In a long-term experimental demography study,excluding ungulates reversed invader's explosive population growth rate and restored natives

A major goal in ecology is to understand mechanisms that increase invasion success of exotic species. A recent hypothesis implicates altered species interactions resulting from ungulate herbivore overabundance as a key cause of exotic plant domination. To test this hypothesis, we maintained an experimental demography deer exclusion study for 6 y in a forest where the native ungulate Odocoileus virginianus (white-tailed deer) is overabundant and Alliaria petiolata (garlic mustard) is aggressively invading. Because population growth is multiplicative across time, we introduce metrics that correctly integrate experimental effects across treatment years, the cumulative population growth rate, λ_c, and its geometric mean, λ_per-year, the time-averaged annual population growth rate. We determined λ_c and λ_per-year of the invader and of a common native, Trillium erectum. Our results conclusively demonstrate that deer are required for the success of Alliaria; its projected population trajectory shifted from explosive growth in the presence of deer (λ_per-year = 1.33) to decline toward extinction where deer are excluded (λ_per-year = 0.88). In contrast, Trillium’s λ_per-year was suppressed in the presence of deer relative to deer exclusion (λ_per-year = 1.04 vs. 1.20, respectively). Retrospective sensitivity analyses revealed that the largest negative effect of deer exclusion on Alliaria came from rosette transitions, whereas the largest positive effect on Trillium came from reproductive transitions. Deer exclusion lowered Alliaria density while increasing Trillium density. Our results provide definitive experimental support that interactions with overabundant ungulates enhance demographic success of invaders and depress natives’ success, with broad implications for biodiversity and ecosystem function worldwide.Steadily increasing pressure by invasive plant species on native biodiversity (1) disrupts both community and ecosystem function (2) and results in staggering economic costs worldwide (3, 4). A major goal in ecology is to understand how changes over time in species interactions affect invasion success of exotic species (5–8). According to ecological theory, the ability of the resident community to limit the success of invading exotics [biotic resistance (9, 10)] will depend upon ecological context that includes the suite of local interactors (11–15). The abundance of herbivores and their local impacts (11, 14, 16) can play a prominent role in how fast plant populations grow or shrink and how much the relative abundance of plant species changes over time (5, 15), including changes associated with plant invasions (11, 16–19). Recently, increased browsing pressure by overabundant ungulate herbivores on native plant communities has been proposed as a fundamental cause of a shift from native to exotic plant domination in forests and rangelands worldwide (11, 16, 20). Wild and domesticated ungulates (e.g., deer, elk, goats, sheep, horses, cows) that are either native or introduced have all been implicated in this process (11, 16, 20).Overabundant ungulates may change the success of invading exotics in numerous ways. Ungulate browsing on natives may depress their abundance and ability to compete (21–24) and increase abiotic resources available to invaders (11, 25, 26), which can act synergistically to decrease communities’ ability to resist invasion (biotic resistance; refs. 8 and 10). Ungulates disperse exotic seeds (27, 28) and create novel abiotic conditions with respect to soil disturbance, soil quality, and light availability (21, 22, 26), which may enhance exotic establishment and growth. Moreover, although ungulates are considered diet generalists, in fact, they frequently behave as selective foragers (21–24, 29), preferring natives to exotics. In this circumstance, unpalatable invaders can have a double advantage over natives—both release from historic enemies (20) and inedible to new potential enemies in the invaded range (30, 31). Together, these mechanisms not only implicate overabundant ungulates in their direct impact on the rate at which populations of palatable native species grow or shrink, but point to their potentially pivotal role in reducing the biotic resistance of the native community to favor invaders (13, 14).To determine how ungulate herbivores affect the fitness of invaders and natives, field experiments that manipulate herbivore access for several years and are spatially well replicated are required (11, 32, 33). The multiyear, population-level demographic data gained in such experiments can be used to estimate the ultimate metric of fitness: population growth rate (λ). However, despite the widespread use of manipulative experiments that alter herbivore access to plants, we still lack appropriate demographic data (i.e., complete schedules of fertility, mortality and growth for all stages) in invaded systems (2, 14, 17, 32, 33). Instead, herbivore–plant invader experiments typically report simple metrics of plant success (e.g., percent cover or counts of individuals) at a single time point. For example, the metric “percent cover” estimates the total leaf area of a species, often relative to other species. Lower leaf area of native plants where ungulates have access could merely be the result of leaf tissue lost to herbivory, with no actual change in invader or native