The promise and pitfalls of β-diversity in ecology and conservation

A key challenge in ecology and conservation is to determine how processes at different scales create variation in community composition (β-diversity). In this issue, Oldén & Halme show that grazers increase β-diversity through multiple processes at different scales. We discuss how β-diversity can elucidate fundamental processes of community assembly, challenges in linking processes to patterns, and unresolved questions across scales

Peak Ventilation Reference Standards from Exercise Testing: From the FRIEND Registry

Peak Ventilation Reference Standards from Exercise Testing: From the FRIEND Registry. Med. Sci. Sports Exerc., Vol. 50, No. 12, pp. 2603–2608, 2018. Purpose: Cardiopulmonary exercise testing (CPX) provides valuable clinical information, including peak ventilation (V˙ Epeak), which has been shown to have diagnostic and prognostic value in the assessment of patients with underlying pulmonary disease. This report provides reference standards for V˙ Epeak derived from CPX on treadmills in apparently healthy individuals. Methods: Nine laboratories in the United States experienced in CPX administration with established quality control procedures contributed to the Fitness Registry and the Importance of Exercise National Database from 2014 to 2017. Data from 5232 maximal exercise tests from men and women without cardiovascular or pulmonary disease were used to create percentiles ofV˙ Epeak for both men and women by decade between 20 and 79 yr. Additionally, prediction equations were developed for V˙ Epeak using descriptive information. Results: V˙ Epeak was found to be significantly different between men and women and across age groups (P G 0.05). The rate of decline in V˙ Epeak was 8.0% per decade for both men and women. A stepwise regression model of 70% of the sample revealed that sex, age, and height were significant predictors ofV˙ Epeak. The equation was cross-validated with data from the remaining 30% of the sample with a final equation developed from the full sample (r = 0.73). Additionally, a linear regression model revealed forced expiratory volume in 1 s significantly predicted V˙ Epeak (r = 0.73). Conclusions: Reference standards were developed for V˙ Epeak for the United States population. Cardiopulmonary exercise testing laboratories will be able to provide interpretation of V˙ Epeak from these age and sex-specific percentile reference values or alternatively can use these nonexercise prediction equations incorporating sex, age, and height or with a single predictor of forced expiratory volume in 1 s

Comments on Multiple M2-branes

Recently a three-dimensional field theory was derived that is consistent with all the symmetries expected of the worldvolume action for multiple M2-branes. In this note we examine several physical predictions of this model and show that they are in agreement with expected M2-brane dynamics. In particular, we discuss the quantization of the Chern-Simons coefficient, the vacuum moduli space, a massive deformation leading to fuzzy three-sphere vacua, and a possible large n limit. In this large n limit, the fuzzy funnel solution correctly reproduces the mass of an M5-brane.Comment: 18 pages. Published versio

The relationship between reproductive outcome measures in DDT exposed malaria vector control workers: a cross-sectional study

BACKGROUND: The utility of blood reproductive endocrine biomarkers for assessing or estimating semen quality was explored. METHODS: A cross-sectional study of 47 DDT exposed malaria vector control workers was performed. Tests included blood basal and post gonadotrophin releasing hormone (GnRH), lutenizing hormone (LH), follicle stimulating hormone (FSH), testosterone, sex hormone binding globulin (SHBG), estradiol (E2) and inhibin; a questionnaire (demographics and general medical history); a physical examination and semen analysis. Semen parameters were determined using either/or or both WHO or the strict Tygerberg criteria. Relationships between semen parameters and endocrine measures were adjusted for age, duration of abstinence before sampling, presence of physical abnormalities and fever in the last two months. All relationships between specific endocrine hormones were adjusted for age and basal SHBG. RESULTS: Multiple logistic regression showed a consistent positive relationship (prevalence odds ratio (POR) = 8.2, CI:1.4–49.2) between low basal inhibin (<100 pg/ml) and low semen count (< 40 million) and density (< 20 million/ml); consistent positive, but weaker relationships (1> POR < 2) between abnormally low semen count as well as density and baseline and post GnRH FSH; and positive relationships (POR = 37, CI:2–655) between the prevalence of high basal estradiol (> 50 pg/ml) and abnormal morphology (proportion < 5%) and low motility (proportion <50%). Most of the expected physiological relationships between specific endocrines were significant. CONCLUSION: The study has demonstrated that low basal inhibin, elevated basal FSH and high basal E2 can serve as markers of impaired semen quality

