1 Studies combining within- and among-population processes are crucial for
understanding ecological and co-evolutionary dynamics in host-pathogen inte
ractions. We report on work over an 18-month period involving multiple beac
h populations of the plant Cakile maritima and its fungal pathogen Alternar
ia brassicicola along the southeast coast of Australia.
2 Results from permanent transects replicated on several beaches show that
disease incidence and prevalence vary significantly with plant age, class a
nd distance from the sea, as well as time during the season. Plant density
is also positively related to disease levels.
3 Results from three subregions indicate that disease persistence depends o
n survival of infected plants behind the foredunes of protected beaches. Po
pulation extinction was more likely on beaches with greater wind exposure a
nd sea access, with the latter also related to colonization consistent with
the dispersal of Cakile seeds via ocean currents,
4 Although disease dynamics during the epidemic were similar across subregi
ons, the severity of the epidemic varied significantly among these areas, s
uggesting that large-scale environmental factors may influence the timing a
nd development of the epidemic.
5 Estimates of synchrony in disease dynamics indicated that populations wit
hin a subregion were significantly correlated with respect to epidemic deve
lopment. There was, however, no evidence for spatial synchrony in disease d
ynamics based on among-population covariances in disease prevalence and int
erbeach distances. Populations within a subregion were thus often at quite
different phases of the epidemic at any given time.