔木 Tree | 耐阴 Tolerance | 23 | 164 |
| 木荷 Schima superba | 常绿 Evergreen | 乔木 Tree | 耐阴 Tolerance | 6 | 37 |
| 石斑木 Rhaphiolepis indica | 常绿 Evergreen | 灌木 Shrub | 耐阴 Tolerance | 20 | 174 |
| 白栎 Quercus fabri | 落叶 Deciduous | 乔木 Tree | 不耐阴 Intolerance | 21 | 65 |
| 乌饭树 Vaccinium bracteatum | 常绿 Evergreen | 灌木 Shrub | 耐阴 Tolerance | 21 | 144 |
| 短柄枹 Quercus serrata var. brevipetiolata | 落叶 Deciduous | 乔木 Tree | 不耐阴 Intolerance | 20 | 112 |
| 毛果南烛 Lyonia ovalifolia | 落叶 Deciduous | 灌木 Shrub | 不耐阴 Intolerance | 10 | 44 |
| 格药柃 Eurya muricata | 常绿 Evergreen | 灌木 Shrub | 耐阴 Tolerance | 21 | 191 |
| 杜鹃 Rhododendron simsii | 落叶 Deciduous | 灌木 Shrub | 不耐阴 Intolerance | 24 | 183 |
| 檵木 Loropetalum chinense | 常绿 Evergreen | 灌木 Shrub | 耐阴 Tolerance | 26 | 240 |
| 短尾越桔 Vaccinium carlesii | 常绿 Evergreen | 灌木 Shrub | 耐阴 Tolerance | 22 | 321 |
新窗口打开
在每株幼苗上, 随机方向上调查3根枝条, 每根枝条带有5枚成熟的完全扩展的叶片, 总共15枚叶片用来评估虫食率。计算由以下植食性昆虫造成的叶面积损伤: 嚼食型、挖食型、潜食型、吸食型和造瘿型(Schuldt et al., 2010)。根据2014年9-10月的预试验结果, 这5类叶片损伤合并计算并划分为6个损伤等级记录(0、0-3%、3%-10%、10%-25%、25%-50%、50%-100%)。叶片损伤百分比=被损伤的叶面积/总的叶面积×100%。每个叶片的损伤等级由人为野外实地估算进行分类并记录。每个叶片的叶面积损伤以各个损伤等级的平均百分比(0、1.5%、6.5%、17.5%、37.5%、75%)计算, 每株幼苗的虫食率以该株幼苗上15枚叶片的平均损伤计算。为确保虫食调查过程中估算的准确性, 所有损伤面积估算按同一分级标准进行, 并用35张标准虫食率的图片在每次调查前进行浏览校对, 以减小调查过程中的误差。
2014年, 在千岛湖库区采集样本, 目标物种随机取5-10株长势良好的成年个体, 具体方法详见文献(余晶晶等, 2017)。在每个个体的冠层采集当年生向阳面的20枚完整无病斑的成熟叶片, 测定如下4个变量来表征植物叶形态性状: 叶厚度、叶面积、叶干物质含量和比叶质量。叶干物质含量表示叶片干质量和叶片鲜质量的比值。比叶质量表示叶片干质量和新鲜叶片的单面面积的比值。还测定了植物的叶片化学性状: 碳含量、氮含量和碳氮比。测量方法为每个物种测量5株个体的碳氮含量, 每株个体取10片干燥叶片, 粉碎过100目筛, 80 ℃烘干至恒质量, 称取50 mg待测样品, 用锡箔纸包裹, 元素分析仪碳氮模式分析测试, 最后对每个物种5株个体的碳氮含量取平均值。此外, 还参考《浙江植物志》和《中国植物志》记录植物物种水平的其他功能性状: 叶生活周期(常绿/落叶)、生长型(乔木/灌木)、光耐受性(耐阴/不耐阴)和最大树高。
2014-2015年, 采用CTFS森林动态样地的标准方法对29个岛屿的样地内胸径1 cm以上的木本植物个体进行复查, 对2009-2010年初次调查中已挂牌的个体重新调查胸径、树高, 对新增个体进行标记和挂牌, 并记录其胸径和树高, 具体调查方法及结果详见文献(Hu et al., 2016)。本研究使用这次复查中各物种的相对多度值, 表示各物种的多度与总的多度的比值。
1.3 数据分析
本研究采用多元线性回归模型分析植物功能性状和物种相对多度等变量对虫食率的影响。首先, 对所有连续型自变量以2倍自变量的标准差作标准化, 保证变量尺度的可比性(Gelman, 2008), 并对各物种叶片虫食百分比取平均值, 并作逻辑斯蒂转换以保证正态性(Warton & Hui, 2011)。然后, 对变量进行共线性检验, 发现叶干物质含量/叶厚度与比叶质量高度相关(Pearson相关系数|r| > 0.60), 由于叶干物质含量对植食作用影响较为显著(Schuldt et al., 2012), 保留叶干物质含量。而另一组高度相关变量碳氮比/叶面积和氮含量, 碳氮比在后续模型中相对氮含量有更低的赤池信息量准则(AICc)值(AICc = -5.13 vs. AICc = -0.86), 保留碳氮比。最后得到包括7个变量的模型: 叶厚度、叶面积、叶干物质含量、碳含量、碳氮比、最大树高和相对多度。对上述模型进行模型选择, 由于最优模型之间具有相近的AICc值(ΔAICc < 2), 对赤池重量(Akaike weight, ω+)累积95%以上的模型组内的变量计算其相对重要性, 筛选出重要的变量得出最佳模型(Burnham & Anderson, 2003), 并对模型的统计假设进行检验。同时, 对分类型变量与虫食率做线性回归, 观察对虫食特征的影响。此外, 对最佳模型使用方差分解, 以解释模型中各个变量对16个物种的平均虫食的独立和联合作用。以上所有数据分析和图形输出都基于R 3.3.2 (R Core Team, 2016)完成。
2 结果
本研究共调查了16个常见木本植物共计1 936株幼苗(共有28 884枚叶片)上的虫食特征情况。各物种平均植食性昆虫损伤叶片面积百分比从3.2% (短尾越桔)到15.3% (白花龙), 总体平均为7.9% (图1)。其中, 虫食率最高的两个物种白花龙(15.3%)和杜鹃(14.5%)的叶片碳氮比相对较低, 在群落中相对多度较低, 都是落叶物种; 而虫食率最低的3个物种短尾越桔(3.2%)、冬青(4.3%)和檵木(4.5%)叶片碳氮比相对较高, 叶片较厚, 是群落中优势常绿物种。根据最佳模型结果, 在95%置信区间内, 碳氮比、叶厚度、相对多度是模型中极为重要的3个变量(ω+ = 0.83; 0.60; 0.53, 图2), 相对重要性大于其他变量(0.08 ≤ ω+ ≤ 0.12)。因此, 包括碳氮比(回归系数(Esti) = -0.22; p = 0.01)、叶厚度(Esti = -0.17; p = 0.03)和相对多度(Esti = -0.18; p = 0.05)的3个变量的预测模型是最佳模型(adjusted R squared = 0.54; p < 0.01)。同时, 根据最佳模型的偏残差图(图3), 验证巩固了该模型的线性, 并直观反映了碳氮比、叶厚度和相对多度对虫食率的影响。最佳模型中的3个自变量均与叶片损伤百分比显著相关, 该物种叶片中的碳氮比越高, 叶厚度越大, 在群落中的相对多度越高, 该物种由虫食引起的叶片损伤越小。其他变量中, 比叶质量和氮含量在与叶片损伤的线性回归中表现显著的相关性(Esti = -0.23, p = 0.03; Esti = 0.25, p = 0.04)。而生长型和光耐受性在与叶片损伤的线性回归中未表现出显著的相关性(p > 0.05)。叶生活周期与碳氮比、叶厚度都高度相关, 在与叶片损伤的线性回归中表现出极显著的相关性(Esti = -0.31, p < 0.001), 常绿物种的叶片损伤百分比远小于落叶物种。
显示原图|下载原图ZIP|生成PPT图2模型平均计算中7个变量的相对重要性对比, 估计为在95%置信集中的赤池重量(ω+)之和。
-->Fig. 2The relative importance of seven variables measured as the sum of Akaike weight (ω+) in 95% confidence set with model averaging. C:N, carbon nitrogen ratio; LA, leaf area; LDMC, leaf dry matter content; LT, leaf thickness; MaxH, maximum tree height; RA, relative abundance.
