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Allelopathy is the stimulatory or inhibitory effect of one plant on another plant by release of phytochemicals. It can affect the competitive interactions between plants, but the strength of the effect may depend on the tissue of the donor plant and the phylogenetic relatedness of the interacting species. Here, we examined the allelopathic effects of the invasive garden lupine Lupinus polyphyllus Lindl. (Fabaceae) on six native herbs from three families (Asteraceae, Caryophyllaceae, Fabaceae). We exposed the test species to aqueous leachates prepared from root or shoot tissue of L. polyphyllus and measured germination rate and germination time. Both leachates inhibited germination in all species (13%–84%), but shoot leachate was more allelopathic than root leachate in case of Fabaceae and Caryophyllaceae. Plants from closely related Fabaceae were least affected by L. polyphyllus leachates in terms of germination rate, but leachates delayed their germination. These results demonstrate that the invasive L. polyphyllus can inhibit the germination of co-occurring native species and suggest that allelopathy likely contributes to its invasion success. Our results have implications for management of invasive L. polyphyllus populations, emphasising the importance of the removal of mown plant material to diminish inhibitory allelopathic effects on local plants.

Intraspecific variation in growth and defence among plant populations can be driven by differences in (a)biotic conditions, such as herbivory and resources. Introduction of species to novel environments affects simultaneously herbivory encountered by a plant and resource availability both directly and via altered competitive environment. Here, we address the question of how growth (leaf mass per area (LMA), plant size) and resistance traits (leaf alkaloids, leaf trichomes, resistance to a generalist snail) vary and covary between native and introduced populations of the garden lupine, Lupinus polyphyllus. We focused specifically on evolved differences among populations by measuring traits from plants grown from seed in a common environment. Plants from the introduced populations were more resistant against the generalist snail, Arianta arbustorum, and they had more leaf trichomes and higher LMA than plants from the native populations. The composition of alkaloids differed between native and introduced populations, with the native populations having more diversity in alkaloids among them. Resistance was positively associated with plant size and LMA across all populations. Other trait associations differed between native and introduced areas, implying that certain trade-offs may be fundamentally different between native and introduced populations. Our results suggest that, for the introduced populations, the loss of native herbivores and the alterations in resource availability have led to a lower diversity in leaf alkaloids among populations and may facilitate the evolution of novel trait optima without compensatory trade-offs. Such phytochemical similarity among introduced populations provides novel insights into mechanisms promoting successful plant invasions.

In order to manage invasive plant species efficiently, it is necessary to have a thorough understanding of different strategies of population control, including the underlying mechanisms of action and the consequences for target populations. Here, I explored the effectiveness of biomass removal as a method of control for the invasive perennial herb Lupinus polyphyllus. More specifically, using seed material from 11 populations, I assessed among-population variation (if any) in plant compensatory growth as a response to annual biomass removal under standardised growing conditions over two consecutive years, and quantified the demographic effects of a single biomass-removal event. In all study populations, annual biomass removal reduced plant size, flowering probability, and shoot and root biomass. Biomass removal also reduced plant survival and the number of flowering shoots, but these effects were pronounced at certain time points only. A population-level demographic analysis revealed that a single biomass-removal event considerably decreased the long-term population growth rate (λ); this decline in λ was due to a reduction in plant fecundity followed by survival and growth. These findings suggest that annual mowing has the potential to curb invasions of L. polyphyllus because plants are not able to fully compensate for drastic biomass loss.

The extrinsic determinants hypothesis emphasizes the essential role of environmental heterogeneity in species' colonization. Consequently, high resident species diversity can increase community susceptibility to colonizations because good habitats may support more species that are functionally similar to colonizers. On the other hand, colonization success is also likely to depend on species traits. We tested the relative importance of environmental characteristics and species traits in determining colonization success using census data of 587 vascular plant species collected about 70 yr apart from 471 islands in the archipelago of SW Finland. More specifically, we explored potential new colonization as a function of island properties (e.g. location, area, habitat diversity, number of resident species per unit area), species traits (e.g. plant height, life-form, dispersal vector, Ellenberg indicator values, association with human impact), and species' historical distributions (number of inhabited islands, nearest occurrence). Island properties and species' historical distributions were more effective than plant traits in explaining colonization outcomes. Contrary to the extrinsic determinants hypothesis, colonization success was neither associated with resident species diversity nor habitat diversity per se, although colonization was lowest on sparsely vegetated islands. Our findings lead us to propose that while plant traits related to dispersal and establishment may enhance colonization, predictions of plant colonizations primarily require understanding of habitat properties and species' historical distributions.

The ecological impacts of invasive species may change or accumulate with time since local invasion, potentially inducing further changes in communities and the abiotic environment. Yet, time since invasion is rarely considered when investigating the ecological impacts of invasive non-native species. To examine the effect of time since invasion on the ecological impacts of Lupinus polyphyllus, a perennial nitrogen-fixing herb, we surveyed vascular plant communities in the presence and absence of L. polyphyllus in young, intermediate, and old semi-natural grassland sites (ca. 5, 10, 15 years representing both time since lupine invasion and plant community age). We analyzed vascular plant community composition, vascular plant species richness, and the cover of various ecological plant groups and L. polyphyllus. In contrast to our hypotheses, we found no change in the mean cover of L. polyphyllus (about 35%) with time since local invasion, and an ordination did not suggest marked changes in plant community composition. L. polyphyllus was associated with lower species richness in invaded plant communities but this effect did not change with time since invasion. Invaded plant communities were also associated with lower occurrence of generalist, oligotrophic (low-nutrient-adapted) and copiotrophic (nutrient-demanding) species but no temporal dynamics were detected. We conclude that even the intermediate cover of L. polyphyllus can reduce plant species richness, but the ecological impact caused by this invader might not dramatically change or accumulate with time since invasion.

