Plant defense against herbivores is multidimensional, and investment into different defense traits is intertwined due to genetic, physiological, and ecological costs. This relationship is expected to generate a trade-off between direct defense and tolerance that is underlain by resource availability, with increasing resources being associated with increased investment in tolerance and decreased investment in direct resistance. We tested these predictions across populations of the shrub Artemisia californica by growing plants sourced from a latitudinal aridity gradient within common gardens located at the southern (xeric) and northern (mesic) portions of its distribution. We measured plant growth rate, resistance via a damage survey, and tolerance to herbivory by experimentally simulating vertebrate herbivory. Plants from more northern (vs. southern) environments were less resistant (received higher percent damage by vertebrate herbivores) and tended to be more tolerant (marginally significant) with respect to change in biomass measured 12 months after simulated vertebrate herbivory. Also, putative growth and defense traits paralleled patterns of resistance and tolerance, such that leaves from northern populations contained lower concentrations of terpenes and increased N, specific leaf area, and % water. Last, plant growth rate did not demonstrate clear clinal patterns, as northern populations (vs. southern populations) grew more slowly in the southern (xeric) garden, but there was no clinal relationship detected in the northern (mesic) garden. Overall, our findings support the prediction of lower resistance and higher tolerance in plant populations adapted to more resource-rich, mesic environments, but this trade-off was not associated with concomitant trade-offs in growth rate. These findings ultimately suggest that plant adaptation to resource availability and herbivory can shape intraspecific variation in multivariate plant defenses.

中文翻译：

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纬度资源梯度塑造长寿灌木的多元防御策略

植物对食草动物的防御是多维的，由于遗传、生理和生态成本，对不同防御特性的投资交织在一起。这种关系预计会在直接防御和容忍之间产生一种权衡，这种平衡是以资源可用性为基础的，资源的增加与容忍投资的增加和直接抵抗投资的减少有关。我们在灌木Artemisia californica种群中测试了这些预测通过在位于其分布的南部 (xeric) 和北部 (mesic) 部分的公共花园内种植来自纬度干旱梯度的植物。我们通过损害调查测量了植物的生长速度、抗性，以及通过实验模拟脊椎动物食草动物对食草动物的耐受性。来自更北部（相对于南部）环境的植物抵抗力较差（脊椎动物食草动物的伤害百分比更高）并且在模拟脊椎动物食草动物后 12 个月测量的生物量变化方面往往更耐受（边际显着）。此外，假定的生长和防御特征与抗性和耐受性模式平行，因此北方种群的叶子含有较低浓度的萜烯和增加的氮、比叶面积和水分百分比。最后的，植物生长率没有表现出明显的临床模式，因为北方种群（相对于南方种群）在南方（干旱）花园中生长得更慢，但在北方（mesic）花园中没有检测到临床关系。总的来说，我们的研究结果支持预测植物种群适应更丰富的中等环境的较低抗性和较高耐受性，但这种权衡与增长率的伴随权衡无关。这些发现最终表明，植物对资源可用性和食草动物的适应可以影响多变量植物防御的种内变异。我们的研究结果支持对适应更丰富的中等环境的植物种群的较低抗性和较高耐受性的预测，但这种权衡与增长率的伴随权衡无关。这些发现最终表明，植物对资源可用性和食草动物的适应可以影响多变量植物防御的种内变异。我们的研究结果支持对适应更丰富的中等环境的植物种群的较低抗性和较高耐受性的预测，但这种权衡与增长率的伴随权衡无关。这些发现最终表明，植物对资源可用性和食草动物的适应可以影响多变量植物防御的种内变异。