Environmental stress, facilitation, competition, and coexistence

The major theories regarding the combined influence of the environment and species interactions on population and community dynamics appear to conflict. Stress/disturbance gradient models of community organization, such as the stress gradient hypothesis, emphasize a diminished role for competition in harsh environments whereas modern coexistence theory does not. Confusion about the role of species interactions in harsh environments is perpetuated by a disconnect between population dynamics theory and data. We linked theory and data using response surface experiments done in the field to parameterize mathematical, population-dynamic competition models. We replicated our experiment across two environments that spanned a common and important environmental stress gradient for determining community structure in benthic marine systems. We generated quantitative estimates of the effects of environmental stress on population growth rates and the direction and strength of intra- and interspecific interactions within each environment. Our approach directly addressed a perpetual blind spot in this field by showing how the effects of competition can be intensified in stressful environments even though the apparent strength of competition remains unchanged. Furthermore, we showed how simultaneous, reciprocal competitive and facilitative effects can stabilize population dynamics in multispecies communities in stressful environments

Spatial arrangement affects population dynamics and competition independent of community composition

Theory suggests that the spatial context within which species interactions occur will have major implications for the outcome of competition and ultimately, coexistence, but empirical tests are rare. This is surprising given that individuals of species in real communities are typically distributed nonrandomly in space. Nonrandom spatial arrangement has the potential to modify the relative strength of intra- and interspecific competition by changing the ratio of conspecific to heterospecific competitive encounters, particularly among sessile species where interactions among individuals occur on local scales. Here we test the influence of aggregated and random spatial arrangements on population trajectories of competing species in benthic, marine, sessile-invertebrate assemblages. We show that the spatial arrangement of competing species in simple assemblages has a strong effect on species performance: when conspecifics are aggregated, strong competitors perform poorly and weaker competitors perform better. The effect of specific spatial arrangements depends on species identity but is also strongly context dependent. When there are large differences in species competitive ability, aggregated spatial arrangements can slow competitive exclusion, and so nonrandom spatial arrangement can work synergistically with other trade-off based mechanisms to facilitate coexistence

Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica.

Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica

Resting and Post-Exercise Blood Pressure Response to Repeated Bouts of Aquatic Treadmill Exercise

Aerobic exercise is known to reduce resting blood pressure as well as induce and acute post-exercise hypotensive response. Purpose: Determine the effect of repeated bouts of aquatic treadmill exercise on consecutive days in physically untrained, pre-hypertensive men. Methods: Nine male subjects (SBP: 132 ± 8 mmHg; DBP: 79 ± 8 mmHG; 33 ± 8 years; 183 ± 7 cm; 103 ± 31 kg; 32 ± 10% Fat; 36 ± 7 ml·kg-1·min-1) participated in the study. All subjects completed an acute aquatic treadmill exercise session (60% VO2max; 300 kcal) on two consecutive days. Prior to each exercise session and following 10 minutes of seated rest, blood pressure and heart rate were automatically taken every 3 minutes for a total of 3 measurements. Following each exercise session, blood pressure and heart rate were measured automatically every 10-minutes from 20 to 60 minutes post while subjects were seated at rest. Pre-exercise and post-exercise measures were averaged. A dependent sample t-test was performed to compare the average values between the first (ATM1) and second (ATM2) exercise sessions. Results: Data are displayed in table below. Both pre-exercise and post-exercise systolic, diastolic, and mean arterial pressures were lower for ATM2. Conclusion: A single bout of ATM exercise resulted in reduced resting blood pressure 24-hours later. Furthermore, post-exercise blood pressure was lower following a second ATM exercise session. These data support both the efficacy of ATM exercise in regulating blood pressure and the cumulative benefit of repeated exercise bouts. Pre-Exercise Post-Exercise SBP DBP MAP HR SBP DBP MAP HR ATM1 Avg 126 78 96 72 124 77 93 83 SD 11 7 7 11 12 7 8 10 ATM2 Avg 121 74 92 70 120 75 91 80 SD 11 7 7 11 10 8 7 13 T-Test 0.035 0.005 0.003 0.113 0.047 0.028 0.034 0.058 All values represent mean ± SD. p-values compare ATM1 vs. ATM

Evolutionary relationships in Panicoid grasses based on plastome phylogenomics (Panicoideae; Poaceae)