numbers. Likewise, “snapshot counts” of invaders often leave out critical life cycle stages and do not provide information on rates of survival, reproduction, or growth, without which population dynamics cannot be analyzed. Thus, it is not surprising that ungulate exclusion experiments that apply such metrics provide no unified answer regarding exotic invaders [effect on invasion success: none (34–36); mixed (37, 38); positive (39–41; reviewed in ref. 16)] because these studies cannot address population viability of invaders or natives. Also, although evidence of ungulates’ influence on native plant population dynamics from exclusion experiments has been previously demonstrated (e.g., refs. 42 and 43), our study is distinct. We know of no other such experiments testing the link between ungulates and invasive exotic population growth rate in invaded systems.Here, we use experimental demography and stage-based data (rates of survival, fertility, and growth) collected over multiple years to test the hypothesis that an overabundant native ungulate herbivore drives positive population growth of invaders (11, 16). We emphasize that in herbivore removal experiments the fitness of plant populations, which is measured by population growth rate, is predicted to rebound with persistent, multiplicative beneficial effects over time. What has not previously been recognized in such experiments is that treatment effects accumulate over the span of an experiment (44), necessitating a quantitative metric that integrates fitness over the entire life cycle and over time. Moreover, population growth is a process that is multiplicative across time. Thus, we introduce the use of cumulative population growth rate, λ_c, at the end of a multiyear experiment as the metric that correctly integrates experimental effects across the observed sequence of demographic changes across time. Our multiyear demographic projection and the corresponding multiyear retrospective sensitivity analysis provide fresh insights. To facilitate comparisons of our results with studies that estimate λ from single-year transitions, we present λ_per-year, the geometric mean of λ_c. Our retrospective sensitivity analyses [similar to life table response experiment analysis for periodic matrices (45, 46)] of λ_c reveal how each part of the life cycle contributes to overall differences in cumulative population dynamics caused by an experimental manipulation. We conclusively show that overabundant deer create conditions favorable for explosive exponential population growth of an exotic plant invader, but that when deer are excluded, populations of the invader are projected to decline exponentially.We focus on the native ungulate Odocoileus virginianus (white-tailed deer; hereafter, deer) and the exotic herbaceous understory invader Alliaria petiolata (Brassicaceae; garlic mustard; hereafter, Alliaria), which both present serious management concerns in North American forests. Relative to historical records, deer densities are currently 4–10 times higher than pre-European settlement densities across North America (47). Overabundant native deer in forests exert the same kinds of pressures as other ungulates (native and nonnative, wild and domesticated) globally, including perturbation of understory communities (22, 27, 39), exotic seed dispersal (27), and alteration of abiotic conditions (21, 39). Likewise, Alliaria ranks among the most problematic forest invaders in North America (48). Introduced by early colonists, it was naturalized on Long Island, New York, by 1868 (reviewed in ref. 48). In its native Eurasia, Alliaria grows in edge or disturbed habitats, whereas in North America it increasingly occupies forest interiors (48). Relative to the slow-growing, long-lived understory community it invades, Alliaria has a rapid, biennial life cycle: spring seedlings form overwintering rosettes by autumn. In their second year, plants reproduce, disperse seeds, and die. In its invaded range, Alliaria has high population growth rates (λ = 1.4–3.4) (48), which project annual increases in numbers of 40–240%. Alliaria’s invasive success has been hypothesized to result from various factors. These include the following: novel allelopathic weapons, enemy release, positive soil feedback, taxonomic novelty, high competitive ability, and specific phenotypic traits. No single factor has yet to explain the broad reach of this tenacious exotic (reviewed in ref. 48). Here, we investigate what has not been previously explored: the role of ungulate disruption of native community biotic resistance (13) on Alliaria’s invasion success. To date, deer and Alliaria have been foci of intense, largely separate, research efforts. Our approach uses experimental demography to jointly examine these two issues. Together, they constitute an ideal system to investigate ungulate–exotic plant invasion linkages (11, 16).Our experiment was conducted in a beech–maple forest in southwestern Pennsylvania (Trillium Trail Nature Reserve, Allegheny County, Pennsylvania: 40° 52′ 01.40″ N; 79° 90″ 10.75″ W). Winter aerial flyovers of this area performed between 1993–2004 revealed overabundant deer: currently 20–42 deer per km² compared with an historic density of 10–12 deer per km² (Fig. S1). In a different area in this same forest, Knight et al. (39) used an indirect metric of plant performance and found that relative percent cover of Alliaria was lower and that there was significantly less bare ground where deer were excluded relative to sites where