Ecological Stoichiometry of Plant-Herbivore Interactions

A complete summary of the data sets, including original citations, can be obtained at http://www.nceas.ucsb.edu/ecostoichiometry. These datasets include: summary of insect nitrogen content; phylogenetic distributions of body nitrogen composition (percent N) among insects; atomic ratios of lake C, N and P; and references for each. Autotrophs: We supplemented the literature with unpublished data to develop databases documenting the C:N:P stoichiometry of terrestrial plants and suspended particulate matter ('seston') in lakes. We restricted our terrestrial autotroph database to elemental analyses of foliage collected under field conditions, excluding agricultural and greenhouse studies. Multiple data fora single species were averaged before analysis. Terrestrial data were most frequently reported in percentage dry weight terms (percent N, percent P); when percent C values were not reported we converted percent N and percent P data to C:N and C:P ratios using the mean percentage C of reported values (46.4 percent C). To evaluate whether this procedure introduced any bias to observed patterns in foliage C:P and C:N, we calculated the mean and variability (coefficient of variation, c.v.) of the C:N and C:P ratios for that subset of species for which percent C, percent N, and percent P were all reported (n = 44). The mean and c.v. of C:N for this limited data set were 35.9 and 0.57, respectively, and 805 and 0.78 for C:P. These values are reasonably close to those for the remaining entries (for C:N, mean was 36.5, c.v. was 0.64; for C:P, mean was 990, c.v. was 0.75); thus, using a fixed percentage C value to estimate C:N and C:P probably did not influence the major patterns observed. A total of 501 plant species from 358 genera, 107 families, 62 orders, 20 subclasses, 8 classes and 5 divisions were included. We assessed C:N:P stoichiometry at the base of freshwater pelagic food webs by compiling a database of seston elemental composition in 226 lakes from published and unpublished reports. Only data for surface waters during the summer growing season were included; multiple observations during a year were averaged, and thus a 'lake-year' was the primary observation unit. Data were generally for lakes of small to moderate size but information for several of the world's great lakes was also included. Lakes were primarily located in North America but seston data for lakes in Europe, Africa and Asia were also obtained. Seston contains a mixture of living algae but also bacteria, protozoa and detritus and forms the food base for relatively indiscriminate planktonic filter-feeders. Although the contribution of these different components probably differs among lakes, various data indicate that, in general, seston particles in stratified lakes are dominated by phytoplankton biomass. For example, even in some lakes where seston C:P was high (and thus the contribution of low-nutrient detritus might be thought relatively important), algae contributed about 70 percent of total seston biomass (bacteria and protozoa contributed, 20 percent and, 5 percent, respectively, implying little influence of detritus). Thus, the freshwater and terrestrial data sets for 'autotrophs' differ in that the terrestrial data involve observations for particular plant species while the lake data correspond to a mixture of particles, living and non-living. Finally, if different seston particles have substantially different C:N:P ratios, bulk seston C:N:P measurements may not accurately quantify actual stoichiometric food quality for particular herbivores that can discriminate among particles, such as some calanoid copepods. Herbivores: