Variation In Recruitment Research Articles

Assessment of the spawning habitat, spatial distribution, and Lagrangian dispersion of the European anchovy (Engraulis encrasicolus) early stages in the Gulf of Cadiz during an apparent anomalous episode in 2016

Modelling the environmental factors influencing the spatial variation of fish early life stages density and their drift history can identify the key biological and physical processes for the recruitment variability. Distance-based linear multivariate techniques were used to characterize the spawning areas of the European anchovy Engraulis encrasicolus in the Gulf of Cadiz (GoC). Chlorophyll is the environmental variable that best characterized its spawning areas with a time-lag of three days. The use of Lagrangian models to simulate the dispersal of small pelagic species more dependent on advection such as the European anchovy early life stages (early larvae and eggs) in the GoC could provide the degree of connectivity between spawning and nursery areas and identify the physical drivers of the recruitment variability. The larval final destination is critical for the survival of a marine species which is coastal-dependent during its early life stages. Simulations with a Lagrangian transport model in the Southwest Iberian Peninsula were performed during the most intense spawning peak of 2016, when a strong and persistent countercurrent event developed. Most of the simulated early life stages were transported to the western Portuguese coast and, to a lesser extent, to the Atlantic oligotrophic waters, suggesting an increase in the connectivity between the subdivision 9a South and West components. Although different environmental processes occurring during ontogenetic stages, as well as overfishing, among others, can explain part of the variability observed in recruitment, events such as the development of coastal countercurrents during the spawning season could partly account for an increase of anchovy on the western Portuguese coast and a decrease in the Gulf of Cadiz one year later.

Variable effects of mycorrhizal fungi on predator-prey dynamics under field conditions.

Interactions between herbivores and their predators are shaped, in part, by plant phenotype. Consequently, ubiquitous symbionts of plants below-ground, such as arbuscular mycorrhizal fungi (AMF), may influence interactions above-ground between predators and their prey by altering plant phenotype. However, the ecological relevance of below-ground organisms on predator-prey interactions under field conditions remains unclear. We assessed how AMF influence herbivore-predator interactions through a field experiment. We planted two milkweed species (Asclepias curassavica and Asclepias incarnata) provided with different amounts of AMF inoculum (zero, medium, and high) in a randomized block design. We added aphids to plants and reduced predator pressure weekly for 5weeks to evaluate effects of AMF on predator recruitment. We then allowed herbivore-predator interactions to re-establish naturally for the remainder of the season to examine whether AMF-mediated variation in predator recruitment influenced the suppression of aphid populations. Arbuscular mycorrhizal fungi availability in soils mediated interactions between predaceous aphid midge flies Aphidoletes aphidimyza and their aphid prey Aphis nerii, but the effects were plant species-specific. On A. curassavica, by mid-season, midges were recruited most strongly on plants under medium AMF availability and least on plants under high AMF availability. In contrast, each midge killed fewer aphids with increasing aphid density on medium AMF plants, but killed more aphids with increasing aphid density on high AMF plants. In combination, aphid mortality rates imposed by midges were greatest on medium AMF plants, followed by high and zero AMF plants. By comparison, on A. incarnata, the recruitment of midges was strongest on high AMF plants and weakest on medium AMF plants. AMF had no effect on the number of aphids killed per midge, relative to aphid density, so mortality rates of aphids imposed by midges mirrored recruitment. Rates of decline in aphid populations following predator recolonization were associated with midge densities, as well as lacewing and syrphid densities, which were unaffected by AMF availability. Therefore, the effects of AMF on aphid population decline were not a simple function of AMF-midge interactions. Our findings demonstrate that the availability of AMF in soils has pervasive, but complex, effects on predator-herbivore dynamics in the field.

