Alternate attractors in the population dynamics of a tree-killing bark beetle

  • Author(s): Martinson, Sharon J.; Ylioja, Tiina; Sullivan, Brian T.; Billings, Ronald F.; Ayres, Matthew P.
  • Date: 2013
  • Source: Population Ecology 55: 95-106
  • Station ID: JRNL-SRS-55

Abstract

Among the most striking changes in ecosystems are those that happen abruptly and resist return to the original condition (i.e., regime shifts). This frequently involves conspicuous changes in the abundance of one species (e.g., an outbreaking pest or keystone species). Alternate attractors in population dynamics could explain switches between low and high levels of abundance, and could underlie some cases of regime shifts in ecosystems; this longstanding theoretical possibility has been difficult to test in nature. We compared the ability of an alternate attractors model versus two competing models to explain population fluctuations in the tree-killing bark beetle Dendroctonus frontalis. Frequency distributions of abundance were distinctly bimodal, a prediction of the alternate attractors model, strongly indicating the lack of a single, noisy equilibrium. Time series abundance data refuted the existence of strong delayed density-dependence or nonlinearities, as required by the endogenous cycles model. The model of alternate attractors was further supported by the existence of positive density-dependence at intermediate beetle abundances. Experimental manipulations show that interactions with competitors and shared enemies could create a locally stable equilibrium in small populations of D. frontalis. High variation among regions and years in the abundance of predators and competitors could permit switches between alternate states. Dendroctonus frontalis now provides the strongest case that we know of for alternate attractors in natural population dynamics. The accompanying demographic instability appears to underlie spatially extensive outbreaks that have lasting impacts on forest ecosystems. Understanding feedbacks in populations with alternate attractors can help to identify thresholds underlying regime shifts, and potentially manage them to avoid undesirable impacts.

  • Citation: . . Alternate attractors in the population dynamics of a tree-killing bark beetle. Population Ecology 55: 95-106. doi: 10.007/s10144-012-0357-y

Requesting Publications

You can order print copies of our publications through our publication ordering system. Make a note of the publication you wish to request, and visit our Publication Order Site.

Publication Notes

  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
  • Our on-line publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unuseable.
  • To view this article, download the latest version of Adobe Acrobat Reader.