Individual plant size often determines the vital rates of growth, survival and reproduction. However, size can be measured in several ways (e.g. height, biomass, leaf length). There is no consensus on the best size metric for modelling vital rates in plants. Demographic datasets are expanding in geographic extent, leading to choices about how to represent size for the same species in multiple ecological contexts. If the choice of size variable varies among locations, inter-population comparative demography increases in complexity. Here, we present a framework to perform size metric selection in large-scale demographic studies. We highlight potential pitfalls and suggest methods applicable to diverse study organisms. We assessed the performance of five different size metrics for the perennial herb Plantago lanceolata, across 55 populations on three continents within its native and non-native ranges, using the spatially replicated demographic dataset PlantPopNet. We compared the performance of each candidate size metric for four vital rates (growth, survival, flowering probability and reproductive output) using generalized linear mixed models. We ranked the candidate size metrics based on their overall performance (highest generalized R2) and homogeneity of performance across populations (lowest total magnitude of, and variance in, population-level error). While all size variables performed well for modelling vital rates, the number of leaves (modelled as a discrete variable, without transformation) was selected as the best size metric, followed by leaf length. We show how to interrogate potential trade-offs between overall explanatory power and homogeneity of predictions across populations in any organism. Synthesis. Size is an important determinant of vital rates. Using a dataset of unprecedented spatial extent, we find (a) consistent size-based models of growth, survival and reproduction across native and non-native populations of this cosmopolitan plant species and (b) that several tested size metrics perform similarly well. This is encouraging for large-scale demographic studies and for comparative projects using different size metrics, as they may be robust to this methodological difference.

Our understanding of plant functional trait variation among populations and how this relates to local adaptation to environmental conditions is largely shaped by above-ground traits. However, we might expect below-ground traits linked to resource acquisition and conservation to vary among populations that experience different environmental conditions. Alternatively, below-ground traits might be highly plastic in response to growing conditions, such as availability of soil resources and association with symbiont arbuscular mycorrhizal fungi (AMF). We assessed (i) the strength of among-population variation in above- and below-ground traits, (ii) the effects of growing conditions on among-population variation and (iii) whether variation among populations is linked to source environment conditions, in a globally distributed perennial Plantago lanceolata. Using seeds from 14 populations across three continents, we grew plants in a common garden experiment and measured leaf and root traits linked to resource acquisition and water conservation. We included two sets of experimental treatments (high or low water availability; with and without AMF inoculation), which enabled us to assess trait responses to growing conditions. Across treatments, the percentage of root trait variation explained by populations and continents was 9%-26%, compared to 7%-20% for leaf trait variation. From principal component analysis (PCA), the first PC axis for both root and leaf traits largely reflected plant size, while the second PC broadly captured mass allocation. Root mass allocation (PC 2) was related to mean annual temperature and mean moisture index, indicating that populations from cooler, wetter environments had longer, thinner roots. However, we found little support for a relationship between source environment and leaf trait PCs, root system size (PC1) or individual traits. Water availability and AMF inoculation effects on size were consistent among populations, with larger plants under AMF inoculation, and less mass allocation to leaves under lower water availability. Plantago lanceolata shows substantial population-level variation in a suite of root traits, but that variation is only partially linked to the source environmental variables studied. Despite considerable differences in source abiotic environments, geographically separated populations have retained a strong and similar capacity for phenotypic plasticity both above and below-ground.Read the free Plain Language Summary for this article on the Journal blog. La comprension de la variacion inter-poblacional en rasgos funcionales de plantas y como esto se relaciona con la adaptacion local a las condiciones ambientales esta en gran medida moldeada por rasgos aereos. Sin embargo, cabe esperar que los rasgos subterraneos vinculados a la adquisicion y conservacion de recursos varien entre poblaciones bajo diferentes condiciones ambientales. Alternativamente, los rasgos subterraneos podrian ser altamente plasticos en respuesta a las condiciones de crecimiento, como la disponibilidad de recursos del suelo y la asociacion con hongos simbiontes micorricicos arbusculares (HMA). Analizamos (i) la magnitud de la variacion entre poblaciones en rasgos aereos y subterraneos, (ii) los efectos de las condiciones de crecimiento en la variacion entre poblaciones y (iii) si la variacion entre poblaciones esta vinculada a las condiciones ambientales de origen, en una planta perenne de distribucion global, Plantago lanceolata. Utilizando semillas de 14 poblaciones de tres continentes, cultivamos plantas en un experimento de jardin comun y medimos rasgos foliares y radiculares relacionados con la adquisicion de recursos y la conservacion de agua. Incluimos dos tipos de tratamientos experimentales (disponibilidad alta o baja de agua; con y sin inoculacion de HMA), lo que nos permitio evaluar las respuestas de los rasgos a las condiciones de crecimiento. Entre los tratamientos, el porcentaje de variacion de rasgos radiculares explicado por las poblaciones y continentes fue del 9%-26%, en comparacion con el 7%-20% para variacion de rasgos foliares. A partir de Analisis de Componentes Principales (ACP, por sus siglas en ingles) tanto para rasgos radiculares como foliares, el primer eje de CP reflejaba principalmente el tamano de la planta, mientras que el segundo CP capturaba en terminos generales la asignacion de biomasa. La asignacion de biomasa radicular (CP 2) estaba relacionado con la temperatura media anual y el indice medio de humedad, indicando que las poblaciones de entornos mas frescos y humedos tenian raices mas largas y delgadas. Sin embargo, encontramos poco respaldo para una relacion entre el ambiente de origen y los CP de rasgos foliares, el tamano del sistema radicular (CP1) o los rasgos individuales. La disponibilidad de agua y los efectos de la inoculacion de HMA en el tamano de planta fueron consistentes entre poblaciones, con plantas mas grandes bajo la inoculacion de HMA y menor asignacion de biomasa a las hojas bajo una menor disponibilidad de agua. Plantago lanceolata muestra una variacion sustancial a nivel de poblacion en una serie de rasgos radiculares, pero esa variacion esta solo parcialmente vinculada a las variables ambientales de origen estudiadas. A pesar de las diferencias considerables en las condiciones abioticas de origen, las poblaciones separadas geograficamente han conservado una capacidad fuerte y similar de plasticidad fenotipica tanto aerea como subterranea. Read the free Plain Language Summary for this article on the Journal blog.image

