我们有许多的奶牛种群和奶牛，但管理奶牛和菜牛是完全不同的事情。
We have lots of dairy herds, dairy cows. But managing dairy and beef cows is a totally different thing.
值得注意的是，松鸡数量必需管理：如果荒野中松鸡过度繁殖，这种鸟类就会得病，导致种群数量暴跌。
Significantly, grouse need to be managed: if moors become over-populated the birds may become diseased and populations can crash.
自1990年代起，科学家和区域性管理机构就已经开始了数据收集工作，通过对“食物链等级”上不同种群间的生态平衡变化进行定量研究。
Since the late 1990s, scientists and regional management organisations have used catch data to measure changes in the balance of species across so-called "trophic levels."
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