Funding Information: The authors acknowledge the French National Research Agency ( ANR-14-CE02-0021 ) and the BNP-Paribas Foundation Climate Initiative for funding the InvaCost project that allowed the construction of the InvaCost database, as well as the Norwegian Research Council's MARINFORSK project PICO ( 302114 ). The present work was conducted following a workshop funded by the AXA Research Fund Chair of Invasion Biology and is part of the AlienScenario project funded by BiodivERsA and Belmont-Forum call 2018 on biodiversity scenarios. LV received funding from the Faculty of Agriculture and Forestry of the University of Helsinki . RC is funded by a fellowship from the Leverhulme Trust ( ECF-2021-001 ). EA's contract comes from the AXA Research Fund Chair of Invasion Biology of University Paris Saclay. CD is funded by the BiodivERsA -Belmont Forum Project “Alien Scenarios” ( BMBF/PT DLR 01LC1807C ). Publisher Copyright: © 2022 A collective understanding of economic impacts and in particular of monetary costs of biological invasions is lacking for the Nordic region. This paper synthesizes findings from the literature on costs of invasions in the Nordic countries together with expert elicitation. The analysis of cost data has been made possible through the InvaCost database, a globally open repository of monetary costs that allows for the use of temporal, spatial, and taxonomic descriptors facilitating a better understanding of how costs are distributed. The total reported costs of invasive species across the Nordic countries were estimated at $8.35 billion (in 2017 US$ values) with damage costs significantly outweighing management costs. Norway incurred the highest costs ($3.23 billion), followed by Denmark ($2.20 billion), Sweden ($1.45 billion), Finland ($1.11 billion) and Iceland ($25.45 million). Costs from invasions in the Nordics appear to be largely underestimated. We conclude by highlighting such knowledge gaps, including gaps in policies and regulation stemming from expert judgment as well as avenues for an improved understanding of invasion costs and needs for future research.

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.

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.

Intermittent breeding may be adaptive for long-lived species subjected to large accessory reproductive costs, but it may also reflect reduced adaptation to the environment, reducing population growth. Nevertheless, environmental influences on breeding propensity, particularly that of predation risk, remain poorly understood and difficult to study, because non-breeders are typically not identified. Female eiders Somateria mollissima from the Baltic Sea provide an excellent testbed, because nesting females have been exposed to intensifying predation and growing male bias that may increase female harassment. We based our study on long-term data (14 years) on females captured and marked at the nest, and females individually identified at sea irrespective of capture status. We hypothesized that breeding propensity decreases with increasing predation risk and male bias, and increases with breeder age. Consistent with our hypotheses, females nesting on islands with higher nest predation risk were more likely to skip breeding, and breeding probability increased with age. In contrast, the steep temporal decline in breeding propensity could not be reliably attributed to annual adult sex ratio or to the abundance of white-tailed sea eagles (Haliaeetus albicilla), the main predator on females, at the nearby Hanko Bird Observatory. Breeding probability showed significant consistent individual variation. Our results demonstrate that spatiotemporal variation in predation risk affects the decision to breed and high incidence of non-breeding was associated with low fledging success. The increased frequency of intermittent breeding in this declining population should be explicitly considered in demographic models, and emphasis placed on understanding the preconditions for successful reproduction.

Invasive plant species generally reduce the abundance and diversity of local plant species, which may translate into alterations at higher tropic levels, such as arthropods. Due to the diverse functional roles of arthropods in the ecosystems, it is critical to understand how arthropod communities are affected by plant invasions. Here, we investigated the impact of the invasive ornamental herb Lupinus polyphyllus (Lindl.) on arthropod communities during its main flowering period in southwestern Finland over two years. The total number of arthropods was about 46% smaller at the invaded sites than at the uninvaded sites in both study years, and this difference was mainly due to a lower abundance of beetles, Diptera, Lepidoptera, and ants. However, the number of bumblebees (particularly Bombus lucorum) was about twice as high at invaded sites compared with uninvaded sites, even though bumblebee richness did not differ between sites. There was no statistically significant difference between invaded and uninvaded sites in the abundances of the other arthropod groups considered (Hymenoptera (excluding bumblebees and ants), Hemiptera, and Arachnida). In addition, L. polyphyllus affected the relative abundance of four arthropod groups, with the order Lepidoptera being less common at invaded sites than at uninvaded sites, while the opposite was true for bumblebees, Hemiptera, and Arachnida. Overall, these results demonstrate that the negative impact of L. polyphyllus on biodiversity goes beyond its own trophic level, suggesting that this species has the potential to alter the abundance of different arthropod groups and, consequently, the structure of arthropod communities at a large scale.

