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Resource dynamic plays a key role in regional fluctuations of the spruce bark beetles Ips typographus

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1 We analysed time series of spruce bark beetles (Nt) caught in pheromone traps from 1979 to 2000 in approximately 100 localities throughout south-east Norway.

2 The analysis was performed at two spatial scales (whole area and 12 subregions), and included additional analyses of the time-series sequences before and after a large windfelling (1987) that appeared to induce a shift in the dynamics.

3 Regression of Rt (logarithmic per-capita growth rate) on Nt − d indicated that the endogenous dynamics were dominated by lag 1 density dependence. This was particularly so in the sequence after the large windfelling (R2 = 0.79), probably due to intraspecific competition for breeding substrate.

4 The sequence before the windfelling (1979–1987) was declining without significant density dependence. We suggest this to be a transition period, reflecting a drop in carrying capacity due to depletion of susceptible trees during the preceding outbreak period (1970s) and a drop in beetle number to below the density required to kill trees.

5 Windfelling (Wt − 1) appears to be an important predictor of the dynamics; however, it was difficult to evaluate the statistical significance of this factor due to only one large windfall event.

6 The weak influence of drought stress (Dt − 1) could be due to the absence of severe drought periods within the time series.

Keywords: Climatic factors; density dependence; endogenous feedback; population dynamic; time series

Document Type: Research Article


Affiliations: 1: Norwegian Forest Research Institute, Høgskoleveien 12, 1432 Ås, Norway, 2: Departments of Entomology and Natural Resource Science, Washington State University, Pullman, WA 99164, U.S.A.

Publication date: May 1, 2004


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