Data from: Maternal provisioning is structured by species’ competitive neighborhoods

Differential maternal provisioning of offspring in response to environmental conditions has been argued as ‘the missing link’ in plant life histories. Although empirical evidence suggests that maternal provisioning responses to abiotic conditions are common, there is little understanding of how differences in maternal provisioning manifest in response to competition. Frequency manipulations are commonly employed in ecological studies to assess the strength of interspecific competition, relative to intraspecific competition, and we used frequency manipulations to test how competition in two soil moisture environments affects maternal provisioning of seed mass. Specifically, for 15 pairs comprised from 25 annual plant species that occur in California, we varied the relative frequencies of conspecific to heterospecific competitors from 90% (intraspecific competition) to 10% (interspecific competition). We found that conspecific frequency affected maternal provisioning (seed mass) in 12 of the 25 species (8 significantly (P<0.05), four marginally significantly (P<0.07)), and that these responses included both increased (5 species) and decreased (6 species) seed mass, as well as one species with opposing directions of response to conspecific frequency that depended on the soil moisture environment. Conspecific frequency also affected per capita fecundity (seed number) for 17 of the 25 species (15 significantly (P<0.05), two marginally significantly (P<0.09)), which generally decreased seed number as conspecific frequency increased. The direction and magnitude of frequency-dependent seed mass depended on the identity of the competitor, even among species whose fecundity was not affected by competitor identity; the latter finding reveals competitive differences among species that would otherwise appear to be competitively equivalent. Our research demonstrates how species responses to different competitive environments manifest through maternal provisioning, and that these responses alter previous estimates of environmentally-determined maternal provisioning and reproductive output; future study is needed to understand their combined effects on population and community dynamics.针对环境条件的子代母源资源分配（maternal provisioning）差异，被认为是植物生活史研究中"缺失的关键一环"。尽管已有实验证据表明，植物针对非生物环境的母源资源分配响应较为普遍，但学界对竞争压力下母源资源分配差异的具体表现机制仍知之甚少。竞争者频率操控实验是生态学研究中用于评估种间竞争（interspecific competition）相较于种内竞争（intraspecific competition）强度的常用方法，本研究通过该方法，探究了两种土壤水分环境下的竞争如何影响植物种子质量相关的母源资源分配。具体而言，我们选取了加州分布的25种一年生植物，构建15个物种配对组合，将同种个体（conspecific）竞争者与异种个体（heterospecific）竞争者的相对频率从90%（即仅存在种内竞争）调整至10%（即仅存在种间竞争）。研究结果显示，25个物种中有12个物种的母源资源分配（即种子质量）受同种个体频率的影响：其中8个物种呈现显著效应（P<0.05），4个物种呈现边际显著效应（P<0.07）；这些响应模式既包括种子质量提升（5个物种）与降低（6个物种），还有1个物种的响应方向因土壤水分环境不同而随同种个体频率变化呈现相反趋势。此外，25个物种中有17个物种的单株繁殖力（per capita fecundity，即种子数量）受同种个体频率的影响：其中15个物种呈现显著效应（P<0.05），2个物种呈现边际显著效应（P<0.09）；总体而言，随着同种个体频率升高，物种的种子产量普遍下降。依赖于竞争者频率的种子质量响应方向与强度，会因竞争者物种身份的不同而产生差异，即使在那些单株繁殖力不受竞争者物种身份影响的物种中亦是如此；这一结果揭示了原本被认为具有同等竞争能力的物种之间，实际存在的竞争差异。本研究阐明了物种对不同竞争环境的响应如何通过母源资源分配得以体现，且这类响应会改变此前基于环境因素预测的母源资源分配与繁殖产出水平；未来仍需进一步研究，以明确这些效应对种群与群落动态的综合影响。