Oxidative stress and hormonal regulation are hallmarks of a/biotic stress responses in plants. However, little is known about their linkage with whole-organismal mortality in long-lived species. Here, we examined the validity of photo-oxidative stress markers and stress-related phytohormones as predictive proxies of mortality risk in the perennial herb Plantago lanceolata. Capitalizing on its broad ecological niche, we examined photo-oxidative stress markers (Fv/Fm ratio, contents of chlorophylls, carotenoids, and tocochromanols, and the extent of lipid per oxidation) and stress-related phytohormones (ABA, salicylic acid and jasmonates contents) as proxies of mortality in three populations of sub-tropical and Mediterranean habitats: Virginia (VA, U.S.A.), Catalonia (CAT, Spain), and Queensland (QLD, Australia). Stress markers were measured together with the vital rates of survival, growth, and reproduction on a total of 279 individuals. Stress marker data were collected during the summer and death/survival was monitored after two and four months. Whole-organism mortality was similarly high in both sub-tropical non-native populations (ca. 30 % after a drought in VA and QLD), but lower in the native population (ca. 10 % in CAT). The contents of antioxidants (lutein, zeaxanthin, beta-carotene) and the de-epoxidation state of the xanthophyll cycle (DPS) were good proxies of mortality risk in VA and QLD. DPS and all carotenoid contents per unit of chlorophyll were lower four months in advance in dead than in alive plants in VA and QLD, thus suggesting reduced photoprotective capacity increased the mortality risk in non-native populations. We show that whole-organismal mortality in P. lanceolata is associated with a reduced capacity to enhance photo protection under abiotic stress conditions. The validity of various stress markers as predictive proxies of mortality risk is discussed.

Simple demographic events, the survival and reproduction of individuals, drive population dynamics. These demographic events are influenced by genetic and environmental parameters, and are the focus of many evolutionary and ecological investigations that aim to predict and understand population change. However, such a focus often neglects the stochastic events that individuals experience throughout their lives. These stochastic events also influence survival and reproduction and thereby evolutionary and ecological dynamics. Here, we illustrate the influence of such non-selective demographic variability on population dynamics using population projection models of an experimental population of Plantago lanceolata. Our analysis shows that the variability in survival and reproduction among individuals is largely due to demographic stochastic variation with only modest effects of differences in environment, genes, and their interaction. Common expectations of population growth, based on expected lifetime reproduction and generation time, can be misleading when demographic stochastic variation is large. Large demographic stochastic variation exhibited within genotypes can lower population growth and slow evolutionary adaptive dynamics. Our results accompany recent investigations that call for more focus on stochastic variation in fitness components, such as survival, reproduction, and functional traits, rather than dismissal of this variation as uninformative noise.

