Proposal summary
| Southern pine beetle: the causes of transitions
between endemic and epidemic conditions US Forest Service Competitive Grant: 2004-2007. Pending. |
| Southern pine beetle populations tend to switch back and forth between endemic and epidemic conditions. As they do, their deleterious impacts on forest switch between minor and extreme. It has been thought that the extreme fluctuations were population “cycles”, in the strict sense of having regular periods and being largely driven by an endogenous feedback system (probably from predator-prey interactions). Re-analysis of the updated time series of population fluctuations in East Texas no longer provides support for strong cyclical tendencies, nor do new analyses of population dynamics across the full range of SPB in the U.S. An alternative to population cycles is that exogenous environmental fluctuations sometimes induce a change between qualitatively different states (endemic vs. epidemic). If this alternative is supported, it could suggest relatively novel strategies for monitoring populations (emphasizing measurements that can anticipate switches between endemic and epidemic states) or even control (e.g., managing for conditions that promote the maintenance of endemic conditions). We propose tests of two hypotheses: (1) interspecific competition within lightning-struck trees can regulate endemic populations of SPB and reduce the risk of epidemic conditions, and (2) the abundance of bluestain fungus can provide a tool for predicting the collapse of epidemic populations. Deliverables will include publication of (1) comprehensive analyses of spatio-temporal patterns in SPB populations, including tests for cyclical dynamics vs. “state changes”; (2) tests for regulation of endemic SPB populations within lightning-struck trees; and (3) tests of bluestain abundance as a predictor of collapsing epidemics. |
| Investigators: Matthew P. Ayres, Sharon Martinson, Rich Hofstetter, Maria Lombardero |