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显示原图|下载原图ZIP|生成PPT图3最佳模型中3个变量对于千岛湖16种木本植物幼苗的平均叶片虫食损伤百分比(排除了其他变量影响的偏残差)的独立影响。A, 碳氮比。B, 叶厚度。C, 相对多度。
-->Fig. 3Independent effects of three variables in the best model on mean percentage of leaf damage (partial residuals excluding the effects of other variables) on seedlings of 16 woody species in the Thousand Island Lake. A, Carbon nitrogen ratio. B, Leaf thickness. C, Relative abundance.
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在方差分解中, 碳氮比、叶厚度和相对多度3个变量共解释了54%的叶片损伤的方差变异。其中, 碳氮比独立解释了28%的方差, 对叶片损伤程度具有更大的影响。而叶厚度和相对多度分别独立解释了16%和14%的方差。3个变量相对独立, 共同解释部分较小, 不能被解释的部分占46%。
3 讨论
本研究通过结合16个常见木本植物的功能性状和群落结构特征, 为探讨物种之间虫食特征差异的影响因素提供了一个新的视角。研究结果表明: (1)碳氮比和叶厚度等性状与虫食率有明显的负相关关系; (2)叶生活周期长的植物叶片上的虫食率相对较低; (3)物种相对多度对种间虫食率差异有较强影响。本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(图3)。碳氮比与虫食率表现出显著的负相关关系, 碳氮比越高的物种遭受的虫食越低。植物叶片中的碳水化合物, 如纤维、糖类和固醇类, 主要作为防御性成分对虫食率有消极影响, 高密度的纤维素、高浓度的糖类常被作为植物防御手段降低昆虫侵害(Awmack & Leather, 2002)。而含氮化合物如氨基酸, 通常表征蛋白质含量, 在大部分植物中作为营养性成分吸引昆虫取食(Poorter et al., 2004; Joern et al., 2012)。因此, 碳氮比作为植物的防御和营养性状能够对虫食率产生影响(Loranger et al., 2012)。植物中越高的碳氮比表明叶片中存在的防御物质含量越高、营养物质含量越少, 从而影响昆虫取食选择并导致较低的虫食率(Mithofer & Boland, 2012), 本研究结果与之一致。而氮含量与碳氮比高度相关, 也表现出与叶片损伤强度的显著相关性, 表明营养性状在种间虫食率差异中的重要影响。此外, 叶厚度与虫食率也表现出显著的负相关关系, 越厚的叶片受到的虫食损伤越小。本研究中叶厚度与比叶质量高度相关(r = 0.67, p = 0.005), 通常较高的叶厚度和比叶质量代表较高的叶片组织密度, 导致叶片营养物质含量和适口性的降低。因此, 叶厚度、比叶质量和叶干物质含量等结构性状在以往大量的研究中被认为与叶片虫食率有持续的负相关关系, 是研究虫食特征的比较稳定的性状(Cingolani et al., 2005; Poorter et al., 2009)。本研究中, 叶厚度和比叶质量作为物理防御性状对虫食率的影响与以往研究结果(Hanley et al., 2007)一致。而叶干物质含量的作用不显著, 在一些种间虫食特征差异的研究中也有类似结果。虽然叶干物质含量与虫食率的负相关关系在单一物种内极为普遍稳定, 但是在种间关系上, 其作用有可能被个别物种的防御性代谢产物或其他防御手段所弱化(Elger & Willby, 2003)。结果表明, 与假设(1)相近, 碳氮比和叶厚度等营养和防御性状共同影响植食性昆虫取食选择, 是影响植物种间虫食率差异的主要因素, 但叶干物质含量对种间虫食率差异的影响不显著。
叶生活周期与碳氮比和叶厚度都有较高的相关性(没有包括在最佳模型中), 在与虫食率的线性回归中显示了极显著的影响。根据成本效益理论, 生活在林荫下的幼苗由于光照少而获得的资源有限, 而叶生活周期长的幼苗往往有更好的防御手段(如高叶片厚度和组织密度)和更低的营养物质含量, 可以有效地降低虫食带来的损伤并提高存活率(Chabot & Hicks, 1982; Kitajima et al., 2013; Silva et al., 2015)。本研究结果验证了叶生活周期更长的植物有更高的碳氮比和叶厚度, 有更低的虫食损伤, 同时相关性分析发现叶生活周期与氮含量等相关性显著, 表明常绿阔叶植物通过提高相关的防御能力、降低营养含量以降低虫食率, 这一结果支持最新的研究结论(Zhang et al., 2017)。
根据相关性分析和模型结果, 相对多度越高的物种, 其幼苗被虫食损伤的强度越小, 与假设(2)一致。植物性状能够显著影响适合度, 而相对多度可以作为该物种适合度的定量替代(Shipley et al., 2016)。本研究中相对多度与其他形态、化学性状没有显著相关性, 除上述性状外还有其他植物性状影响虫食特征, 能够解释种间虫食率变异的14%。这与密度制约的理论不符, 但是本研究未对植食性昆虫进行调查, 仅在虫食调查过程中观察昆虫种类, 观察到的多为鳞翅目蛾类幼虫等寡食性昆虫, 这可能是违背假设的一个原因(Schuldt et al., 2010); 也有研究指出, 密度制约对常见物种的作用比对稀有物种的作用弱(Johnson et al., 2012)。因此, 在千岛湖地区相对多度较高的物种适合度高, 密度制约的作用较小, 受虫食损伤也较低。
综上所述, 本研究结果表明, 叶片碳氮比和叶厚度等作为营养和防御性状在千岛湖地区共同影响植食性昆虫的取食选择, 而相对多度高、适合度高的物种受虫食损伤低。在模型中, 碳氮比、叶厚度和相对多度所代表的其他性状能解释本研究地区16个植物物种平均叶片虫食率变异的54%。而其他性状如叶面积、叶干物质含量和光耐受性等对虫食率没有表现出明显的影响(Moles & Westoby, 2000; Kitajima & Poorter, 2010; Salgado-Luarte & Gianoli, 2010)。这些性状对虫食特征的独立及联合影响还需要进一步结合植物群落结构特征, 对植物物种种内和种间各项性状以及植食性昆虫种类的调查来进行分析。本研究探讨在以往研究中较少衡量的植物功能性状和相对多度在植物种间叶片虫食率差异中的相对重要性, 表明叶片营养和防御性状与相对多度在植食性昆虫取食过程中的重要作用, 对促进动植物相互作用研究有重要意义。
致谢 浙江淳安新安江开发总公司对项目实施提供支持, 浙江大学南歌、巫东豪、戎福仁、秦雪妍、邬劼和当地村民在野外调查中给予帮助, 在此一并表示感谢。
The authors have declared that no competing interests exist.