Contrasting links between growth and survival in the early life stages of two flatfish species

Understanding the causes of variation in recruitment of marine fishes has been a central goal over the last century. However, the relationship between year class strength and larval growth and survival is poorly known for most species. The main goal of this study was to investigate the relationships between larval traits and year class strength of two flatfish species in an nursery estuary. We examined the effects of the variation in the early life characteristics (pelagic larval growth, pelagic larval duration, size-at-hatching and size-at-settlement) on post-settlement survival of flounder Platichthys flesus and common sole Solea solea in the Mondego estuary (Portugal) over a 5-year period (2011–2015). The two flatfish species showed distinct larval traits variation during the study period, mainly related with location of the spawning ground and intrinsic biologic patterns. Flounder was able to delay metamorphosis while gathering energy and/or waiting for suitable environmental cues from estuarine origins while sole take advantage of better environmental conditions due to a later hatching. Early fast growth were strongly related with subsequent growth, affecting larval survival. Both growth and larval traits variation during the studied period were strongly related with temperature. This study highlights the importance of early growth for fish survival and contributes with key information on fish early life stages that will support a better management of fish stocks.

Prefledging Growth and Recruitment of Female Lesser Scaup

ABSTRACTAnnual variation in juvenile recruitment is an important component of duck population dynamics, yet little is known about the factors affecting the probability of surviving and breeding in the first year of life. Two hypothesized mechanisms to explain annual variability are indirect carry‐over effects (COEs) from conditions experienced during the prefledging period and direct effects from climatic conditions during the postfledging period. We used Cormack‐Jolly‐Seber models to estimate apparent survival and detection rates of 643 juvenile female lesser scaup (Aythya affinis) marked just prior to fledging at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, 2010–2018. We evaluated COEs from hatch date, a hatch date × spring phenology interaction, and conspecific duckling density in addition to a direct climatic effect of winter conditions (indexed by the El Niño Southern Oscillation [ENSO]) and spring habitat conditions on the study area. We used growth data from a subset (n = 190) of known‐aged ducklings to estimate the influence of hatch date and conspecific density on prefledging growth to help identify mechanisms underlying COEs. Prefledging growth and juvenile apparent survival were negatively related to measures of conspecific duckling density. We found evidence that detection probability varied annually for juvenile (but not adult) scaup, possibly representing decisions to delay breeding and not return to or remain at the study site in their first year of life. Like with apparent survival, there was suggestive evidence that detection probability decreased with increasing duckling density in the previous year. Hatching date was weakly negatively related to detection probability, but unrelated to apparent survival, whereas neither vital rate was related to winter ENSO index. Our results are consistent with a process where density‐dependent growth rates in the prefledging period carry over to influence fitness in subsequent life‐cycle stages. If this pattern generalizes to other systems, this density COE may have important implications for our understanding of duck population dynamics and reaffirms the importance of maintaining abundant brood‐rearing habitats in conservation and management of ducks. © 2021 The Wildlife Society.

Research Article: The decline in the size of ribbonfish, Trichiurus lepturus (Linnaeus 1758), over the past decade in the Persian Gulf

Size-dependent variation in growth, mortality, and recruitment over time are potentially controlled by changes in length -frequency distribution that is dependent to capture probability. The changes in the length-frequency distribution of ribbonfish, Trichiurus lepturus were studied along northern coasts of the Persian Gulf during the period 2008-2017. The length-frequency distribution of ribbonfish indicated the exploitation of larger sizes over the past decade. The mean total length was significantly smaller than the mean length recorded a decade earlier in 2008 (p <0.05). The length-weight relationship (WT=0.00004LT3.44) was found to be significant at 1% level of significance and indicated positive allometric growth. The Von Bertalanffy growth parameters of all fish were =119.35 cm, K=0.3 year-1, and t0 = -0.38 year. Total, natural, and fishing mortality were estimated as 1.16 year-1, 0.53 year-1, and 0.63 year-1. The annual instantaneous rate of fishing mortality was higher than the target (Fopt= 0.26 year−1) and limit (Flim=0.35 year−1) reference points, indicating that the ribbonfish stock is at the risk of unsustainable exploitation.

