| Abstrak/Abstract |
Background: Dispersal is a key process in the response of insect populations to rapidly changing environmentalconditions. Variability among individuals, regarding the timing of dispersal initiation and travelled distance fromsource, is assumed to contribute to increased population success through risk spreading. However, experimentsare often limited in studying complex dispersal interactions over space and time. By applying a local-scaledindividual-based simulation model we studied dispersal and emerging infestation patterns in a host ? bark beetlesystem (Picea abies – Ips typgraphus). More specifically, we (i) investigated the effect of individual variability inbeetle physiology (flight capacity) and environmental heterogeneity (host susceptibility level) on population-leveldispersal success, and (ii) elucidated patterns of spatial and/or temporal variability in individual dispersal success,host selectivity, and the resulting beetle density within colonized hosts in differently susceptible environments.Results: Individual variability in flight capacity of bark beetlescausespredominantlypositiveeffectsonpopulation-level dispersal success, yet these effects are strongly environment-dependent: Variability is mostbeneficial in purely resistant habitats, while positive effects are less pronounced in purely susceptible habitats,and largely absent in habitats where host susceptibility is spatially scattered. Despite success rates being highestin purely susceptible habitats, scattered host susceptibility appeared most suitable for dispersing bark beetlepopulations as it ensures population spread without drastically reducing success rates. At the individual level,dispersal success generally decreases with distance to source and is lowest in early flight cohorts, while hostselectivity increased and colonization density decreased with increasing distance across all environments. Conclusions: Our modelling approach is demonstrated to be a powerful tool for studying movement ecology inbark beetles. Dispersal variability largely contributes to risk spreading among individuals, and facilitates the response ofpopulations to changing environmental conditions. Higher mortality risk suffered by a small part of the dispersingpopulation (long-distance dispersers, pioneers) is likelypaidoffbyreduceddeferredcostsresultinginfitnessbenefits for subsequent generations. Both, dispersal variability in space and time, and environmental heterogeneity arecharacterized as key features which require particular emphasis when investigating dispersal and infestationpatterns in tree-killing bark beetles. |
