Department of Mathematics and Statistics, Utah State University, Logan, UT 84322-3900, USA.
J Theor Biol. 2013 Oct 21;335:40-50. doi: 10.1016/j.jtbi.2013.06.012. Epub 2013 Jun 18.
As global climate patterns continue to change and extreme weather events become increasingly common, it is likely that many ecological interactions will be affected. One such interaction is the multipartite symbiosis that exists between the mountain pine beetle and two species of fungi, Grosmannia clavigera and Ophiostoma montium. In this mutualism, the fungi provide nutrition to the beetle, while the fungi benefit by being dispersed to new host trees. Multi-partite mutualisms are predicted to be unstable due to strong direct competition among symbionts or natural selection for superior over inferior mutualists. However, this mutualism has remained stable over long periods of evolutionary time. In this paper, we developed a temperature-based model for the spread of fungi within a tree and connected it to an existing model for mountain pine beetle development. Using this integrated model for fungal growth, we explored the possibility that temperature variability is a stabilizing mechanism for the mountain pine beetle-fungi mutualism. Of the three types of temperature variability we tested: intra-year, inter-year and variability due to transitioning between different thermal habitats (thermal migration), we found that thermal migration was the most robust stabilizing mechanism. Additionally, we found that the MPB attack density or spacing between fungal lesions also had a significant effect on the stability of the system. High attack densities or close lesion spacings also tended to stabilize the system, regardless of temperature.
随着全球气候模式的持续变化和极端天气事件的日益频繁，许多生态相互作用可能会受到影响。山松甲虫与两种真菌 Grosmannia clavigera 和 Ophiostoma montium 之间的多部分共生关系就是其中之一。在这种共生关系中，真菌为甲虫提供营养，而真菌则通过传播到新的宿主树中受益。多部分共生关系预计由于共生体之间的强烈直接竞争或自然选择优越于较差的共生体而不稳定。然而，这种共生关系在很长的进化时间内保持稳定。在本文中，我们开发了一种基于温度的真菌在树内传播模型，并将其与现有的山松甲虫发育模型连接起来。使用这种真菌生长的综合模型，我们探讨了温度可变性是否是山松甲虫-真菌共生关系稳定的一种机制。在我们测试的三种温度可变性类型中：年内、年际和由于在不同热生境之间转换（热迁移）引起的可变性，我们发现热迁移是最稳定的机制。此外，我们还发现山松甲虫的攻击密度或真菌病变之间的间隔也对系统的稳定性有重大影响。高攻击密度或紧密的病变间隔也往往会稳定系统，而与温度无关。
