From the Cover: Megafauna and ecosystem function from the Pleistocene to the Anthropocene

Large herbivores and carnivores (the megafauna) have been in a state of decline and extinction since the Late Pleistocene, both on land and more recently in the oceans. Much has been written on the timing and causes of these declines, but only recently has scientific attention focused on the consequences of these declines for ecosystem function. Here, we review progress in our understanding of how megafauna affect ecosystem physical and trophic structure, species composition, biogeochemistry, and climate, drawing on special features of PNAS and Ecography that have been published as a result of an international workshop on this topic held in Oxford in 2014. Insights emerging from this work have consequences for our understanding of changes in biosphere function since the Late Pleistocene and of the functioning of contemporary ecosystems, as well as offering a rationale and framework for scientifically informed restoration of megafaunal function where possible and appropriate.     

Sensitivity to wild vegetation

74 patients suspected of having allergic contact dermatitis to wild vegetation were patch tested with either extracts of 13 plants of the family Compositae and 7 other weeds or trees. Anthemis cotula (dog fennel) and Xanthium strumarium (cocklebur) gave the most frequent positive results, demonstrating a change of frequency in sensitivity compared to the 1950s, when Ambrosia artemisiifolia (ragweed) was recognized as the most frequently sensitizing weed. The reasons for these changes of incidence and clinical patterns are examined.     

Discovery of fairy circles in Australia supports self-organization theory

Vegetation gap patterns in arid grasslands, such as the “fairy circles” of Namibia, are one of nature’s greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomass–water feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil–water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass–water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known.Pattern-formation theory (1) and the influence of Alan Turing’s work on understanding biological morphogenesis (2) are increasingly recognized in environmental sciences (3). Vegetation patterns resulting from self-organization occur frequently in water-limited ecosystems and, similar to Turing patterns, show pattern morphologies that change from gaps to stripes (labyrinths) to spots with decreasing plant-available moisture (4–6). The patterns may emerge on completely flat and homogeneous substrate and are induced by positive feedbacks between local vegetation growth and water transport toward the growth location. The depletion of water in the vicinity of the growing vegetation inhibits the growth there and promotes the development of large-scale patterns with a typical periodicity (5, 7–9). Spatial self-organization by scale-dependent pattern-forming feedbacks of this kind is a population-level response to water stress that complements phenotype changes at the organism level (10).Banded or striped vegetation patterns such as tiger bush or mulga are well known from remote sensing (4, 11, 12), but landscape-scale evidence for gap patterns with circular bare-soil patches is very rare. The archetype of such a gap pattern is that of the fairy circles (FCs) of Namibia, which cover vast areas in a narrow range of climatic conditions (13, 14). However, the origin of the Namibian FCs is still unknown. Several competing hypotheses exist ranging from vegetation self-organization (13–17), termite-induced activity (18), and Euphorbia poisoning (19) to abiotic gas leakage (20). Among these, vegetation self-organization stands out as the most solid mechanism that explains the emergence of large-scale order (15, 16) and the strong dependence of fairy-circle distribution on mean annual precipitation (13). Furthermore, only self-organized biomass–water feedbacks can explain the shrinking in size and disappearance of fairy circles after above-average rainfall years and the typical enlargement and increased appearance of FCs after below-average rainfall years (21).According to pattern-formation theory, the large-scale order that emerges from a uniform state obeys a universal pattern whose particular form is dictated by the instability that the uniform state undergoes (8, 22). The fairy-circle gap pattern observed in Namibia (15) is likely an example of a universal hexagonal pattern that, according to pattern-formation theory, is induced by a nonuniform stationary instability (3, 21–24). The mechanisms inducing the instability may differ among ecosystems, but the resulting hexagonal order of the pattern is the same. This suggests that gap patterns similar to the Namibian FCs should be observable in other water-limited landscapes, even if the mechanism of their formation is different. Also, the opponents of the self-organization hypothesis argue “if the model of self-organization were correct, it should be generic and circular bare patches should occur globally” (25).Here, we report on the discovery and analysis of such a hexagonal gap pattern, 10,000 km away from Namibia in the remote outback of Western Australia. Using a comprehensive approach consisting of fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling we reveal in the following that this gap pattern is the consequence of a pattern-forming biomass–water feedback that differs from the feedback that drives the formation of FCs in Namibia.     