deer were present (39). However, in that study Alliaria nevertheless remained abundant (the second most abundant species) even where deer were excluded. That study (39), which used relative percent cover as a response metric, left several questions unanswered, including the following: Was Alliaria’s relative decline due to the native species increasing in cover with no actual change in cover of the invader? Did the tenacious invader’s population growth rate actually decline? Given these unanswered questions from the earlier study, the Trillium Trail forest was an ideal location to address these questions and to conduct a definitive demographic experiment that could distinguish among these mechanisms. In 2002, we established paired plots (n = 6 pairs of 14 × 14-m plots) with one plot per pair randomly assigned to a fenced treatment that excluded deer (see Materials and Methods for details). The other plot in each pair remained unfenced and experienced ambient levels of deer and other animals. We compared population-level responses of native understory herbaceous perennial species and Alliaria between treatments for 6 y. For three focal native herbs that are palatable to deer (e.g., ref. 49) and the unpalatable Alliaria, we quantified reproductive success each year. For Alliaria and one of the natives, Trillium erectum (Melanthiaceae, hereafter Trillium), we additionally quantified the complete schedule of survival, fertility, and growth rates each year. We selected Trillium as a counterpoint to Alliaria as it is the most common flowering herbaceous species found at Trillium Trail Nature Reserve. Moreover, Trillium species are a preferred food source for deer (49) and well-known phytoindicators of deer browse (e.g., ref. 49; but see ref. 50). In a nonexperimental study, deer browse levels within a population were negatively correlated with population growth rate for another species in the genus, Trillium grandiflorum (51). Accordingly, Trillium represents a model for understanding the impact of deer on native species, and the loss of such browse-sensitive species can be a metric of decline in forest integrity (52). We predicted that, if ungulates disrupt the native community and enhance exotic invasion success, then in plots experimentally protected from deer: (i) native species would have higher reproductive success, (ii) Trillium fitness would increase and its density would increase, (iii) Alliaria fitness would decrease and its density would decline. Meanwhile, in plots where deer were allowed access, we expected either the opposite trends or no change from initial conditions. Alternatively, if any of the other previously hypothesized mechanisms for Alliaria’s success (e.g., novel weapons, enemy release) are at play and more important than herbivore impacts, then we would expect Alliaria’s population growth rate to remain high despite deer exclusion, while predictions for the effects of deer on the natives remain the same.In brief, from 2003 to 2008 at annual censuses, we scored reproduction and survival of individuals of Alliaria and of the three native perennials that are preferred food sources for deer (49): Trillium, Maianthemum racemosum (Ruscaceae), and Polygonatum biflorum (Ruscaceae). In plots accessible to deer, we also scored deer browse. To assess the effect of deer exclusion on the fitness of Trillium and Alliaria, we implemented our multiyear matrix projection analysis to calculate cumulative population growth rates from 2003 to 2007 for each treatment. To construct matrices, we defined five life cycle stages for the perennial Trillium (germinant bank, seedling, one-leafed juvenile, three-leafed nonflowering, and three-leafed flowering; Fig. S2A) and three life cycle stages for Alliaria (dormant seed in the seed bank, rosette, and fruiting adult; Fig. S3A). Matrix elements were calculated as a function of the vital rates associated with each stage transition (Figs. S2A and S3A). We captured cumulative effects of deer exclusion or continued deer overabundance over time, parameterizing multiyear projection matrix models B, for each species and treatment by multiplication of annual projection matrices A_{YEAR-TREATMENT} (e.g., B_DEER = A_2006-DEER A_2005-DEER A_2004-DEER A_2003-DEER). The matrix B, at the heart our analyses, contains the rates at which individuals that were at a given stage at the beginning of the experiment will have either become or produced individuals of each stage after four transition years. Our analyses of multiyear matrices provide integrative measures of plant fitness over the time frame of the experiment, including treatment-specific cumulative population growth rates (λ_c, the dominant eigenvalue of B), time-averaged λ’s (λ_{per-year-TREATMENT} = the fourth root of the dominant eigenvalue, λ_c, of B), and an overall measure of the effect of protecting plants from deer on plant fitness Δλ_per-year = λ_{per-year-NO_DEER} – λ_{per-year-DEER}. [Note: Pooled plot data (Trillium) and individual plot data (Alliaria) were used. See Materials and Methods, Matrix Construction for Each Species and Treatment.] Finally, to uncover mechanistic differences between the response of the native and the exotic to deer exclusion, we use a life table response experiment retrospective sensitivity analysis (45, 46). The analysis shows how important each of these 4-y demographic rates is to differences in λ_c between treatments, quantified by contributions made during transitions from stage j to stage i, c_ij.     

