Elevational Limits Research Articles

Niche Theory and Species Range Limits Along Elevational Gradients: Perspectives and Future Directions

Despite two centuries of research, the mechanisms underlying the formation of species’ elevational range limits remain poorly understood. The climatic variability hypothesis highlights the role of climatic conditions in shaping species’ thermal tolerance and distribution ranges, while the species interactions–abiotic stress hypothesis underscores the relative importance of biotic factors and abiotic stress along environmental gradients. We emphasize Darwin's perspective on the ubiquity of interspecific competition across climatic gradients and the importance of understanding how climate modulates biotic interactions to shape species distributions. Niche theory provides a comprehensive framework, combined with empirical research, to explore how environmental gradients influence species traits, leading to context-dependent species interactions that constrain distributions. In particular, the application of the concept of environmentally weighted performance can further elucidate these complex ecological mechanisms. Future research should integrate multiple approaches, including field and laboratory manipulative experiments, theoretical modeling, and interdisciplinary collaboration, to improve our understanding of species distributions in mountain regions and to inform biodiversity conservation strategies in the face of rapid environmental change.

Surprisingly wide climatic niche breadth of a relict mountain species raises hope for survival under climate change

AbstractAimsWe assessed the juvenile climatic niche breadth of a relict mountain species by comparing field observations and transplant experiments within and beyond the elevational limits of its distribution range.LocationLebanon – Near East – Mediterranean region.MethodsWe studied the survival and growth of the Cedar of Lebanon (Cedrus libani) to determine the lower and upper elevational range limits of its juvenile stage through an experimental setup with and without water supplementation and with potentially competing species as a control. The experiment included eight common gardens at elevations ranging from 110 to 2330 m, within and far beyond the warm and cold limits of Cedar distribution observed under natural conditions.ResultsWe observed unexpectedly high survival and growth rates of Cedar at elevations well below the range of its natural distribution in Lebanon. Below the observed warm limit, water stress at very low elevations and competition at low and medium elevations limited juvenile survival. In contrast, cold temperature and water stress limited survival at elevations slightly above the observed upper natural limit. The experimental setup demonstrated that the elevation range suitable for Cedar growth and survival was twice as wide as the range within which Cedar is observed under natural conditions.Main ConclusionsHigh survival rates experimentally observed beyond the warm limit of the natural distribution range of the Cedar of Lebanon raise hope for its resilience to ongoing climate warming. If this pattern were frequent among montane species, it would challenge predictions of massive extinction with climate change and pave the way for promoting adaptive actions such as competition management to improve their survival.

Coexistence of congenital superior rectus muscle fibrosis and Marcus Gunn jaw-winking phenomenon

A 6-year-old male involving a coexistence of congenital fibrosis of the superior rectus muscle (SR) with Marcus Gunn Jaw-Winking phenomenon presented with an elevation of the upper eyelid along with a chronically open mouth that had been present since early infancy. There was extropia and hypertropia, a limitation of elevation and depression in the right eye, and an abnormal head posture (AHP) with a left head tilt, right face turn, and a chin-up head position. He also displayed an upper eyelid retraction and a 2-mm lagophthalos in the right eye. Results of the forced duction test indicated a constricted SR of the right eye. A dissection of the SR from the levator palpebrae superioris and a 5-mm SR recession was performed within the right eye. At 2 months post surgery, there was a 3 prism diopters (PD) hypertropia in the right eye when the left eye was fixated on the target and a 10 PD hypotropia in the left eye when the right eye was fixated on the target, along with an improvement in his AHP. In this rare case with a coexistence of congenital fibrosis of the SR and Marcus Gunn jaw-winking phenomenon, we found that the performance of an individualized surgical protocol proved effective in reducing the vertical deviation and improving AHP.

Challenging conventional views on the elevational limits of pronghorn habitat.

Challenging conventional views on the elevational limits of pronghorn habitat.