Data for the C:N:P stoichiometry of terrestrial herbivorous insects and lake zooplankton were compiled from published and unpublished sources. Multiple data for a single species were averaged before analysis. As for terrestrial plants, when values of percentage C were not given, data reported as percent N and percent P were converted to C:N and C:P ratios using the mean percentage C value for the remainder of the herbivore database (48 percent C). We followed the same procedure used in analyses of the foliage data to evaluate possible bias introduced by assuming this fixed percentage C value. However, data for few species included all three parameters (percent C, percent N, percent P); we thus confined our assessment of possible biases to data on herbivore C:N. The mean and c.v. values of C:N for the data subset with direct measurements of percent C and percent N (n = 67) were 5.9 and 0.21 whereas values for entries for which the fixed percentage C value was used (n = 97) were 6.7 and 0.28. Here again, using a fixed value of percentage C to estimate C:N and C:P from percent N and percent P probably did not unduly influence theobserved patterns. A total of 130 species of insects from 93 genera, 40 families and 7 orders were included. By far, most insects included were leaf-eating, though a minority were phloem-feeding herbivores (such as aphids). Leaf-eaters and phloem-feeders did not differ in C:N:P ratios and therefore all taxa were analysed together. Predatory zooplankton were excluded from the compilation but several omnivorous taxa were retained. A total of 43 species of zooplankton from 23 genera, 12 families, 8 orders, 4 classes and 2 phyla were included. The majority of the taxa were crustaceans (mainly branchiopods ('cladocera'), malacostracans and copepods) but data for several rotifers were also compiled. All stoichiometric ratios were calculated on an atomic basis.完整的数据集汇总（包括原始引用）可通过http://www.nceas.ucsb.edu/ecostoichiometry 获取。本数据集包含：昆虫氮含量汇总数据；昆虫体内氮组成（氮百分比含量）的系统发育分布数据；湖泊碳（C）、氮（N）、磷（P）原子比数据，以及各数据集的参考文献。 自养生物：本研究补充未发表文献数据以构建数据库，记录陆生植物与湖泊悬浮颗粒物（seston）的碳氮磷化学计量比（stoichiometry）。本陆生自养生物数据库仅纳入野外条件下采集的叶片元素分析数据，排除农业及温室研究数据。同一物种的多条数据在分析前先进行平均处理。陆生数据多以干重百分比形式报告（氮百分比、磷百分比）；当未报告碳百分比数据时，我们采用已报告数据的平均碳百分比（46.4% C），将氮、磷百分比数据转换为碳氮比（C:N）与碳磷比（C:P）。为评估该转换流程是否会对叶片碳磷比、碳氮比的观测格局引入偏差，我们针对同时报告了碳、氮、磷百分比的物种子集（n=44），计算了其碳氮比与碳磷比的均值及变异系数（coefficient of variation, c.v.）。该子集的碳氮比均值与变异系数分别为35.9与0.57，碳磷比则为805与0.78。这些数值与剩余条目数值较为接近（碳氮比均值36.5，变异系数0.64；碳磷比均值990，变异系数0.75）；因此，采用固定碳百分比估算碳氮比与碳磷比，大概率不会对观测到的主要格局产生影响。本数据集共纳入来自5个界、8个纲、20个亚纲、62个目、107个科、358个属的501个植物物种。 我们通过汇编已发表及未发表的报告数据，构建了226个湖泊的悬浮物元素组成数据库，以此评估淡水浮游食物网基部的碳氮磷化学计量比。本数据集仅纳入夏季生长季的表层水数据；同一年份的多次观测值将被平均，因此“湖泊年份”为主要观测单元。数据涵盖的湖泊多为中小型湖泊，但也纳入了部分世界大型湖泊。湖泊主要分布于北美，但同时也获取了欧洲、非洲及亚洲湖泊的悬浮物数据。悬浮物包含活藻类、细菌、原生动物及碎屑，是相对非选择性浮游滤食性动物的食物基础。尽管不同组分的占比在不同湖泊中存在差异，但多项数据表明，分层湖泊中的悬浮物颗粒总体以浮游植物生物量为主。例如，即便在部分碳磷比较高（因此低营养碎屑的占比可能相对较高）的湖泊中，藻类仍约占悬浮物总生物量的70%（细菌与原生动物分别占20%与5%，这意味着碎屑的影响较小）。因此，陆生与淡水自养生物数据集存在差异：陆生数据为特定植物物种的观测结果，而湖泊数据则为活与非活颗粒的混合样本。最后，若不同悬浮物颗粒的碳氮磷比存在显著差异，对于能够区分颗粒的特定草食动物（如部分哲水蚤桡足类（calanoid copepods））而言，整体悬浮物的碳氮磷测量值可能无法准确反映其实际的化学计量食物质量。 草食动物：陆生植食性昆虫与湖泊浮游动物的碳氮磷化学计量比数据，均从已发表及未发表来源汇编得到。同一物种的多条数据在分析前先进行平均处理。与陆生植物的处理流程一致，当未报告碳百分比数据时，我们采用其余草食动物数据库的平均碳百分比（48% C），将报告的氮、磷百分比数据转换为碳氮比与碳磷比。我们沿用叶片数据的分析流程，评估采用固定碳百分比可能引入的偏差。但仅有极少数物种同时提供了碳、氮、磷百分比的完整数据；因此我们仅针对草食动物的碳氮比数据评估潜在偏差。针对直接测量了碳、氮百分比的数据子集（n=67），其碳氮比的均值与变异系数分别为5.9与0.21；而采用固定碳百分比估算的数据条目（n=97）的对应数值为6.7与0.28。同样地，采用固定碳百分比从氮、磷百分比估算碳氮比与碳磷比，大概率不会对观测格局产生过度影响。本数据集共纳入来自7个目、40个科、93个属的130个昆虫物种。绝大多数纳入的昆虫为植食性叶食者，少数为韧皮部取食者（如蚜虫）。叶食者与韧皮部取食者的碳氮磷比并无差异，因此所有类群被合并分析。掠食性浮游动物未被纳入本汇编，但部分杂食性类群被保留。本数据集共纳入来自2个门、4个纲、8个目、12个科、23个属的43个浮游动物物种。多数类群为甲壳动物（主要为鳃足亚纲（branchiopods）、枝角类（cladocera）、软甲纲及桡足类），但同时也汇编了部分轮虫的数据。所有化学计量比均以原子基准计算。