EFFECT OF FERTILITY-CONTROL ON A POPULATIONS PRODUCTIVITY

The effect of a sterilising agent upon the productivity of vertebrate pests, such as feral horses, feral dogs, wild rabbits or fruit-eating birds, depends upon the population's social structure and mating system. We investigated the theoretical effect on productivity of three forms of dominance, two effects of sterilisation on dominance, and four modes of transmission. Seventeen of the possible 24 combinations are feasible but lead to only four possible outcomes. Three of these result in lowered productivity. The fourth, where the breeding of a dominant female suppresses breeding in the subordinate females of her group, leads to a perverse outcome. Productivity increases with sterilisation unless the proportion of females sterilised exceeds (n - 2)/(n - 1) where n (> 2) is the number of females in the group. A knowledge of social structure and mating system is therefore highly desirable before population control by suppressing female fertility is attempted or even contemplated.