What does the S term represent, and how does it alter the Impact component in the IPAT model used to evaluate the total impact of human populations on the environment?

sensitivity$,$ to denote how sensitive a given environment is to these pressures, causing more damage for sensitive habitats

sex ratio, to denote number of mating pairs, so as it shifts from $\frac{50}{50}$ there is a reduction in impact

sensitivity$,$ to denote how sensitive a given human population is to population control, thereby reducing its impact

suitability, to denote the appropriateness of human activity for environmental protection, thus lowering the environmental damage