Populations with "young" age structures are growing populations, for the most part, if the sex ratio is not too badly skewed one way or the other . Populations with an "old" age structure may be stable (in the absence of significant predation and with recruitment equaling mortality), or declining (i.e., recruitment is less than mortality).
I agree. My point being that sport hunting tends to keep populations VERY young, and we probably choose to kill certain individuals that in a hunted population that wouldn't normally die so soon (ie: mature males for example) and skew male-female ratios, female-calf ratios, and age structure in a way that may have long term effects that occur over such a long period of time it may not be easy to detect. More like a slow "drift".
I am not familiar with the data from Banff that Casey cited, but I cannot remember having seen cervid populations with sex ratios greater than 1:2 (males to females) that were not intensively managed to achieve these levels. That includes a lot of unhunted populations around the globe. All of the life table data that I have reviewed indicates that males naturally suffer higher mortality rates than females at all ages, but especially in the first 2 years of life.
I would be interested to see some population data for free-ranging elk herds with naturally high male/female sex ratios in the absence of hunting...
Our problem is almost all the data comes from hunted populations, whether it is sport hunting in North America, Western Europe, or parts of Africa, or moderate/heavy subsistance hunting like other parts of Africa or regions of Russia/Eurasia. Because large mammal populations are almost always the first to be killed when humans show up, there is very little data available to suggest what is "natural".
I've never seen the actual studies or population surveys from Banff, but have seen it quoted in other studies and popular publications.
I have a couple long time buddies who are/were biologists in the CDOW, and 20 years ago the common wisdom among biologists were elk in the Southern/Central Rockies only live 10-12 years. Then the Canadian biologists showed elk living a lot longer in the wild. Also, simply tagging more elk in recent times have showed some wild elk living a lot longer than expected--if they aren't killed by hunters, cars, or other "human induced" mortality. So that idea has changed some.
Casey
