Thomas Mang

Biological Flora of the British Isles: Ambrosia Artemisiifolia

This account presents information on all aspects of the biology of Ambrosia artemisiifolia L. (Common ragweed) that are relevant to understanding its ecology. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history, conservation, impacts and management. n nAmbrosia artemisiifolia is a monoecious, wind-pollinated, annual herb native to North America whose height varies from 10 cm to 2.5 m, according to environmental conditions. It has erect, branched stems and pinnately lobed leaves. Spike-like racemes of male capitula composed of staminate (male) florets terminate the stems, while cyme-like clusters of pistillate (female) florets are arranged in groups in the axils of main and lateral stem leaves. n nSeeds require prolonged chilling to break dormancy. Following seedling emergence in spring, the rate of vegetative growth depends on temperature, but development occurs over a wide thermal range. In temperate European climates, male and female flowers are produced from summer to early autumn (July to October). nAmbrosia artemisiifolia is sensitive to freezing. Late spring frosts kill seedlings and the first autumn frosts terminate the growing season. It has a preference for dry soils of intermediate to rich nutrient level. n nAmbrosia artemisiifolia was introduced into Europe with seed imports from North America in the 19th century. Since World War II, it has become widespread in temperate regions of Europe and is now abundant in open, disturbed habitats as a ruderal and agricultural weed. n nRecently, the North American ragweed leaf beetle (Ophraella communa) has been detected in southern Switzerland and northern Italy. This species appears to have the capacity to substantially reduce growth and seed production of A. artemisiifolia. n nIn heavily infested regions of Europe, A. artemisiifolia causes substantial crop-yield losses and its copious, highly allergenic pollen creates considerable public health problems. There is a consensus among models that climate change will allow its northward and uphill spread in Europe.

Ancient and recent alien species in temperate forests: steady state and time lags

Temperate forests are relatively little affected by invasions globally. However, it remains unclear if these low invasion levels can be attributed to high invasion resistance, or if particularly long time lags in forests have lead to wide-spread invasion debt at the landscape and habitat scales, thus masking the invasibility of forests. Using linear and generalized linear mixed-effects models, we tested which factors determine the level of invasion of old (archaeophytes, pre-1500 alien species) and new (neophytes, post-1500 alien species) invaders across 30 study sites (5xa0ha size) and 16 transects in lowland forests in eastern Austria, Central Europe. We analysed the importance of different forest types, adjacent habitats, introduction pathways, species’ local residence time and proximity to human settlements as proxy for propagule pressure. We recorded 109 neophyte and 50 archaeophyte species, with significant differences between both groups with respect to region of origin, pathways, and life form. The number of neophyte species per study site varied by more than an order of magnitude and was dependent on both proximity to settlements and residence time in a non-linear manner, with proximity to settlements showing a particularly strong effect for recently introduced neophytes. In contrast, archaeophyte species numbers were only marginally affected by distance to the nearest settlement. Within habitats, transect plots close to the forest edge and adjacent to settlements showed significantly higher numbers and cover of neophyte species, whereas for archaeophytes and native species no such effect could be detected. Our results suggest that time lag phenomena stemming from dispersal limitation (e.g. aggravated by isolation of forest patches), heterogeneity in species’ local residence time as well as increases in local levels of propagule pressure (e.g. created by expanding settlements), may result in wide-spread invasion debt at the landscape and habitat scales, hence masking invasibility of forests. Spread of new invaders may ultimately, although possibly only over long time periods, result in increased frequency and impact of neophyte species in temperate forests.

Little, but increasing evidence of impacts by alien bryophytes.

