EFFECT OF SEED DIMORPHISM ON THE DENSITY-DEPENDENT DYNAMICS OF EXPERIMENTAL POPULATIONS OF ATRIPLEX TRIANGULARIS (CHENOPODIACEAE)

The importance of seed size and density in determining individual plant performance and plant population dynamics in experimental populations of the halophyte Atriplex triangularis was studied. Two distinct seed morphs—large, light seeds and small, dark seeds—are produced by individual A. triangularis plants. Experimental populations consisting of seed size monocultures (large or small seeds) and seed size mixtures were established at three different densities, and the time of germination, plant size, plant survivorship, and plant fecundity were monitored. Marked variation in time of germination was observed among treatments and between seed sizes, but germination within any given treatment occurred over a five- to ten-day period. Large seeds produced larger plants than small seeds did, and this dichotomy was maintained over the course of the entire experiment. Germination date and seed size interacted such that larger plants grew from seeds which germinated earlier than those which germinated later, regardless of seed size. Germination date had a more pronounced effect than seed size did on plant mortality in high density populations. At high density, large seed monocultures experienced greater mortality than small seed monocultures did, but in seed size mixtures, the mortality was evenly distributed between plants from the two seed sizes. Regardless of density conditions and parentage, large and small seeds were produced in equal proportion by the plants. Total seed production, however, was dramatically affected by plant density, and to a lesser degree by germination date. Although seed size effects alone did not appear to affect directly final plant biomass and fecundity, effects of seed size early in ontogeny may have contributed to differences in fecundity.     

The relationship between reproductive success and demographic structure in remnant populations of Primula veris

Plants often suffer reductions in fecundity due to fragmentation, degradation and destruction of populations and their sites. Whether this decrease in seed production has population-level consequences is generally unknown. Here, we aimed to determine the current status of remnant populations in the perennial herb Primula veris in Belgium. Furthermore, we investigated the effects of reduced population size and morph bias on reproductive success and explored if changes in demographic structure could be associated with population fecundity. We studied 69 populations that differed in population size from three to nearly 1500 flowering plants. Three different population types could be distinguished: (a) “dynamic” populations, characterized by high densities of 1 year old juveniles, (b) “normal” populations with adult age-stages prevailing, but still a considerable number of juveniles, and (c) “regressive” populations, in which only flowering adults dominate and rejuvenation hardly occurs. The three population types differed with respect to population size and morph frequency. Dynamic populations were significantly larger and showed a weaker morph bias compared to the intermediate normal and the small regressive populations. Reproductive success, studied the previous year in 26 populations, decreased significantly with decreasing population size and was significantly associated with the demographic structure of the populations. Coefficients of variation for the proportion of flowers setting fruit, the number of seeds per fruit and the total number of seeds per plant decreased significantly with increasing population size. Hence, the observed variability in seed set may be one of the causal factors affecting the observed types of population demographic structure.     

Effects of intraspecific and community density on the lifetime fecundity of long-lived shrubs

Intra- and interspecific density dependence has profound consequences for plant population and community dynamics. In long-lived plants, however, lifetime patterns and mechanisms of density dependence are difficult to study. Here, we examine effects of intraspecific and community density on the lifetime fecundity of two long-lived shrub species from South African Fynbos: Protea repens (animal-pollinated, hermaphroditic) and Leucadendron rubrum (wind-pollinated, dioecious). Both species are serotinous, retaining seeds in cones until fire kills the mother plant. We measured lifetime fecundity as the product of cone number, proportion of cones that are not damaged by predation and seed set (fertile seeds per intact cone). Intraspecific and community densities were quantified by counting individuals of target species and all Proteaceae in small- and large-scale neighbourhoods (10 m and 50 m radius) around each focal individual. Additionally, we determined the age and size of focal individuals. We found that lifetime fecundity of the wind-pollinated L. rubrum is density independent. In contrast, the lifetime fecundity of the animal-pollinated P. repens increases with large-scale intraspecific density and shows a hump-shaped relationship to large-scale community density. Community density has a hump-shaped effect on seed set (probably through partial absence of generalized pollinators at low and competition for pollinators at high densities) and negatively affects cone number per individual. For both species, plant age decreases seed set while increasing lifetime fecundity. The qualitative differences in the density dependence of lifetime fecundity may arise from differences between animal and wind pollination. In particular, interactions with generalized animal pollinators may cause community-level Allee effects with profound consequences for the future dynamics of long-lived plant populations and communities.     