Background: Panicoideae are the second largest subfamily in Poaceae (grass family), with 212 genera and approximately 3316 species. Previous studies have begun to reveal relationships within the subfamily, but largely lack resolution and/or robust support for certain tribal and subtribal groups. This study aims to resolve these relationships, as well as characterize a putative mitochondrial insert in one linage. Results: 35 newly sequenced Panicoideae plastomes were combined in a phylogenomic study with 37 other species: 15 Panicoideae and 22 from outgroups. A robust Panicoideae topology largely congruent with previous studies was obtained, but with some incongruences with previously reported subtribal relationships. A mitochondrial DNA (mtDNA) to plastid DNA (ptDNA) transfer was discovered in the Paspalum lineage. Conclusions: The phylogenomic analysis returned a topology that largely supports previous studies. Five previously recognized subtribes appear on the topology to be non-monophyletic. Additionally, evidence for mtDNA to ptDNA transfer was identified in both Paspalum fimbriatum and P. dilatatum, and suggests a single rare event that took place in a common progenitor. Finally, the framework from this study can guide larger whole plastome sampling to discern the relationships in Cyperochloeae, Steyermarkochloeae, Gynerieae, and other incertae sedis taxa that are weakly supported or unresolved.Fil: Burke, Sean V.. Northern Illinois University; Estados UnidosFil: Wysocki, William P.. Northern Illinois University; Estados UnidosFil: Zuloaga, Fernando Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Craine, Joseph M.. Jonah Ventures; Estados UnidosFil: Pires, J. Chris. University of Missouri; Estados UnidosFil: Edger, Patrick P.. Michigan State University; Estados UnidosFil: Mayfield Jones, Dustin. Donald Danforth Plant Science Center; Estados UnidosFil: Clark, Lynn G.. Iowa State University; Estados UnidosFil: Kelchner, Scot A.. University of Idaho; Estados UnidosFil: Duvall, Melvin R.. Northern Illinois University; Estados Unido

Digital Orthopaedics: A Glimpse Into the Future in the Midst of a Pandemic.

BackgroundThe response to COVID-19 catalyzed the adoption and integration of digital health tools into the health care delivery model for musculoskeletal patients. The change, suspension, or relaxation of Medicare and federal guidelines enabled the rapid implementation of these technologies. The expansion of payment models for virtual care facilitated its rapid adoption. The authors aim to provide several examples of digital health solutions utilized to manage orthopedic patients during the pandemic and discuss what features of these technologies are likely to continue to provide value to patients and clinicians following its resolution.ConclusionThe widespread adoption of new technologies enabling providers to care for patients remotely has the potential to permanently change the expectations of all stakeholders about the way care is provided in orthopedics. The new era of Digital Orthopaedics will see a gradual and nondisruptive integration of technologies that support the patient's journey through the successful management of their musculoskeletal disease

Infectious diseases consultation reduces 30-day and 1-year all-cause mortality for multidrug-resistant organism infections

Abstract Background Multidrug-resistant organism (MDRO) infections are associated with high mortality and readmission rates. Infectious diseases (ID) consultation improves clinical outcomes for drug-resistant Staphylococcus aureus bloodstream infections. Our goal was to determine the association between ID consultation and mortality following various MDRO infections. Methods This study was conducted with a retrospective cohort (January 1, 2006–October 1, 2015) at an academic tertiary referral center. We identified patients with MDROs in a sterile site or bronchoalveolar lavage/bronchial wash culture. Mortality and readmissions within 1 year of index culture were identified, and the association of ID consultation with these outcomes was determined using Cox proportional hazards models with inverse weighting by the propensity score for ID consultation. Results A total of 4214 patients with MDRO infections were identified. ID consultation was significantly associated with reductions in 30-day and 1-year mortality for resistant S. aureus (hazard ratio [HR], 0.48; 95% confidence interval [CI], 0.36–0.63; and HR, 0.73, 95% CI, 0.61–0.86) and Enterobacteriaceae (HR, 0.41; 95% CI, 0.27–0.64; and HR, 0.74; 95% CI, 0.59–0.94), and 30-day mortality for polymicrobial infections (HR, 0.51; 95% CI, 0.31–0.86) but not Acinetobacter or Pseudomonas. For resistant Enterococcus, ID consultation was marginally associated with decreased 30-day mortality (HR, 0.81; 95% CI, 0.62–1.06). ID consultation was associated with reduced 30-day readmission for resistant Enterobacteriaceae. Conclusions ID consultation was associated with significant reductions in 30-day and 1-year mortality for resistant S. aureus and Enterobacteriaceae, and 30-day mortality for polymicrobial infections. There was no association between ID consultation and mortality for patients with resistant Pseudomonas, Acinetobacter, or Enterococcus, possibly due to small sample sizes. Our results suggest that ID consultation may be beneficial for patients with some MDRO infections. </jats:sec