Establishing monarch butterfly overwintering sites for future climates: Abies religiosa upper altitudinal limit expansion by assisted migration

Climate change projections suggest a precarious future for the Monarch butterfly (Danaus plexippus) as the suitable climatic habitat of its exclusive overwintering host Abies religiosa (oyamel, Sacred fir, a conifer endemic to Mexico) inside the Monarch Butterfly Biosphere Reserve (MBBR) is expected to disappear by 2090. Since the upper elevation limit of A. religiosa is approximately 3,500 m and the summits of mountains within the MBBR are ca. 3,550 m, we tested the feasibility of establishing A. religiosa at four locations outside its current geographic range in the MBBR, on a geographically close volcano, Nevado de Toluca at 4000 (timberline, an extreme site), 3,800, and 3,600 m (to test species range expansion upward in elevation), and at 3400 m (a reference site, slightly lower than the upper elevation limit of A. religiosa). Using existing shrubs as nurse plants to protect the seedlings from extreme temperatures, at each site we planted five to eight populations, originating between 3,100 and 3,500 m within the MBBR. After three growing seasons in the field (6 years after sowing), we found that: (a) survival and height increment declined steeply with test site elevation; (b) even at the highest sites (3,800 and 4,000 m), survival was acceptable, at 68 and 44%, respectively, although the growth was very poor at 4000 m; (c) populations responded similarly to transfer; (d) transfer effects were best accounted for by annual dryness index; (e) to compensate for the expected 2.3°C increase in mean annual temperature or 0.009 √°Cmm−1 increase of annual dryness index from the reference period (1961–1990) to the decade centered in 2060, it would be necessary to shift populations approximately 500 m to higher elevations; and (f) upward transfers to compensate for the 2.3°C increase in mean annual temperature are expected to result in height increment and survival that are approximately 47 and 21% lower, respectively, than values expected at zero transfer distance. We conclude that the establishment of A. religiosa at 3600 and 3,800 m is feasible and that planted stands could eventually serve as overwintering sites for the Monarch butterfly under projected future climates.

Unveiling the Biodiversity and Conservation Significance of Medog: A Camera-Trapping Survey on Mammals in the Southeastern Tibetan Mountains.

The Medog in southeastern Tibet is home to a diverse range of wild animals. However, research on these mammals' species directories, distribution, and conservation status remains insufficient, despite their crucial role in maintaining ecological balance. The study carried out a camera-trapping survey to assess mammal biodiversity and the significance of mammal protection in their natural habitats in Gedang, Medog. Future directions and application prospects of the study for wildlife conservation in the southeastern Tibetan mountains were also discussed. The survey, spanning from April 2023 to May 2024, with 19,754 camera trap days, revealed 25 mammalian species across five orders and 14 families. Among these, four classified as Endangered, five as Vulnerable, two as Near Threatened on the IUCN Red List, nine were categorized as Critically Endangered or Endangered on the Red List of China's Vertebrates, and seven were China's national first-class key protected wildlife. The order Carnivora exhibited the highest diversity, comprising 12 species. Furthermore, the study filled the knowledge gap regarding the underrepresentation of Gongshan muntjac Muntiacus gongshanensis in IUCN and provided new insights into the recorded coexistence of the Himalayan red panda Ailurus fulgens and Chinese red panda Ailurus styani along the Yarlung Zangbo River for the first time, and also documented new upper elevation limits for four large to medium-sized species. Regarding the relative abundance indices (RAI) captured by camera traps, the most prevalent species identified was the White-cheeked macaque Macaca leucogenys, followed by the Gongshan muntjac and Himalayan serow Capricornis thar. The monitoring also captured a number of domestic dogs and livestock, as well as human disturbances. These findings underscore the importance of conserving these mammals and emphasize the need for conservation efforts to protect their habitats and reduce human activities that threaten their survival, thereby maintaining the ecological balance of the region. Additionally, the research highlighted Gedang's significance to global conservation efforts for mammalian diversity, providing essential data for effective wildlife conservation strategies.