Effects of range position,inter-annual variation and density on demographic transition rates of <Emphasis Type="Italic">Hornungia petraea</Emphasis> populations

The central-marginal model assumes unfavourable and more variable environmental conditions at the periphery of a species’ distribution range to negatively affect demographic transition rates, finally resulting in reduced population sizes and densities. Previous studies on density-dependence as a crucial factor regulating plant population growth have mainly focussed on fecundity and survival. Our objective is to analyse density-dependence in combination with the effect of inter-annual variation and range position on all life stages of an annual plant species, Hornungia petraea, including germination and seed incorporation into the seed bank. As previous studies on H. petraea had revealed a pattern opposite to existing theory with lower population densities at the distribution centre in Italy than at the periphery in Germany, we hypothesised that (1) demographic transition rates are lower, (2) the inter-annual variation in demographic transition rates is higher and (3) the intensity of density-dependence is weaker in Italy than in Germany. To analyse demographic transition rates, we used an autoregressive covariance strategy for repeated measures including density and inter-annual variation. All the three hypotheses were confirmed, but the impact of range position, density-dependence and inter-annual variation differed among the transition steps. All transition rates except fecundity were higher in the German populations than in the Italian populations. Germination rate and incorporation rate into the seed bank were strongly density-dependent. Central populations showed a larger inter-annual variation in fecundity and winter survival rate. Winter survival rate was the only transition step with a stronger density-dependence in peripheral populations. In most cases, these differences between distribution centre and periphery would not have emerged without taking density-dependence and inter-annual variation into account. We conclude that including range position, inter-annual variation and density-dependence in one single statistical model is an important tool for the interpretation of demographic patterns regarding the central-marginal model. Electronic Supplementary Material Supplementary material is available for this article at     

POLLINATOR EFFECTIVENESS AND SEED SET IN POPULATIONS OF AGALINIS STRICTIFOLIA (SCROPHULARIACEAE)

Examining variation in pollinator effectiveness and seed production resulting from single pollinator visits can provide a deeper understanding of how pollinators may influence reproduction in plant populations. When comparing populations, differences in the number of seeds produced from single pollinator visits to flowers may not always be attributable to differences in pollen deposition, but rather to differences in plant fecundity or resource availability. Pollinator effectiveness and seed production were studied for two populations over a 4-year period and were measured using single bee visit manipulations of flowers. No significant difference in pollinator effectiveness (pollen deposited on stigmas) was observed between the two populations. However, a significant difference between the two populations was observed in the number of seeds produced per flower. The Wellhouse population produced approximately three times as many seeds/flower from a single pollinator visit as did the Firefly Meadow population. Within each population, pollinators (Bombus pennsylvanicus and Apis mellifera) did not differ in the number of pollen grains deposited on stigmas or seeds produced per flower from single visit experiments. Differences in plant density, pollen viability, and ovules per flower also could not account for a significant amount of the variation. A resource augmentation experiment (water and fertilizer application) resulted in a decrease in seeds per flower per bee visit for the water treatment at the Wellhouse population only. For both populations, pollen deposition, pollen viability, and ovules per flower were unaffected by the resource augmentation. Alternative possibilities for the observed differences in seeds per flower per bee visit are discussed.     

Niche breadth and resource partitioning by four sympatric species of bark beetles (Coleoptera: Scolytidae)

Summary In a North Carolina population of Diamorpha smallii, densities were artificially manipulated by thinning stands to predetermined densities. Individuals in areas of high density produce fewer seeds than individuals at low density in the same habitat. Three components of fecundity, the number of flowers per plant, the number of fruits per plant, and the number of seeds per fruit, were negatively correlated with density. The relationship of components of fecundity to density were used to develop a model of population regulation for this species. These results and predictions from the model are discussed in relation to other density studies.     

