Figure 1. (a) The Charnov model of optimal foraging. The curves indicate the trajectories of net energy uptake from three hosts ‘a’ ‘b’ and ‘c’. Optimal foraging, that is optimizing the energy gained to the energy invested, is indicated by the dotted asymptotes to each curve. The very thick straight line joins together the points of asymptote contact for each host to indicate how optimal foraging works for different hosts. Failure to go through the zero point indicates biological error in foraging. Based on the Charnov (1976) model for optimal foraging for animals. and (b) The parasite Dodder forages according to the Charnov (1976) animal optimal foraging model. Six different hosts were used to estimate energy invested versus energy gain during parasitical exploitation by Dodder. Energy gained was measured after 28 days as net increase in weight. Energy invested was calculated from the coil length used to parasitize the host. Note the identity with Charnov theory (Figure 1a) indicating that Dodder optimally forages and that Dodder determines energy investment well before any net energy gain. Data redrawn from Kelly (1990).

Figure 2. The genetic assimilation of a behavioural character varying quantitatively between two different environments E1 and E2. The figure charts the trajectories of behaviour of three individuals, a, b, c during an environmental shift from E1 to E2 and then perhaps back to E1. ‘a’ shows limited plasticity and dies in the initial environmental shift. ‘b’ and ‘c’ are sufficiently plastic in behaviour to quantitatively change the character and survive the environmental shift. For example, the environmental shift might result from higher volcanic activity increasing areas of bare soil. Individual plants who respond behaviourally to bare soil by producing larger numbers of smaller seeds, more rapidly colonize this new environment. With time gene combinations arise that enables this behaviour to develop with greater rapidity, higher probability or lower cost thus honing the genotype but by epigenetic means. On return to E1 (if this happens) or to a different E (such as temporary bare soil in forest regeneration), the character expression is now shifted to the different, in this case, higher value. The mechanism emphasizes the survival of the adaptable. Modified from Waddington (1957).