PEBE 117, Friday February 24th, 2005

Speaker: James Powell
               Department of Mathematics and Statistics
               Utah State University

Title: Ghost Forests, Global Warming and Mountain Pine Beetles, or
        The Mathematical Basis for Modelling Insect Seasonality

Abstract:
In this talk we explore the potential consequence of global warming on the
distribution and outbreak status of mountain pine beetle (Dendroctonus
ponderosae). Mountain pine beetle serve an important ecological role in
western US pine forests, which have evolved with bark beetle disturbance
as an integral part of an adapted system. The reproductive strategy of mountain
pine beetles requires new hosts each year, and pines under attack defend
themselves strongly. There is thus strong selective pressure for
dispersed populations of beetles to mature and emerge simultaneously (synchrony),
and at an appropriate time of year (seasonality). Interestingly, the
development and timing of mountain pine beetle development seems to be under direct
thermal control, operating without the benefit of diapause (which often serves to
`time' the development of other insects). A very simple model for insect
development uses a combination of stage-dependent developmental rates and
temperature thresholds below which development can not occur. In
combination with seasonal temperature swings a natural consequence of this simple
model is that oviposition and emergence will occur in fixed, attractive cycles
corresponding to one, two, or half generations per year. The dynamical
properties of the thermal habitat are therefore characterized by regions
of adaptive seasonality separated by regions of maladaptive, asynchronous
seasonality, which (with host availability) set the limits on mountain
pine beetle habitat. These results are used to analyze the transient
dynamics and outbreak potential of mountain pine beetle populations in the mountainous
west of North America.