Convex-upward trade-off curves lead to:
Under the convention intended here, a convex-upward trade-off makes distributed reproductive effort advantageous, so iteroparity yields better lifetime fitness than concentrating all effort at once. The conclusion depends on what the axes represent and how curvature is defined. Biologically, the shape describes whether incremental reproductive investment causes accelerating or decelerating costs to survival and future fecundity. Selection can favor a large terminal effort when future survival is poor or when concentrating resources yields accelerating fecundity gains. Repeated breeding is favored when adults commonly survive and spreading reproduction buffers bad years. These predictions are conditional; a familiar species example illustrates a principle but does not define it for every environment. This causal chain is what makes the keyed content ecologically meaningful rather than merely definitional. This interpretation connects individual-level processes with measurable changes in survival, reproduction, recruitment, or abundance across the population. Field evidence should therefore be compared with the model assumptions before extending the conclusion to every species, habitat, or time period.
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 5