Nonrandom,diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

A variety of ecological processes influence diversity and species composition in natural communities. Most of these processes, whether abiotic or biotic, differentially filter individuals from birth to death, thereby altering species’ relative abundances. Nonrandom outcomes could accrue throughout ontogeny, or the processes that generate them could be particularly influential at certain stages. One long-standing paradigm in tropical forest ecology holds that patterns of relative abundance among mature trees are largely set by processes operating at the earliest life cycle stages. Several studies confirm filtering processes at some stages, but the longevity of large trees makes a rigorous comparison across size classes impossible without long-term demographic data. Here, we use one of the world’s longest-running, plot-based forest dynamics projects to compare nonrandom outcomes across stage classes. We considered a cohort of 7,977 individuals in 186 species that were alive in 1971 and monitored in 13 mortality censuses over 42 y to 2013. Nonrandom mortality with respect to species identity occurred more often in the smaller rather than the larger size classes. Furthermore, observed nonrandom mortality in the smaller size classes had a diversifying influence; species richness of the survivors was up to 30% greater than expected in the two smallest size classes, but not greater than expected in the larger size classes. These results highlight the importance of early life cycle stages in tropical forest community dynamics. More generally, they add to an accumulating body of evidence for the importance of early-stage nonrandom outcomes to community structure in marine and terrestrial environments.Processes that operate nonrandomly with respect to species identity contribute to the structure of natural communities (1–3). Evidence from diverse rain forests includes demographic transitions from seeds to seedlings (4, 5), at the seedling (6, 7) and sapling stages (8) and among large trees (9–12). Although the relative contributions of nonrandom processes at each life cycle stage to determining patterns of abundance and diversity in the mature canopy are unknown, one long-standing paradigm is that community assembly is mediated primarily by events occurring from seed dispersal through seedling germination and small-sapling establishment (13–17). However, despite suggestive patterns (6, 7, 18, 19), evidence is lacking for the comparative strength of early-stage dynamics in determining canopy abundance and diversity.Numerous studies demonstrate significant interspecific variation in the susceptibility of tropical tree seedlings to postgermination hazards, including natural enemies (20, 21), adverse climatic or edaphic conditions (22), physical damage (23), and the crowding or shared-enemies effects of con- and heterospecific neighbors (24, 25). In other words, the per capita probability of seedling mortality is nonrandom because the probability of death is not the same for all individuals in a local community – it is dependent to some degree on species identity. In plant communities in which generation times are relatively short, experiments have demonstrated that nonrandom mortality through these early transitions can be sufficiently strong to affect the species composition of mature plants (26–29). Such demonstrations are impossible in studies of a few decades or less in duration when generation times are long and even juveniles live for several decades or centuries, such as in many tropical forests. Even so, some hypotheses explicitly identify stressors that affect plants at the earliest life cycle stages (such as pests and pathogens, 13, 14, 30) as disproportionately influential. In addition, some empirical studies find a lack of support for nonrandom processes operating among larger stems (31, 32). Together these hypotheses and observations provide the rationale underpinning the considerable body of research on seed and seedling dynamics in tropical forests worldwide. However, no empirical or experimental assessment has been made of the relative contributions across life cycle stages from nonrandom mortality.Here, we evaluate the comparative contribution of early-stage dynamics using a multidecadal study of a tropical forest dynamics plot initiated by one of us (J.H.C.) in 1963 at a site in north Queensland, Australia. We considered a cohort of 7,977 individuals in 186 species that were alive on the plot in 1971, from tiny seedlings to large canopy trees, whose fates were monitored in 13 mortality censuses over 42 y to 2013. Individuals were assigned to one of six size classes (