Nonbreeding distributions of four declining Nearctic–Neotropical migrants are predicted to contract under future climate and socioeconomic scenarios

ABSTRACT Climate and land use/land cover change are expected to influence the stationary nonbreeding distributions of 4 Nearctic–Neotropical migrant bird species experiencing population declines: Cardellina canadensis (Canada Warbler), Setophaga cerulea (Cerulean Warbler), Vermivora chrysoptera (Golden-winged Warbler), and Hylocichla mustelina (Wood Thrush). Understanding how and where these species’ distributions shift in response to environmental drivers is critical to inform conservation planning in the Neotropics. For each species, we quantified current (2012 to 2021) and projected future (2050) suitable climatic and land use/land cover conditions as components of stationary nonbreeding distributions. Multi-source occurrence data were used in an ensemble modeling approach with covariates from 3 global coupled climate models (CMCC-ESM2, FIO-ESM-2-0, MIROC-ES2L) and 2 shared socioeconomic pathways (SSP2-RCP4.5, SSP5-RCP8.5) to predict distributions in response to varying climatic and land use/land cover conditions. Our findings suggest that distribution contraction, upslope elevational shifts in suitable conditions, and limited shifts in latitude and longitude will occur in 3 of 4 species. Cardellina canadensis and S. cerulea are expected to experience a moderate distribution contraction (7% to 29% and 19% to 43%, respectively), primarily in response to expected temperature changes. The V. chrysoptera distribution was modeled by sex, and females and males were projected to experience a major distribution contraction (56% to 79% loss in suitable conditions for females, 46% to 65% for males), accompanied by shifts in peak densities to higher elevations with minimal changes in the upper elevation limit. Expected changes in precipitation had the greatest effect on V. chrysoptera. Hylocichla mustelina experienced the smallest distribution change, consistent with the species’ flexibility in habitat selection and broader elevational range. We recommend defining priority areas for conservation as those where suitable conditions are expected to remain or arise in the next 25 years. For V. chrysoptera in particular, it is urgent to ensure that mid-elevation forests in Costa Rica and Honduras are adequately managed and protected.

Clinal variation in quantitative traits but not in evolutionary potential along elevational and latitudinal gradients in the widespread Anthyllis vulneraria.

Strong elevational and latitudinal gradients allow the study of genetic differentiation in response to similar environmental changes. However, it is uncertain whether the environmental changes along the two types of gradients result in similar genetically based changes in quantitative traits. Peripheral arctic and alpine populations are thought to have less evolutionary potential than more central populations do. We studied quantitative traits of the widespread Anthyllis vulneraria in a common garden. Plants originated from 20 populations along a 2000-m elevational gradient from the lowlands to the elevational limit of the species in the Alps, and from 20 populations along a 2400-km latitudinal gradient from the center of the distribution of the species in Central Europe to its northern distributional margin. Most traits showed similar clinal variations with elevation and latitude of origin, and the magnitude of all measured traits in relation to mean annual temperature was similar. Higher QST values than FST values in several traits indicated diversifying selection, but for others QST was smaller than FST. Genetic diversity of quantitative traits and neutral molecular markers was not correlated. Plasticity in response to favorable conditions declined with elevation and less strongly with latitude of origin, but the evolvability of traits did not. The clinal variation suggests adaptive differentiation of quantitative traits along the two gradients. The evolutionary potential of peripheral populations is not necessarily reduced, but lower plasticity may threaten their survival under rapidly changing climatic conditions.