作者声明没有竞争性利益冲突.
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| [1] | |
| [2] | Abstract Tropical forests are important reservoirs of biodiversity, but the processes that maintain this diversity remain poorly understood. The Janzen-Connell hypothesis suggests that specialized natural enemies such as insect herbivores and fungal pathogens maintain high diversity by elevating mortality when plant species occur at high density (negative density dependence; NDD). NDD has been detected widely in tropical forests, but the prediction that NDD caused by insects and pathogens has a community-wide role in maintaining tropical plant diversity remains untested. We show experimentally that changes in plant diversity and species composition are caused by fungal pathogens and insect herbivores. Effective plant species richness increased across the seed-to-seedling transition, corresponding to large changes in species composition. Treating seeds and young seedlings with fungicides significantly reduced the diversity of the seedling assemblage, consistent with the Janzen-Connell hypothesis. Although suppressing insect herbivores using insecticides did not alter species diversity, it greatly increased seedling recruitment and caused a marked shift in seedling species composition. Overall, seedling recruitment was significantly reduced at high conspecific seed densities and this NDD was greatest for the species that were most abundant as seeds. Suppressing fungi reduced the negative effects of density on recruitment, confirming that the diversity-enhancing effect of fungi is mediated by NDD. Our study provides an overall test of the Janzen-Connell hypothesis and demonstrates the crucial role that insects and pathogens have both in structuring tropical plant communities and in maintaining their remarkable diversity. |
| [3] | , |
| [4] | Summary 1. 68Although secondary metabolites are recognized as fundamental to the defence of plants against insect and mammalian herbivores, their relative importance compared to other potential defensive plant traits (e.g. physical resistance, gross morphology, life-history, primary chemistry and physiology) are not well understood. 2. 68We conducted a meta-analysis to answer the question: What types of genetically variable plant traits most strongly predict resistance against herbivores? We performed a comprehensive literature search and obtained 499 separate measurements of the strength of covariation (measured as genetic correlations) between plant traits and herbivore susceptibility – these were extracted from 72 studies involving 19 plant families. 3. 68Surprisingly, we found no overall association between the concentrations of secondary metabolites and herbivore susceptibility – plant traits other than secondary metabolites most strongly predicted herbivore susceptibility. Specifically, genetic variation in life-history traits (e.g. flowering time, growth rate) consistently exhibited the strongest genetic correlations with susceptibility. Genetic variation in gross morphological traits (e.g. no. branches, plant size) and physical resistance traits (e.g. latex, trichomes) were also frequently correlated with variation in herbivore susceptibility, but these relationships depended on attributes of the herbivores (e.g. feeding guild) and plants (e.g. longevity). 4. 68These results call into question the conventional wisdom that secondary metabolites are the most important anti-herbivore defence of plants. We propose the hypothesis that herbivores select most strongly on genetic variation in life-history, morphological and physical resistance traits, but the greater pleiotropic effects of genes controlling these traits impose strong constraints on their evolution. Meanwhile, secondary metabolites could have evolved to be important defensive mechanisms not because they have the largest effect on herbivores, but because the constraints on their evolution are the weakest. |
| [5] | ABSTRACT The adaptive significance of leaf life spans has been examined from several different points of view. Evergreenness has been explained in terms of nutrient conservation, improving carbon balance, and as a general adapatation to environmental stress. In this review we consider these theories and attempt to synthesise divergent viewpoints. We consider the question "How is the length of a leafs life span related to environmental factoprs?" In particular, what are the comparative advantages of the evergreen and deciduous habits and how can adaptive differences be related to distributional patterns and climatic gradients? |
| [6] | 1. In some ecosystems there is a positive feedback between forage quality and grazing intensity. This involves three components of plant tolerance to grazing: functional traits, herbivore selectivity and response to grazing. We analysed the relationships between these components at species and community levels in Patagonian steppe grasslands. 2. We measured plant functional traits [height, specific leaf area (SLA) and foliar toughness] and estimated sheep selectivity and grazing response indices for 35 plant species. Sheep selectivity indices were obtained from microhistological and species' availability data, and grazing response indices from species' abundances in sites with contrasting grazing intensities. We performed correlations and multiple regressions among the three types of variables across the pool of 35 species. 3. To analyse data at the community level, we computed weighted averages of traits and sheep selectivity indices for 34 floristic samples taken from each side of 17 fence lines with contrasting grazing intensities. Correlations between mean trait values and sheep selectivity across the 34 samples, and paired comparisons of those variables between sides of the fences, were performed. 4. Taller plants had leaves with lower SLA and/or higher toughness. Short species of intermediate toughness were selected more often by sheep, while SLA was not related to sheep selectivity. Short species with high SLA increased with grazing, while toughness and sheep selectivity were unrelated to grazing response. 5. At the community level, short swards with high average SLA had high selectivity indices and were more abundant on the most intensively grazed sides of fence lines. Leaf toughness was unrelated to other traits or to sheep selectivity, and showed no significant response to grazing. 6. Synthesis and applications. Intensive grazing can increase the forage value of grasslands by the creation of lawns dominated by tolerant species. However, results from this study showed that some plant species that were avoided by grazers also increased, indicating a potential risk of a shift in composition of grazing lawns towards states of low forage value. This suggests that periodic resting of lawns could be a good management strategy to favour palatable species, thereby minimizing the risk of undesirable shifts in the overall species composition. |
| [7] | |
| [8] | The factors determining species commonness and rarity are poorly understood, particularly in highly diverse communities. Theory predicts that interactions with neighbors of the same (conspecific) and other (heterospecific) species can influence a species' relative abundance, but empirical tests are lacking. By using a hierarchical model of survival for more than 30,000 seedlings of 180 tropical tree species on Barro Colorado Island, Panama, we tested whether species' sensitivity to neighboring individuals relates to their relative abundance in the community. We found wide variation among species in the effect of conspedfic, but not heterospecific, neighbors on survival, and we found a significant relationship between the strength of conspedfic neighbor effects and spedes abundance. Specifically, rare spedes suffered more from the presence of conspedfic neighbors than common spedes did, suggesting that conspedfic density dependence shapes species abundances in diverse communities. |
| [9] | 1. We examined the possibility of using the dry matter content (DMC) of macrophytes (the ratio of dry mass to wet mass) as an integrative variable to predict their palatability to generalist invertebrate grazers. 2. We assessed the palatability of 20 macrophyte species, using the snail Lymnaea stagnalis (L.) in non-choice feeding experiments. Three of the species were studied at two different dates in the year, at two or four sites. 3. The average dry mass consumed by L. stagnalis ranged widely between species, and was negatively correlated to plant DMC. At the intraspecific level, the dry mass consumed varied over time but was not related to site location. Again, the dry mass consumed was negatively correlated to plant DMC. 4. The DMC of the macrophytes studied explained about 30% of interspecific variability, and >80% of seasonal variability, in snail consumption rate. Therefore this trait could be used as a shortcut to predict variations in macrophyte palatability, especially at the intraspecific level. At the interspecific level, the relationship between DMC and palatability might be weakened by the presence in some plants of low molecular weight chemical deterrents. |