Demographic models are widely used to produce management recommendations for different species. For invasive plants, current management recommendations to control local population growth are often based on data from a limited number of populations per species, and the assumption of stable population structure (asymptotic dynamics). However, spatial variation in population dynamics and deviation from a stable structure may affect these recommendations, calling into question their generality across populations of an invasive species. Here, I focused on intraspecific variation in population dynamics and investigated management recommendations generated by demographic models across 37 populations of a short-lived, invasive perennial herb (Lupinus polyphyllus). Models that relied on the proportional perturbations of vital rates (asymptotic elasticities) indicated an essential role for plant survival in long-term population dynamics. The rank order of elasticities for different vital rates (survival, growth, retrogression, fecundity) varied little among the 37 study populations regardless of population status (increasing or declining asymptotically). Summed elasticities for fecundity increased, while summed elasticities for survival decreased with increasing long-term population growth rate. Transient dynamics differed from asymptotic dynamics, but were qualitatively similar among populations, that is, depending on the initial size structure, populations tended to either increase or decline in density more rapidly than predicted by asymptotic growth rate. These findings indicate that although populations are likely to exhibit transient dynamics, management recommendations based on asymptotic elasticities for vital rates might be to some extent generalised across established populations of a given short-lived invasive plant species.

Significance We found that long-distance dispersal and repeated introductions by humans have shaped adaptive potential in a globally distributed invasive species. Some plant species, therefore, do not need strong demographic changes to overcome environmental constraints that exist in the native range; simply mixing genetic stock from multiple populations can provide an adaptive advantage. This work highlights the value of preventing future introduction events for problematic invasive species, even if the species already exists in an area., 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.

In boreal herb-rich forests, the dominance of Norway spruce (Picea abies) decreases light availability for understory species, many of which depend on canopy gaps for reproduction. Here, we explored the response of a rare clonal understory herb, the lady’s slipper orchid (Cypripedium calceolus), to tree removal. We used demographic data spanning 16 years from ten unharvested control sites and ten harvest sites which were divided into three treatments with differing harvest intensity: (1) dense spruce forests, where half of the total tree basal area (TBA) was cut, (2) sparse spruce forests, where one-fourth of the spruce TBA was cut and (3) sparse broadleaf forests, where one-fourth of the total TBA was cut. The effects of harvesting on different demographic rates (ramet density, reproduction, survival, and dormancy) were studied with generalized linear mixed models with harvest intensity, time since harvest and the starting level of the response variable as explanatory variables. Tree removal sites had 2.2 times higher orchid ramet density, 2.4 times higher odds of survival, and 2.1–3.1 times higher odds of flowering and fruiting than the control sites, but these effects were not seen at all treatment levels at all times. Tree removal had no effect on dormancy or seedling or flower density. Orchid flowering and fruiting probabilities increased only at the most intensively harvested sites (both spruce forest sites, and dense spruce forest with 50% TBA removal, respectively), while survival and ramet density increased at the moderately harvested broadleaf forest sites. The effects on flowering and fruiting probabilities and survival disappeared quickly (after three years) when the canopy gaps closed, whereas ramet density responded only with a lag of over three years and was maintained to the end of the study. Our results thus demonstrate that for the lady’s slipper orchid, selective tree harvest might be a suitable management method that increases population size at the ramet level.

The establishment success of an invasive species in its introduced range may be promoted by local adaptation and (or) phenotypic plasticity. Here, I tested for local adapation in the seedling establishment of the perennial herb Lupinus polyphyllus (Lindl.) in Finland, where the species has been invasive since the late 1800s. Reciprocal seed-sowing experiments conducted in multiple populations revealed that seedling establishment increased with the increasing genetic variation of the source population. However, there was no evidence for local adaptation when assessed in terms of seedling establishment; that is, establishment was not higher in the home population than in more distant populations located either in the same or in a different geographic region. Overall, these results suggest that the seedling establishment of L. polyphyllus is robust to changes in environmental conditions, and that genetic variation together with phenotypic plasticity — rather than local adaptation — may have contributed to its invasion success in this part of its introduced range.

Analysis of the amount and distribution of genetic variation can yield information about the number of introductions and history of an invasive species, which may be relevant for understanding the evolutionary potential and spread of invaders, as well as for creating best management practices for curbing them. We explored the genetic patterns and invasion history of the perennial, ornamental herb Lupinus polyphyllus Lindl. in Finland, where the species has spread rapidly during the past hundred years. Using 13 microsatellite loci, we determined the genetic variation of L. polyphyllus in 51 sites across a latitudinal gradient that reflected the invasion history of the species in this country. We found that the sampled populations were significantly genetically differentiated among sites, as indicated by the global F′ST value (0.19) and AMOVA results (16.7 % of total genetic variation occurred among sites), and this differentiation slightly increased with increasing geographic distance (r = 0.11, P = 0.006), indicating limited gene flow. Genetic variation of L. polyphyllus, measured as the average number of alleles per site or the average number of unshared alleles between pairs of individuals per site, was not associated with latitude. Our results suggest that the invasive populations of L. polyphyllus are genetically differentiated in Finland, but show no evidence of a loss of genetic variation during the invasion process. Overall, this pattern reflects human-mediated dispersal with multiple introductions from different sources rather than the natural spread of L. polyphyllus from a single or few sources in Finland.