Modeling of Resistive Forces and Buckling Behavior in Variable Recruitment Fluidic Artificial Muscle Bundles

Fluidic artificial muscles (FAMs), also known as McKibben actuators, are a class of fiber-reinforced soft actuators that can be pneumatically or hydraulically pressurized to produce muscle-like contraction and force generation. When multiple FAMs are bundled together in parallel and selectively pressurized, they can act as a multi-chambered actuator with bioinspired variable recruitment capability. The variable recruitment bundle consists of motor units (MUs)—groups of one of more FAMs—that are independently pressurized depending on the force demand, similar to how groups of muscle fibers are sequentially recruited in biological muscles. As the active FAMs contract, the inactive/low-pressure units are compressed, causing them to buckle outward, which increases the spatial envelope of the actuator. Additionally, a FAM compressed past its individual free strain applies a force that opposes the overall force output of active FAMs. In this paper, we propose a model to quantify this resistive force observed in inactive and low-pressure FAMs and study its implications on the performance of a variable recruitment bundle. The resistive force behavior is divided into post-buckling and post-collapse regions and a piecewise model is devised. An empirically-based correction method is proposed to improve the model to fit experimental data. Analysis of a bundle with resistive effects reveals a phenomenon, unique to variable recruitment bundles, defined as free strain gradient reversal.

Differences in sugarcane stool branching within Saccharum spontaneum genotypes and compared to Saccharum officinarum and commercial varieties

Commercial sugarcane varieties are hybrids between Saccharum officinarum, known for its high sucrose content but poor ratooning growth, and Saccharum spontaneum, known for its low sucrose but greater propensity to produce tillers and better disease resistance. While only 20% of the Saccharum hybrid genome originates from S. spontaneum, the genes underlying the ability to produce more tillers over successive harvests have historically been associated with this species. In order to assess the variation in stool branching and tiller recruitment, 10 genotypes were assessed, including four S. spontaneum, two S. officinarum, two recent S. spontaneum introgressed lines and 2 commercial hybrids. Differences in branching were observed amongst the S. spontaneum genotypes; while all were classified as sympodial rhizome types lacking a terminal bud, there were differences in the degree of branching and the lengths of the underground internodes, with some classified as sprawling (with seven levels of branching) and others as clumping (with four to five levels of branching) depending on the stem nodes. In contrast, the S. officinarum genotypes had limited branching, expanding to only three levels. The S. hybrids and S. spontaneum backcrosses had greater similarity to the clumping S. spontaneum genotypes than to the S. officinarum genotypes. Principal component analysis separated the genotypes of sprawling S. spontaneums, clumping S. spontaneum, hybrids/introgressed lines and S. officinarum. The variation in stool branching may be used to select S. spontaneum parents that would yield better ratooning abilities in their hybrids with S. officinarum, without the ‘weediness’ associated with sprawling rhizomes, for commercial sugarcane production.

Northern Shortfin Squid (Illex illecebrosus) Fishery Footprint on the Northeast US Continental Shelf

Northern shortfin squid (Illex illecebrosus) have presented a challenge for US fishery management because of their life history traits and broad population distribution. They are characterized by a short semelparous lifespan and high interannual variability in recruitment. Much of the stock resides outside of the boundaries of existing US fisheries surveys and US fishing effort. Based on the annual migration pattern and broad geographic distribution of shortfin squid, it is believed that the US squid fishery in the Mid-Atlantic has not had a substantial impact on the stock; however, recent catches are viewed as tightly constrained by quotas. To better estimate the potential impact of fishing on the resource, we worked with industry representatives, scientists, and managers to estimate the availability of the northern shortfin squid stock on the US continental shelf to the US fishery. Taking a novel analytical approach, we combine a model-based estimate of the area occupied by northern shortfin squid with the empirical US commercial shortfin squid fishery footprint to produce estimates of the area of overlap. Because our method overestimates the fishery footprint and underestimates the full distribution of the stock, we suggest that our estimates of the overlap between the area occupied by the squid and the fishery footprint is a way to develop a conservative estimate of the potential fishery impact on the stock. Our findings suggest a limited degree of overlap between the US fishery and the modeled area occupied by the squid on the US continental shelf, with a range of 1.4–36.3%. The work demonstrates the value of using high-resolution, spatially explicit catch and effort data in a species distribution model to inform management of short-lived and broadly distributed species, such as the northern shortfin squid.

Assets and Challenges to Recruiting and Engaging Families in a Childhood Obesity Treatment Research Trial: Insights From Academic Partners, Community Partners, and Study Participants.