Genetic differentiation and phenotypic plasticity jointly shape intraspecific trait variation, but their roles differ among traits. In short-lived plants, reproductive traits may be more genetically determined due to their impact on fitness, whereas vegetative traits may show higher plasticity to buffer short-term perturbations. Combining a multi-treatment greenhouse experiment with observational field data throughout the range of a widespread short-lived herb, Plantago lanceolata, we (1) disentangled genetic and plastic responses of functional traits to a set of environmental drivers and (2) assessed how genetic differentiation and plasticity shape observational trait-environment relationships. Reproductive traits showed distinct genetic differentiation that largely determined observational patterns, but only when correcting traits for differences in biomass. Vegetative traits showed higher plasticity and opposite genetic and plastic responses, masking the genetic component underlying field-observed trait variation. Our study suggests that genetic differentiation may be inferred from observational data only for the traits most closely related to fitness.

Phenotypic plasticity can mask population genetic differentiation, reducing the predictability of trait-environment relationships. In short-lived plants, reproductive traits may be more genetically determined due to their direct impact on fitness, whereas vegetative traits may show higher plasticity to buffer short-term perturbations. Combining a multi-treatment greenhouse experiment with global field observations for the short-lived Plantago lanceolata, we 1) disentangled the genetic and plastic responses of functional traits to a set of environmental drivers and 2) assessed the utility of trait-environment relationshisps inferred from observational data for predicting genetic differentiation. Reproductive traits showed distinct genetic differentiation that was highly predictable from observational data, but only when correcting traits for differences in their (labile) biomass component. Vegetative traits showed higher plasticity and contrasting genetic and plastic responses, leading to unpredictable trait patterns. Our study suggests that genetic differentiation may be inferred from observational data only for the traits most closely related with fitness.

Age‐dependence of the demographic rates survival, fecundity and individual growth is a fundamental aspect of population biological theory. Knowledge about plant ageing can also be important for conservation and agriculture as it will improve the accuracy of population viability assessments and long‐term performance assessments in perennial crops. Recent studies show age effects on demographic rates for several plant species, yet much remains to be learned about the patterns and mechanisms of plant ageing, particularly about how age effects interact with the environment and with plant size. We collected age‐and‐size‐based demographic data, as well as individual‐based environmental data, for the perennial herb Plantago lanceolata in Denmark over three annual transitions (4 years). We combined frequent field monitoring of carefully mapped individuals with the underused technique of root histology to determine age of herbaceous plants. We used generalized linear mixed effects models to assess how age, soil properties and year influenced survival, growth and reproduction. Our results show no strong evidence of consistent age declines, rather, we found mostly positive effects of age on vital rates. For all vital rates, i.e. survival, growth, flowering and reproductive output, age effects also differed significantly among years. Additionally, we detected an interactive effect of age and size in the growth model. Size, and temporal and spatial environmental variation also affected vital rates independently of age. Synthesis . Our study shows that age‐dependence of demographic rates can depend both on individual size and environmental variation. These results suggest that a consideration of potential age‐interactions may improve the accuracy of comparative studies of ageing and population projections. Moreover, this study shows that much is still unknown about how plant ageing can be affected by the environment.

An increasing number of studies have shown that senescence, the functional decline in traits and increased risk of mortality with increasing age, occurs in organisms in wild populations, but there is a wide range of diversity in the patterns of senescence across species. The antagonistic pleiotropy and the disposable soma theories of senescence predict that there will be life‐history trade‐offs between performance at early‐ and late‐life stages. Plants show variation in senescence patterns and thus provide an opportunity to evaluate life‐history trade‐offs and senescence. Many plant species can be easily followed demographically and their environments, resources and allocation to reproduction can be manipulated, which makes them particularly good models to address these questions. We compared the results from 22 studies of plant senescence in the wild and compiled 20 examples of life‐history trade‐offs in plants. Some of the unique features of plants that may influence senescence patterns and trade‐offs in the wild are highlighted through the results. We found all three age‐specific patterns: age decline, age improvement and no change with age for plants in the wild. Most species showed an age‐dependent decline in at least one trait but, even within a species, the age‐specific patterns of traits varied. Results also showed that trade‐offs vary across environments and that plants can manipulate their resource pool through increases in photosynthesis, which will influence the manifestation of trade‐offs. We conclude that aspects of plant biology including dynamic resource pools, the impact of size, dormancy and below‐ground storage may influence both the patterns of senescence and life‐history trade‐offs. The diversity of plant life forms and life cycles provide a wealth of opportunities to experimentally study senescence in the context of life‐history trade‐offs. A free Plain Language Summary can be found within the Supporting Information of this article.

