Investment in survival and reproduction along a semelparity-iteroparity gradient in the Beta species complex

The Beta species complex shows a gradient of life histories from pronounced semelparity (big-bang reproduction) to pronounced iteroparity (repeated reproduction). Models assume a trade-off between investment in reproduction and survival. Reproductive effort is thought to increase with decreasing life span, and to be invariable in semelparous plants and susceptible to environmental conditions in iteroparous plants. These assumptions and hypotheses were verified by a greenhouse experiment testing six different life cycles at three contrasting nutrient levels. This study suggests that reproductive effort is negatively correlated with mean life span along the life-cycle gradient. Unlike semelparous beets, reproductive effort in iteroparous beets is extremely sensitive to nutrient level. Phenotypic correlation between allocation to reproduction and allocation to survival generally appeared significantly negative in the longest-lived iteroparous beets, nonsignificant in intermediate life histories and obviously positive in semelparous beets (no trade-off control).