Where there is a trade-off between production and defence, figure 8.18 illustrates the likely form of the relationship. The trade-off curve has the following features: (i) even when growth rate is maximal (zero allocation to defence), growth rate is finite equal to the limiting production rate in the study environment; (2) even if all resources are allocated to defence, mortality rate is still greater than zero, equivalent to the 'extrinsic' mortality rate in that environment. The simplest curve having these general features is convex viewed from below, and has the general form of the curve shown in figure 8.18. The evolutionary implications of this trade-off are considered in section 13.3