Geographical differentiation of populations can be interpreted as a result of adaptive processes in response to environmental gradients and biotic interactions. Such adaptations are particularly interesting in invasive alien species which have been present in an area for a relatively short time. There are few observations of latitudinal trends in alien plants, and no account exists for Impatiens glandulifera, a problematic annual weed in most countries of central and north‐western Europe. Here we describe variation in growth and phenology in 26 populations of this species from nine European regions in a common garden in Denmark. Above‐ground biomass (an estimate of fecundity), height and basal diameter were lower in the northern populations which were first to produce flowers. Some differences were also observed in biomass allocation to leaves, flowers and fruits, albeit without a latitudinal pattern. The latitudinal trends in growth and survival disappeared in a field experiment, probably due to suboptimal site conditions. Most variation in plant traits was explained by differences among regions with some minor effects of populations within regions. Besides latitude, no other geographical, climatic or population trait correlated with the observed differences in growth and phenology. Differences in latitude may mainly represent variation in length of the growing season. The causes and potential consequences of such latitudinal trends for population dynamics and dispersal of alien plants are discussed.

We studied the patterns of habitat availability and use by the Cantabrian capercaillie Tetrao urogallus cantabricus, an isolated and endangered population at the southwestern edge of the species distribution. We combined field surveys and GIS analyses to show that this population differs from its conifer-specialist conspecifics in that it inhabits beech Fagus sylvatica and oak Quercus petraea forests, without specialisation as regards the tree species as long as enough forest cover remains. The habitat of Cantabrian capercaillie is highly fragmented, and smaller forest patches have been abandoned during the last few decades; the display areas that remain occupied are now located farther from forest edges. Lower tree density and more widespread distribution of bilberry Vaccinium myrtillus characterised the occupied display grounds. However, even abandoned areas showed tree densities well within the optimum range for capercaillie and bilberry in other populations, a result that should be taken into account before any habitat management action is considered. We found that some non-forested habitats were also used by capercaillie, especially during the autumn and winter. We suggest that the protection of Cantabrian capercaillie should be tightly coupled with an effective, strict protection of the few remaining large forest fragments in the range, and that information about nesting and brood rearing habitat should be obtained. Conditions for understory development should be favoured, preventing overgrazing by ungulates. The natural, non-forested matrix should also be considered in management plans, as a direct source of food and shelter and an important feature determining connectivity among patches.

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The Cantabrian capercaillie Tetrao urogallus cantabricus, a subspecies of the western capercaillie, is endemic to the Cantabrian Mountains of northwest Spain. The range is separated from its nearest neighbouring capercaillie population by a distance of more than 300 km. High genetic differentiation compared to capercaillie elsewhere qualifies the subspecies as an Evolutionarily Significant Unit. An assessment according to the IUCN Red List categories and criteria showed that the subspecies qualifies as Endangered due to rapid population declines, small population size, and severely fragmented range. The implementation of a range-wide recovery plan is vital for the survival of this subspecies.

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