Sulphur dioxide sensitivity in South African asthmatic children

Sulphur dioxide (SO2) is a well-known precipitant of asthmatic attacks. Many foodstuffs are preserved with SO2 and other sulphites. In this study 37 asthmatic children attending the Allergy Clinic at the Red Cross Children's Hospital were challenged with SO2 in apple juice in a dose similar to that commonly ingested in soft-drinks containing this preservative. The responses of these children were compared with the responses of 22 asthmatics challenged with apple juice alone.Sixteen out of 37 children (43,2%) challenged with SO2 reacted with a fall in forced expiratory volume in 1 second (FEV1) of more than 10% compared with none of the 22 control asthmatic children challenged with apple juice alone (P = 0,0016). Girls were found to be more sensitive than boys. A 20% or more fall in FEV1 occurred in 8 (21,6%) of the children challenged with SO2 compared with none in the control group (P = 0,039). There was an individual variability in the responses of sensitive individuals to the SO2 challenge. Reactions occurred in spite of maintenance medication and occurred within 5 - 30 minutes of challenge. Since sulphite sensitivity is common in asthmatic children, ingestion of sulphites should be avoided

Scale effects on the body size frequency distributions of African birds: patterns and potential mechanisms

Aim To describe and analyse the body size frequency distributions (BSFDs) of avian assemblages at several spatial scales in the Afrotropics. We also tested if the variation in median body size across assemblages at different spatial scales was related to environmental variables and whether purely stochastic processes could explain BSFDs. Location The Afrotropical biogeographic realm. Methods Avian body masses for 1960 species where analysed at continental, biome, ecoregion and local spatial scales with standardmetrics.Variation inmedian assemblage body size was modelled as a function of environmental and spatial explanatory variables to assess non-random assemblage structure. We tested if BSFDs of smaller spatial scale distributions are random subsets of the larger spatial scale assemblages in which they are embedded, and used three different null model randomizations to investigate the influence of stochastic processes on BSFDs. Results The African avifauna’s continental BSFD is unimodal and right-skewed. BSFDs generally become less skewed and less modal with decreasing spatial scale. The best-fit model explained 71% of median body size values at the ecoregion scale as a function of latitude, latitude2, longitude, species richness and species range size. BSFDs at smaller scales show non-random assembly from larger scale BSFDs distributions. Main conclusion African avifaunal BSFDs are quantitatively dissimilar to African mammal BSFDs, which are bimodal at all spatial scales.Much of the change in median body size with spatial scale can be captured by a range-weighted null model, suggesting that differential turnover between smaller- and larger-bodied species might explain the shift in the central tendency of the BSFD. At the local scale, energy may well contribute to structuring BSFDs, but this pattern is less pronounced at larger spatial scales

Ecologically relevant measures of tolerance to potentially lethal temperatures

The acute thermal tolerance of ectotherms has been measured in a variety of ways; these include assays where organisms are shifted abruptly to stressful temperatures and assays where organisms experience temperatures that are ramped more slowly to stressful levels. Ramping assays are thought to be more relevant to natural conditions where sudden abrupt shifts are unlikely to occur often, but it has been argued that thermal limits established under ramping conditions are underestimates of true thermal limits because stresses due to starvation and/or desiccation can arise under ramping. These confounding effects might also impact the variance and heritability of thermal tolerance. We argue here that ramping assays are useful in capturing aspects of ecological relevance even though there is potential for confounding effects of other stresses that can also influence thermal limits in nature. Moreover, we show that the levels of desiccation and starvation experienced by ectotherms in ramping assays will often be minor unless the assays involve small animals and last for many hours. Empirical data illustrate that the combined effects of food and humidity on thermal limits under ramping and sudden shifts to stressful conditions are unpredictable; in Drosophila melanogaster the presence of food decreased rather than increased thermal limits, whereas in Ceratitis capitata they had little impact. The literature provides examples where thermal limits are increased under ramping presumably because of the potential for physiological changes leading to acclimation. It is unclear whether heritabilities and population differentiation will necessarily be lower under ramping because of confounding effects. Although it is important to clearly define experimental methods, particularly when undertaking comparative assessments, and to understand potential confounding effects, thermotolerance assays based on ramping remain an important tool for understanding and predicting species responses to environmental change. An important area for further development is to identify the impact of rates of temperature change under field and laboratory conditions

