Ecological drivers of an endemic state in a population of a non-aggregative bark beetle species in Mediterranean area

Marion DURAND-GILLMANN

Population cycles are one of the most remarkable characteristics of animal population dynamics. Many
forest insect populations can periodically or sporadically reach very high densities over large areas,
and the resulting episodes of massive defoliation and/or tree mortality constitute major disturbances that
fundamentally affect forest ecosystem processes. Bark beetles are a relevant model to study such host-
parasite interactions because they alternate endemic and epidemic phases that depend on two major
factors: the availability of trees weakened by biotic and/or abiotic factors and the level of insect p
opulations. We developed a multidisciplinary approach combining the characterization of ecophysiological
and dendrometrical traits involved in susceptibility/resistance of tree populations to bark beetle attacks
with this assessment of key ecological factors involved in bark beetles demography. We focused on a
healthy Aleppo pine interacting with a bark beetle population at an endemic state in South-eastern
France. Our results suggested that all attacks remained in patches formed by dead trees following the
attacks. Attacked trees, but resistant, have a higher vulnerability to cavitation and a significantly
lowergrowth in previous drought years before the attacks
.
T. destruens dispersal strategies seem to favor the exploitation of a scarce resource.
Our results are expected to allow in the long term the development of models predicting the joint response of insect comm
unities and forest dynamics to climate change.