Wiseman, you haven’t shown that it really is beneficial to reproduce less in the scenario that you are describing. Yes, a smaller group will consume less food—but if there are six foxes, then the probability than at least one of them will survive can very well be higher than if there is only one. The group that reproduces less will still be outbred by the one that reproduces more, so the faster-breeding one could on average have more surviving members.
This might not be the case in situations where food is extremly scarce, but it should be so in situations where there is only enough food for, say, 80% of the population. Without running the numbers, it would intuitively feel that the fast-breeders have an advantage most of the time with the slow-breeders only having an advantage a small portion of the time—so while the exact gene frequencies will fluctuate, they won’t give the slow-breeders a decisive advantage.
Wiseman, you haven’t shown that it really is beneficial to reproduce less in the scenario that you are describing. Yes, a smaller group will consume less food—but if there are six foxes, then the probability than at least one of them will survive can very well be higher than if there is only one. The group that reproduces less will still be outbred by the one that reproduces more, so the faster-breeding one could on average have more surviving members.
This might not be the case in situations where food is extremly scarce, but it should be so in situations where there is only enough food for, say, 80% of the population. Without running the numbers, it would intuitively feel that the fast-breeders have an advantage most of the time with the slow-breeders only having an advantage a small portion of the time—so while the exact gene frequencies will fluctuate, they won’t give the slow-breeders a decisive advantage.