1. A paradigm in the plant defence literature is that defending against herbivores comes at a cost to growth, resulting in a growth–defence trade-off. However, while there is strong evidence for growth–defence trade-offs across species, evidence is mixed within species.
2. Several mechanisms can account for this equivocal support within species, but teasing them apart requires examining growth–defence relationships both within and among populations, an approach seldom employed.
3. We examined correlations between plant biomass (growth) and terpene production (defence) within and among populations of Monarda fistulosa, a perennial herb. We sampled populations from Montana and Wisconsin, regions that differ in resource availability characterized by different summer precipitation and associated abiotic conditions that influence plant productivity.
4. We found negative, neutral and positive growth–defence correlations, depending on the scale examined. Negative correlations occurred across populations originating from divergent regions, positive correlations occurred across populations originating from within the high-resource region and neutral correlations were found within single populations.
5. Collectively, these results challenge the general expectation of ubiquitous trade-offs and support emerging views that resource availability (as it affects productivity) shapes the evolution of defence at different scales.

中文翻译：

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生长和防御之间的种内相关性因资源可用性而异，并且在种群内部和种群之间有所不同

1. 植物防御文献中的一个范例是，防御食草动物是以生长为代价的，导致生长-防御权衡。然而，虽然有强有力的证据表明跨物种的生长防御权衡，但物种内部的证据却是混合的。
2. 几种机制可以解释物种内这种模棱两可的支持，但将它们分开需要检查种群内部和种群之间的生长防御关系，这种方法很少采用。
3. 我们研究了多年生草本植物Monarda fistulosa种群内和种群间植物生物量（生长）和萜烯生产（防御）之间的相关性。我们对来自蒙大拿州和威斯康星州的种群进行了采样，这些地区的资源可用性不同，其特征是不同的夏季降水和影响植物生产力的相关非生物条件。
4. 我们发现了负、中和正增长-防御相关性，这取决于所检查的量表。来自不同地区的种群之间出现负相关，来自高资源区域内的种群之间出现正相关，在单个种群中发现中性相关。
5. 总的来说，这些结果挑战了普遍存在的权衡取舍的普遍预期，并支持了资源可用性（因为它影响生产力）在不同尺度上塑造防御演变的新观点。