Artificial light at night (ALAN) has been shown to alter aspects of plant growth, but we are not aware of any studies that have examined whether the effects of ALAN on plants depend upon the backdrop of variation in other abiotic factors that plants encounter in field populations. We conducted a field experiment to investigate whether ALAN affects the growth and anti-herbivore defenses of common milkweed, Asclepias syriaca, and whether the effects of ALAN are influenced by plant density or soil moisture content. Artificial light at night, soil moisture, and plant density were manipulated according to a split-plot factorial design. Although increasing soil moisture by watering had no significant effects on latex exudation, attributes of plant growth generally responded positively to watering. The basal stem diameter (BSD) and height of plants were affected by ALAN × soil moisture interactions. For both of these variables, the positive effects of ALAN were greater for plants that were not watered than for plants that were. Basal stem diameter was also affected by an ALAN × plant density interaction, and the positive effect of ALAN on BSD was greater in the low-density treatment than in the high-density treatment. Our results demonstrate that the effects of ALAN on plant growth can be altered by soil moisture and plant density. Consequently, the effects of ALAN on plants in nature may not be consistent with existing frameworks that do not account for critical abiotic variables such as water availability or biotic interactions between plants such as competition.

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata. Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

Predicting ecological and evolutionary population dynamics requires understanding how genetic and environmental parameters influence variation in survival and reproduction among individuals. However such a focus often neglects the stochastic events that individuals experience throughout their lives that also influence survival and reproduction. With an illustrative example, we quantify and illustrate the influence of such non-selective demographic variability on population dynamics using size-structured matrix models of an experimental population of Plantago lanceolata . Our analysis shows that variation in survival and reproduction among individuals explained by environment, genes, and their interaction was modest compared to the stochastic variation in lifespan and reproduction. We illustrate how expectations on population growth, based on expected lifetime reproduction and generation time, can be misleading when variance in reproduction among individuals of the same genotype (full sibs) was large. Such large within genotype variance can lower population growth, fitness. Our results accompany recent investigations that call for more focus on stochastic variation in survival and reproduction, rather than dismissal of this variation as uninformative noise.

Little is known about plant age-dependent trait expression and how environmental conditions might affect ageing in the wild. This study evaluates age variation in multiple traits of a short-lived perennial herb using a manipulative field experimental design. Two different-aged cohorts were followed in a field plot for over a year to evaluate trait expression in response to a competition treatment and seasonal stress. Traits measured included size, mortality, reproduction, and physiology, including photosynthetic efficiency and chlorophyll content (SPAD). We hypothesized that the stress of competition and seasonal changes would accentuate age-dependent trait declines in older plants. The results highlight consistent age differences in plant size, mortality, and seed size with older plants being smaller, more likely to die, and producing smaller seeds. Some of the ageing declines were sensitive to environmental conditions such that it was only during certain seasons when older plants had higher mortality, lower photosynthetic efficiency, and lower chlorophyll content than young plants. Age-dependent trait expression also varied in response to competition such that age differences in size were only present in the "no competition treatment," and old individuals in the competition treatment had a higher mortality than all other age-environment combinations. Synthesis. These findings show that ageing in plants is a complex phenotype where declines in traits are uncoordinated and can be, but are not always, sensitive to environmental conditions. This study shows age-dependent maternal effects on offspring quality which, together with the decline in performance of older individuals, may have impacts on an individual's fitness and on natural population demography.

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Although invasion processes have been intensely studied, the mechanisms underlying the success of some invasive clonal species remain a mystery. Using the specific example of Carpobrotus edulis, we illustrate how invasion success can be facilitated by a unique spatio-temporal regulation of growth and senescence of plant parts.

Do all species experience the declines of old age? No. Do we currently have theories that accurately predict which species escape these declines? In PNAS, Warner et al. (1) demonstrate that the answer to this question is also “no.” Understanding the breadth and diversity of the patterns of aging across the tree of life is central to life history evolution, and recent studies demonstrate that there is considerable variation in the age trajectories of traits across species (2⇓–4). In general, the decline in function and increase in mortality that is associated with increasing age is expected, according to classic evolutionary theories, because of the decline in the strength of selection with age (5⇓–7). In other words, the alleles that predispose us to heart disease or dementia have effects primarily at late ages, after we have reproduced, thus their impact on Darwinian fitness is minimal and these deleterious traits—and many others like them—persist. In natural populations, as we look across species, a central premise of the evolutionary theories of aging is that the rate of aging in different species will depend on levels of environmentally imposed mortality (7). All living organisms are subject to a constant risk of mortality posed by accidents, predation, and disease. This environmental, or extrinsic, mortality will influence the probability that individuals will survive to a given age. The hypothesis is that species with the highest levels of environmental mortality should evolve high levels of early reproduction and rapid aging. Conversely, slower rates of aging … [↵][1]1Email: droach{at}virginia.edu. [1]: #xref-corresp-1-1