Populational dynamics of three annual species of alpine plants in the Rocky Mountains

Summary Survivorship, fecundity, and seed bank size were measured over two years in alpine populations of the annuals, Koenigia islandica, Polygonum confertiflorum, and P. douglasii. The major loss of individuals from all populations occurred between seed dispersal and germination. Survival of vegetative plants to maturity was high in all species, usually above 80%, and the average number of seeds produced per plant was less than 10 in all species in both years. Seed banks existed for all three species but were small since more than 80% of the viable seeds in the soil germinated in the spring. Both survival and fecundity were negatively correlated with density in P. confertiflorum. These patterns of population dynamics are similar to those found in many annuals of temperate environments.     

Seed predation,pathogen infection and life-history traits in Brassica rapa

Herbivory and disease can shape the evolution of plant populations, but their joint effects are rarely investigated. Families of plants of Brassica rapa (Brassicaceae) were grown from seeds collected in two naturalized populations in an experimental garden. We examined leaf infection by the fungus Alternaria, seed predation by a gall midge (Cecidomyiidae) and plant life-history traits. Plants from one population had heavier seeds, were more likely to flower, had less fungal infection, had more seed predation and were more fecund. Fungal infection score and seed predation rate increased with plant size, but large plants still had the greatest number of undamaged fruits. Spatial heterogeneity in the experimental garden was significant; seed predation rate and fecundity varied among blocks. An apparent tradeoff existed between susceptibility to disease and seed predation: plants with the highest fungal infection score had the lowest seed predation rate. Alternaria infection varied between populations, but the disease had no effect on fecundity. Seed predation did reduce fecundity. Damaged fruits had 31.4% fewer intact seeds. However, evidence for additive genetic variation in resistance to seed predation was weak. Therefore, neither disease nor seed predation was likely to be a strong agent of genetically based fecundity selection.     

The role of the tolerance–fecundity trade‐off in maintaining intraspecific seed trait variation in a widespread dimorphic herb

Coexistence of species with different seed sizes is a long‐standing issue in community ecology, and a trade‐off between fecundity and stress tolerance has been proposed to explain co‐occurrence in heterogeneous environments. Here we tested an intraspecific extension of this model: whether such trade‐off also explains seed trait variation among populations of widespread plants under stress gradients. We collected seeds from 14 populations of Plantago coronopus along the Atlantic coast in North Africa and Europe. This herb presents seed dimorphism, producing large basal seeds with a mucilaginous coat that facilitates water absorption (more stress tolerant), and small apical seeds without coats (less stress tolerant). We analysed variation among populations in number, size and mucilage production of basal and apical seeds, and searched for relationships between local environment and plant size. Populations under higher stress (higher temperature, lower precipitation, lower soil organic matter) had fewer seeds per fruit, higher predominance of basal relative to apical seeds, and larger basal seeds with thicker mucilaginous coats. These results strongly suggest a trade‐off between tolerance and fecundity at the fruit level underpins variation in seed traits among P. coronopus populations. However, seed production per plant showed the opposite pattern to seed production per fruit, and seemed related to plant size and other life‐cycle components, as an additional strategy to cope with environmental variation across the range. The tolerance–fecundity model may constitute, under stress gradients, a broader ecological framework to explain trait variation than the classical seed size–number compromise, although several fecundity levels and traits should be considered to understand the diverse strategies of widespread plants to maximise fitness in each set of local conditions.     

Density‐dependent demographic responses of a semelparous plant to natural variation in seed rain