Mangrove extent reflects estuarine typology and lifecycle events

Ecosystem services provided by mangrove forests are increasingly recognised worldwide. These values have led to numerous ecosystem protection and restoration measures, including recent blue carbon economic incentives to re-establish mangroves at scale. However, our current ability to predict mangrove extent is based mainly on inundation averages (e.g. hydroperiod) or tidal planes of mature mangrove forests. This study investigates the validity of existing methods to accurately predict mangrove extent by comparing the location of existing mangroves at 27 sites (in 23 estuaries in southeast Australia) against commonly used approaches. To this aim, the downslope and upslope surface elevation limits of the mangrove species Avicenna marina were measured on-site using high-resolution RTK-GPS equipment across different estuarine typologies, including drowned river valleys, strong and weakly tidal estuaries, tidal lakes, and intermittently open/closed estuaries. These measurements were analysed against long-term (8–30+ years) tidal records to estimate inundation characteristics within the estuary. Study results indicate that the commonly used tidal plane method for predicting mangrove extent can incorrectly predict vertical extent by over 40 per cent. Likewise, hydroperiod is a poor predictor of extent as similar hydroperiods can be calculated across significantly different estuarine inundation patterns.Interestingly, the results indicate that mangrove elevations and inundation patterns are not uniform within or across estuaries, although there is uniformity across related estuarine typologies. For instance, inundation patterns in drowned river valley estuaries are more consistent (less extreme inundation and exposure events) than in estuaries with a variable tidal range, such as tidal lakes. Ultimately, this study highlights that predictions of mangrove extent should consider estuarine typology, the lifecycle of mangroves, and potential physio-adaptations to changing inundation patterns. Importantly, future tidal conditions may encourage biophysical adaptations in mangroves which may confound the extent of existing predictive techniques.

Heavy tails and probability density functions to any nonlinear order for the surface elevation in irregular seas

The probability density function (PDF) for the free surface elevation in an irregular sea has an integral formulation when based on the cumulant generating function. To leading order, the result is Gaussian, whereas nonlinear extensions have long been limited to Gram–Charlier series approximations. As shown recently by Fuhrman et al. (J. Fluid Mech., vol. 970, 2023, A38), however, the second-order integral can be represented exactly in closed form. The present work extends this further, enabling determination of this PDF to even higher orders. Towards this end, a new ordinary differential equation (ODE) governing the PDF is first derived. Asymptotic solutions in the limit of large surface elevation are then found, utilizing the method of dominant balance. These provide new analytical forms for the positive tail of the PDF beyond second order. These likewise clarify how high-order cumulants (involving statistical moments such as the kurtosis) govern the tail, which is shown to get heavier with each successive order. The asymptotic solutions are finally utilized to generate boundary conditions, such that the governing ODE may be solved numerically, enabling novel determination of the PDF at third and higher order. Successful comparisons with challenging data sets confirm accuracy. The methodology thus enables the PDF of the surface elevation to be determined numerically, and the asymptotic tail analytically, to any desired order. Results are worked out explicitly up to fifth order. The theoretical probability of extreme surface elevations (typical of rogue waves) may thus be assessed quantitatively for highly nonlinear irregular seas, requiring only relevant statistical quantities as input.

GIS and Machine Learning Models Target Dynamic Settlement Patterns and Their Driving Mechanisms from the Neolithic to Bronze Age in the Northeastern Tibetan Plateau

