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Spatio-temporal patterns in population dynamics of the southern pine beetle.
Ylioja, Tiina1, Ayres, Matthew1, Billings, Ronald2, Pye, John3, 1 2 3
ABSTRACT- Population dynamics can have structure in space and time. Furthermore, temporal patterns could change in predictable ways across space. We analyzed 10-40 years of abundance data for the southern pine beetle, Dendroctonus frontalis, across 1,000,000 km2. Time series analyses indicated that endogenous dynamics account for 40-50% of the variation in population growth rates throughout the southeastern US, but that delayed density-dependence and cyclical dynamics were stronger in the warmer, southern regions. High spatial synchrony of outbreaks (at a scale far beyond the dispersal of beetles or their natural enemies) implicated spatially autocorrelated exogenous effects throughout the range. Variability in annual population growth rates was lower in southern populations, where D. frontalis has 6 generations per year compared to northern populations with 4 generations per year. This suggests stronger density-dependence within years in the south and/or stronger exogenous effects in the north. Indeed, interannual growth rate in the north was negatively correlated with the occurrence of lethal winter temperatures, suggesting that minimum annual air temperature are a driver of northern population dynamics. Apparent population dynamics were generally similar whether abundance was measured as number of infestations, m3 of trees colonized, or trap captures, but exceptions suggested that the relevant demographic processes can have different effects at different scales. Evidently, understanding and predicting beetle population dynamics requires models that include regional patterns in the strength and nature of exogenous and endogenous drivers.
KEY WORDS: spatial synchrony, endogenous and exogenous effects, regional patterns, scale