The link between reproductive and vegetative ecology of flowering plants is rarely explored, despite its importance for understanding population processes and fitness. This link can be studied by using experimental or natural variation in seed input to the soil to assess how reproductive success affects vital rates of offspring. We previously reported for Ipomopsis aggregata that per‐seed probability of germinating is insensitive to density of seeds sown into plots, whereas per capita flower production among adults that grow from the seedlings declines in nonlinear fashion with density. Here we describe a parallel non‐experimental study. We related seedling emergence to estimated natural seed input (‘seed rain’) in three populations across ten summers and monitored seedlings that emerged in the first two summers throughout their life histories. Seedling emergence in 1996 was linearly related to seed rain from plants that flowered in 1995. This density independent seed‐to‐seedling transition recurred over the next nine summers, but the slope varied with springtime precipitation. Total numbers of 1996 seedlings that survived to flower and numbers of flowers they produced increased linearly with seed rain in one population, but did not vary detectably in the other two, consistent with negative density dependence. In consequence λ (the dominant eigenvalue of a population projection matrix) decreased from high values at low densities of seed rain to a relatively constant low value with greater seed rain. We also detected density dependence in the 1995 seedling cohort in survival and flower production. The similarity of results from natural and experimental studies supports a conclusion of nonlinear density dependence and shows that characterizing it requires the full life history. For this plant species and others, studies of pollination and fecundity alone may not suffice to draw conclusions about population change or fitness.     

Partitioning the sources of demographic variation reveals density‐dependent nest predation in an island bird population

Ecological factors often shape demography through multiple mechanisms, making it difficult to identify the sources of demographic variation. In particular, conspecific density can influence both the strength of competition and the predation rate, but density‐dependent competition has received more attention, particularly among terrestrial vertebrates and in island populations. A better understanding of how both competition and predation contribute to density‐dependent variation in fecundity can be gained by partitioning the effects of density on offspring number from its effects on reproductive failure, while also evaluating how biotic and abiotic factors jointly shape demography. We examined the effects of population density and precipitation on fecundity, nest survival, and adult survival in an insular population of orange‐crowned warblers (Oreothlypis celata) that breeds at high densities and exhibits a suite of traits suggesting strong intraspecific competition. Breeding density had a negative influence on fecundity, but it acted by increasing the probability of reproductive failure through nest predation, rather than through competition, which was predicted to reduce the number of offspring produced by successful individuals. Our results demonstrate that density‐dependent nest predation can underlie the relationship between population density and fecundity even in a high‐density, insular population where intraspecific competition should be strong.     

Fitness components and the determinants of fecundity in populations of a native perennial grass (Tridens flavus)

Understanding intraspecific variation in traits that determine fitness is foundational to a trait-based approach to plant ecology. This study examined fitness components during 3 years of reproduction in a polycarpic perennial bunchgrass (Tridens flavus) native to eastern North America that could prove useful in revegetating disturbed habitats. Plants were cultured from seeds of five populations in central New Jersey, USA, and planted in July 2015 into two undisturbed gardens 30 m apart that differed in availability of sunlight and soil moisture. Following flowering in 2016, 2017 and 2018, the number of panicles, seed set, seed number (fecundity) and seed mass were recorded. Final dry aboveground mass was determined. Seed set was high (>70%) in all populations and gardens. Panicle production varied with population and was strongly correlated with fecundity, but populations were not differentiated for other fitness components. Panicle and seed number were greatest in the drier garden with greater daily light availability. Mass per seed was reduced as more seeds were produced in the second and third year but showed low variation compared to fecundity. Vegetative mass was the most important variable determining fecundity. Close proximity of sampled sites and an outcrossed, wind-pollinated mating strategy may have precluded detection of differentiation among T. flavus populations in the common gardens. High seed set, prodigious seed production on multiple panicles and high seed germinability and overwinter survival account for the occurrence of large populations of this native grass along roadsides and within successional fields and young woodlands throughout the region.     

Widespread seed limitation affects plant density but not population trajectory in the invasive plant Centaurea solstitialis

In some plant populations, the availability of seeds strongly regulates recruitment. However, a scarcity of germination microsites, granivory or density-dependent mortality can reduce the number of plants that germinate or survive to flower. The relative strengths of these controls are unknown for most plant populations and for exotic invaders in particular. We conducted a seed addition experiment with a granivore exclusion treatment in a field setting to explore how these factors interact to regulate populations of the widespread invader Centaurea solstitialis (yellow starthistle) at three study sites across the plant’s range in California. We coupled the experimental approach with observational studies within established C. solstitialis populations to estimate seed rain, recruitment and mortality at natural densities. Seed limitation occurred in both experimental and observational plots in all populations. Although vertebrate granivores were active at each site, they had no effect on C. solstitialis recruitment. Density increased mortality, but the effect was variable and weak relative to its effect on fecundity. The seed limitation that was evident at the seedling stage persisted to flowering. Seed-limited populations such as these ought to be highly sensitive to losses to seed predators, and many biological control agents, including those established for C. solstitialis, are seed predators. However, flowering plant density was decoupled from seed production by a strong compensatory response in the surviving plants; seed production was nearly constant in plots across all seed addition levels. Thus, flowering plant density is reduced by the established biocontrol agents, but seed production compensates to replace the population every generation, and no long-term decline is predicted.     