| [10] | I evaluated the hypothesis that leaf-cutting ants are more common in early successional forests than in old-growth forests because pioneer species, which dominate in early successional habitats, appear more susceptible to leafcutters than shade-tolerant species, which dominate primary forests (palatable forage hypothesis). The relative importance of pioneer and shade-tolerant species as plant resources for leaf-cutting ant colonies was evaluated (1) by literature review of leaf-cutting ants' diet, and (2) experimentally, using field assays to determine leafcutter's selectivity. Pioneer species were harvested three times more frequently than shade-tolerant species and made up the largest component of the diet in all the studies reviewed. The amount harvested was not correlated with the plant species abundance. In addition, leaves from pioneer plants were selected eight times more than leaves from shade-tolerant species in the field assays. These results support the palatable forage hypothesis. Leafcutters probably select pioneer leaves because of their low level of chemical defenses and high nutrient content. The high availability of pioneer species in early successional forest probably decreases the cost to locate palatable resources. Therefore, early successional habitats support more ant colonies than old-growth forests. On the other hand, the effective defense mechanisms of mature plant species and the high dispersion of palatable plants could explain the low density of leaf-cutting ant colonies in old-growth forests. The palatable forage hypothesis is compared with other hypotheses that explain leaf-cutting ant density. The preference of foundress queens for forest clearings, the dependence of small colonies on herbs, and the importance of pioneer plant species for mature colonies (palatable forage hypothesis) can be considered complementary, because they focus on different stages of the colony's life history. Consequently, the availability of pioneer plants appears to be one of the most influential factors determining mature leaf-cutting ant nest densities in Neotropical forests. |
| [11] | Interpretation of regression coefficients is sensitive to the scale of the inputs. One method often used to place input variables on a common scale is to divide each numeric variable by its standard deviation. Here we propose dividing each numeric variable by two times its standard deviation, so that the generic comparison is with inputs equal to the mean 卤1 standard deviation. The resulting coefficients are then directly comparable for untransformed binary predictors. We have implemented the procedure as a function in R. We illustrate the method with two simple analyses that are typical of applied modeling: a linear regression of data from the National Election Study and a multilevel logistic regression of data on the prevalence of rodents in New York City apartments. We recommend our rescaling as a default option - an improvement upon the usual approach of including variables in whatever way they are coded in the data file - so that the magnitudes of coefficients can be directly compared as a matter of routine statistical practice. Copyright 漏 2007 John Wiley & Sons, Ltd. |
| [12] | We consider the role that key structural traits, such as spinescence, pubescence, sclerophylly and raphides, play in protecting plants from herbivore attack. Despite the likelihood that many of these morphological characteristics may have evolved as responses to other environmental stimuli, we show that each provides an important defence against herbivore attack in both terrestrial and aquatic ecosystems. We conclude that leaf-mass 揳rea is a robust index of sclerophylly as a surrogate for more rigorous mechanical properties used in herbivory studies. We also examine herbivore counter-adaptations to plant structural defence and illustrate how herbivore attack can induce the deployment of intensified defensive measures. Although there have been few studies detailing how plant defences vary with age, we show that allocation to structural defences is related to plant ontogeny. Age-related changes in the deployment of structural defences plus a paucity of appropriate studies are two reasons why relationships with other plant fitness characteristics may be obscured, although we describe studies where trade-offs between structural defence and plant growth, reproduction, and chemical defences have been demonstrated. We also show how resource availability influences the expression of structural defences and demonstrate how poorly our understanding of plant structural defence fits into contemporary plant defence theory. Finally, we suggest how a better understanding of plant structural defence, particularly within the context of plant defence syndromes, would not only improve our understanding of plant defence theory, but enable us to predict how plant morphological responses to climate change might influence interactions at the individual (plant growth trade-offs), species (competition), and ecosystem (pollination and herbivory) levels. |
| [13] | Research on plant tolerance to herbivory has been so far largely focussed on herbaceous plants partly due to the implicit assumption that woody plants are inherently lower in their compensatory potential as compared to herbs. However, tolerance to herbivory should be an important part of resistance of woody plants because their apparency to herbivory is high due to a large size and long life span, and their defence systems cannot completely exclude herbivory. Moreover, the longer life span, more complex modularity and higher sectorality of woody plants as compared to herbs imply that compensatory responses in woody plants may take several years to develop, and that consequences of herbivore damage to individual modules may profoundly differ from whole-plant responses. Therefore, short-term studies using branches or ramets as experimental units are likely to underestimate the tolerance of woody plants to herbivory. In addition, defoliation by insects (the most common type of herbivory experienced by woody plants) is less likely to release apical dominance and trigger biomass compensation than mammalian grazing on herbaceous plants. We conclude, therefore, that the seemingly different recovery potentials exhibited by woody and herbaceous plants are more likely to be the consequences of differences between the two types of plants in modular architecture, longevity and the type of herbivory they commonly experience rather than indications of inherent differences in compensatory ability. |
| [14] | Habitat fragmentation is one of the principal causes of biodiversity loss and hence understanding its impacts on community assembly and disassembly is an important topic in ecology. We studied the relationships between fragmentation and community assembly processes in the land-bridge island system of Thousand Island Lake in East China. We focused on the changes in species diversity and phylogenetic diversity that occurred between life stages of woody plants growing on these islands. The observed diversities were compared with the expected diversities from random null models to characterize assembly processes. Regression tree analysis was used to illustrate the relationships between island attributes and community assembly processes. We found that different assembly processes predominate in the seedlings-to-saplings life-stage transition (SS) vs. the saplings-to-trees transition (ST). Island area was the main attribute driving the assembly process in SS. In ST, island isolation was more important. Within a fragmented landscape, the factors driving community assembly processes were found to differ between life stage transitions. Environmental filtering had a strong effect on the seedlings-to-saplings life-stage transition. Habitat isolation and dispersal limitation influenced all plant life stages, but had a weaker effect on communities than area. These findings add to our understanding of the processes driving community assembly and species coexistence in the context of pervasive and widespread habitat loss and fragmentation. |