The application of uniform conservation schemes often fails to account for small-scale spatial variation in the drivers of population decline. Demographic comparisons of imperilled populations across locations are therefore crucial for successful conservation, but progress is hampered by lack of long-term data from more than a single population. The recent large-scale decline of eider ducks (Somateria mollissima) in the Baltic Sea is ideal for determining to what extent mechanisms underlying population decline can be extrapolated over larger areas. We utilized stochastic demographic methods incorporating both environmental and sampling variation to assess small-scale spatial and temporal variation in the population dynamics of eiders at Soderskar (eastern range-margin) and Tvarminne (core breeding area), situated 130 km apart. The stochastic growth rate models accurately predicted the observed differences in the rate of decline between sites and time periods. At Soderskar, established breeder survival had by far the greatest elasticity, whereas elasticity was more evenly distributed among vital rates at Tvarminne. Although the study sites showed the single largest difference in fecundity, stochastic life table response experiment analyses revealed that reduced adult female survival at Tvarminne mainly determined the observed difference in growth rates between sites. In contrast, reduced fecundity primarily differentiated the past population increase from the present population decline at Soderskar. Our results demonstrate that different mechanisms may be associated with population decline across adjacent geographic locations, and indicate that dispersal of first-time breeders may be important for population dynamics. Safeguarding adult female survival and/or fecundity should be prioritized in management efforts.

The success of plant invasions may be limited by the availability of propagules and/or of suitable microsites, with microsite availability being affected by, for example, disturbance and interspecific competition. A mechanistic understanding of the contributions of propagule pressure and microsite limitation to plant invasions is therefore required to minimise future invasions. Here, we investigated the relative roles of propagule pressure, the availability of microsites, and their interaction on the establishment of an invasive herb, Lupinus polyphyllus, in two geographic regions representing different climate and growth conditions in Finland (a more productive southern region and a harsher central region). We carried out a field experiment in 14 L. polyphyllus populations, in which we manipulated both propagule pressure and disturbance. In a complementary greenhouse experiment, we manipulated propagule pressure and interspecific competition. Seedling establishment of L. polyphyllus was higher in the more productive southern region than in the harsher central region. The number of L. polyphyllus seedlings increased with increasing propagule pressure regardless of disturbance or interspecific competition. However, the number of L. polyphyllus seedlings per sown seed (relative establishment) tended to decrease with increasing propagule pressure, indicating that the positive effect of propagule pressure on early invasion is partially counteracted by density-dependent mortality at high seed densities. Our results highlight the dominant role of propagule pressure over disturbance and interspecific competition in the establishment of L. polyphyllus, suggesting that the early stage of invasion is limited by the availability of propagules rather than the availability of suitable microsites.

Exotic plant species can reduce the abundance and biodiversity of native plant species. However, the underlying demographic mechanisms for the population declines of native plants through individual fitness components are unclear. To assess the impact of exotic plant species on the fitness components of native plants (establishment, growth, biomass, reproduction, and survival), we used a global meta-analysis of 75 articles representing 232 data points. We examined how the characteristics of native and exotic species, environmental conditions, and methodological factors modify the magnitude and direction of impacts on native fitness. We found that the impact of exotic plant species on native plants varied across fitness components. Exotic plant species generally reduced the biomass, reproduction, and survival of native plants, while they had no impact on the establishment and growth of natives. Most studies included in the data set were conducted in temperate grasslands and forests focusing on a few life-forms of exotic species, making it difficult to draw more specific conclusions of the impacts of exotic plant species on native plants. Overall, our results indicate that exotic plants may limit the population growth of co-occurring native plant species primarily by reducing the biomass, reproduction, and survival of individual plants, most likely through resource competition. To enable generalisations to be made, we suggest that the impacts of exotic plant species on native plants should be assessed based on multiple fitness components, preferably across different habitat types. Moreover, we encourage impact studies to be carried out beyond temperate regions using a wider range of exotic plant species.

Climate-induced phenological shifts may have serious consequences for organisms and populations, but it is challenging to link such shifts to demographic change. Here, we present an overview of current methodological approaches for studying the demographic consequences of phenological shifts, based on a literature survey of 62 studies on diverse taxa. The majority of these studies (66%) were conducted using an approach that linked phenological shifts to demography through the measurement of vital rates (survival, growth, and fecundity). About 18% of the studies used a population-based approach that linked the phenological shifts to changes in population size, and 16% took a combined approach by considering changes in both vital rates and population size. Birds and mammals were overrepresented in studies of the demographic consequences of phenological shifts, compared to their occurrence in nature, while insects were heavily underrepresented. The effects of phenological shifts often varied according to the particular vital rate under consideration, in many cases even within a single species. In the few studies that examined changes in phenology together with both vital rate and population data, the changes in vital rates did not always predict changes in population size. To better understand the ultimate causes of population-level effects we argue that further study is needed on density-dependent aspects of population dynamics and on the sensitivity of population dynamics to perturbations in vital rates. We encourage re searchers to observe multiple vital rates throughout organisms' life-cycles in order to enable more meaningful examination of the consequences of phenological shifts for population dynamics. (Less)