Traditional GIS-based statistical models are intended to extrapolate patterns of settlements and their interactions with the environment. They contribute significantly to our knowledge of past human–land relationships. Yet, these models are often criticized for their empiricism, lopsided specific factors, and for overlooking the synergy between variables. Though largely untested, machine learning and artificial intelligence methods have the potential to overcome these shortcomings comprehensively and objectively. The northeastern Tibetan Plateau (NETP) is characterized by diverse environments and significant changes to the social system from the Neolithic to Bronze Age. In this study, this area serves as a representative case for assessing the complex relationships between settlement locations and geographic environments, taking full advantages of these new models. We have explored a novel modeling case by employing GIS and random forests to consider multiple factors, including terrain, vegetation, soil, climate, hydrology, and land suitability, to construct classification models identifying environmental variation across different cultural periods. The model exhibited strong performance and a high archaeological prediction value. Potential living maps were generated for each cultural stage, revealing distinct environmental selection strategies from the Neolithic to Bronze Age. The key environmental parameters of elevation, climate, soil erosion, and cultivated land suitability were calculated with high weights, influencing human environmental decisions synergistically. Furthermore, we conducted a quantitative analysis of temporal dynamics in climate and subsistence to understand driving mechanisms behind environmental strategies. These findings suggest that past human environmental strategies were based on the comprehensive consideration of various factors, coupled with their social economic scenario. Such subsistence-oriented activities supported human beings in overcoming elevation limitation, and thus allowed them to inhabit wider pastoral areas. This study showcases the potential of machine learning in predicting archaeological probabilities and in interpreting the environmental influence on settlement patterns.

Extreme High-Elevation Mammal Surveys Reveal Unexpectedly High Upper Range Limits of Andean Mice.

AbstractIn the world's highest mountain ranges, uncertainty about the upper elevational range limits of alpine animals represents a critical knowledge gap regarding the environmental limits of life and presents a problem for detecting range shifts in response to climate change. Here we report results of mountaineering mammal surveys in the Central Andes, which led to the discovery of multiple species of mice living at extreme elevations that far surpass previously assumed range limits for mammals. We livetrapped small mammals from ecologically diverse sites spanning >6,700 m of vertical relief, from the desert coast of northern Chile to the summits of the highest volcanoes in the Andes. We used molecular sequence data and whole-genome sequence data to confirm the identities of species that represent new elevational records and to test hypotheses regarding species limits. These discoveries contribute to a new appreciation of the environmental limits of vertebrate life.

Modeling Nonlinear Dynamics of Functionalization Layers: Enhancing Gas Sensor Sensitivity for Piezoelectrically Driven Microcantilever.

This article presents a parametrized response model that enhances the limit of detection (LOD) of piezoelectrically driven microcantilever (PD-MC) based gas sensors by accounting for the adsorption-induced variations in elastic properties of the functionalization layer (binder) and the nonlinear motional dynamics of the PD-MC. The developed model is demonstrated for quantifying cadaverine, a volatile biogenic diamine whose concentration is used to assess the freshness of meat. At low concentrations of cadaverine, an increase in the resonance frequency is observed, contrary to the expected reduction due to mass added by adsorption. The study explores the variations in the elastic modulus vis-à-vis the adsorbed mass of cadaverine and derives the resonance frequency to the adsorbed mass response function. We advance a blended technique involving the analysis of atomic force microscopy (AFM) force-distance (f-d) curves and fitting of the quartz crystal microbalance (QCM) impedance response spectrum to deduce the adsorption-induced changes in the viscoelastic properties of the functionalization layer. The findings obtained are subsequently employed in modeling the response function for a structurally nonhomogenous PD-MC, highlighting the significance of the functionalization layer to the global elastic properties. The structural composition of the PD-MC beam adopted herein features a trapezoidal base hosting the actuating piezoelectric stratum and a rectangular free end with a functionalization layer. The Euler-Bernoulli beam theory coupled with Hamilton's principle is used to develop the equation of motion, which is subsequently discretized into a set of nonlinear ordinary differential equations via Galerkin expansion, and the solutions to the first fundamental mode of vibration are determined using the method of multiple scales. The obtained solutions provide a basis for deducing the nonlinear response function model to the adsorbed mass. The derived model is validated by recorded resonance frequency changes resulting from exposure to known concentrations of cadaverine. We demonstrate that the increase in resonance frequency for low concentrations of cadaverine is due to the dominance of the variation of the elastic modulus of the functionalization layer originating from the initial binder-analyte interactions over damping due to added mass. It is concluded that the developed nonlinear response function model can reliably be used to quantify the cadaverine concentration at low concentrations with an elevated Limit of Detection.