TRY plant trait database – enhanced coverage and open access

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Interaction intensity and importance along two stress gradients: adding shape to the stress-gradient hypothesis

The stress-gradient hypothesis (SGH) predicts that the community-wide prevalence of positive interactions, relative to negative interactions, is greater under more severe environmental conditions. Because the frequency of positive and negative interactions within a community is the aggregate of multiple pair-wise interactions, one approach to testing the SGH is to examine how pair-wise interactions vary along severity gradients. While the SGH suggests that the net outcome of an interaction should monotonically become more positive with increasing environmental severity, recent studies have suggested that the severity-interaction relationship (SIR) may rather be unimodal. We tested which of the proposed shapes of the SIR best fits the variation in the interaction between two species along two types of severity gradients on sub-Antarctic Marion Island. This was done by comparing the performance of the grass Agrostis magellanica in the presence and absence of the cushion plant Azorella selago, along both species’ entire altitudinal ranges (transects spanning 4–8 km), and along a shorter (transect = 0.4 km) wind exposure gradient. Along the altitudinal transects the relative intensity, but not the absolute intensity or the importance, of the Azorella selago–Agrostis magellanica interaction increased with altitude, consistently forming a plateau-shaped SIR with a positive symptote. Thus, while the performance of Agrostis magellanica was negatively affected by Azorella selago at low altitudes, the grass benefited from growing on the cushion plant under greater environmental severity. Along the wind exposure gradient the intensity of the interaction also became more positive with increasing environmental severity for most performance measures. This suggests that the switch from a net negative to a net positive interaction can occur across both short and long distances. Therefore, this study provides strong evidence for a plateau-shaped SIR, and confirms that the SIR is unimodal along the particular non-resource severity gradients of this study.Centre of Excellence for Invasion Biolog

Rapid range expansion and community reorganization in response to warming

Species ranges are expected to expand along their cooler boundaries in response to rising temperatures associated with current global climate change. However, this ‘fingerprint’ of climate change is yet to be assessed for an entire flora. Here, we examine patterns of altitudinal range change in the complete native vascular flora of sub-Antarctic Marion Island. We demonstrate a rapid mean upslope expansion in the flora since 1966, in response to 1.2˚C warming on the island. The 3.4 ±0.8myr-1 (mean ±SE) upslope expansion rate documented is amongst the highest estimates from partial floras. However, less than half of the species in the flora were responsible for the expansion trend, demonstrating that the global fingerprint of warming may be driven by a highly responsive subset of the species pool. Individual range expansion rates varied greatly, with species-specific niche requirements explaining some of this variation. As a result of the idiosyncratic expansion rates, altitudinal patterns of species richness and community composition changed considerably, with the formation of no-analog communities at high and intermediate altitudes. Therefore, both species- and community-level changes have occurred in the flora of Marion Island over a relatively short period of rapid warming, demonstrating the sensitivity of high latitude communities to climate change. Patterns of change within this flora illustrate the range of variation in species responses to climate change and the consequences thereof for species distributions and community reorganization.Centre of Excellence for Invasion Biolog

Alien plant species that invade high elevations are generalists: support for the directional ecological filtering hypothesis