Plant populations may have evolved different demographic strategies to cope with temporal environmental variation. According to the demographic buffering hypothesis, vital rates that are most critical to population persistence are buffered against environmental variation and vary little over time, whereas the demographic lability hypothesis suggests that populations may track and benefit from environmental variation. While the hypotheses of demographic strategies have been widely tested in plant and animal species, they have not been explicitly examined for invasive plants, or in relation to different modelling methods (deterministic vs. stochastic). Here, we tested the demographic buffering and lability hypotheses for 23 populations of eight invasive plant species in relation to life form (woody vs. herbaceous species) and population growth rate using deterministic and stochastic modelling methods, and absolute and relative scales. We found that conclusions of demographic strategies depended on scale, with an absolute scale resulting in stronger negative correlations between the variability and importance of vital rates (i.e., buffering) than a relative scale. Conclusions of demographic strategies were also affected by life form that interacted with method. The populations of woody invaders exhibited buffering regardless of the method used, while for the populations of herbaceous species, deterministic calculations suggested buffering and stochastic calculations suggested lability. Overall, our findings emphasise the role of life form and methodological issues that need to be considered when exploring demographic strategies in fluctuating environments.

Disturbances, such as fire and grazing, are often claimed to facilitate plant species richness and plant invasions in particular, although empirical evidence is contradictory. We conducted a meta-analysis to synthesize the literature on how non-native plant species are affected by disturbances. We explored whether the observed impact of disturbance on non-native plant communities is related to its type and frequency, to habitat type, study approach (observational or experimental), and to the temporal and spatial scales of the study. To put the results in a broader context, we also conducted a set of parallel analyses on a data set involving native plant species. The diversity and abundance of non-native plant species were significantly higher at disturbed sites than at undisturbed sites, while the diversity and abundance of native plant species did not differ between the two types of sites. The effect of disturbance on non-native plant species depended on the measure used to evaluate the impact (species diversity or abundance) and on disturbance type, with grazing and anthropogenic disturbances leading to higher diversity and abundance of non-native plant species than other disturbance types examined. The impact of disturbance on non-natives was also associated with study approach, habitat type and temporal scale, but these factors covaried with disturbance type, complicating the interpretation of the results. Overall, our results indicate that disturbance has a positive impact particularly on non-native plant species (at least when they are already present in the community), and that the strength of this impact depends primarily on the disturbance type. Synthesis Empirical evidence of the effect of disturbances on plant species richness is contradictory. Here we use a meta-analysis to synthesize the published literature on how different types of disturbances influence the diversity and abundance of plant species, focusing in particular on non-native plants. Our study supports the hypothesis that disturbances generally facilitate the diversity and abundance of non-native plant species, although the strength of this facilitation depends primarily on the disturbance type.

Temperature and precipitation determine the conditions where plant species can occur. Despite their significance, to date, surprisingly few demographic field studies have considered the effects of abiotic drivers. This is problematic because anticipating the effect of global climate change on plant population viability requires understanding how weather variables affect population dynamics. One possible reason for omitting the effect of weather variables in demographic studies is the difficulty in detecting tight associations between vital rates and environmental drivers. In this paper, we applied Functional Linear Models (FLMs) to long-term demographic data of the perennial wildflower, Astragalus scaphoides, and explored sensitivity of the results to reduced amounts of data. We compared models of the effect of average temperature, total precipitation, or an integrated measure of drought intensity (standardized precipitation evapotranspiration index, SPEI), on plant vital rates. We found that transitions to flowering and recruitment in year t were highest if winter/spring of year t was wet (positive effect of SPEI). Counterintuitively, if the preceding spring of year t - 1 was wet, flowering probabilities were decreased (negative effect of SPEI). Survival of vegetative plants from t - 1 to t was also negatively affected by wet weather in the spring of year t - 1 and, for large plants, even wet weather in the spring of t - 2 had a negative effect. We assessed the integrated effect of all vital rates on life history performance by fitting FLMs to the asymptotic growth rate, log(λt). Log(λt) was highest if dry conditions in year t - 1 were followed by wet conditions in the year t. Overall, the positive effects of wet years exceeded their negative effects, suggesting that increasing frequency of drought conditions would reduce population viability of A. scaphoides. The drought signal weakened when reducing the number of monitoring years. Substituting space for time did not recover the weather signal, probably because the weather variables varied little between sites. We detected the SPEI signal when the analysis included data from two sites monitored over 20 yr (2 × 20 observations), but not when analyzing data from four sites monitored over 10 yr (4 × 10 observations).

Biomass removal by herbivores usually incurs a fitness cost for the attacked plants, with the total cost per unit lost tissue depending on the value of the removed tissue (i.e., how costly it is to be replaced by regrowth). Optimal defense theory, first outlined in the 1960s and 1970s, predicted that these fitness costs result in an arms race between plants and herbivores, in which selection favors resistance strategies that either repel herbivores through morphological and chemical resistance traits in order to reduce their consumption, or result in enemy escape through rapid growth or by timing the growth or flowering to the periods when herbivores are absent. Such resistance against herbivores would most likely evolve when herbivores are abundant, cause extensive damage, and consume valuable plant tissues. The purpose of this Special Feature is to celebrate the 30th anniversary of the phenomenon of overcompensation, specifically, where the finding has brought us and where it is leading us 30 yr later. We first provide a short overview of how the phenomenon of overcompensation has led to broader studies on plant tolerance to herbivory, summarize key findings, and then discuss some promising new directions in light of six featured research papers.

