如“舞毒蛾”、“松毛虫”和“叶蜂”等食叶昆虫的间歇性泛滥，会对商业森林造成严重损失。尽管人们进行了广泛的研究，但仍然不清楚为什么这些森林害虫会泛滥以及什么时候泛滥。对种群变化的两个经典解释（专食性病原体或拟寄生物未能将这些害虫消灭；普食性掠食者偶尔未能将这些害虫消灭），无法解释实际观测结果。但通过将普食性掠食者添加进寄主-病原体模型所建立的一个新的生态学模型，却能对实际观测结果做出解释。在这一新模型中，同在真实森林中一样，随着食叶昆虫密度在由掠食者维持的一个平衡状态和由病原体驱动的周期之间波动，害虫泛滥以漫长而不规则的时间间隔出现。
Nature 430, 341 - 345 (15 July 2004); doi:10.1038/nature02569
The combined effects of pathogens and predators on insect outbreaks
The economic damage caused by episodic outbreaks of forest-defoliating insects has spurred much research1, yet why such outbreaks occur remains unclear2. Theoretical biologists argue that outbreaks are driven by specialist pathogens or parasitoids, because host–pathogen and host–parasitoid models show large-amplitude, long-period cycles resembling time series of outbreaks3, 4. Field biologists counter that outbreaks occur when generalist predators fail, because predation in low-density defoliator populations is usually high enough to prevent outbreaks5-8. Neither explanation is sufficient, however, because the time between outbreaks in the data is far more variable than in host–pathogen and host–parasitoid models1, 2, and far shorter than in generalist-predator models9-11. Here we show that insect outbreaks can be explained by a model that includes both a generalist predator and a specialist pathogen. In this host–pathogen–predator model, stochasticity causes defoliator densities to fluctuate erratically between an equilibrium maintained by the predator, and cycles driven by the pathogen12, 13. Outbreaks in this model occur at long but irregular intervals, matching the data. Our results suggest that explanations of insect outbreaks must go beyond classical models to consider interactions among multiple species.