Ecological covariates of Ascaris lumbricoides infection in schoolchildren from rural KwaZulu-Natal, South Africa

OBJECTIVES: To identify environmental factors that could serve to predict Ascaris lumbricoides infection patterns and thus guide control efforts in the absence of epidemiological information; to assess whether A. lumbricoides infection is positively associated with the soil clay content. METHODS: Information on A. lumbricoides infection and re-infection in a cohort of primary schoolchildren and interview data on their socioeconomic background and behaviour were combined with environmental data using a geographical information system (GIS). Multivariate models served to explore the covariation of environmental and infection patterns adjusted for possible confounders. RESULTS: Prevalence maps and spatial statistics revealed considerable spatial clustering of infection in the small study area. Logistic multivariate regression models showed strong positive associations of infection with vegetation density measured as the normalized difference vegetation index (NDVI) at baseline [odds ratio (OR) for a 10% increase: 1.82; 95% confidence interval (95% CI): 1.24-2.68; P=0.002] and after re-infection (OR: 2.22; 95% CI: 1.71-2.87; P<0.001). We also found a strong negative association of re-infection with the sun exposure of the soil surface as estimated from digital elevation models (OR: 0.78; 95% CI: 0.88; P<0.001). The soil clay content was only moderately positively associated with infection and re-infection. Socioeconomic and behavioural variables, although correlated with A. lumbricoides infection, did not appear to confound the above associations in the demographically homogeneous study area. Spatial analysis of the model residuals suggested that as the models accounted for most of the spatial pattern, the model standard errors should not be affected by spatial clustering. CONCLUSION: NDVI seems to have a high potential for the prediction of A. lumbricoides infection as it was strongly associated with infection patterns in the study area. Further advantages are that NDVI information is easy to use, affordable and available with global coverage.     

天山北坡中段蒿类荒漠草地土壤变化与植被退化关系的分析

本文以天山北坡中段伊犁绢蒿荒漠草地为对象,采用系统聚类和关联度数值分析方法,分析未退化、中度退化、重度退化和极度退化阶段下土壤养分和植被之间的关系。结果表明：当草地植被达到极度退化时,土壤养分仍保持着一定的稳定性;运用关联分析的计算表明。土壤容重和有机质对草地产量、盖度、密度有正的相关性．其关联度在0．69以上。     

Giant vegetation mimicking cardiac tumor in tricuspid valve endocarditis after catheter ablation

A 33-year-old man suffered from fever of unknown origin and developed right-sided heart failure. A transeshophageal echocardiogram revealed an progressive enlarging mass in the right atrium mainly attached to the tricuspid valve and a previous ablation site, which mimicked a cardiogenic tumor. He was operated on to remove the mass and intraoperative pathology showed it was large vegetation and secondary granulation due to tricuspid endocarditis. Tricuspid valve replacement was performed combined with reconstruction of the right atrial wall.     

Intracardiac Thrombi in Acute Myeloid Leukemia: An Echocardiographic and Autopsy Correlation

Two-dimensional echocardiography is the primary diagnostic imaging modality for the evaluation of cardiac masses. We describe an adult male suffering from acute myeloid leukemia who was detected to have right atrial and right ventricular mass on echocardiography. Based on the clinical data metastasis, coincidental primary cardiac tumor, vegetation, and thrombi were considered as possible differential diagnosis. Chemotherapy for acute myeloid leukemia failed and patient succumbed to septicemia. Later, clinical autopsy confirmed the diagnosis of intracardiac thrombi. Occurrence of intracardiac thrombi in acute myeloid leukemia is extremely rare. This report also emphasises the importance of histopathological or clinical autopsy examination of the mass in certain clinical scenario with diagnostic dilema. (Echocardiography 2010;27:E4-E8)     

Implications for the hydrologic cycle under climate change due to the expansion of bioenergy crops in the Midwestern United States

To meet emerging bioenergy demands, significant areas of the large-scale agricultural landscape of the Midwestern United States could be converted to second generation bioenergy crops such as miscanthus and switchgrass. The high biomass productivity of bioenergy crops in a longer growing season linked tightly to water use highlight the potential for significant impact on the hydrologic cycle in the region. This issue is further exacerbated by the uncertainty in the response of the vegetation under elevated CO(2) and temperature. We use a mechanistic multilayer canopy-root-soil model to (i) capture the eco-physiological acclimations of bioenergy crops under climate change, and (ii) predict how hydrologic fluxes are likely to be altered from their current magnitudes. Observed data and Monte Carlo simulations of weather for recent past and future scenarios are used to characterize the variability range of the predictions. Under present weather conditions, miscanthus and switchgrass utilized more water than maize for total seasonal evapotranspiration by approximately 58% and 36%, respectively. Projected higher concentrations of atmospheric CO(2) (550 ppm) is likely to decrease water used for evapotranspiration of miscanthus, switchgrass, and maize by 12%, 10%, and 11%, respectively. However, when climate change with projected increases in air temperature and reduced summer rainfall are also considered, there is a net increase in evapotranspiration for all crops, leading to significant reduction in soil-moisture storage and specific surface runoff. These results highlight the critical role of the warming climate in potentially altering the water cycle in the region under extensive conversion of existing maize cropping to support bioenergy demand.