Summary Climate change is predicted to affect range expansion of harmful C4 weeds into the boreal region, given that they are able to successfully colonise both C3 and C4 crops. We studied the impact of a 3°C elevation in temperature on the establishment and maintenance of populations of two annual C4 weeds (Amaranthus retroflexus and Echinochloa crus-galli) with and without a competing C3 (barley) or C4 (maize) crop. Data obtained from field and glasshouse experiments were modelled using a periodic matrix population model. Competition of a weed with a crop appeared to be a more important factor for limiting the maintenance of weed populations than elevation in temperature, as neither of the weed species was able to maintain populations in competition with crops. Even an increase in the frequency of warm years did not result in viable weed populations establishing. However, A. retroflexus was able to form persistent populations in competition with maize when released from competition every fifth year. Simulations parameterised from glasshouse data predicted that both weed species would persist without competition in the current climate, whereas simulations parameterised from field data suggested only A. retroflexus to be able to persist. These results demonstrate that competition affects the range expansion of arable weed species more than elevation in temperature, necessitating the inclusion of crop–weed interactions in models of range shifts as a consequence of climate change.

Intraspecific variation in seed size may result from life-history constraints or environmental conditions experienced. This variation in seed size is likely to affect the early stage of invasion as seed size may contribute to the success or failure of population establishment. However, only a few studies have examined seed size variability and its causes and consequences for invaders so far. Using the invasive herb Lupinus polyphyllus, we estimated seed mass variation within and among 39 populations from two different geographic regions in a part of the invaded range. We empirically and experimentally evaluated the effect of seed number and environmental conditions (e.g. geographic region, habitat type, intraspecific competition) on seed mass, emergence and seedling performance. Seed mass varied threefold, being largest among individual plants within populations and smallest among populations. Variation in seed mass was neither related to seed number nor the environmental conditions examined, but led to differences in offspring performance, with emergence and seedling size increasing with seed mass. Larger L. polyphyllus seeds were better establishers than smaller seeds regardless of environmental conditions, indicating that the success of L. polyphyllus invasions is likely to depend positively on seed mass. Our results suggest that some plant species such as the invasive L. polyphyllus may not show an adaptive response in seed mass to resources or environmental conditions, which may partly explain their ability to colonise a range of different habitats.

Senescence is characterized by a decline in survival, fecundity and reproductive value with age among adult individuals. Simple age-dependent life cycles progress forward through developmental stages, with each successive stage being characterized by age-specific vital rates. In contrast, size- or stage-based life cycles for perennial plants are more complex and often include stasis and retrogression to previous vegetative or reproductive life stages, indicating possible slowing or even reversing the developmental progress. Many plants remain in nonemergent, below-ground stages during the growing season (prolonged dormancy), which may affect the process of senescence. Stasis in the dormant stage implies that senescence is interrupted while plants are below-ground. We explored the underlying assumptions of size- or stage-based life cycle graphs and developed four different demographic models for how prolonged dormancy may mediate the relationship between age and vital rates. We then tested these models using more than 20years of demographic data on 2 perennial herbs, Astragalus scaphoides and Silene spaldingii. Results from model fitting suggest that prolonged dormancy interacts with the age dependence of vital rates. The model using true biological age (time since germination) of emergent and dormant plants to estimate vital rates was never the best model for our data. For both species, the model assuming that dormancy resets plants to the same postdormant state experienced earlier in life independent of their predormant age resulted in the best fit, though not for every vital rate. Older Astragalus plants had declining annual survival probabilities and reproductive value, suggesting senescence. Silene showed the opposite pattern for reproductive value that increased with age, indicating negative senescence. Synthesis. Using long-term demographic data from two perennial herbs, this study shows mixed evidence for senescence in perennial plants. Our results indicate that prolonged dormancy interacts with the age dependence of vital rates and may sometimes retard the process of senescence. (Less)

Selection is assumed to eliminate life-histories showing high variability in vital rates that have the greatest influence on population performance. Therefore, an inverse variability-importance relationship of vital rates is believed to be a universal pattern for diverse life-histories. We tested for such a relationship using multi-year demographic data on a large number of populations of two perennial plant species. Applying different approaches, we first examined the overall variability-importance relationship for the average main vital rates (survival, growth, retrogression, fecundity) per species, and then separately for each population. We found an overall inverse relationship between temporal variation and importance of the average main vital rates for both study species, but these negative species-level correlations were mainly caused by different scales of the examined vital rates. When variability-importance relationships were examined across individual demographic transitions within populations, the abundance of positive and negative correlations depended largely on the method used, and positive correlations were more common after correcting vital rates for sampling variation than when using uncorrected vital rates. Our results cast doubt on the generality of the demographic buffering hypothesis, suggesting that the inverse variability-importance relationship may not be a universal pattern when vital rates are examined for multiple populations of the same plant species.

The effects of plant invasions on plant communities are often assessed at a few sites or in a particular type of habitat, while studies in different habitat types are scarce. We investigated plant communities in the presence and absence of the invasive ornamental herb, Lupinus polyphyllus, in four habitat types: meadow, forest, road verge and wasteland, in two geographic regions by comparing vascular plant species richness, vegetation structure based on species traits, community composition and the reproductive success of native plant species at invaded and non-invaded locations. The invader was associated with declines in the number of vascular plant species in all habitat types but was unassociated with differences in plant community composition in terms of species identity or species relative cover. However, sites with large lupin invasions (≥1,000 m2) contained fewer vascular plant species, a larger proportion of clonal species and more lighter-seeded species than sites with small invasions. The reproductive output of native plants varied across habitats from declines to increases in the presence of L. polyphyllus, and depended on species status (meadow, non-meadow species) rather than species identity, with meadow species generally showing an increase in the reproductive output in the presence of the invader. Overall, our results demonstrate that lupin invasions are associated with declines in local plant species richness across habitats. Although we did not detect systematic differences in species composition between invaded and non-invaded locations, species with particular traits may still be more persistent in invaded plant communities than others.

