Reeve John D
Southern Research Station, USDA Forest Service, 2500 Shreveport Hwy., Pineville, LA 71360, USA Fax: (318) 473-7222; e-mail:
Oecologia. 1997 Sep;112(1):48-54. doi: 10.1007/s004420050282.
Bark beetle populations may undergo dramatic fluctuations and are often important pests in coniferous forests. Their dynamics are thought to be primarily driven by factors affecting the resistance of the host tree to attack, i.e., bottom-up forces, while natural enemies are usually assigned a minor role in these systems. I present behavioral experiments that suggest that the clerid beetle Thanasimus dubius may be an important source of mortality for the bark beetle Dendroctonus frontalis during attack of the host tree, and determine the nature of the functional response of T. dubius under conditions close to natural. I also examine the numerical response of T. dubius to large-scale fluctuations in D. frontalis density, and the relationship between bark beetle population trends and predator density, and find that beetle populations tend to decline when predator densities are high. Combined with the effects of clerid larvae on bark beetle broods, these results suggest that top-down forces generated by natural enemies could also be an important component of bark beetle dynamics. The implications of these results for bark beetle dynamics are discussed in relation to the prolonged life-cycle of clerid beetles.
树皮甲虫种群数量可能会出现剧烈波动，并且在针叶林中常常是重要害虫。其动态变化被认为主要受影响寄主树抗虫性的因素驱动，即自下而上的力量，而在这些系统中，天敌通常被认为作用较小。我展示了行为实验，这些实验表明，在寄主树遭受攻击期间，郭公甲Thanasimus dubius可能是树皮甲虫Dendroctonus frontalis死亡的一个重要来源，并确定了在接近自然的条件下T. dubius功能反应的性质。我还研究了T. dubius对D. frontalis密度大规模波动的数量反应，以及树皮甲虫种群趋势与捕食者密度之间的关系，发现当捕食者密度较高时，甲虫种群数量往往会下降。结合郭公甲幼虫对树皮甲虫幼虫的影响，这些结果表明，天敌产生的自上而下的力量也可能是树皮甲虫动态变化的一个重要组成部分。结合郭公甲生命周期较长的情况，讨论了这些结果对树皮甲虫动态变化的影响。
