Nonlinear costs of reproduction in a long-lived plant

Abstract

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 three to five 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 nonlinearly with diminishing costs at high RE. Fecundity costs increased linearly with RE in the long-season population, but nonlinearly with diminishing costs at high RE in the other. The results demonstrate that the shape of the cost function may be nonlinear 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.