Explaining variation in population growth rates is fundamental to predicting population dynamics and population responses to environmental change. In this study, we used matrix population models, which link birth, growth and survival to population growth rate, to examine how and why population growth rates vary within and among 50 terrestrial plant species. Population growth rates were more similar within species than among species; with phylogeny having a minimal influence on among-species variation. Most population growth rates decreased over the observation period and were negatively autocorrelated between years; that is, higher than average population growth rates tended to be followed by lower than average population growth rates. Population growth rates varied more through time than space; this temporal variation was due mostly to variation in post-seedling survival and for a subset of species was partly explained by response to environmental factors, such as fire and herbivory. Stochastic population growth rates departed from mean matrix population growth rate for temporally autocorrelated environments. Our findings indicate that demographic data and models of closely related plant species cannot necessarily be used to make recommendations for conservation or control, and that post-seedling survival and the sequence of environmental conditions are critical for determining plant population growth rate.

1. Multiple modelling techniques are currently used to describe population dynamics of established invasions, where intraspecific competition is likely to reduce survival, growth and/or fecundity, suppressing population growth rate. To date, it remains unanswered whether these modelling techniques produce similar management recommendations for density-dependent weed populations and how to model density dependence to better inform management. 2. We constructed demographic models for a short-lived weed based on data on multiple manipulated densities in a glasshouse and data from the literature using three germination strategies. We compared management recommendations produced by two main modelling techniques for density-dependent weed populations and examined whether periodic matrix population models constructed from different densities without characterization of density-dependent processes (implicit models) produce management recommendations similar to that of the same models with density dependence explicitly characterized and simulated (explicit models). The use of a periodic matrix population model enabled us to target simulated management on either vital rates or entire life stages, and to examine the role of a weed's germination strategy on model outcomes.

Summary 1. A primary goal of evolutionary ecology is to understand factors selecting for the diversity of life histories. Life-history components, such as time-to-reproduction, adult survivorship and fecundity, might differ among species because of variation in direct and indirect benefits of these life histories in different environments or might have lower-than-expected variability because of phylogenetic constraints. Here, we present a phylogenetic examination of demography and life histories using a data base of 204 terrestrial plant species. 2. Overall, statistical models without phylogeny were preferred to models with phylogeny for vital rates and elasticities, suggesting that they lacked phylogenetic signal and are evolutionarily labile. However, the effect of phylogeny was significant in models including sensitivities, suggesting that sensitivities exhibit greater phylogenetic signal than vital rates or elasticities. 3. Species with a greater age at first reproduction had lower fecundity, consistent with a cost of delayed reproduction, but only in some habitats (e.g. grassland). We found no evidence for an indirect benefit of delayed reproduction via a decrease in variation in fecundity with age to first reproduction. 4. The greater sensitivity and lower variation in survival than in fecundity was consistent with buffering of more important vital rates, as others have also found. This suggests that studies of life-history evolution should include survival, rather than only fecundity, for the majority of species. 5. Synthesis. Demographic matrix models can provide informative tests of life-history theory because of their shared construction and outputs and their widespread use among plant ecologists. Our comparative analysis suggested that there is a cost of delayed reproduction and that more important vital rates exhibit lower variability. The absolute importance of vital rates to population growth rates (sensitivities) exhibited phylogenetic signal, suggesting that a thorough understanding of life-history evolution might require an understanding of the importance of vital rates, not just their means, and the role of phylogenetic history.

Summary 1. Matrix population models are widely used to describe population dynamics, conduct population viability analyses and derive management recommendations for plant populations. For endangered or invasive species, management decisions are often based on small demographic data sets. Hence, there is a need for population models which accurately assess population performance from such small data sets. 2. We used demographic data on two perennial herbs with different life histories to compare the accuracy and precision of the traditional matrix population model and the recently developed integral projection model (IPM) in relation to the amount of data. 3. For large data sets both matrix models and IPMs produced identical estimates of population growth rate (k). However, for small data sets containing fewer than 300 individuals, IPMs often produced smaller bias and variance for k than matrix models despite different matrix structures and sampling techniques used to construct the matrix population models. 4. Synthesis and applications. Our results suggest that the smaller bias and variance of k estimates make IPMs preferable to matrix population models for small demographic data sets with a few hundred individuals. These results are likely to be applicable to a wide range of herbaceous, perennial plant species where demographic fate can be modelled as a function of a continuous state variable such as size. We recommend the use of IPMs to assess population performance and management strategies particularly for endangered or invasive perennial herbs where little demographic data are available.