Background: There is need for the childhood obesity treatment literature to identify effective recruitment and engagement strategies for rural communities that are more likely to lack supportive infrastructure for healthy lifestyles and clinical research relative to their urban counterparts. This community case study examines recruitment and engagement strategies from a comparative effectiveness research (CER) trial of two family-based childhood obesity (FBCO) treatment interventions conducted in a medically underserved, rural region. Guided by a Community Based Participatory Research (CBPR) and systems-based approach, the primary aim was to analyze interviews from academic partners, community partners, and parent study participants for recruitment and engagement assets, challenges, and lessons learned.Methods: Over the 3-year lifespan of the study, researchers conducted 288 interviews with Community Advisory Board members (n = 14), Parent Advisory Team members (n = 7), and study participants (n = 100). Using an inductive-deductive approach, interviews were broadly coded for recruitment and engagement assets, challenges, and recommendations; analyzed for descriptive sub-coding; and organized into stakeholder/organization and participant level themes. Codes were analyzed aggregately across time and examined for differences among stakeholders and parent study participants.Results: Adherence to CBPR principles and development of strong community partnerships facilitated recruitment and engagement; however, variability in recruitment and engagement success impacted partner confidence, threatened outcome validity, and required additional resources. Specifically, assets and challenges emerged around eight key needs. Three were at the stakeholder/organization level: (1) readiness of stakeholders to conduct CBPR research, (2) development of sustainable referral protocols, and (3) development of participant engagement systems. The remaining five were at the participant level: (1) comfort and trust with research, (2) awareness and understanding of the study, (3) intervention accessibility, (4) intervention acceptability, and (5) target population readiness. Future recommendations included conducting readiness assessments and awareness campaigns, piloting and evaluating recruitment and engagement strategies, identifying participant barriers to engagement and finding a priori solutions, and fostering stakeholder leadership to develop sustainable protocols.Conclusion: Collective findings from multiple perspectives demonstrate the need for multi-leveled approaches focusing on infrastructure supports and strategies to improve stakeholder and participant awareness of, and capacity for, recruiting and engaging medically underserved, rural families in a FBCO CER trial.

Was historical cisco Coregonus artedi yield consistent with contemporary recruitment and abundance in Lake Superior?

AbstractHistorically, cisco Coregonus artedi Lesueur was the predominant prey fish and target of commercial fisheries throughout Lake Superior, but most spawning stocks collapsed by the mid‐1900s. Stocks partially recovered by the early 1990s, but contemporary abundance is considered to be below historical levels and driven by intermittent recruitment. Stochastic, age‐structured simulation models were used to determine whether historical (pre‐1955) cisco yield in Lake Superior was consistent with contemporary (1992–2015) abundance, life‐history characteristics and recruitment dynamics. When compared to contemporary stocks, the findings suggest historical stocks had: (1) similar recruits per spawner at low spawning stock sizes; (2) lower rates of compensatory density dependence; (3) similar or lower recruitment variation depending on the area and (4) higher median adult and age‐1 density. These findings are consistent with the hypothesis that eutrophication during the historical period supported greater recruitment and adult abundance and that re‐oligotrophication during the contemporary period may be limiting full recovery.

Spatial and temporal genetic variation in an exploited reef fish: The effects of exploitation on cohort genetic structure.

Many coral reef fishes are fished, often resulting in detrimental genetic effects; however, reef fishes often show unpredictable patterns of genetic variation, which potentially mask the effects of fishing. Our goals were to characterize spatial and temporal genetic variation and determine the effects of fishing on an exploited reef fish, Plectropomus leopardus, Lacepède (the common coral trout). To determine population structure, we genotyped 417 Great Barrier Reef coral trout from four populations sampled in 2 years (1996 and 2004) at nine microsatellite loci. To test for exploitation effects, we additionally genotyped 869 individuals from a single cohort (ages 3–5) across eight different reefs, including fished and control populations. Genetic structure differed substantially in the two sampled years, with only 1 year exhibiting isolation by distance. Thus, genetic drift likely plays a role in shaping population genetic structure in this species. Although we found no loss of genetic diversity associated with exploitation, our relatedness patterns show that pulse fishing likely affects population genetics. Additionally, genetic structure in the cohort samples likely reflected spatial variation in recruitment contributing to genetic structure at the population level. Overall, we show that fishing does impact coral reef fishes, highlighting the importance of repeated widespread sampling to accurately characterize the genetic structure of reef fishes, as well as the power of analysing cohorts to avoid the impacts of recruitment‐related genetic swamping. The high temporal and spatial variability in genetic structure, combined with possible selection effects, will make conservation/management of reef fish species complex.

