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

Revisiting competition in a classic model system using formal links between theory and data

Formal links between theory and data are a critical goal for ecology. However, while our current understanding of competition provides the foundation for solving many derived ecological problems, this understanding is fractured because competition theory and data are rarely unified. Conclusions from seminal studies in space-limited benthic marine systems, in particular, have been very influential for our general understanding of competition, but rely on traditional empirical methods with limited inferential power and compatibility with theory. Here we explicitly link mathematical theory with experimental field data to provide a more sophisticated understanding of competition in this classic model system. In contrast to predictions from conceptual models, our estimates of competition coefficients show that a dominant space competitor can be equally affected by interspecific competition with a poor competitor (traditionally defined) as it is by intraspecific competition. More generally, the often-invoked competitive hierarchies and intransitivities in this system might be usefully revisited using more sophisticated empirical and analytical approaches

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

A Validation Study of a Noninvasive Lactate Threshold Device

International Journal of Exercise Science 12(2): 221-232, 2019. The lactate threshold is considered a key marker of endurance exercise performance and identification of this threshold is important in writing an exercise training program. Unfortunately, assessment of the lactate threshold has traditionally required venous or capillary blood samples and a specialized meter to assess blood lactate concentrations. Recently, a consumer grade, non-invasive device was developed to determine muscle oxygenation and estimate the lactate threshold. Purpose: The aim of this study was to assess the validity of a noninvasive lactate threshold device (NID) to determine lactate threshold heart rate (LTHR). Methods: Twenty-one recreational athletes (14 females, 39 ± 7 years, 29.1 ± 5.2% fat, 37.8 ± 6.0 ml·kg-1·min-1; 7 males, 42 ± 9 years, 16.8 ± 2.2% fat, 45.9 ± 6.4 ml·kg-1·min-1) completed a personalized graded exercise test on a treadmill. All participants wore the NID and blood lactate samples were taken at the end of 3-minute stages. LTHR was then calculated using two traditional methods (4 mmol/L and \u3e1 mmol/L increase) and compared against the same heart rate values calculated by the NID. Results: No significant differences (p = .87) were found in LTHR between the NID and the traditional lactate methods (NID: 167 ± 9 bpm, 4 mmol/L: 167 ± 12 bpm, \u3e1 mmol/L: 167 ± 12 bpm). Conclusions: This study provides preliminary support for the validity of the NID for estimation of LTHR

A new physical interpretation of optical and infrared variability in quasars

Changing-look quasars are a recently identified class of active galaxies in which the strong UV continuum and/or broad optical hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of months to years. The physical processes responsible for this behaviour are still debated, but changes in the black hole accretion rate or accretion disk structure appear more likely than changes in obscuration. Here we report on four epochs of spectroscopy of SDSS J110057.70-005304.5, a quasar at a redshift of $z=0.378$ whose UV continuum and broad hydrogen emission lines have faded, and then returned over the past $\approx$20 years. The change in this quasar was initially identified in the infrared, and an archival spectrum from 2010 shows an intermediate phase of the transition during which the flux below rest-frame $\approx$3400\AA\ has decreased by close to an order of magnitude. This combination is unique compared to previously published examples of changing-look quasars, and is best explained by dramatic changes in the innermost regions of the accretion disk. The optical continuum has been rising since mid-2016, leading to a prediction of a rise in hydrogen emission line flux in the next year. Increases in the infrared flux are beginning to follow, delayed by a $\sim$3 year observed timescale. If our model is confirmed, the physics of changing-look quasars are governed by processes at the innermost stable circular orbit (ISCO) around the black hole, and the structure of the innermost disk. The easily identifiable and monitored changing-look quasars would then provide a new probe and laboratory of the nuclear central engine.Comment: 13 pages, 4 figures, 3 tables. Published in MNRAS. All code and data links on GitHub, https://github.com/d80b2t/WISE_L

Comparison of Post-Activation Potentiating Stimuli on Jump and Sprint Performance