PREMISE OF THE STUDY The ecological consequences of plant competition have frequently been tested, but the evolutionary outcomes of these interactions have gone largely unexplored. The study of species invasions can make an important contribution to this field of research by allowing us to watch ecological and evolutionary processes unfold as a novel species is integrated into a plant community. We explored the ecological and evolutionary impact of an invasive jewelweed, Impatiens glandulifera, on a closely related native congener, I. capensis and asked: (1) Does the presence of the invasive jewelweed alter the fitness of native jewelweed populations? (2) Does the invasive jewelweed affect the vegetative growth of the native congener? and (3) Does the invasive jewelweed alter phenotypic selection on the vegetative traits of the native congener? METHODS We used a greenhouse competition experiment, an invasive species removal field experiment, and a survey of natural populations. KEY RESULTS We show that when the invasive jewelweed is present, phenotypic selection favors native jewelweed individuals investing less in rapid upward growth and more in branching and fruiting potential through the production of nodes. CONCLUSIONS This research demonstrates that invasive plants have the potential to greatly alter natural selection on native competitors. Studies investigating altered selection in invaded communities can reveal the potential evolutionary impact of invasive competitors, while deepening our understanding of the more general role of competition in driving plant evolution and permitting species coexistence.

PREMISE OF THE STUDY:Mammalian herbivores, particularly white-tailed deer, can have a major impact on plant abundance and distribution. However, plants can tolerate herbivory by increasing seed production or seed quality. We used the monocarpic perennial Prenanthes roanensis to examine tolerance to mammalian herbivory through seed quality and modeled the effects of tolerance on population growth rate.METHODS:We examined seed quality (proportion of viable seeds, seed mass, germination, and seedling size) on damaged and undamaged plants to determine the extent to which plants tolerate herbivory. We then varied seed quality parameters over a range of values in population models to compare population growth rates under "no-tolerance" conditions (herbivory, but no tolerance) to those under "tolerance" conditions.KEY RESULTS:In most populations, plants damaged by herbivores had a greater proportion of viable seeds per plant or a greater probability of seed germination. Incorporating observed tolerance into population models did not significantly increase population growth rate. However, at low germination rates, increased germination of seeds from damaged plants has the potential to significantly increase population growth rate.CONCLUSIONS:Damaged plants can compensate for loss of reproductive heads by increasing seed viability and germination rates in the remaining seeds. This study is one of the first to demonstrate that tolerance through seed quality has the potential to affect population growth rate. Our results suggest that incorporating tolerance into population models may help elucidate mechanisms by which plant populations persist despite herbivory.

UNLABELLED:•PREMISE OF STUDY:Recent studies suggest that invasive plants compete reproductively with native plants by reducing the quantity or quality of pollinator visits. Although these studies have revealed ecological consequences of pollinator-mediated competition between invasive and native plants, the evolutionary outcomes of these interactions remain largely unexplored.•METHODS:We studied the ecological and evolutionary impact of pollinator-mediated competition with an invasive jewelweed, Impatiens glandulifera, on a co-occurring native congener, I. capensis. Using a pollinator choice experiment, a hand pollination experiment, and a selection analysis, we addressed the following questions: (1) Do native pollinators show preference for the invasive or native jewelweed, and do they move between the two species? (2) Does invasive jewelweed pollen inhibit seed production in the native plant? (3) Does the invasive jewelweed alter phenotypic selection on the native plant's floral traits?•KEY RESULTS:The pollinator choice experiment showed that pollinators strongly preferred the invasive jewelweed. The hand pollination experiment demonstrated that invasive pollen inhibited seed production in the native plant. The selection analysis showed that the presence of the invasive jewelweed altered phenotypic selection on corolla height in the native plant.•CONCLUSIONS:Invasive plants have the potential to alter phenotypic selection on floral traits in native plant populations. If native plants can evolve in response to this altered selection pressure, the evolution of floral traits may play an important role in permitting long-term coexistence of native and invasive plants.