Southern pine beetle populations fluctuate from low endemic to high epidemic densities. During peak years beetles cause enormous economic losses and ecological consequences to pine forests in the southeastern United States. Delayed density dependence is considered to be the general cause of cyclical population dynamics. Large scale synchrony in outbreaks would suggest a role for climatic effects on population dynamics. In the northern part of their distribution, southern pine beetle populations could be more strongly influenced by exogenous climatic effects (especially from extreme winter temperatures), while southern populations could be more strongly influenced by endogenous dynamics. We tested this hypothesis by analyzing 14 years of standardized trapping records from multiple locations throughout 12 southeastern states. Nested ANOVAs of relative abundance indicated broad spatial synchrony of population dynamics (42-73% of the variation was among forest areas of ca. 1000 km2 vs. only 9-27% of the variation among sites within forests. This synchrony is consistent with exogenous climatic effects on population dynamics. Abundance of beetle individuals (as recorded by pheromone trapping) were positively correlated with number of infestations (as detected from aerial surveys). However, time series analyses only indicated delayed density dependence in the number of infestations, not the number of beetle individuals. This pattern was consistent throughout the northern and southern distributions. Populations of beetles and populations of beetle infestations may have different dynamics due to (emergent) properties of infestations within landscapes that cannot be easily deduced from the abundance of individuals within landscapes.
Species 1: Coleoptera Scolytidae Dendroctonus frontalis (southern pine beetle)
Keywords: population ecology, spatial scale
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