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 re production). Models assume a trade-off between investment in reproduction a nd survival. Reproductive effort is thought to increase with decreasing lif e span, and to be invariable in semelparous plants and susceptible to envir onmental 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 reproductiv e effort is negatively correlated with mean life span along the life-cycle gradient. Unlike semelparous beets, reproductive effort in iteroparous beet s is extremely sensitive to nutrient level. Phenotypic correlation between allocation to reproduction and allocation to survival generally appeared si gnificantly negative in the longest-lived iteroparous beets, nonsignificant in intermediate life histories and obviously positive in semelparous beets (no trade-off control).