Negative density dependence resulting from intraspecific competition can regulate plant populations by limiting demographic rates (survival, growth, fecundity). However, the strength of intraspecific competition can vary within and among populations due to spatial or temporal environmental heterogeneity, or genetic differences. Quantification of variation under a relatively constant environment is needed to assess the inherent potential for density dependence to vary. This knowledge will help adjust data collection effort required for parameterisation of density dependence. Our review of published plant demographic studies revealed that only half of the studies included the whole life-cycle in the analysis of density dependence. Approximately half of the studies manipulated density, while the rest examined density dependence from observed densities in the field. Regardless of the design used, density dependence was estimated from a small number of replicates. To investigate inherent variation in density dependence during the life-cycle, and the effect of low replication on density dependence estimates, we combined an experimental approach with simulations for an invasive herb Senecio madagascariensis. We found significant negative density dependence for five out of six examined demographic rates in a constant environment, with the strength of density dependence increasing during the life-cycle. An exception was plant growth, in which the direction of density dependence varied from positive to negative depending on the life stage. Simulations showed substantial deviation for density dependence parameterised from a small number of replicates even when environmental variation was minimal. This suggests that data collection procedures currently used to assess the effect of density on plant demographic rates may produce inaccurate estimates, increasing uncertainty in demographic models. Due to variation in the direction and strength of density dependence during the life-cycle, multiple life stages with multiple replicated density levels are required to parameterise density dependence for demographic rates.

In conservation management, there is an urgent need for estimates of population viability and for knowledge of the contributions of different life-history stages to population growth rates. Collection of long-term demographic data from a study population is time-consuming and may considerably delay the start of proper management actions. We examined the possibility of replacing a long-term temporal data set (demographic data from several years within a population) with a short-term spatial data set (demographic data from different populations for the same subset of two continuous years) for stochastic estimates of population viability. Using matrix population models for ten perennial plant species, we found that the matrix elements of spatial data sets often deviated from those of temporal data sets and that matrix elements generally varied more spatially than temporally. The appropriateness of replacing temporal data with spatial data depended on the subset of years and populations used to estimate stochastic population growth rates (log λs). Still, the precision of log λs estimates measured as variation in the yearly change of logarithmic population size rarely differed significantly between the spatial and temporal data sets. Since a spatiotemporal comparison of matrix elements and their variation cannot be used to assess whether spatial and temporal data sets are interchangeable, we recommend further research on the topic.

Summary 1. General guidelines for invasive plant management are currently lacking. Population declines may be achieved by focusing control on demographic processes (survival, growth, fecundity) with the greatest impact on population growth rate. However, we often have little demographic information on populations in the early stages of an invasion when control can be most effective. Here we determine whether synthesis of existing demographic data on invasive and native plant populations can address this knowledge problem. 2. We compared population dynamics between invasive and native species using published matrix population models for 21 invasive and 179 native plant species. We examined whether the population growth rate responsiveness to survival, growth and fecundity perturbations varied between invasive and native species, and determined which demographic processes of invaders to target for reductions in population growth rate. 3. Invaders had higher population growth rates ( λ ) than natives, resulting in differences in demographic processes. Perturbations of growth and fecundity transitions (elasticities) were more important for population growth of invaders, whereas perturbations of survival had greater importance for population growth of natives. 4. For both invasive and native species, elasticities of λ to survival increased with life span and decreased with λ ; while elasticities to growth and fecundity decreased with life span and increased with λ . 5. For long-lived invaders, simulated reductions in either survival, growth or fecundity transitions were generally insufficient to produce population declines, whereas multiple reductions in either survival + growth or survival + fecundity were more effective. For short-lived invaders, simulated reductions in growth or fecundity and all pairwise multiple reductions produced population declines. 6. Synthesis and applications . Life history and population growth rate of invasive species are important in the selection of control targets. For rapidly growing populations of short-lived invaders, growth and fecundity transitions should be prioritized as control targets over survival transitions. For long-lived invaders, simultaneous reductions in more than one demographic process, preferably survival and growth, are usually required to ensure population decline. These general guidelines can be applied to rapidly growing new plant invasions and at the invasion front where detailed demographic data on invasive species are lacking.

The timing of damage plays an important role in plant fitness but its effect on population performance has received relatively little attention. I examined the effect of the timing of damage on nin ...

Small population size of many rare or endangered plant species makes a quantitative assessment of population status challenging because of the lack of detailed demographic data on different life-history stages. However, an urgent assessment is often required to start possible management actions. We performed a count-based population viability analysis (PVA) using discontinuous time series to quantitatively assess the viability of a rare, monocarpic, grassland herb Carlina biebersteinii Bernh. ex Hornem. (synonyms: C. vulgaris L. ssp. longifolia, C. vulgaris L. ssp. stricta) and examined demographic and environmental factors contributing to its viability. Based on 12 abundance counts of eight C. biebersteinii populations in Finland, we found that seven out of the eight population sizes declined during the observation period, and that annual population growth rates were slightly synchronised among the populations. Synchrony in annual population growth rates declined with increasing geographic distances among the populations, while fluctuations in the number of flowering plants were unrelated to geographic distances among the populations. According to stochastic simulations, the risk of losing all flowering individuals during the next 20 years will be high for unmanaged populations. To prevent the populations from gradually declining, our results suggest that summer grazing or removal of woody vegetation is required to increase habitat openness and consequently, to improve fecundity and seedling recruitment.

In monocarpic plants, which die after flowering once, the timing of reproduction plays an important role. The optimal time for reproduction is when reproductive output and survival are maximized. T ...