如“舞毒蛾”,、“松毛蟲”和“葉蜂”等食葉昆蟲的間歇性泛濫，會對商業(yè)森林造成嚴(yán)重?fù)p失,。盡管人們進(jìn)行了廣泛的研究,，但仍然不清楚為什么這些森林害蟲會泛濫以及什么時候泛濫。對種群變化的兩個經(jīng)典解釋（專食性病原體或擬寄生物未能將這些害蟲消滅,；普食性掠食者偶爾未能將這些害蟲消滅）,，無法解釋實際觀測結(jié)果。但通過將普食性掠食者添加進(jìn)寄主-病原體模型所建立的一個新的生態(tài)學(xué)模型,，卻能對實際觀測結(jié)果做出解釋,。在這一新模型中，同在真實森林中一樣,，隨著食葉昆蟲密度在由掠食者維持的一個平衡狀態(tài)和由病原體驅(qū)動的周期之間波動,，害蟲泛濫以漫長而不規(guī)則的時間間隔出現(xiàn)。
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.
