Data from: Non-linear costs of reproduction in a long-lived plant

A trade-off between current reproduction and future performance is a key component of life-history theory, but the shape of this trade-off for any specific fitness component remains elusive. We induced 3-5 levels of reproductive effort (RE) by manipulating fruit set of a long-lived orchid in two populations that differed in the length of the growing season and local climate, and examined survival, size and fecundity the following year. Natural fruit set was 72% higher in the long-season population, but was not associated with a significant survival cost in any population. Survival decreased linearly with experimentally increased RE in the short-season population. In both populations, natural RE incurred growth and fecundity costs, and growth costs increased non-linearly with diminishing costs at high RE. Fecundity costs increased linearly with RE in the long-season population, but non-linearly with diminishing costs at high RE in the other. The results demonstrate that the shape of the cost function may be non-linear with context-dependent intercept, slope and curvature. They are consistent with the prediction that survival costs appear only when RE exceeds natural levels, while growth and fecundity costs are evident at natural RE. Synthesis. We suggest that studies inducing multiple levels of RE are required to understand life-history trade-offs and their context-dependence. This kind of information is fundamental for an understanding of the link between environmental heterogeneity, adaptive differentiation and life-history evolution.当前繁殖投入与未来适合度之间的权衡是生活史理论的核心组成部分，但针对任一特定适合度组分的权衡形式仍尚不明确。我们通过调控两个生长季长度与局地气候存在差异的种群中长寿命兰科植物的坐果率，设置了3至5个梯度的繁殖投入（reproductive effort, RE），并于次年调查了植株的存活率、个体大小与繁殖力。长生长季种群的自然坐果率较短生长季种群高出72%，但在两个种群中均未观测到显著的存活成本。在短生长季种群中，实验诱导升高的繁殖投入会导致存活率线性下降。在两个种群中，自然状态下的繁殖投入均会产生生长与繁殖力成本，且生长成本随繁殖投入升高呈非线性变化，高繁殖投入水平下的成本增幅逐渐趋缓。长生长季种群的繁殖力成本随繁殖投入线性升高，而短生长季种群的繁殖力成本则呈非线性变化，高繁殖投入水平下的成本增幅同样逐渐趋缓。本研究结果表明，成本函数的形式可能为非线性，且其截距、斜率与曲率均依赖于实验背景。该结果与下述预测相符：仅当繁殖投入超过自然水平时，才会出现存活成本，而生长与繁殖力成本在自然繁殖投入水平下即可观测到。综合来看，我们认为，若要阐明生活史权衡及其环境背景依赖性，需开展设置多梯度繁殖投入的相关研究。这类信息对于理解环境异质性、适应性分化与生活史演化之间的关联至关重要。