Proposal summary
| The role of antagonism, commensalism, and
mutualism in bark beetle communities NSF DEB-Ecology: 2003-06. |
| Positive associations between species (mutualisms
and commensalisms), although ubiquitous in nature, are not well integrated
within the theoretical structure of community ecology. Furthermore, feedback
systems from community interactions involving mutualisms are a plausible,
but rarely explored, mechanism for generating complex population dynamics,
including the cyclical behavior of many pest populations. We propose studies
of community interactions involving Dendroctonus bark beetles
to test hypothesized consequences of mutualisms for populations and communities.
D. frontalis, the southern pine beetle, has an obligate mutualism
with two species of fungi. The fungi are transported by adult beetles
within specialized glandular structures (mycangia), and inoculated within
the phloem of host trees during oviposition. Larval nutrition depends
upon successful development of mycangial fungi within the phloem. A common
cause of larval mortality is poor growth of the mycangial fungi due to
competition from a bluestain fungus, Ophiostoma minus. O.
minus has a strong mutualism with Tarsonemus mites, which
transport ascospores between trees, and feed upon O. minus within
the phloem. The mites, in turn, are transported by the beetles (phoresy).
These direct interactions create an interaction system with the form of
a negative feedback loop. These system properties are hypothesized to
impact the entire community and influence the outbreak population dynamics
of D. frontalis, which kills pines, and is a dominant source
of disturbance in forests of the southeastern U.S. Recent exploration
of a sister species, D. mexicanus, has revealed a community that
is very similar except that the bluestain fungus is absent and mites instead
have a mutualism with one of the mycangial fungi. If our general model
of community interactions is valid, this should produce a state change
from negative feedback to positive feedback. We propose to exploit this
opportunity by testing for changes in community attributes that are predicted
to arise from a species deletion. Our studies of the D. frontalis
community have also revealed marked differences between mites and beetles
in their growth-temperature response, which suggests that seasonal and
regional variation in climate should modulate the community feedback system.
We will test whether autecological differences among species lead to predictable
responses of the intact community with (1) experimental manipulations
of intact communities, (2) surveys of natural patterns in community structure
across climatic regions, and (3) comparisons of predicted demographic
pattens with time series data of beetle abundance.
Scientific value and broader beneficial impacts |
| Investigators: Matthew P. Ayres, Kier Klepzig, John Moser, Richard Hofstetter |
| Related feature article in Science |