| [15] | The relationship between plant nutrient content and insect herbivore populations and community structure has long interested ecologists. Insect herbivores require multiple nutrients, but ecologists have focused mostly on nitrogen (an estimate of plant protein content), and more recently phosphorus (P); other nutrients have received little attention. Here we document nutrient variation in grass and forb samples from grassland habitats in central Nebraska using an elemental approach; in total we measured foliar concentrations of 12 elements (N and P, plus S, B, Ca, Mg, Na, K, Zn, Fe, Mn, and Cu). We detected significant variability among sites for N, P, Mg, Na, K, and Cu. We next used a model selection approach to explore how this nutritional variation and plant biomass correlate with grasshopper densities (collectively and at the feeding-guild level), and principal component analysis to explore nutrient correlations with grasshopper community species composition. When all grasshoppers were pooled, densities varied among sites, but only P was associated with abundance of the elements shown to vary between sites. Different responses occurred at the feeding-guild level. For grass specialists, densities were associated with N, plus P, Mg, and Na. For forb specialists, N and P were often associated with density, but associations with Na and K were also observed. Finally, mixed-feeder abundance was strongly associated with biomass, and to a lesser extent P, Mg, Na, and Cu. At the community level, B, Ca, Zn, and Cu, plus biomass, explained >30% of species composition variation. Our results confirm the positive association of N and P with insect herbivore populations, while suggesting a potential role for Mg, Na, and K. They also demonstrate the importance of exploring effects at the feeding-guild level. We hope our data motivate ecologists to think beyond N and P when considering plant nutrient effects on insect herbivores, and make a call for studies to examine functional responses of insect herbivores to dietary manipulation of Mg, Na, and K. Finally, our results demonstrate correlations between variation in nutrients and species assemblages, but factors not linked to plant nutrient quality or biomass likely explain most of the observed variation. |
| [16] | Tree seedlings have a harder time establishing themselves in forests containing many adults of the same species. |
| [17] | Leaf life span is widely recognized as a key life history trait associated with herbivory resistance, but rigorous comparative data are rare for seedlings. The goal of this study was to examine how light environment affects leaf life span, and how ontogenetic development during the first year may influence leaf fracture toughness, lamina density and stem density that are relevant for herbivory resistance, leaf life span and seedling survival.Data from three experiments encompassing 104 neotropical woody species were combined. Leaf life span, lamina and vein fracture toughness, leaf and stem tissue density and seedling survival were quantified for the first-year seedlings at standardized ontogenetic stages in shade houses and common gardens established in gaps and shaded understorey in a moist tropical forest in Panama. Mortality of naturally recruited seedlings till 1 year later was quantified in 800 1-m(2) plots from 1994 to 2011.Median leaf life span ranged widely among species, always greater in shade (ranging from 151 to 1790 d in the understorey and shade houses) than in gaps (115867 d), but with strong correlation between gaps and shade. Leaf and stem tissue density increased with seedling age, whereas leaf fracture toughness showed only a weak increase. All these traits were positively correlated with leaf life span. Leaf life span and stem density were negatively correlated with seedling mortality in shade, while gap mortality showed no correlation with these traits.The wide spectrum of leaf life span and associated functional traits reflects variation in shade tolerance of first-year seedlings among coexisting trees, shrubs and lianas in this neotropical forest. High leaf tissue density is important in enhancing leaf toughness, a known physical defence, and leaf life span. Both seedling leaf life span and stem density should be considered as key functional traits that contribute to seedling survival in tropical forest understoreys. |
| [18] | Leaf toughness is thought to enhance physical defense and leaf lifespan. Here, we evaluated the relative importance of tissue-level leaf traits vs lamina thickness, as well as their ontogenetic changes, for structure-level leaf toughness and regeneration ecology of 19 tropical tree species. We measured the fracture toughness of the laminas and veins of sapling leaves with shearing tests, and used principal component analysis and structural equation modeling to evaluate the multivariate relationships among traits that contribute to leaf toughness and their links to ecological performance traits. Tissue traits (density and fracture toughness of lamina and vein) were correlated positively with each other, but independent of lamina thickness. The tissue traits and lamina thickness contributed additively to the structure-level toughness (leaf mass per area and work-to-shear). Species with dense and tough leaves as saplings also had dense and tough leaves as seedlings and adults. The patterns of ontogenetic change in trait values differed between the seedling-to-sapling and sapling-to-adult transitions. The fracture toughness and tissue density of laminas and veins, but not the lamina thickness, were correlated positively with leaf lifespan and sapling survival, and negatively with herbivory rate and sapling regeneration light requirements, indicating the importance of tissue-level leaf traits. |
| [19] | |
| [20] | |
| [21] | Leaves are most vulnerable to herbivory during expansion. We hypothesised that one factor favouring small leaves could be that smaller-leaved species have shorter expansion times and are therefore exposed to high levels of herbivory for a shorter period than large leaves. In order to test this hypothesis, leaf expansion time and leaf area loss were measured for 51 species from Sydney, Australia. Strong positive correlations were found between leaf length and area and leaf expansion time, confirming that small leaves do expand in a shorter time than large leaves. The amount of leaf area lost was highly variable (from 0.5 to 90% of total leaf area), but was significantly related to both leaf expansion time and log leaf area. The amount of leaf area lost was not significantly correlated with specific leaf area nor with the presence of distasteful substances in the leaves, but was lower on species with hairy expanding leaves. |
| [22] | Abstract Here, we analysed a wide range of literature data on the leaf dry mass per unit area (LMA). In nature, LMA varies more than 100-fold among species. Part of this variation (c. 35%) can be ascribed to differences between functional groups, with evergreen species having the highest LMA, but most of the variation is within groups or biomes. When grown in the same controlled environment, leaf succulents and woody evergreen, perennial or slow-growing species have inherently high LMA. Within most of the functional groups studied, high-LMA species show higher leaf tissue densities. However, differences between evergreen and deciduous species result from larger volumes per area (thickness). Response curves constructed from experiments under controlled conditions showed that LMA varied strongly with light, temperature and submergence, moderately with CO2 concentration and nutrient and water stress, and marginally under most other conditions. Functional groups differed in the plasticity of LMA to these gradients. The physiological regulation is still unclear, but the consequences of variation in LMA and the suite of traits interconnected with it are strong. This trait complex is an important factor determining the fitness of species in their environment and affects various ecosystem processes. |
| [23] | We evaluated leaf characteristics and herbivory intensities for saplings of fifteen tropical tree species differing in their successional position. Eight leaf traits were selected, related to the costs of leaf display (specific leaf area [SLA], water content), photosynthesis (N and P concentration per unit mass), and herbivory defence (lignin concentration, C : N ratio). We hypothesised that species traits are shaped by variation in abiotic and biotic (herbivory) selection pressures along the successional gradient. All leaf traits varied with the successional position of the species. The SLA, water content and nutrient concentration decreased, and lignin concentration increased with the successional position. Herbivory damage (defined as the percentage of damage found at one moment in time) varied from 0.9 - 8.5 % among the species, but was not related to their successional position. Herbivory damage appeared to be a poor estimator of the herbivory rate experienced by species, due to the confounding effect of leaf lifespan. Herbivory rate (defined as percentage leaf area removal per unit time) declined with the successional position of the species. Herbivory rate was only positively correlated to water content, and negatively correlated to lignin concentration, suggesting that herbivores select leaves based upon their digestibility rather than upon their nutritive value. Surprisingly, most species traits change linearly with succession, while resource availability (light, nutrients) declines exponentially with succession. |
