The demographic effects of functional traits: an integral projection model approach reveals population-level consequences of reproduction-defense tradeoffs

Quantitatively linking individual variation in functional traits to demography is a necessary step to advance our understanding of trait-based ecological processes. We constructed a population model for Asclepias syriaca to identify how functional traits affect vital rates and population growth and whether tradeoffs in chemical defense and demography alter population growth. Plants with higher foliar cardenolides had lower fiber, cellulose, and lignin levels, as well as decreased sexual and clonal reproduction. Average cardenolide concentrations had the strongest effect on population growth. In both the sexual and clonal pathway, the tradeoff between reproduction and defense affected population growth. We found that both increasing the mean of the distribution of individual plant values for cardenolides and herbivory decreased population growth. However, increasing the variance in both defense and herbivory increased population growth. Functional traits can impact population growth and quantifying individual-level variation in traits should be included in assessments of population-level processes.

将功能性状的个体间变异与种群动态进行定量关联，是深化对基于性状的生态过程认知的必要环节。我们构建了叙利亚马利筋（Asclepias syriaca）的种群模型，旨在明确功能性状对种群生活史速率与种群增长的调控作用，以及化学防御与种群动态间的权衡是否会改变种群增长格局。叶强心苷水平更高的植株，其纤维、纤维素与木质素含量更低，同时有性繁殖与克隆繁殖能力均有所降低。平均叶强心苷浓度对种群增长的影响最为显著。在有性繁殖与克隆繁殖两条路径中，繁殖与防御间的权衡均会对种群增长产生影响。研究发现，提升植株个体叶强心苷含量的分布均值以及植食压力，均会降低种群增长速率；而提升防御性状与植食压力的变异程度，则会提高种群增长速率。功能性状可对种群增长产生调控作用，在种群水平生态过程的评估中，应纳入性状个体间变异的量化分析。