运动想象脑电多视角深度森林解码算法

针对运动想象脑电信号特征提取操作繁琐及解码精度低等问题,提出一种基于多视角深度森林的运动想象脑电解码算法。首先,通过子频带滤波及时间窗口划分对原始信号进行细粒度分析,生成空时频能量特征。然后,对上述空时频能量特征分别进行稀疏选择和时序扫描得到重要的浅层能量特征及多示例先验类别特征。继而,将上述两类特征进行融合构建运动想象脑电多视角特征集。最后,利用级联森林的逐层特征变换挖掘深层次的抽象特征进行脑电解码。根据脑机接口竞赛数据和自行采集的数据进行算法测试,并与单视角特征模型、传统共空间模式方法以及深度神经网络算法进行对比。在2个脑机接口竞赛数据集和1个真实数据集上分别取得了91.4%、75.2%和70.7%的最高平均分类准确率,结果表明该文所提多视角深度森林算法具有更优的分类识别准确率。     

基质金属蛋白酶-9与自发性高血压大鼠心肌纤维化的相关性研究

目的:探讨基质金属蛋白酶-9(MMP-9)与自发性高血压大鼠(SHR)心肌纤维化的相关性。方法:将16只14周龄雄性SHR随机平分为ACEI组和对照组,另以8只同龄雄性SD大鼠作为正常对照组。ACEI组以卡托普利100mg/(kg.d)灌胃,SHR对照组不灌药,于灌药12周后麻醉下取出大鼠心脏。免疫组化分析MMP-9、Collagen和的表达;RT-PCR检测MMP-9mRNA表达;MASSON染色测量胶原容积分数(CVF);碱水解法测定羟脯氨酸(Hypro)含量。结果:(1)SHR对照组LVI、CVF、Hypro、MMP-9、Collagen和的表达明显高于正常对照组(P<0.01);相对于SHR对照组,ACEI组各参数则显著降低(P<0.05);(2)MMP-9与上述指标呈高度正相关(P<0.01)。结论:MMP-9与SHR心肌纤维化密切相关,ACEI能抑制MMP-9的表达。     

Prediction of Mortality in Coronary Artery Disease: Role of Machine Learning and Maximal Exercise Capacity