| [24] | |
| [25] | Differential herbivory and/or differential plant resistance or tolerance in sun and shade environments may influence plant distribution along the light gradient. Embothrium coccineum is one of the few light-demanding tree species in the temperate rainforest of southern South America, and seedlings are frequently attacked by insects and snails. Herbivory may contribute to the exclusion of E. coccineum from the shade if 1) herbivory pressure is greater in the shade, which in turn can result from shade plants being less resistant or from habitat preferences of herbivores, and/or 2) consequences of damage are more detrimental in the shade, i.e., shade plants are less tolerant. We tested this in a field study with naturally established seedlings in treefall gaps (sun) and forest understory (shade) in a temperate rainforest of southern Chile. Seedlings growing in the sun sustained nearly 40% more herbivore damage and displayed half of the specific leaf area than those growing in the shade. A palatability test showed that a generalist snail consumed ten times more leaf area when fed on shade leaves compared to sun leaves, i.e., plant resistance was greater in sun-grown seedlings. Herbivore abundance (total biomass) was two-fold greater in treefall gaps compared to the forest understory. Undamaged seedlings survived better and showed a slightly higher growth rate in the sun. Whereas simulated herbivory in the shade decreased seedling survival and growth by 34% and 19%, respectively, damaged and undamaged seedlings showed similar survival and growth in the sun. Leaf tissue lost to herbivores in the shade appears to be too expensive to replace under the limiting light conditions of forest understory. Following evaluations of herbivore abundance and plant resistance and tolerance in contrasting light environments, we have shown how herbivory on a light-demanding tree species may contribute to its exclusion from shade sites. Thus, in the shaded forest understory, where the seedlings of some tree species are close to their physiological tolerance limit, herbivory could play an important role in plant establishment. |
| [26] | 1. Insect herbivory can strongly affect ecosystem processes, and its relationship with plant diversity is a central topic in biodiversity unctioning research. However, very little is known about this relationship from complex ecosystems dominated by long-lived individuals, such as forests, especially over gradients of high plant diversity.2. We analysed insect herbivory on saplings of 10 tree and shrub species across 27 forest stands differing in age and tree species richness in an extraordinarily diverse subtropical forest ecosystem in China. We tested whether plant species richness significantly influences folivory in these highly diverse forests or whether other factors play a more important role at such high levels of phytodiversity.3. Leaf damage was assessed on 58 297 leaves of 1284 saplings at the end of the rainy season in 2008, together with structural and abiotic stand characteristics.4. Species-specific mean damage of leaf area ranged from 3% to 16%. Herbivory increased with plant species richness even after accounting for potentially confounding effects of stand characteristics, of which stand age-related aspects most clearly covaried with herbivory. Intraspecific density dependence or other abiotic factors did not significantly influence overall herbivory across forest stands.5. Synthesis. The positive herbivory 損lant diversity relationship indicates that effects related to hypotheses of resource concentration, according to which a reduction in damage by specialized herbivores might be expected as host plant concentration decreases with increasing plant diversity, do not seem to be major determinants for overall herbivory levels in our phytodiverse subtropical forest ecosystem. We discuss the potential role of host specificity of dominant herbivores, which are often expected to show a high degree of specialization in many (sub)tropical forests. In the forest system we studied, a much higher impact of polyphagous species than traditionally assumed might explain the observed patterns, as these species can profit from a broad dietary mix provided by high plant diversity. Further testing is needed to experimentally verify this assumption. |
| [27] | Differences in herbivory among woody species can greatly affect the functioning of forest ecosystems, particularly in species-rich (sub)tropical regions. However, the relative importance of the different plant traits which determine herbivore damage remains unclear. Defence traits can have strong effects on herbivory, but rarely studied geographical range characteristics could complement these effects through evolutionary associations with herbivores. Herein, we use a large number of morphological, chemical, phylogenetic and biogeographical characteristics to analyse interspecific differences in herbivory on tree saplings in subtropical China. Unexpectedly, we found no significant effects of chemical defence traits. Rather, herbivory was related to the plants' leaf morphology, local abundance and climatic niche characteristics, which together explained 70% of the interspecific variation in herbivory in phylogenetic regression. Our study indicates that besides defence traits and apparency to herbivores, previously neglected measures of large-scale geographical host distribution are important factors influencing local herbivory patterns among plant species. |
| [28] | Abstract The promise of "trait-based" plant ecology is one of generalized prediction across organizational and spatial scales, independent of taxonomy. This promise is a major reason for the increased popularity of this approach. Here, we argue that some important foundational assumptions of trait-based ecology have not received sufficient empirical evaluation. We identify three such assumptions and, where possible, suggest methods of improvement: (i) traits are functional to the degree that they determine individual fitness, (ii) intraspecific variation in functional traits can be largely ignored, and (iii) functional traits show general predictive relationships to measurable environmental gradients. |
| [29] | Laubwerfende und immergrüne Baumarten koexistieren in tropischen Trockenw01ldern, aber sie zeigen unterschiedliche Blattsyndrome hinsichtlich der Effizienz der Ressourcennutzung und der Verteidigung gegen Herbivore. Darüberhinaus k02nnen diese funktionellen Gruppen unterschiedliche Muster der zeitlichen Variation bei den Blattmerkmalen und des Herbivorenfra08es im Laufe der Blattentwicklung aufweisen. Wir testeten diese Vorhersagen durch den Vergleich einer Anzahl von Blatteigenschaften mit Bezug zu Wasserstress und Verteidigung und des Herbivorenfra08es bei jungen und voll entwickelten Bl01ttern von immergrünen Blattwechslern und laubwerfenden Arten. Wir untersuchten solche B01ume im selben Habitattyp, einem tropischen Trockenwald mit 90 bis 100% Blattwurf w01hrend der Trockenzeit. Wir beprobten jeweils zehn B01ume von drei laubwerfenden und drei immergrünen Arten. Immergrüne besa08en dickere Bl01tter und h02here Konzentrationen von Phenolen und Tanninen. Laubwerfende B01ume wiesen einen h02heren Stickstoffgehalt der Bl01tter und eine h02here spezifische Blattfl01che auf. Blattwerfende B01ume verloren doppelt so viel Blattfl01che durch Herbivorenfra08 wie die Immergrünen (6.48% gegenüber 3.20%), und die Sch01den an den Bl01ttern waren positiv mit dem Gehalt an phenolischen Komponenten und Stickstoff verbunden. Reife Bl01tter von beiden ph01nologischen Gruppen wiesen h02here Gehalte an Tanninen und phenolischen Verbindungen und geringere Stickstoffgehalte sowie geringeren Herbivorenfra08 auf als junge Bl01tter. Unsere Ergebnisse legen nahe, dass bei unterschiedlichen Arten innerhalb der beiden ph01nologischen Gruppen eine adaptive Konvergenz bei den mit Wasserstress verbundenen Blattmerkmalen besteht. Einige dieser Merkmale spielen auch eine Rolle in Hinblick auf die Genie08barkeit, obwohl die Auswirkungen auf die Fitness der absoluten Differenz zwischen immergrünen und laubwerfenden Arten bei den Blattsch01den (ca. 3%) unklar bleiben. |
