You read the studies, they say that most of the time the mechanism that causes the birth regulation to "kick in" is the increased population density. Apparently, the higher density of animals increases aggression (road rage during rush hour?) which cause fertility and the desire to mate to decrease. It is a mechanism that mimics anticipation of a starvation event by responding to increase in population density. It is interesting that in the study of mice, lemmings, and rats that it wasn't just the increase in the target species population density that triggered the response but also increases in other species (that interacted competitively with the target species) population density. Those other species would be in contact with the target species during competition for food, providing the same impact as an increase in the target species population density. Like a big crowd at the salad bar. It increased aggression.

So it is not actually anticipation of the starvation event that lead to reproduction reduction but the reaction to an event (increase in population density) that would have lead to the starvation event. The increase in aggressive behavior caused the population density to lower and avoid the starve off. So, in the case of these animals, their aggression in a crowded condition turns out to be a positive adaptation for their species.


If that is what you got from my answer, you will have to show me where I misspoke because I did not say anything about "rigging the results".