Strategies for Successful Scallops Spat Collection on Artificial Collectors in the Taranto Gulf (Mediterranean Sea)

The high variability in natural recruitment of Pectinidae is a common feature of many marine invertebrates with a pelagic larval stage, but may negatively affect aquaculture activities. Detailed information on settlement patterns and spat availability is required to reduce costs and labor. In this regard, we attempted to establish the precise immersion time and the deployment dates for spat collectors in the Taranto Gulf (Mediterranean Sea, Italy). The first experiment was carried out from June to October 2013, deploying collectors every 15 days and retrieving them after 4, 6, 8, and 10 weeks. Results from the first experiment allowed us to select 8 weeks as the best immersion time for spat collection. The second experiment was carried out from June 2013 to July 2014 when we deployed spat collectors every 15 days and recovered them after 8 weeks to detect the favorable periods to place the collectors in water to obtain the highest scallop spat harvest rate. Mimachlamys varia was the most abundant pectinid (greater than 90%), whose recruits were collected during most of the year studied, followed by Flexopecten glaber with the highest rates in July (87%) and Pecten jacobaeus, which never exceeded 17% of collected spat. M. varia had a long recruitment period (from October to early June), F. glaber showed a high number of spat during autumn months and from June to July while P. jacobaeus showed a restricted period of spawning. Our experiments provide useful insights into strategies for establishing scallop aquaculture in order to promote these mollusks as alternative candidates for aquaculture farming in the area.

Temperature, maternal effects and density-dependent processes during early life stages of Argentine hake as relevant recruitment drivers

We analyzed the annual variability in total egg production and recruitment of the Patagonian stock of Argentine hake since 1990 and correlated these indices with some environmental variables as temperature and larval density estimated in the spawning area. We used data from research surveys carried out between 2001 and 2018 during the reproductive peak of this stock and information from the assessment model. The optimal spawning area of Argentine hake was associated with a bottom thermal front, with temperature values between 9° and 13 °C. The study revealed that reproductive success is positively influenced by the oldest females of the stock and negatively influenced by the egg density in the spawning area. In the first case, a larger proportion of older spawning females (≥ 7 years-old) produces larvae with greater survival rates; while in the second case, a greater abundance of early larvae in a more limited optimum spawning area could produce a higher rate of mortality due to competition.

An updated life‐history scheme for marine fishes predicts recruitment variability and sensitivity to exploitation

ABSTRACTAimPatterns of population renewal in marine fishes are often irregular and lead to volatile fluctuations in abundance that challenge management and conservation efforts. Here, we examine the relationship between life‐history strategies and recruitment variability in exploited marine fish species using a macroecological approach.LocationGlobal ocean.Time period1950–2018.Major taxa studiedBony and cartilaginous fish.MethodsBased on trait data for 244 marine fish species, we extend the established equilibrium–periodic–opportunistic (E‐P‐O) life‐history classification scheme objectively to include two additional emergent life‐history strategies: “bet‐hedgers” (B) and salmonic (S) strategists. The B strategists include rockfishes and other species inhabiting patchy benthic habitats with life histories that blend characteristics of E and P species; they combine very long life spans with elevated investments in both parental care and fecundity. The S strategists mainly comprise salmonids that share life‐history characteristics with E and O species: elevated investments in parental care reminiscent of E strategists, but with reduced fecundity and short life spans characteristic of O species. We analysed how the E‐B‐P‐O‐S life‐history classification mapped onto patterns of recruitment variability observed in population time series data (n = 156 species).ResultsGeneralized linear models suggested that life‐history strategy explained a modest, yet significant amount of recruitment variability across species. Greater predictive power arose after controlling for increased recruitment variance associated with variable fishing pressure, with O strategists showing the strongest sensitivity. The B strategists were susceptible to exploitation in a similar manner to P stocks, but their longer times to maturity made them particularly vulnerable to overfishing.Main conclusionsA broader recognition of the distinct ecology of salmonic and bet‐hedger groups is important when studying life‐history strategies in marine fish. More generally, our results stress the importance of considering life‐history strategies for understanding patterns of recruitment variability across fish stocks.