Disturbance alters beta-diversity but not the relative importance of community assembly mechanisms

Ecological disturbances are often hypothesized to alter community assembly processes that influence variation in community composition (β-diversity). Disturbance can cause convergence in community composition (low β-diversity) by increasing niche selection of disturbance-tolerant species. Alternatively, disturbance can cause divergence in community composition (high β-diversity) by increasing habitat filtering across environmental gradients. However, because disturbance may also influence β-diversity through random sampling effects owing to changes in the number of individuals in local communities (community size) or abundances in the regional species pool, observed patterns of β-diversity alone cannot be used to unambiguously discern the relative importance of community assembly mechanisms. We compared β-diversity of woody plants and inferred assembly mechanisms among unburned forests and forests managed with prescribed fires in the Missouri Ozarks, USA. Using a null-model approach, we compared how environmental gradients influenced β-diversity after controlling for differences in local community size and regional species abundances between unburned and burned landscapes. Observed β-diversity was higher in burned landscapes. However, this pattern disappeared or reversed after controlling for smaller community size in burned landscapes. β-diversity was higher than expected by chance in both landscapes, indicating an important role for processes that create clumped species distributions. Moreover, fire appeared to decrease clumping of species at broader spatial scales, suggesting homogenization of community composition through niche selection of disturbance-tolerant species. Environmental variables, however, explained similar amounts of variation in β-diversity in both landscapes, suggesting that disturbance did not alter the relative importance of habitat filtering. Our results indicate that contingent responses of communities to fire reflect a combination of fire-induced changes in local community size and scale-dependent effects of fire on species clumping across landscapes. Synthesis. Although niche-based mechanisms of community assembly are often invoked to explain changes in community composition following disturbance, our results suggest that these changes also arise through random sampling effects owing to the influence of disturbance on community size. Comparative studies of these processes across disturbed ecosystems will provide important insights into the ecological conditions that determine when disturbance alters the interplay of deterministic and stochastic processes in natural and human-modified landscapes

Wildfire disturbance and productivity as drivers of plant species diversity across spatial scales

Wildfires influence many temperate terrestrial ecosystems worldwide. Historical environmental heterogeneity created by wildfires has been altered by human activities and will be impacted by future climate change. Our ability to predict the impact of wildfire-created heterogeneity on biodiversity is limited because few studies have investigated variation in community composition (beta-diversity) in response to fire. Wildfires may influence beta-diversity through several ecological mechanisms. First, high-severity fires may decrease beta-diversity by homogenizing species composition when they create landscapes dominated by disturbance-tolerant or rapidly colonizing species. In contrast, mixed-severity fires may increase beta-diversity by creating mosaic landscapes containing habitats that support species with differing environmental tolerances and dispersal traits. Moreover, the effects of fire severity on beta-diversity may change depending on site conditions. Disturbance is hypothesized to increase local species richness at higher productivity and decrease local species richness at lower productivity, a process that can have important, but largely unexamined, consequences on beta-diversity in fire-prone ecosystems. We tested these hypotheses by comparing patterns of beta-diversity and species richness across 162 plant communities in three sites that span a large-scale gradient in climate and productivity in the Northern Rockies of Montana. Within each site, we used spatially explicit fire-severity data to stratify sampling across unburned forests and forests burned with mixed- and high-severity wildfires. We found that beta-diversity (community dispersion) of forbs was higher in mixed-severity compared to high-severity fire, regardless of productivity. Counter to our predictions, local species richness of forbs was higher in burned landscapes compared to unburned landscapes at the low-productivity site, but lower in burned landscapes at the high-productivity site. This pattern may be explained by rapid regeneration of woody plants after fire in high-productivity forests. Moreover, forbs and woody plants had disproportionately higher overall species richness in mixed-severity fire compared to high-severity fire, but only at the low-productivity site. These patterns suggest that mixed-severity fires promote higher landscape-level biodiversity in low-productivity sites by increasing species turnover across landscapes with a diverse mosaic of habitats. Our study illustrates the importance of understanding the mechanisms by which patterns of wildfire severity interact with environmental gradients to influence patterns of biodiversity across spatial scales