Seasonal variation of fresh bunch production is difficult to explain and predict. A population scale model, EcoPalm, was developed to explain those using new physiological hypotheses. A central hypothesis was that day length influences time of flowering during a photosensitive period (PSP) at the scale of individual fronds (phytomers). The variable PSP duration between successive phytomers result in a queue of phytomers in "waiting state", which partly explains seasonal variations. The monthly, potential number of harvested bunches, based on a 100% sex ratio, and the absence of abortions and failures of fruit set, was simulated. The second hypothesis was that sex ratio, intensity of bunch abortion and bunch failure, , depend on the trophic status of a given phytomer during sensitive phases of its development, expressed through a plant-scale Index of Competition for assimilates (Ic), which is the ratio between instantaneous assimilate supply and aggregate demand. Annual demand for vegetative organ growth was assumed to be constant (stabilized growth). Bunch dry matter production was assumed to be variable. If Ic < 1 during sensitive stages of bunch development, (high competition among sinks), sex ratio was considered to be low and abortion and bunch failure high. If Ic > 1, sex ratio was high. The 3rd hypothesis was that resulting sink-source imbalances are buffered by stem carbohydrate reserves. If Ic > 1, demand was not down-sized and excess assimilates were stored (overflow model). If Ic < 1 reserves were mobilized. The model was tested on a multi-annual period in La Mé (Ivory Coast) on a control progeny, LM2T X D10D. Sensitive periods to Ic were adjusted by optimization of parameters using evolutionary algorithm method. The PSP occurs at the early stage of development of phytomer, begin 36 months before harvest (mbh) and ends 28 mbh. The sex determination is very complex and occurs during PSP. The initial sex ratio of palm population was determined by