Science Source

Cross-scale Drivers of Natural Disturbances Prone to Anthropogenic Amplification: The Dynamics of Bark Beetle Eruptions

States that biome-scale disturbances by eruptive herbivores provide valuable insights into species interactions, ecosystem function, and impacts of global change
Presents a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales
Looks at bark beetles, which are major natural disturbance agents in western North American forests
States that recent bark beetle population eruptions have exceeded the frequencies, impacts, and ranges documented during the previous 125 years
States that extensive host abundance and susceptibility, concentrated beetle density, favorable weather, optimal symbiotic associations, and escape from natural enemies must occur jointly for beetles to surpass a series of thresholds and exert widespread disturbance
States that eruptions occur when key thresholds are surpassed, prior constraints cease to exert influence, and positive feedbacks amplify across scales
States that climate change and reduced habitat heterogeneity increase the likelihood that key thresholds will be exceeded, and may cause fundamental regime shifts
Concludes that systems in which endogenous feedbacks can dominate after external forces foster the initial breach of thresholds appear particularly sensitive to anthropogenic perturbations