Anterior transposition of the inferior oblique and anti-elevation syndrome – how far to go?

ABSTRACT Purpose: To study the incidence of postoperative anti-elevation syndrome in relation to the magnitude of anterior transposition of the inferior oblique. Methods: A retrospective chart review was conducted for all patients submitted to anterior transposition of the inferior oblique from 2000 to 2020. Anti-elevation syndrome was defined as limitation of elevation of the abducting eye, resulting in a secondary upshoot of the contralateral adducting eye. Results: A total of 312 eyes of 170 patients were enrolled in the study. The incidence of anti-elevation syndrome was 20.4% when the inferior oblique was positioned 4 mm posterior to the temporal border of the inferior rectus insertion; 23.5% when sutured 2 mm posterior to the temporal border of the inferior rectus insertion and 32.8% when placed at the same level of the inferior rectus insertion with two sutures vertically aligned. When the posterior border of the inferior oblique was horizontally aligned with the anterior border and positioned adjacent to the inferior rectus insertion, in a “J shape” fashion, the incidence of anti-elevation was 41.8%. Conclusions: The anterior transposition of the inferior oblique with “J” deformity increases the risk of anti-elevation syndrome. Additionally, placing the sutures more anteriorly than 2 mm posterior to the inferior rectus insertion increases the incidence of this finding.

Abstract 7094: Clinical metabolomics reveals baseline biomarkers of hepatic dysfunction correlating with irregular drug-induced ALT and bilirubin elevations

Abstract AZD4573 is a highly potent and selective Cyclin-Dependent Kinase 9 inhibitor. The AZD4573 First-in-Human (FIH) study revealed variable alanine transaminase (ALT) and/or bilirubin elevation and a clear correlation to dose or PK exposure could not be defined. While concurrent ALT elevation ≥3x upper limit of normal (ULN) and bilirubin elevation ≥2x ULN (potential Hy’s law) is a biochemical finding indicating potential drug-induced liver injury, quantitative modeling disconnected ALT and bilirubin elevation demonstrating that the observations were not Hy’s Law cases. Furthermore, we implemented a targeted metabolomics workflow to investigate the ALT and bilirubin elevation mechanism and identify predictive biomarkers to better understand and/or predict any hepatic stress liabilities associated with AZD4573 clinical development. We implemented an established metabolomics methodology to 359 samples from 15 patients yielding 47,000 total data points. Data was separated into 98 different dosing intervals from the 15 patients to identify the ALT and bilirubin-associated metabolic changes conserved across all patients while incorporating metabolic differences in individual patents with ALT and bilirubin elevation in only a fraction of multiple doses. Orthogonal Partial Least Squares modeling identified several metabolites and pathways altered as a function of maximum ALT or bilirubin levels. Post-dose conjugated bile acids were elevated when ALT and bilirubin were elevated. Pre-dose creatine levels were decreased when ALT and bilirubin elevation occurred, and pre-dose glutamate levels were elevated when ALT elevation occurred. Pre-dose decreased total carnitines and kynurenine pathway activation were observed when ALT and bilirubin elevation occurred, but the effect did not reach statistical significance. Elevated bile acids are an established characteristic of cholestasis and suggest cholestasis as a probable mechanism for AZD4573-induced reversible liver stress. Interestingly, decreased creatine, glutamate elevation, decreased total carnitine, and kynurenine pathway activation are all associated with some form of liver stress or disfunction which may explain the irregular ALT and bilirubin elevations observed in patients receiving AZD4573; while ALT itself is a biomarker of liver damage, these pre-dose biochemical changes may illuminate potential preceding liver stress. Dosing patients already experiencing higher liver stress levels may be more susceptible to drug-induced ALT and bilirubin elevation, and patients with increasing in-study liver stress may only present at later doses. This work demonstrates metabolomics utility to elucidate possible mechanisms of liver toxicity as well as to identify potential predictive biomarkers for further investigation to explore individual patient risk in clinical studies. Citation Format: John K. Meissen, Kevin Contrepois, Sophie Regan, Jennifer Tan, Alison J. Foster, Jiaqi Yuan, Shringi Sharma, Dominic Williams, Anton I. Rosenbaum. Clinical metabolomics reveals baseline biomarkers of hepatic dysfunction correlating with irregular drug-induced ALT and bilirubin elevations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7094.

