Data from: Parental optimism versus parental pessimism in plants: how common should we expect pollen limitation to be?

Many organisms exhibit 'parental optimism', producing more of the initial stages of offspring (e.g., eggs, embryos) than they can usually mature. For plants, parental optimism may be linked to the risk of seed production being limited by pollen receipt (pollen limitation). Here we elaborate a stochastic model of pollen limitation developed by Haig and Westoby (1988) and Burd (2008) and link it with published data on the magnitudes of pre-pollination versus post-pollination costs of seed production in 80 plant species. We demonstrate that parental optimism should be expected when pre-pollination costs of seed production are small relative to post-pollination costs. This was observed for most (62/80) of the plant taxa surveyed. Under parental optimism, plants over-invest in securing fertilized ovules, and consequently pollen limitation is predicted to be uncommon. However, for a sizable minority of plant species (18/80), pre-pollination costs approach or exceed post-pollination costs. For these species, parental pessimism is instead optimal. Parents initiate fewer zygotes than they can usually mature, and pollen limitation is predicted to be severe. Because the relative magnitudes of pre-pollination and post-pollination costs vary by >1000-fold across plant taxa, parental outlook (optimism versus pessimism) and levels of pollen limitation are predicted to vary widely.