Acute Blood Pressure Response to Aquatic and Land Treadmill Exercise

PURPOSE: To determine the acute blood pressure response of aquatic treadmill (AT) exercise compared to land treadmill (LT) exercise. METHODS: 11 Subjects (6 male; 23 ± 2 years; 70 ± 1 inches; 164 ± 32 pounds) completed 3 to 5, 5-minute graded exercise stages (~20, 26, 32 ml-1∙kg-1∙min-1 for stages 1, 2, and 3, respectively) up to 85% age predicted maximal heart rate on AT. Blood pressure (BP) was measured manually at the conclusion of each stage while subjects straddled the treadmill belt for 20-30 seconds. Heart rate (HR) and oxygen consumption (VO2) were measured continuously. Within 3-5 days, subjects completed an equivalent exercise bout on LT with stages matched for VO2. Resting BP and HR was measured with an automated BP cuff following 10 minutes of seated rest before exercise and every 3 minutes for 30 minutes during recovery. Pre-exercise BP was also measured manually following 5 minutes of standing on AT and LT immediately before exercise. A paired sample t-test was used to compare seated resting and pre-exercise standing measures between modes. Since all subjects completed at least 3 matched stages on each mode, a 3 (stage) x 2 (mode) ANOVA was used to analyze the dependent variables: VO2, HR, SBP, diastolic BP (DBP), mean BP (MAP), pulse pressure (PP), rate pressure product (RPP), and oxygen pulse (OP). SBP, DBP, MAP, and HR during seated recovery were analyzed by an 11 (time) x 2 (mode) ANOVA. All values presented as mean ± SE. RESULTS: Seated resting measures prior to exercise did not differ between modes. Pre-exercise standing SBP was greater (AT: 118 ± 9; LT: 113 ± 8; p = 0.05) and HR was lower (AT: 64 ± 10; LT: 77 ± 12; p \u3c 0.05) for AT relative to LT. During exercise, significant main effects for mode were found for DBP (AT: 65 ± 2; LT: 71 ± 2) and PP (AT: 81 ± 4; LT: 62 ± 4) with a trend toward significance in SBP (AT: 146 ± 4; LT: 135 ± 4; p = 0.057). Main effects for stage were significant for VO2, HR, RPP, and OP. No interactions were significant. During recovery, main effects for mode were observed only for HR (AT: 87 ± 1; LT: 78 ± 1), while there was a main effect for time for DBP, MAP, and HR. CONCLUSION: Hydrostatic pressure from AT increases exercise SBP and may lower HR

Precipitating Ordered Skyrmion Lattices from Helical Spaghetti

Magnetic skyrmions have been the focus of intense research due to their potential applications in ultra-high density data and logic technologies, as well as for the unique physics arising from their antisymmetric exchange term and topological protections. In this work we prepare a chiral jammed state in chemically disordered (Fe, Co)Si consisting of a combination of randomly-oriented magnetic helices, labyrinth domains, rotationally disordered skyrmion lattices and/or isolated skyrmions. Using small angle neutron scattering, (SANS) we demonstrate a symmetry-breaking magnetic field sequence which disentangles the jammed state, resulting in an ordered, oriented skyrmion lattice. The same field sequence was performed on a sample of powdered Cu2OSeO3 and again yields an ordered, oriented skyrmion lattice, despite relatively non-interacting nature of the grains. Micromagnetic simulations confirm the promotion of a preferred skyrmion lattice orientation after field treatment, independent of the initial configuration, suggesting this effect may be universally applicable. Energetics extracted from the simulations suggest that approaching a magnetic hard axis causes the moments to diverge away from the magnetic field, increasing the Dzyaloshinskii-Moriya energy, followed subsequently by a lattice re-orientation. The ability to facilitate an emergent ordered magnetic lattice with long-range orientation in a variety of materials despite overwhelming internal disorder enables the study of skyrmions even in imperfect powdered or polycrystalline systems and greatly improves the ability to rapidly screen candidate skyrmion materials