AbstractBased on data of bryophyte invasions into 82 regions on five continents of both hemispheres, we aim here at a first comprehensive overview of the impacts that bryophytes may have on biodiversity and socio-economy. Of the 139 bryophytes species which are alien in the study regions seven cause negative impacts on biodiversity in 26 regions, whereas three species cause negative impacts on socio-economic sectors in five regions. The vast majority of impacts stem from anecdotal observations, whereas only 14 field or experimental studies (mostly on Campylopus introflexus in Europe) have quantitatively assessed the impacts of an alien bryophyte. The main documented type of impact on biodiversity is competition (8 alien bryophytes), with native cryptogams being most affected. In particular, C. introflexus (9 regions) and Pseudoscleropodium purum (7 regions) affect resident species composition. The few socio-economic impacts are caused by alien bryophytes which form dense mats in lawns and are then considered a nuisance. Most negative impacts on biodiversity have been recorded in natural grasslands, forests, and wetlands. Impacts of alien bryophytes on biodiversity and socio-economy are a recent phenomenon, with >85xa0% of impacts on biodiversity, and 80xa0% of impacts on socio-economy recorded since 1990. On average, 40xa0years (impacts on biodiversity) and 25xa0years (impacts on socio-economy) elapsed between the year a bryophyte species has been first recorded as alien in a region and the year impacts have been recorded first. Taking into account the substantial time lag between first record and first recorded impact in a region, it seems to be likely that the currently moderate impacts of alien bryophytes will continue to increase. As quantitative studies on impacts of alien bryophytes are rare and restricted to few environments and biogeographic regions, there is a need for addressing potential impacts of alien bryophytes in yet understudied settings.n

Telling a different story: a global assessment of bryophyte invasions

We assess and review spatio-temporal patterns, habitat affiliations, pathways, impacts, and management experience of bryophyte invasions in extra-tropical countries and regions (nxa0=xa082) from five continents and maritime islands spanning both hemispheres. Distribution data were extracted and critically checked from a wide range of sources and supplemented with data on biology and introduction history. We identified 139 bryophytes species which we consider to be alien in at least one of our study regions (106 mosses, 28 hepatics and 5 hornworts). Numbers of average alien bryophyte species are significantly higher on islands than in continental regions of similar size, and peak on maritime islands. Cumulative numbers of first records have grown slowly until 1950 and have strongly increased since then. Accidental import as hitch-hiker (34 species) or with ornamental plants (27 species) constitute the most important introduction pathways. We found a remarkably high contribution from distant donor regions to alien bryophyte floras, especially from the complementary hemisphere. Most alien bryophytes prefer strongly modified habitats (e.g. ruderal vegetation, roadsides, lawns), and only few natural ecosystems (forests, rocks) are regularly invaded. Evidence for an ecological impact of bryophyte invasions is scarce and competitive replacement of native moss species, or vascular plant seedlings, by alien bryophytes has only been documented in a few cases. We conclude that bryophytes differ profoundly in many respects from vascular plants, and so do their invasion patterns at large scale. Our global bryophyte invasion state assessment provides the basis for future, more explicit considerations of this largely neglected taxonomic group in invasion ecology, a step we suggest to be urgently needed as studying them might provide novel insights into patterns and processes of plant invasions in general.

Uncertainty in predicting range dynamics of endemic alpine plants under climate warming.

Correlative species distribution models have long been the predominant approach to predict species range responses to climate change. Recently, the use of dynamic models is increasingly advocated for because these models better represent the main processes involved in range shifts and also simulate transient dynamics. A well-known problem with the application of these models is the lack of data for estimating necessary parameters of demographic and dispersal processes. However, what has been hardly considered so far is the fact that simulating transient dynamics potentially implies additional uncertainty arising from our ignorance of short-term climate variability in future climatic trends. Here, we use endemic mountain plants of Austria as a case study to assess how the integration of decadal variability in future climate affects outcomes of dynamic range models as compared to projected long-term trends and uncertainty in demographic and dispersal parameters. We do so by contrasting simulations of a so-called hybrid model run under fluctuating climatic conditions with those based on a linear interpolation of climatic conditions between current values and those predicted for the end of the 21st century. We find that accounting for short-term climate variability modifies model results nearly as differences in projected long-term trends and much more than uncertainty in demographic/dispersal parameters. In particular, range loss and extinction rates are much higher when simulations are run under fluctuating conditions. These results highlight the importance of considering the appropriate temporal resolution when parameterizing and applying range-dynamic models, and hybrid models in particular. In case of our endemic mountain plants, we hypothesize that smoothed linear time series deliver more reliable results because these long-lived species are primarily responsive to long-term climate averages.