Questions: The richness of invasive alien plant species tends to decrease with increasing elevation. This pattern may be due to alien plant species requiring traits allowing survival at high elevations (the Abiotic Limitation Hypothesis; ALH). In contrast, the more recent Directional Ecological Filtering Hypothesis (DEFH) suggests that only species with broad environmental tolerances will successfully spread from lowlands (where most introductions occur) to high elevations. Here we test support for the DEFH and ALH along an elevational gradient by asking: (1) are alien species that occur at higher elevations generalists; and (2) do alien species occurring at higher elevations exhibit traits that distinguishes them fromlowland alien species? Location: Sani Pass, Maloti-Drakensberg Transfrontier Conservation Area, South Africa. Methods: A nestedness analysis was conducted to test whether alien species were nested along the elevational gradient, and ANOVA and Chi2 tests (supplemented by resampling procedures) were used to determine if functional traits differed between high- and low-elevation alien species. Results: Significant nestedness of the alien flora indicates that alien species occurring at high elevations are generalists, being widespread across the elevational gradient. Compared to low-elevation aliens, plant height was lower and cold toleranceweaker for high-elevation species. Conclusion: We found support for the DEFH, with the majority of high-elevation aliens being widespread generalists. Overall only two of the 11 functional traits differed between high- and low-elevation alien species, with only one trait supporting the ALH: shorter plant stature at higher elevations. Therefore, complementing nestedness analyses with trait data provides a more nuanced insight into the determinants of alien richness patterns along elevational gradients, and highlights how the two contemporary hypotheses might not be mutually exclusive

Repeated monitoring as an effective early detection means: first records of naturalised Solidago gigantea Aiton (Asteraceae) in southern Africa

Early detection of emerging invasive plants depends on maximizing the probability of detecting new populations. Repeated surveys along a gradient of environmental conditions or in areas exposed to high propagule pressure provide a potentially efficient strategy for early detection of alien species. The long-term monitoring of such an area resulted in the documentation of the first naturalised Solidago gigantea Aiton (Asteraceae) population for southern Africa. This population consisted of c. 45 individuals growing in two locations on unmanaged grassland in the Drakensberg Mountains at an elevation of 1619 m a.s.l. Solidago gigantea readily invades unmanaged European grasslands, altering biomass and transforming habitats. Moreover, since goldenrods (Solidago spp) are perennial species reproducing through a large number of wind-dispersed seeds and belowground rootstocks, these species appear well pre-adapted to the fire-prone grassland biome of South Africa. We therefore suggest early-stage eradication of S. gigantea before it potentially becomes an unmanageable and costly invasive species in this region. This study supports long-term monitoring programmes as an effective means for early detection of new invasive species

Outcomes of biotic interactions are dependent on multiple environmental variables

Question: Can variation in the outcome of biotic interactions in relation to environmental severity be more accurately predicted when considering multiple stress and/or disturbance variables? Location: Arctic-alpine tundra in Kilpisjarvi, North Finland. Methods: To test the impact of including multiple environmental variables in analyses of the outcomes of biotic interactions, we modelled reproductive effort and cover of 17 arctic-alpine species as a function of Empetrum nigrum subsp. hermaphroditum cover, geomorphological disturbance and soil moisture with statistical interactions of the explanatory variables included. We implemented a best-subset approach using generalized linear models (GLM) and selected the best model for each species based on Akaike's information criterion (AIC). Results: For the majority of species, models including multiple environmental variables were selected as best. Reproductive effort depended on one or both environmental variables for all species, and 14 species were additionally influenced by Empetrum, with the impact of Empetrum varying with abiotic conditions in all but one of those species. Moreover, the three-way interaction of three explanatory variables was included in the best-fit models for six species. The impact of Empetrum on species cover showed a similar pattern, with 11 species affected by Empetrum and its statistical interactions with one or both abiotic variables. Conclusions: Biotic interactions have an important role in arctic-alpine vegetation, but to fully understand variation in their effects multiple environmental factors should be explicitly considered. In this study, the outcome of biotic interactions was frequently dependent on two abiotic variables (and occasionally additionally on their statistical interaction). Therefore, we demonstrate that studies based on only one environmental factor may cause misleading interpretations of the nature of biotic interactions in plant communities where there are multiple independent variables underlying the habitat severity gradient