| [30] | Although the impacts of the loss of biodiversity on ecosystem functioning are well established, the importance of the loss of biodiversity relative to other human-caused drivers of environmental change remains uncertain. Results of 11 experiments show that ecologically relevant decreases in grassland plant diversity influenced productivity at least as much as ecologically relevant changes in nitrogen, water, CO60, herbivores, drought or fire. Moreover, biodiversity became an increasingly dominant driver of ecosystem productivity through time, whereas effects of other factors either declined (nitrogen addition) or remained unchanged (all others). In particular, a change in plant diversity from four to 16 species caused as large an increase in productivity as addition of 54 kg·ha6301·y6301 of fertilizer N, and was as influential as removing a dominant herbivore, a major natural drought, water addition, and fire suppression. A change in diversity from one to 16 species caused a greater biomass increase than 95 kg·ha6301·y6301 of N or any other treatment. Our conclusions are based on >7,000 productivity measurements from 11 long-term experiments (mean length, ~ 13 y) conducted at a single site with species from a single regional species pool, thus controlling for many potentially confounding factors. Our results suggest that the loss of biodiversity may have at least as great an impact on ecosystem functioning as other anthropogenic drivers of environmental change, and that use of diverse mixtures of species may be as effective in increasing productivity of some biomass crops as fertilization and may better provide ecosystem services. |
| [31] | . During the long-term interactions or survival competition with biotic and abiotic environments, plants have developed a set of defensive strategies to resist adverse conditions. Two major defensive strategies, physical defense and chemical defense, were usually defined to address this issue. The physical defense strategy is adopted by plants through changing the morphological structure, such as leaf vein network structure, stem and leaf toughness, hardness, cellulose, hemicellulose and lignin content, etc; while the chemical defense strategy refers to physiological and biochemical responses, such as some secondary metabolites and defensive enzymes which often serve as a critical biochemical basis for the resistance and response to pathogens, pests and the abiotic environmental stresses. In this paper, we firstly reviewed important traits of the two distinctively defensive strategies, and then analyzed their driven mechanisms from the perspectives of biological violations, climate factors, and resource allocation in plants. The paper would, to some extent, contribute to further understanding the internal relationship between plant traits and environment, and also provide some references for plant regional adaptation, selective breeding in insect-resistant germplasm resources, and forest management. |
| [32] | |
| [33] | The performance and population dynamics of insect herbivores depend on the nutritive and defensive traits of their host plants(1). The literature on plant-herbivore interactions focuses on plant trait means(2,3,4), but recent studies showing the importance of plant genetic diversity for herbivores suggest that plant trait variance may be equally important(5,6). The consequences of plant trait variance for herbivore performance, however, have been largely overlooked. Here we report an extensive assessment of the effects of within-population plant trait variance on herbivore performance using 457 performance datasets from 53 species of insect herbivores. We found that variance in plant nutritive traits substantially reduces mean herbivore performance via nonlinear averaging of performance relationships that were overwhelmingly concave-down. In contrast, relationships between herbivore performance and plant defense levels were typically linear, such that plant defense variance does not affect herbivore performance via nonlinear averaging. Our results demonstrate that plants contribute to the suppression of herbivore populations by having variable nutrient levels, not just by having low average quality as is typically thought. We propose that this phenomenon could play a key role in the suppression of herbivore populations in natural systems, and that increased nutrient heterogeneity within agricultural crops could contribute to the sustainable control of insect pests in agroecosystems. |
| [34] | . |
| [35] | . 在植物与植食性昆虫长期的进化过程中,双方形成了一系列的防御与反防御策略.本文将这些策略归为3个层 次:第一层次起始于植物对植食性昆虫相关分子模式的识别,并由此激活植食性昆虫分子模式相关的免疫反应.这种免疫反应对于不能产生效应子的植食性昆虫种群 是有效的;第二层次是一些植食性昆虫种群可以通过释放特异性效应子抑制植物产生的植食性昆虫分子模式相关的免疫反应,从而在植物上正常生长与繁衍;第三层 次是一些植物基因型可以通过特异抗性基因识别植食性昆虫的效应子,进而激活效应子诱导的免疫反应,表现出特异的抗虫性.深入揭示植物与植食性昆虫间的这种 分子互作机制,不仅在理论上有助于理解昆虫与植物的协同进化机制,而且在实践上可为作物抗性品种的培育提供重要的技术指导. |
| [36] | . |
| [37] | . |
| [38] | Abstract Herbivory is well known to be a major selective pressure that affects plant communities, but the leaf traits that mediate variations in herbivory at the interspecific level remain controversial. We collected published data on background insect herbivory and leaf traits from a wide variety of species to test the hypothesis that species with intermediate leaf lifespans, lower fiber, and higher nutrient contents in leaves should have higher levels of herbivory. We found that at the interspecific level herbivory had a hump-shaped relationship with leaf lifespan and a positive relationship with leaf size. Surprisingly, our data show that nutritional traits have little relationship to herbivory. Our study provides new insights relevant to the recent debate on leaf trait-herbivory relationships. These findings are especially helpful in explaining the general patterns of herbivory detected on the global scale. This article is protected by copyright. All rights reserved. |
3
2002
... 植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(
... ).叶干物质含量和比叶质量越高的叶片含有越高的组织密度, 通常可以防御植食性动物从而较少受到植食侵害.化学成分表征植物化学组成包括碳水化合物、含氮化合物和防御性代谢产物等, 这些化合物能够直接影响植物的营养性和防御性成分组成.碳水化合物中,纤维素含量影响植食性动物的消化,高浓度可溶性糖能稀释其他营养物质而产生对虫食的负作用(
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Pathogens and insect herbivores drive rainforest plant diversity and composition.
1
2014
... 植食性动物对植物的植食作用(herbivory)是生态系统中动植物之间重要的相互关系(
Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach. Springer-Verlag
1
2003
... 对上述模型进行模型选择, 由于最优模型之间具有相近的AICc值(ΔAICc < 2), 对赤池重量(Akaike weight, ω+)累积95%以上的模型组内的变量计算其相对重要性, 筛选出重要的变量得出最佳模型(
Plant traits that predict resistance to herbivores.
1
2011
... 植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(
The ecology of leaf life spans.
1
1982
... 叶生活周期与碳氮比和叶厚度都有较高的相关性(没有包括在最佳模型中), 在与虫食率的线性回归中显示了极显著的影响.根据成本效益理论, 生活在林荫下的幼苗由于光照少而获得的资源有限, 而叶生活周期长的幼苗往往有更好的防御手段(如高叶片厚度和组织密度)和更低的营养物质含量, 可以有效地降低虫食带来的损伤并提高存活率(
Plant functional traits, herbivore selectivity and response to sheep grazing in Patagonian steppe grasslands.
1
2005
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Effects of leaf age and plant life history patterns on herbivory.
1
1980
... 植物的其他特征, 如相对多度等被认为可能是影响虫食率的因素(
Asymmetric density dependence shapes species abundances in a tropical tree community.
1
2010
... 植物的其他特征, 如相对多度等被认为可能是影响虫食率的因素(
Leaf dry matter content as an integrative expression of plant palatability: The case of freshwater macrophytes.
1
2003
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Why are leaf-cutting ants more common in early secondary forests than in old-growth tropical forests? An evaluation of the palatable forage hypothesis.
1
2001
... 植物的其他特征, 如相对多度等被认为可能是影响虫食率的因素(
Scaling regression inputs by dividing by two standard deviations.
1
2008
... 本研究采用多元线性回归模型分析植物功能性状和物种相对多度等变量对虫食率的影响.首先, 对所有连续型自变量以2倍自变量的标准差作标准化, 保证变量尺度的可比性(
Plant structural traits and their role in anti-herbivore defence.
1
2007
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Tolerance to herbivory in woody vs. herbaceous plants.
1
2000
... 植物的其他特征, 如相对多度等被认为可能是影响虫食率的因素(
Habitat fragmentation drives plant community assembly processes across life stages.
2
2016
... 千岛湖(29.37°-29.83° N, 118.57°-119.25° E)位于浙江省西南部, 是1959年建成的新安江水电站截新安江而成的大型人工湖泊, 水域面积约为 573 km2.在最高水位海拔108 m时, 水库拥有1 078个0.25 hm2以上的岛屿.该地区属亚热带季风气候, 年平均气温约17.0 ℃, 1月份最低气温-7.6 ℃, 7月份最高气温41.8 ℃; 年降水量1 430 mm, 降雨集中在4月到6月的雨季.本研究位于千岛湖中心湖区, 选取29个面积跨度0.08-1 158.00 hm2的岛屿(据最新的GIS计算结果), 每个岛屿的植被以次生马尾松(Pinus massoniana)林为主, 种类组成高度相似(
... 2014-2015年, 采用CTFS森林动态样地的标准方法对29个岛屿的样地内胸径1 cm以上的木本植物个体进行复查, 对2009-2010年初次调查中已挂牌的个体重新调查胸径、树高, 对新增个体进行标记和挂牌, 并记录其胸径和树高, 具体调查方法及结果详见文献(
Not just the usual suspects: Insect herbivore populations and communities are associated with multiple plant nutrients.