Indirect interactions between browsers and seed predators affect the seed bank dynamics of a chaparral shrub

Interactions between herbivores and seed predators may have long-term consequences for plant populations that rely on persistent seed banks for recovery after unpredictable fires. We assessed the effects of browsing by deer and seed predation by rodents, ants and birds on the densities of seeds entering the seed bank of Ceanothus cuneatus var. rigidus, a maritime chaparral shrub in coastal California. Ceanothus produced many more seeds when protected from browsers in long-term experimental exclosures than did browsed plants, but the seed densities in the soil beneath browsed and unbrowsed Ceanothus were the same at the start of an intensive one-year study. The density of seeds in the soil initially increased in both treatments following summer seed drop: while densities returned to pre-drop levels within a few weeks under browsed plants, soil seed densities remained high for 5–8 months beneath unbrowsed plants. Rodent abundance (especially deer mice) was higher near unbrowsed plants than >30 m away, and rodents removed Ceanothus seeds from dishes in the experimental plots. At least in the short term, rodent density and rates of seed removal were inversely related to the intensity of browsing. Our data have management implications for maintaining viable Ceanothus populations by regulating the intensity of browsing and the timing, intensity and frequency of fires.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Site‐to‐site variation in the demography of a fire‐affected perennial. Acacia suaveolens,at Ku‐ring‐gai Chase National Park,New South Wales,Australia

Abstract Acacia suaveolens (Sm.) Willd is a perennial shrub that forms even‐aged stands, recruited from a soil seed‐bank following fire. It has previously been subject to demographic studies, which used a space‐for‐time substitution to investigate temporal patterns following fire. In the present study the potential for spatial variation across sites was investigated by sampling at several similarly aged populations in Ku‐ring‐gai Chase National Park, northern Sydney, Australia. Significant variation in mean size and fecundity of A. suaveolens individuals was observed among sites, over a 2‐4.6‐fold range in plant size, and a sevenfold range in mean fecundity. The observed variation at 3 years after fire encapsulated most of the variation previously observed among sites 0‐17 years since fire, emphasizing the importance of spatial variation in this species. For each site a two‐stage (seed, plant) matrix model was constructed, and projected from 3 to 25 years following fire. Population growth was measured as number of seeds per 3‐year‐old plant, and found to vary 1.4‐fold across models for different sites. This site‐to‐site variation, as well as that in size, fecundity and survival, was statistically significant. Variation in projected seeds per plant could mostly be attributed to differences in fecundity rather than plant survival. Sensitivity analyses emphasized the biological significance of the variation in fecundity. Whereas previous studies have focused on temporal variation, this work demonstrates the importance of extending our understanding of a species to include the spatial component of population dynamics.     

Effects of population density on male and female reproductive success in the wind-pollinated, wind-dispersed tree species Betula maximowicziana

The effects of population density on male and female reproductive success of Betula maximowicziana were evaluated in two mixed and two post-fire stands, with various population densities, ranging from 1.9 to 300.0 trees per ha, in central Hokkaido, Japan. First, we investigated ecological determinants of reproductive success (seed set and germination) of both seeds collected from the trees (tree seeds) and dispersed seeds collected from seed traps (dispersed seeds). We then evaluated the effects of population density on seed set and germination of tree seeds and dispersed seeds using a generalized linear mixed model (GLMM). Subsequently, we genotyped 950 seeds collected from mother trees and 940 seeds trapped after dispersal derived from tree seeds and dispersed seeds, respectively, using eleven microsatellite loci. Using the acquired data, we then evaluated the outcrossing rate and effective number of pollen donors (N _ep) of the tree seeds, and the genetic structure of both pollen pools and dispersed seed populations. The seed set and germination rate of dispersed seeds was significantly lower both in the lowest-density stand and in the highest-density stand. The GLMM revealed that seed set and germination rates of dispersed seeds may be maximal at approximately 120 trees per hectare (optimal density). Outcrossing rates were consistently high (t _m = 0.995), regardless of the population density. In contrast, N _ep was lower in the lowest-density stands. Significant genetic structure of the dispersed seed population was found in two low-density stands, probably due to the limitation of overlapping seed shadows.     

