A couple of theories of wildlife population dynamics are summarized here in order to reveal the "Miracle of Compensatory Mortality" and the "harvestable surplus."
Readers can claim extra credit for remembering that these are not the only theories in population dynamics (or biology or ecology), that they don't explain everything that happens in natural or artificial systems, and that there's always more to know than what the lobbyists and the conspiracy theorists are choosing to say.
General Population Dynamics.
A basic reality of life for wild animals is that each year, some will be born and some (including some of the newborns) will die.
A basic theory of wildlife population dynamics is that the size (and other characteristics) of a population of a given species in a given environment will tend to stabilize somewhere near the environmental carrying capacity (e.g. somewhere near the point at which the animals have enough food and cover to be successful on an ongoing basis).
On the birth side of the above population-stabilizing equation, wild animals tend to reproduce in excess. Not all of the young survive, but some do, to replace individuals from previous generations who don't.
Following from the general population dynamics described above, a basic theory of recreational hunting & fishing (i.e. "game management" which some might overextend and call "wildlife management") is that wildlife populations will tend to compensate for animals that are taken by hunting & fishing. Although there are at least two compensatory functions--increased birth rate or decreased mortality from other sources--the latter makes for much better media coverage, so it's the only one we hear most about.
First, the "good news" is that, even though the particular causes of mortality might vary from year to year, the overall levels of mortality in a stable population will tend to stabilize. So, the theory goes, if recreational hunting & fishing cause modest levels of mortality (below the natural, overall level of mortality), then nature will tend to "compensate" with lower levels of mortality from other causes. Thus the theory of "compensatory mortality," that animals that are taken through hunting & fishing are spared worse deaths from other causes.
And then the "bad news"--without such a pretty interpretation--that the compensatory reaction can also be through increased birth rate. In other words, although the hunting & fishing mortality will add to the overall level mortality, the animals that are taken will be replaced by their orphaned young. Right, that doesn't make for such great media coverage. It's more along the lines of the recovery of human populations following natural and man-made disasters. If one takes a high-level view (say from an aircraft window) the recovery of a destroyed human city might be spun as a testimony to the courage and determination of human civilization. At ground level, however, it is cruel.
Many, many corollaries spring from the theory of compensatory mortality--as if it's not just a theory, and as if they're not just corollaries. The faith-based approach to "game management" is to spin as many hunting & fishing practices possible into "Revelations of the Miracle of Compensatory Mortality" including (but not limited to) the following:
Snapshot of the abstract:
Cooley, Hilary S., Robert B. Wielgus, Gary M. Koehler, Hugh S. Robinson, and Benjamin T. Maletzke. 2009.
Ecology 90 (10): 2913–21.