1
2012
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Conspecific negative density dependence and forest diversity.
1
2012
... 根据相关性分析和模型结果, 相对多度越高的物种, 其幼苗被虫食损伤的强度越小, 与假设(2)一致.植物性状能够显著影响适合度, 而相对多度可以作为该物种适合度的定量替代(
Leaf life span spectrum of tropical woody seedlings: Effects of light and ontogeny and consequences for survival.
1
2013
... 叶生活周期与碳氮比和叶厚度都有较高的相关性(没有包括在最佳模型中), 在与虫食率的线性回归中显示了极显著的影响.根据成本效益理论, 生活在林荫下的幼苗由于光照少而获得的资源有限, 而叶生活周期长的幼苗往往有更好的防御手段(如高叶片厚度和组织密度)和更低的营养物质含量, 可以有效地降低虫食带来的损伤并提高存活率(
Tissue-level leaf toughness, but not lamina thickness, predicts sapling leaf lifespan and shade tolerance of tropical tree species.
1
2010
... 综上所述, 本研究结果表明, 叶片碳氮比和叶厚度等作为营养和防御性状在千岛湖地区共同影响植食性昆虫的取食选择, 而相对多度高、适合度高的物种受虫食损伤低.在模型中, 碳氮比、叶厚度和相对多度所代表的其他性状能解释本研究地区16个植物物种平均叶片虫食率变异的54%.而其他性状如叶面积、叶干物质含量和光耐受性等对虫食率没有表现出明显的影响(
Predicting invertebrate herbivory from plant traits: Evidence from 51 grassland species in experimental monocultures.
1
2012
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Plant defense against herbivores: Chemical aspects.
1
2012
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Do small leaves expand faster than large leaves, and do shorter expansion times reduce herbivore damage?
1
2000
... 综上所述, 本研究结果表明, 叶片碳氮比和叶厚度等作为营养和防御性状在千岛湖地区共同影响植食性昆虫的取食选择, 而相对多度高、适合度高的物种受虫食损伤低.在模型中, 碳氮比、叶厚度和相对多度所代表的其他性状能解释本研究地区16个植物物种平均叶片虫食率变异的54%.而其他性状如叶面积、叶干物质含量和光耐受性等对虫食率没有表现出明显的影响(
Causes and consequences of variation in leaf mass per area (LMA): A meta-analysis.
2
2009
... 植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
Leaf traits and herbivory rates of tropical tree species differing in successional status.
2
2004
... 植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(
... 本研究发现, 碳氮比是影响植物种间虫食率差异的最显著的变量(
R: A language and environment for statistical computing.
1
2016
... 对上述模型进行模型选择, 由于最优模型之间具有相近的AICc值(ΔAICc < 2), 对赤池重量(Akaike weight, ω+)累积95%以上的模型组内的变量计算其相对重要性, 筛选出重要的变量得出最佳模型(
Herbivory on temperate rainforest seedlings in sun and shade: Resistance, tolerance and habitat distribution.
1
2010
... 综上所述, 本研究结果表明, 叶片碳氮比和叶厚度等作为营养和防御性状在千岛湖地区共同影响植食性昆虫的取食选择, 而相对多度高、适合度高的物种受虫食损伤低.在模型中, 碳氮比、叶厚度和相对多度所代表的其他性状能解释本研究地区16个植物物种平均叶片虫食率变异的54%.而其他性状如叶面积、叶干物质含量和光耐受性等对虫食率没有表现出明显的影响(
Tree diversity promotes insect herbivory in subtropical forests of south-east China.
2
2010
... 在每株幼苗上, 随机方向上调查3根枝条, 每根枝条带有5枚成熟的完全扩展的叶片, 总共15枚叶片用来评估虫食率.计算由以下植食性昆虫造成的叶面积损伤: 嚼食型、挖食型、潜食型、吸食型和造瘿型(
... 根据相关性分析和模型结果, 相对多度越高的物种, 其幼苗被虫食损伤的强度越小, 与假设(2)一致.植物性状能够显著影响适合度, 而相对多度可以作为该物种适合度的定量替代(
Plant traits affecting herbivory on tree recruits in highly diverse subtropical forests.
1
2012
... 本研究采用多元线性回归模型分析植物功能性状和物种相对多度等变量对虫食率的影响.首先, 对所有连续型自变量以2倍自变量的标准差作标准化, 保证变量尺度的可比性(
Reinforcing loose foundation stones in trait-based plant ecology.
3
2016
... 植物的其他特征, 如相对多度等被认为可能是影响虫食率的因素(
... ).植物整个生活史阶段的若干个功能性状的共同作用在很大程度上决定了植物的适合度.适合度高的物种通常多度也高, 具有较高的个体生存、繁殖和生长率, 可反映为受到较低的虫食影响等(
... 根据相关性分析和模型结果, 相对多度越高的物种, 其幼苗被虫食损伤的强度越小, 与假设(2)一致.植物性状能够显著影响适合度, 而相对多度可以作为该物种适合度的定量替代(
Leaf traits and herbivory on deciduous and evergreen trees in a tropical dry forest.
1
2015
... 叶生活周期与碳氮比和叶厚度都有较高的相关性(没有包括在最佳模型中), 在与虫食率的线性回归中显示了极显著的影响.根据成本效益理论, 生活在林荫下的幼苗由于光照少而获得的资源有限, 而叶生活周期长的幼苗往往有更好的防御手段(如高叶片厚度和组织密度)和更低的营养物质含量, 可以有效地降低虫食带来的损伤并提高存活率(
Biodiversity impacts ecosystem productivity as much as resources, disturbance, or herbivory.
1
2012
... 植食性动物对植物的植食作用(herbivory)是生态系统中动植物之间重要的相互关系(
植物防御策略及其环境驱动机制
1
2015
... 植食性动物对植物的植食作用(herbivory)是生态系统中动植物之间重要的相互关系(
The arcsine is asinine: The analysis of proportions in ecology.
1
2011
... 本研究采用多元线性回归模型分析植物功能性状和物种相对多度等变量对虫食率的影响.首先, 对所有连续型自变量以2倍自变量的标准差作标准化, 保证变量尺度的可比性(
Variability in plant nutrients reduces insect herbivore performance.
1
2016
... 植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(
植物组成型防御对植食性昆虫的影响
1
2012
... 植物的叶片形态性状和化学成分一直被认为是影响虫食率的主要因素(
植物与植食性昆虫防御与反防御的三个层次
1
2015
... 植食性动物对植物的植食作用(herbivory)是生态系统中动植物之间重要的相互关系(
千岛湖被子植物枝叶性状分化及其与种多度关系
1
2017
... 2014年, 在千岛湖库区采集样本, 目标物种随机取5-10株长势良好的成年个体, 具体方法详见文献(
森林生态系统中植食性昆虫与寄主的互作机制、假说与证据
1
2014
... 植食性动物对植物的植食作用(herbivory)是生态系统中动植物之间重要的相互关系(
The association of leaf lifespan and background insect herbivory at the interspecific level.
1
2017
... 叶生活周期与碳氮比和叶厚度都有较高的相关性(没有包括在最佳模型中), 在与虫食率的线性回归中显示了极显著的影响.根据成本效益理论, 生活在林荫下的幼苗由于光照少而获得的资源有限, 而叶生活周期长的幼苗往往有更好的防御手段(如高叶片厚度和组织密度)和更低的营养物质含量, 可以有效地降低虫食带来的损伤并提高存活率(
