Dispersal variability and associated population-level consequences in tree-killing bark beetles

Background: Dispersal is a key process in the response of insect populations to rapidly changing environmental conditions. Variability among individuals, regarding the timing of dispersal initiation and travelled distance from source, is assumed to contribute to increased population success through risk spreading. However, experiments are often limited in studying complex dispersal interactions over space and time. By applying a local-scaled individual-based simulation model we studied dispersal and emerging infestation patterns in a host − bark beetle system (Picea abies – Ips typgraphus). More specifically, we (i) investigated the effect of individual variability in beetle physiology (flight capacity) and environmental heterogeneity (host susceptibility level) on population-level dispersal 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 beetles causes predominantly positive effects on population-level dispersal success, yet these effects are strongly environment-dependent: Variability is most beneficial 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 highest in purely susceptible habitats, scattered host susceptibility appeared most suitable for dispersing bark beetle populations 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 host selectivity 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 in bark beetles. Dispersal variability largely contributes to risk spreading among individuals, and facilitates the response of populations to changing environmental conditions. Higher mortality risk suffered by a small part of the dispersing population (long-distance dispersers, pioneers) is likely paid off by reduced deferred costs resulting in fitness benefits for subsequent generations. Both, dispersal variability in space and time, and environmental heterogeneity are characterized as key features which require particular emphasis when investigating dispersal and infestation patterns in tree-killing bark beetles

Networks and dominance hierarchies: does interspecific aggression explain flower partitioning among stingless bees?

The distribution of consumers among resources (trophic interaction network) may be shaped by asymmetric competition. Dominance hierarchy models predict that asymmetric interference competition leads to a domination of high quality resources by hierarchically superior species

Defensive behavior and chemical deterrence against ants in the stingless bee genus Trigona (Apidae, Meliponini)

Five species of Trigona (Apidae, Meliponini) in Borneo were tested for anti-predator deterrents, which potentially contribute to the protection of individual bees as well as their colony. Feeding choice experiments were performed with three predatory ant species. In most cases, ants significantly preferred bees that were washed with solvents (hexane and chloroform respectively) over untreated bees. This shows that stingless bees possess ant-deterrent substances. We suggest that plant-originated terpenes on the bees' cuticles contribute to this deterrent effect. Furthermore, we observed behavioral defences of two Trigona species at their colony entrance. Upon simulated nest intrusion of ant workers, bees predominantly reacted with aggressive biting, but also utilized resin-like substances as glue against intruders. Therefore, stingless bees utilize a combination of defences that may help to deter ants as potential predators inside and outside the nest

Foraging loads of stingless bees and utilisation of stored nectar for pollen harvesting

We compared nectar, pollen and resin loads of individual workers among colonies from six Trigona species in Sabah, Borneo. Individual bees rarely collected large amounts of both nectar and pollen during the same foraging trip. Instead, comparison of crop contents across departing, flower-visiting, and returning bees suggests that pollen-collecting workers often carried highly concentrated nectar in their crop upon nest departure. During their foraging trip, this crop nectar volume decreased progressively until crops were largely empty when they returned to their nest. Individually marked pollen foragers carried highly concentrated nectar when they left their nest, while crops and corbiculae from marked nectar foragers were empty upon departure. We suggest that a large proportion of previously stored and highly concentrated nectar may be required for pollen adhesion to corbiculae and/or serve as fuel during foraging on nectar-poor flowers

Foraging loads of stingless bees and utilisation of stored nectar for pollen harvesting

International audienc

Adoption of the Euro in the Czech Republic

The thesis deals with the adoption of euro in the Czech Republic. The main goal is to identify and analyse the most important economic aspects related to adoption of single European currency and then asses the most appropriate timing of euro adoption in the Czech Republic and its consequences. The opening chapter briefly summarizes the development of monetary integration in Europe up to now. The second chapter provides theoretical insight into monetary integration in view of the theory of optimum currency areas. The following chapter focuses on real and nominal convergence of the Czech Republic to Eurozone. The fourth and fifth chapter describes the plan of the euro adoption in the Czech Republic and its institutional framework. Integral part of the thesis is the chapter describing public opinion related to the adoption of euro in the new member states targeting to the opinion in the Czech Republic. Final chapter asseses readiness of the Czech Republic for entry monetary union especially by convergence criteria point of view and compares the situation with the other new member states. At last but not at least the thesis provides recommendation of the timing of euro adoption in the Czech Republic. Powered by TCPDF (www.tcpdf.org