Post-activation potentiation (PAP) is a phenomenon characterized by improved muscle performance based on the previous contractile activity of the muscle. The purpose of this study was to determine the effect of different potentiating stimuli on jump and sprint performance in 13 resistance trained, college-aged men and women. After determining back squat 1 repetition max, subjects returned for testing on separate days to complete one of four interventions (dynamic resistance, weighted plyometric, isometric, or control) in a randomized order. A standardized warmup was performed, followed by a baseline countermovement jump (CMJ) and 20m sprint. Following warm-up and baseline measurements, subjects performed one of the four experimental conditions. CMJ and 20m sprint measurements were completed again at 20-seconds, 4, 8, 12, 16, and 20-minutes. Results revealed significantly faster 0-20m sprint times (p \u3c .05) at the 4, 8, 12, 16, and 20-minute time points compared to baseline and 20-second time points. Significantly faster 0-20m sprint times (p \u3c .05) were also shown for the squat intervention compared to control at 4-minutes, the plyometric and squat intervention compared to control at 8-minutes, the isometric intervention compared to control at 12 and 16- minutes, and the isometric intervention compared to the squat at 20-minutes. These findings indicate that while all PAP stimuli utilized can be effective at improving sprint performance, specific optimal time points may exist

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

Attempting to Acutely Manipulate Ground Contact Time Imbalances Impairs Running Economy

Running economy (RE) is a key performance determinant. Biomechanical markers have been linked to RE, including ground contact time (GCT), cadence, and vertical oscillation (VO). Recently, we showed a strong relationship between GCT imbalances and RE. Because these markers can be tracked real-time with consumer-wearable devices, runners now have access to instant feedback concerning their mechanics. PURPOSE: Determine if attempting to correct GCT imbalances real-time alters mechanics and RE. METHODS: 7 recreational runners (38 ± 15 years, 24.7 ± 2.8 kg/m2, 5 male) completed 2, 10-minute running trials (9.65 km/hr) on separate days. For both trials, subjects ran with a heart rate (HR) monitor/watch that measured GCT, GCT imbalances, cadence, and VO. For the control (CT) trial, subjects were not permitted to receive feedback from the watch. During the feedback (FB) trial, the watch was set to display GCT imbalances, and subjects were prompted every 20-30 seconds to monitor/attempt to correct any imbalances. Both trials were preceded by a dynamic warmup and 5-minute jog. For the FB trial warmup, subjects were acclimated to the watch and allowed to experiment with manipulating their GCT imbalances. VO2 was monitored continuously throughout each 10-minute trial, and average values from 6 to 9 minutes were determined for each trial. Average values for all running biomechanical variables were calculated from 0.5 minutes to 9.5 minutes. Comparisons between trials were made with a dependent sample t-test. RESULTS: The FB trial elicited a significantly higher (p = .011) working VO2 (35.5 ± 1.6 ml/kg/min) compared to the CT trial (33.4 ± 1.8 ml/kg/min). There were no other significant differences between trials for the other measured variables. Average values for each variable by trial were as follows: RER (CT: .91 ± .04; FB: .92 ± .05), HR (CT: 159 ± 26 bpm; FB: 163 ± 24 bpm), GCT % difference (CT: 1.69 ± .67%; FB: 1.70 ± 1.70%), GCT absolute difference (CT: 9 ± 3 ms; FB: 8 ± 7 ms), GCT (CT: 272 ± 26 ms; FB: 268 ± 31 ms), Cadence (CT: 165 ± 9 steps/min; FB: 167 ± 9 steps/min); VO (CT: 9.3 ± 2.0 cm; FB: 9.2 ± 1.9 cm), VO ratio (CT: 9.5 ± 1.6 cm/m; FB: 9.5 ± 1.6 cm/m). CONCLUSIONS: Acutely attempting to correct GCT imbalances did not result in improved mechanics and actually impaired RE. Altering mechanics based on real-time feedback from consumer-wearable devices may impair performance in the short term. Given that GCT imbalances have been linked to impaired RE, future research should determine how to better correct these imbalances rather than attempting to acutely manipulate them