Animals that feed on forest tree seeds, such as Apodemus mice, increase in number after a mast year. At high latitudes, there is a similar delayed response by Myodes voles to high seed crops of bilberry (Vaccinium myrtillus), but here the mechanism is hypothesised to be increased forage quality, caused by a trade-off between reproduction and defence in the plants. Both Apodemus mice and Myodes voles eat berries, but only the latter feed on bilberry plants. Hence, only Myodes voles are predicted to respond to bilberry peak years. A second prediction is that the effect should last longer than any possible direct impacts of bilberries, because the plants would not be able to rebuild their defence until the succeeding summer. During a 21-year snap-trapping study of small rodents in Southern Norway, the spring population of bank vole (Myodes glareolus) was positively related to a bilberry seed index of the previous year, indicating increased winter survival, whereas the wood mouse (Apodemus sylvaticus) was not affected. Also the succeeding autumn population index of the bank vole was positively related to the bilberry index of the previous year, even when controlling for spring population levels. The wood mouse population responded to mast years of sessile oak (Quercus petraea), whereas seeds of Norway spruce (Picea abies) seemed to have some impact on both species. It is concluded that these rodents are mainly limited from below, but by different mechanisms for the granivorous and the herbivorous species.

中文翻译：

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挪威南部木鼠（Apodemus sylvaticus）和田鼠（Myodes glareolus）种群自下而上机制不同的证据

肥大后一年，以林木种子为食的动物（例如姬鼠属）数量增加。在高纬度地区，Myodes田鼠对越桔的高种子作物（Vaccinium myrtillus）有类似的延迟反应，但据推测在此机制是由于植物繁殖与防御之间的权衡而导致的草料质量提高。两个黑线姬鼠和Myodes田鼠吃浆果，但仅限于越桔植物后者饲料。因此，只有Myodes田鼠预计将对越橘高峰年份做出反应。第二个预测是，这种作用的持续时间应比越桔的任何可能的直接影响要长，因为这种植物要到下个夏天才能重建防御能力。在挪威南部对小型啮齿动物进行的为期21年的诱捕研究中，河岸田鼠（Myodes glareolus）的春季种群与前一年的越桔种子指数呈正相关，表明冬季存活率提高，而木鼠（Apodemus西尔维蒂克）不受影响。此外，即使控制春季人口水平，银行田鼠的后续秋季人口指数也与上一年的越桔指数成正相关。木鼠种群对无柄栎（Quercus petraea）的肥大年做出了响应，而挪威云杉（Picea abies）的种子似乎对这两种物种都有一定的影响。可以得出结论，这些啮齿动物主要受下面的限制，但受食肉和草食物种的机制不同。