ObjectiveTo develop a prediction model for survival of patients with coronary artery disease (CAD) using health conditions beyond cardiovascular risk factors, including maximal exercise capacity, through the application of machine learning (ML) techniques.MethodsAnalysis of data from a retrospective cohort linking clinical, administrative, and vital status databases from 1995 to 2016 was performed. Inclusion criteria were age 18 years or older, diagnosis of CAD, referral to a cardiac rehabilitation program, and available baseline exercise test results. Primary outcome was death from any cause. Feature selection was performed using supervised and unsupervised ML techniques. The final prognostic model used the survival tree (ST) algorithm.ResultsFrom the cohort of 13,362 patients (60±11 years; 2400 [18%] women), 1577 died during a median follow-up of 8 years (interquartile range, 4 to 13 years), with an estimated survival of 67% up to 21 years. Feature selection revealed age and peak metabolic equivalents (METs) as the features with the greatest importance for mortality prediction. Using these 2 features, the ST generated a long-term prediction with a C-index of 0.729 by splitting patients in 8 clusters with different survival probabilities (P<.001). The ST root node was split by peak METs of 6.15 or less or more than 6.15, and each patient’s subgroup was further split by age or other peak METs cut points.ConclusionApplying ML techniques, age and maximal exercise capacity accurately predict mortality in patients with CAD and outperform variables commonly used for decision-making in clinical practice. A novel and simple prognostic model was established, and maximal exercise capacity was further suggested to be one of the most powerful predictors of mortality in CAD.     

Repetition and variation in motor practice: A review of neural correlates

Random practice results in more effective motor learning than either constant or blocked practice. Recent studies have investigated the effects of practice schedules at the neurophysiological level. This study aims to conduct a literature review of the following issues: (a) the differential involvement of premotor areas, the primary motor cortex, the dorsolateral prefrontal cortex and the posterior parietal cortex in different types of practice; (b) changes in the participation of these areas throughout practice; and (c) the degree of support that current neurophysiological findings offer to strengthen the behavioral proposition that distinct cognitive processes are generated by different practice schedules. Data from 10 studies that investigated associations between practice structures and neurobiological substrates were analyzed. The participation of the indicated areas was found to depend on practice structure and varied during the learning process. Greater cognitive engagement was associated with random practice. In conclusion, distinct neural processes are engendered by different practice conditions. The integration of behavioral and neurophysiological findings promotes a more comprehensive view of the phenomenon.     

基于随机森林的中药寒、热药性代谢组学判别方法研究

目的:建立中药寒、热药性判别模型与方法。方法:利用中药寒、热药动物实验,获取代谢组学数据;再采用随机森林算法构建中药寒、热药性分类判别模型。结果:基于随机森林构建的中药寒、热药性代谢组学分类判别模型,能够很好地实现分类判别,总体准确率超过90%;用前30个最重要的M/Z值构建的分类判别模型,同样有很高的分类准确率;经7∶3测试,准确率也超过90%。结论:基于随机森林的中药寒、热药性代谢组学分类判别模型,经实验数据建模验证表明其可行有效。     

Sequential Monte Carlo tracking of the marginal artery by multiple cue fusion and random forest regression

Given the potential importance of marginal artery localization in automated registration in computed tomography colonography (CTC), we have devised a semi-automated method of marginal vessel detection employing sequential Monte Carlo tracking (also known as particle filtering tracking) by multiple cue fusion based on intensity, vesselness, organ detection, and minimum spanning tree information for poorly enhanced vessel segments. We then employed a random forest algorithm for intelligent cue fusion and decision making which achieved high sensitivity and robustness. After applying a vessel pruning procedure to the tracking results, we achieved statistically significantly improved precision compared to a baseline Hessian detection method (2.7% versus 75.2%, p < 0.001). This method also showed statistically significantly improved recall rate compared to a 2-cue baseline method using fewer vessel cues (30.7% versus 67.7%, p < 0.001). These results demonstrate that marginal artery localization on CTC is feasible by combining a discriminative classifier (i.e., random forest) with a sequential Monte Carlo tracking mechanism. In so doing, we present the effective application of an anatomical probability map to vessel pruning as well as a supplementary spatial coordinate system for colonic segmentation and registration when this task has been confounded by colon lumen collapse.