Strong differences in egg heat tolerance between closely related lowland and alpine butterfly species

Abstract Temperature variation is one of the best‐known and studied factor constraining life history along the altitudinal gradients. Ectotherms such as insects are sensitive to temperature across all life stages, resulting in a wide range of adaptations in populations and species living at different elevations. In butterflies, the egg stage is particularly sensitive to temperature variation as eggs cannot move and deploy behavioural responses to overheating. Using a gradient polymerase chain reaction thermocycler to finely control temperature treatments, we tested for differences in egg heat tolerance between five closely related Coenonympha (Nymphalidae: Satyrinae) species living at different elevations. We found strong differences in egg heat tolerance ranges between lowland species (C. arcania (Linnaeus) and C. pamphilus (Linnaeus)) and two high elevation alpine species (C. gardetta (Prunner) and C. cephalidarwiniana Verity). Surprisingly, the third alpine species (C. darwiniana Staudinger) showed a heat tolerance range closer to that of the lowland species than that of alpine species. The sensitivity of eggs to overheating matched the temperature regimes recorded in the microhabitats utilised for oviposition and may explain the oviposition site selection of females observed in the wild. The narrower egg heat tolerance of some of alpine species may partly explain the position of their lower elevational limit but also raises concern about the fate of these species in the face of current climate change. Our results highlight the need to study all life stages, as well as microclimate choice for oviposition, to understand species distribution and the threats to their persistence.

Zip-up Loop Myopexy in Heavy Eye Syndrome.

To describe and report the results of a zip-up modification for loop myopexy for facilitating a muscle union procedure in heavy eye syndrome. A retrospective chart review was conducted on patients with heavy eye syndrome in whom the modified surgical technique was performed. Superior and lateral rectus muscle bellies were approximated using a suture 4 to 5 mm from the muscle insertion. Muscles were then zipped together by 5-0 polyester sutures placed in an anteroposterior direction using a hand-over-hand technique. Details of the surgical technique were reported. Ductions, versions, and angles of strabismus were evaluated before and after surgery. Complications were reported. A total of 8 patients were identified (mean age: 60.8 ± 7 years). Mean axial length was 33.2 ± 1.2 mm. Mean preoperative horizontal and vertical angles of deviation were 78 ± 20 prism diopters (PD) (range: 50 to 120 PD) and 34 ± 4 PD (range: 30 to 40 PD), respectively. Preoperative limitation of abduction and elevation was -4 to -5 in all patients. An average of seven to eight sutures were used. No intraoperative complications were reported. In 7 patients, both vertical and horizontal angles of deviation were reduced to within 8 PD from orthophoria and limitation of ductions was reduced to null or -1 after surgery. Undercorrection occurred in 1 patient with bilateral heavy eye syndrome who had unilateral surgery. No recurrences developed over a median of 6 months of follow-up. A zip-up modification for loop myopexy can facilitate the surgical procedure to achieve a satisfactory outcome in heavy eye syndrome. [J Pediatr Ophthalmol Strabismus. 2024;61(4):279-286.].

The sensitivity of root water uptake to cold root temperature follows species-specific upper elevational distribution limits of temperate tree species.