Single- and multi-slice spiral computed tomography of the paediatric kidney

Single- and multi-slice computed tomography (CT) is regarded as the primary imaging tool in traumatology, both in adults and children. For complicated infectious disease and renal tumours, these techniques are recommended only as secondary diagnostic tools. Specifically, multi-slice CT (MSCT) provides excellent spatial resolution, which is a particular advantage for the evaluation of small structures as they are typical in children. However, MSCT offers more information than is required for diagnosis. Therefore, low-dose protocols are necessary for paediatric examinations. The CT dose-index (CTDI(vol)) should not exceed 2 mGy for newborns, 4 mGy for toddlers, 5 mGy for elementary school children, and 8 mGy for adolescents.

Accounting for imperfect observation and estimating true species distributions in modelling biological invasions

The documentation of biological invasions is often incomplete with records lagging behind the species’ actual spread to a spatio-temporally heterogeneous extent. Such imperfect observation bears the risk of underestimating the already realised distribution of the invading species, misguiding management efforts and misjudging potential future impacts. In this paper, we develop a hierarchical modelling framework which disentangles the determinants of the invasion and observation processes, models spatio-temporal heterogeneity in detection patterns, and infers the actual, yet partly undocumented distribution of the species at any particular time. We illustrate the model with a case study application to the invasion of Common ragweed Ambrosia artemisiifolia in Austria. The invasion part of the model reconstructs the historical spread of this species across a grid of ~ 6×6 km2 cells as driven by spatio-temporal variation in physical site conditions, propagule production, dispersal, and ‘background’ introductions from unknown sources. The observation part models the detection of the species occurrences based on heterogeneous sampling efforts, human population density, and estimated local invasion level. We fitted the hierarchical model using a Bayesian inference approach with parameters estimated by Markov Chain Monte Carlo (MCMC). The actual spread of A. artemisiifolia concentrated on the climatically well-suited lowlands and was mainly driven by spatio-temporal propagule pressure from source cells with long-distance dispersal occurring rather frequently. Annual detection probabilities were estimated to vary between about 1% and up to 28%, depending mainly on sampling intensity. The model suggested that by 2005 about half of the actual distribution of the species was not yet documented. Our hierarchical model offers a flexible means to account for imperfect observation and spatio-temporal variability in detection efficiency. Inferences can be used to disentangle aspects of the invasion dynamics itself from patterns of data collection, develop improved future surveying schemes, and design more efficient invasion management strategies. n nThis article is protected by copyright. All rights reserved.

Remoteness promotes biological invasions on islands worldwide

Significance Islands are hotspots of alien species invasions, and their distinct biodiversity is particularly vulnerable to invading species. While isolation has shaped natural colonization of islands for millions of years, globalization in trade and transport has led to a breakdown of biogeographical barriers and subsequent colonization of islands by alien species. Using a large dataset of 257 subtropical and tropical islands, we show that alien richness increases with increasing isolation of islands. This pattern is consistent for plants, ants, mammals, and reptiles, and it cannot simply be explained by island economics and trade alone. Geographical isolation does not protect islands from alien species, and island species richness may reach a new dynamic equilibrium at some point, likely at the expense of many endemic species. One of the best-known general patterns in island biogeography is the species–isolation relationship (SIR), a decrease in the number of native species with increasing island isolation that is linked to lower rates of natural dispersal and colonization on remote oceanic islands. However, during recent centuries, the anthropogenic introduction of alien species has increasingly gained importance and altered the composition and richness of island species pools. We analyzed a large dataset for alien and native plants, ants, reptiles, mammals, and birds on 257 (sub) tropical islands, and showed that, except for birds, the number of naturalized alien species increases with isolation for all taxa, a pattern that is opposite to the negative SIR of native species. We argue that the reversal of the SIR for alien species is driven by an increase in island invasibility due to reduced diversity and increased ecological naiveté of native biota on the more remote islands.