Forest insect pests and large-mammal food webs

An insect pest that damages the forest canopy has a reverberating impact on predator-prey interactions of large mammals, a study finds. Insect pests are considered to be ecosystem engineers because their destruction of the tree canopy can stimulate the growth of forest understory, generating resources for various organisms and altering food webs. Daniel Fortin and colleagues report that the cascading effects of the highly destructive spruce budworm in boreal forests can ultimately increase the mortality rate of threatened ungulates, especially when human activities further disturb the ecosystem. Field sampling in Québec, Canada showed that stands with more severe spruce budworm infestation had a greater proportion of deciduous vegetation, a primary food source for moose but not caribou. During an outbreak between 2006 and 2018, there was a 70% increase in moose density, which was positively associated with the proportion of deciduous vegetation. The greater availability of prey may have increased the number of wolves, leading to higher caribou mortality rates. In support of this idea, caribou that remained alive during this period avoided areas with high outbreak severity, whereas those that died from predation tended to select severely infested stands. Moreover, harvesting infested trees exacerbated these effects by increasing moose density, attracting wolves, and increasing caribou mortality. According to the authors, the study carries implications for boreal caribou management and conservation planning.

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Article #20-22892: “Insect-mediated apparent competition between mammals in a boreal food web,” by Guillemette Labadie, Philip D. McLoughlin, Mark Hebblewhite, and Daniel Fortin.

MEDIA CONTACT: Daniel Fortin, Université Laval, Québec City, CANADA; tel: 418-656-2131; email: <

[email protected]

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