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Evaluating the importance of multiple drivers in outbreak population dynamics.
Hofstetter, Richard*,1, Ayres, Matthew1, Klepzig, Kier2, Moser, John1, 1 Dartmouth College, Hanover, NH, USA2 USDA Forest Service, Pineville, LA, USA
ABSTRACT- Understanding how and why populations fluctuate has remained a central focus of ecology. Several bark beetle species exhibit dramatic fluctuations in abundance and are capable of causing massive mortality within pine forests during outbreaks. Bark beetle population dynamics are often attributed to variations in natural enemies, climate, or host tree resistance, and multivoltine bark beetle species are likely differentially impacted by various mortality factors throughout the year. The relative impact of each of these factors in driving oscillations within years and across many years is not well understood. Annual growth rates of multivoltine species are the collective result of mortality and reproduction of each generation throughout the year. Without accurately sampling mortality factors at each generation, the biological mechanisms that drive prey population dynamics can be misleading. For example, how do univoltine predators affect the within-year dynamics of multivoltine prey? Here, we present results that suggest that within-year dynamics play an important role in the long-term (years) dynamics of the southern pine beetle, and model the important biological mechanisms (predators, competitors, climate) that drive within-year and multi-year fluctuations in southern pine beetle populations. Specifically we demonstrate that seasonal variation in mortality associated with tree defenses (spring), major beetle predators (spring, fall), and antagonistic fungi (late spring-fall) can result in complex, non-linear dynamics in beetle population dynamics.
Key words: Dendroctonus, predator-prey, population dynamics, mutualism