Shedding light on the link between the spatial distribution of eggs and survival in Northeast Arctic cod

AbstractSpreading the offspring in space and time may offer bet‐hedging benefits by buffering environmental influences on parts of the offspring distribution. It has previously been shown that high mean age and size of spawners in the Northeast Arctic stock of Atlantic cod (Gadus morhua) is positively associated with high abundance and wide spatiotemporal distribution of eggs. However, little support has been found for a wide egg distribution acting as a buffer against environmental influences by leading to higher mean or less variable recruitment. The lacking relation between egg distribution and recruitment can be due to data limitation or alternatively that wide egg distributions may be of limited relevance for survival in later stages. To investigate these two alternatives, we analysed the output from a mechanistic coupled physical–biological drift model that projected the abundance of juvenile cod on the nursing grounds in the Barents Sea from empirically estimated egg distributions. The projections were performed with initial egg distributions reflecting the expected distributions at high and low mean weight of the spawners. We found that the extended distribution at the fringes only marginally contributed to recruitment, as a large proportion of the extra eggs at high mean age and size of spawners did not reach suitable nursing areas or failed to grow to a suitable size by the end of the season. In conclusion, our results suggest that the buffering effect of a geographically wide distribution of spawning products is insignificant compared to other effects on recruitment.

Kinetically Tunable, Active Auxetic, and Variable Recruitment Active Textiles from Hierarchical Assemblies

AbstractMultifunctional textiles with programmable, multi‐axial, distributed, and scalable actuation are highly desirable and presently unrealized. 1D torque‐unbalanced active yarns within 2D textile structures are exploited to produce soft and scalable active textiles that exhibit tunable displacements, forces, stiffnesses, and kinematic deformations. Through a textile hierarchy spanning active material composition, yarn construction, textile geometry, and system architecture, these active textiles accomplish kinetic tunability, variable recruitment behaviors, and auxetic effects without mechanical contact, called active auxetic effects. New modes of pre‐programmed multi‐axial performance are enabled by geometrically manipulating—specifically pre‐stressing and constraining—active filaments in torsion and leveraging their structural elastic instability within a textile geometry. The new kinematic motion afforded by torque‐unbalanced active yarns enhances the performance of active textiles, which accomplish tensile strokes over 40%, generated blocked forces up to 308 N m−1, and specific work over 0.4. kJ kg−1. Advances in active textiles are demonstrated through multifunctional 3D applications, including a variable constriction pump that exhibits sequential actuation, a wearable that conforms multi‐axially around the body, and a soft exoskeleton that performs assistive motions and on‐body anchoring simultaneously. By harnessing the capabilities of active materials within a textile hierarchy, advances in the potentiality of multifunctional textiles are presented.

Spatiotemporal variation in coral recruitment and its association with seawater temperature

AbstractThe supply of propagules mediates recruitment and population dynamics, thereby driving community resilience following disturbances. These relationships are of interest on tropical reefs, where coral populations have drastically declined in abundance and sexual recruitment is the only means by which they will recover. To better understand the causes and implications of variation in this vital rate (i.e., recruitment), coral recruitment was measured in Mo'orea, French Polynesia, and St. John, U.S. Virgin Islands, using settlement tiles deployed from 2005 to 2019. The results were used to test two hypotheses: (1) annual variation in recruitment is a weak predictor of long‐term variation in recruitment, but (2) it is associated with seawater temperature. Coral recruitment varied over space and time, so that differences in recruitment between consecutive years were uninformative of long‐term trends. Recruitment varied among years in an apparently chaotic manner, but the variation reflected linear and quadratic associations with mean annual temperature and the daily variation in temperature. These associations are consistent with theory addressing the mechanisms by which temperature affects coral larvae and recruitment. Comprehension of these mechanisms is required to accurately interpret evidence of coral recruitment collapse, and to elucidate the conditions favoring recovery of coral communities through recruitment.

Effect of muscle stimulation intensity on the heterogeneous function of regions within an architecturally complex muscle.