Physiological water stress induced by low root temperatures might contribute to species-specific climatic limits of tree distribution. We investigated the low temperature sensitivity of root water uptake and transport in seedlings of 16 European tree species which reach their natural upper elevation distribution limits at different distances to the alpine treeline. We used 2H-H2O pulse-labelling to quantify the water uptake and transport velocity from roots to leaves in seedlings exposed to constant 15°C, 7°C or 2°C root temperature, but identical aboveground temperatures between 20°C and 25°C. In all species, low root temperatures reduced the water transport rate, accompanied by reduced stem water potentials and stomatal conductance. At 7°C root temperature, the relative water uptake rates among species correlated positively with the species-specific upper elevation limits, indicating an increasingly higher sensitivity to lower root zone temperatures, the lower a species'natural elevational distribution limit. Conversely, 2°C root temperature severely inhibited water uptake in all species, irrespective of the species'thermal elevational limits. We conclude that low temperature-induced hydraulic constraints contribute to the cold distribution limits of temperate tree species and are a potential physiological cause behind the low temperature limits of plant growth in general.

Interspecific competition impacts the occupancy and range limits of two ptarmigan species along the elevation gradient in Norway

Many mountain species are expected to respond to climate change through upslope shifts of their range limits, but competition may restrict or alter this response. Under traditional range‐limit theory, it is expected that lower‐elevation species are better competitors than closely related higher‐elevation species. However, recent work finds that this prediction is often unmet. We investigated evidence for the impact of competition during breeding season on the elevational range limits of a pair of closely related bird species, willow ptarmigan Lagopus lagopus and rock ptarmigan L. muta, in mainland Norway. The species share overlapping ranges that loosely divide slightly upslope from the treeline ecotone, with willow ptarmigan generally occupying lower sites and rock ptarmigan occupying higher sites. We used multi‐species occupancy models to test four competing hypotheses for how competition may affect the range limit between willow ptarmigan and rock ptarmigan: 1) asymmetric competition that restricts the lower range limit of rock ptarmigan; 2) asymmetric competition that restricts the upper range limit of willow ptarmigan; 3) condition‐specific competition that restricts both species' range limits; and 4) range limits unaffected by competition. We found evidence for a negative pairwise interaction between the two species. Changes in interaction strength along the elevation gradient suggested evidence for condition‐specific competition. However, a strong positive correlation between rock ptarmigan and higher‐elevation habitat resulted in a highly asymmetric outcome, where the upper range limit of willow ptarmigan was restricted but rock ptarmigan occupancy was fairly independent of willow ptarmigan. This outcome is opposite to the prediction of traditional range‐limit theory and may suggest a greater climate threat to willow ptarmigan than has been previously projected. Thus, our results demonstrate the importance of considering biotic interactions at both the higher and lower ends of species' range limits along elevation gradients.

Patterns in the genetic structure of 49 lowland rain forest tree species co‐distributed on opposite sides of the northern Andes

AbstractThe Andes are a major dispersal barrier for lowland rain forest plants and animals, yet hundreds of lowland tree species are distributed on both sides of the northern Andes, raising questions about how the Andes influenced their biogeographic histories and population genetic structure. To explore these questions, we generated standardized datasets of thousands of SNPs from paired populations of 49 tree species co‐distributed in rain forest tree communities located in Panama and Amazonian Ecuador and calculated genetic diversity (π) and absolute genetic divergence (dXY) within and between populations, respectively. We predicted (1) higher genetic diversity in the ancestral source region (east or west of the Andes) for each taxon and (2) correlation of genetic statistics with species attributes, including elevational range and life‐history strategy. We found that genetic diversity was higher in putative ancestral source regions, possibly reflecting founder events during colonization. We found little support for a relationship between genetic divergence and species attributes except that species with higher elevational range limits exhibited higher dXY, implying older divergence times. One possible explanation for this pattern is that dispersal through mountain passes declined in importance relative to dispersal via alternative lowland routes as the Andes experienced uplift. We found no difference in mean genetic diversity between populations in Central America and the Amazon. Overall, our results suggest that dispersal across the Andes has left enduring signatures in the genetic structure of widespread rain forest trees. We outline additional hypotheses to be tested with species‐specific case studies.