Skeletal muscle has fiber architectures ranging from simple to complex, alongside variations in fiber-type and neuro-anatomical compartmentalization. However, the functional implications of muscle subdivision into discrete functional units remain poorly understood. The rat medial gastrocnemius has well-characterized regions with distinct architectures and fiber type composition. Here, force-length and force-velocity contractions were performed for two stimulation intensities (supramaximal and submaximal) and for three structural units (whole muscle belly, proximal region, and distal region) to assess the effect of muscle compartmentalization on contractile force-length-velocity relationships and optimal speed for power production. Additionally, fiber strain, fiber rotation, pennation, and architectural gearing were quantified. Our results suggest that the proximal and distal muscle regions have fundamentally different physiological function. During supramaximal activation, the proximal region has shorter (8.4 ± 0.8 mm versus 10.9 ± 0.7 mm) fibers and steeper (28.7 ± 11.0° versus 19.6 ± 6.3°) fiber angles at optimum length, and operates over a larger (17.9 ± 3.8% versus 12.6 ± 2.7%) range of its force-length curve. The proximal region also exhibits larger changes in pennation angle (5.6 ± 2.2°/mm versus 2.4 ± 1.5°/mm muscle shortening) and architectural gearing (1.82 ± 0.53 versus 1.25 ± 0.24), whereas the distal region exhibits greater peak shortening speed (96.0 mm/s versus 81.3 mm/s) and 18-27% greater optimal speed. Overall, similar patterns were observed during submaximal activation. These regional differences in physiological function with respect to the whole muscle highlight how variation in motor recruitment could fundamentally shift regional functional patterns within a single muscle, which likely has important implications for whole muscle force and work output in vivo.NEW & NOTEWORTHY We show that muscle compartmentalization can influence whole muscle contractile properties, with slower-fibered proximal rat medial gastrocnemius undergoing larger changes in pennation angle and architectural gearing, whereas the faster-fibered distal region achieves greater peak and optimal shortening velocity, and power output. Consequently, regional variation in motor recruitment can fundamentally influence functional patterns within a single muscle.

Understory plant diversity and composition across a postfire tree density gradient in a Siberian Arctic boreal forest

Cajander larch (Larix cajanderi Mayr.) forests of the Siberian Arctic are experiencing increased wildfire activity in conjunction with climate warming. These shifts could affect postfire variation in the density and arrangement of trees and understory plant communities. To better understand how understory plant composition, abundance, and diversity vary with tree density, we surveyed understory plant communities and stand characteristics (e.g., canopy cover, active layer depth, and soil organic layer depth) within 25 stands representing a density gradient of similarly-aged larch trees that established following a 1940 fire near Cherskiy, Russia. Understory plant diversity and mean total plant abundance decreased with increased canopy cover. Canopy cover was also the most important variable affecting individual species’ abundances. In general, tall shrubs (e.g., Betula nana subsp. exilis) were more abundant in low-density stands with high light availability, and mosses (e.g., Sanionia spp.) were more abundant in high-density stands with low light availability. These results provide evidence that postfire variation in tree recruitment affects understory plant community composition and diversity as stands mature. Therefore, projected increases in wildfire activity in the Siberian Arctic could have cascading impacts on forest structure and composition in both overstory and understory plant communities.

Local landscape position impacts demographic rates in a widespread North American steppe bunchgrass

AbstractUnderstanding the environmental drivers of demographic rates and population dynamics over space and time is critical for anticipating how species will respond to climate change. While the influence of temporal environmental variation and large environmental gradients are well recognized, less is known about how local topography and landscape position influence demography over small spatial scales. Here, we investigate how local landscape position (north‐ vs. south‐facing aspects) influence the demographic rates and population growth of a common bunchgrass in western North America, bluebunch wheatgrass (Pseudoroegneria spicata), using 6 annual censuses measuring growth, survival, and reproductive output. We found notably lower survival on south‐facing slopes, particularly among smaller individuals. In contrast, south‐facing slopes maintained comparatively high reproductive output in most years, measured both as spikes per plant and spikelets per spike. When we combined these data in demographic models, we found that lower survival among small individuals and greater reliance on reproduction mean south‐facing slopes would generally have to maintain higher recruitment for a stable population. Our results highlight the important influence that landscape position and local topography can have in driving population trends. As conditions warm and dry with climate change (north‐faces becoming similar to current south‐facing slope conditions), bluebunch wheatgrass may become more reliant on reproduction to maintain viable populations and more sensitive to variability in recruitment.