Rodent seed predation promotes differential recruitment among bird-dispersed trees in temperate secondary forests

We investigated the role of seed predation by rodents in the recruitment of the fleshy-fruited trees Taxus baccata, Ilex aquifolium and Crataegus monogyna in temperate secondary forests in NW Spain. We measured the densities of dispersed seeds, early emerged seedlings, established recruits and adults, at four sites over a period of 2 years. Seed predation among species was compared by seed removal experiments and analysis of rodent larder-hoards. The three species differed markedly in local regeneration patterns. The rank order in the seed rain following decreasing seed density was Ilex, Taxus and Crataegus. However, Crataegus established 3.3 times more seedlings than Taxus. For all species, there was a positive linear relationship between the density of emerged seedlings and seed density, suggesting that recruitment was seed- rather than microsite-limited. A consistent pattern of seed selection among species was exerted by rodents, which preferred Taxus and, secondarily, Ilex seeds to Crataegus seeds. Predation ranking was the inverse of that of seed protection against predators, measured as the mass of woody coat per mass unit of the edible fraction. Recruitment potential, evaluated as the ratio of seedlings to seeds, was negatively related to seed predation, with the rank order Crataegus > Ilex > Taxus. The selective early recruitment limitation exerted by predation may have a demographic effect in the long term, as judged by the positive relationship between early seedling emergence and the density of established recruits. By modulating the pre-emptive competition for seed safe sites, rodents may preclude the progressive exclusion of species that produce low numbers of seeds (i.e. Crataegus) by those dominant in seed number (i.e. Ilex, Taxus), or at least foster the evenness for site occupation among seedlings of different species.     

Reintroduction of a Rare Plant (Gladiolus imbricatus) Population to a River Floodplain—How Important is Meadow Management?

In seminatural grasslands, the success of reintroduction of locally extinct rare plant species may depend on the ambient management regime. We aimed to study to what extent the success of the restoration of a rare species (Gladiolus imbricatus) depends on management conditions. A management experiment with traditional cutting by scythe and hay removal, mowing (machine cutting and hay removal), mulching (machine cutting without hay removal), spring burning, and unmanaged control, combined with reintroduction of seeds of Gladiolus, was conducted in an Estonian flooded meadow in which the species had become extinct. Seeds were reintroduced in 2003 in all management treatments and populations monitored until 2006. Mulching, mowing, and traditional management resulted in the greatest establishment, whereas the subsequent mortality was not influenced greatly by management regime. The population started to increase in mulching treatment in the third season due to vegetative growth. The results indicate that the establishment of G. imbricatus is primarily seed limited under current conditions, whereas favorable management significantly enhances establishment in a river floodplain meadow. Successful restoration depends on seed addition and proper grassland management—mowing to a height of approximately 15 cm and mulching.     

Habitat protection,cattle grazing and density‐dependent reproduction in a desert tree

Anthropogenic activities usually trigger changes in the population density of plants. Thus, land management practices can influence density‐dependent demographic parameters and species interactions. We investigated plant‐pollinator interactions and reproduction in Prosopis flexuosa, the largest tree species in the Central Monte desert of Argentina, an important economic and cultural resource for humans and a functionally prominent species. We hypothesized that reproductive output of P. flexuosa would be limited at low densities, and that exclusion of catle grazing would enhance population density and consequently interaction frequency with pollinators and reproductive success. The study was conducted in and around Ñacuñán Biosphere Reserve (Mendoza, Argentina), where cattle grazing has been excluded for over 35 years. Working in five pairs of protected and cattle grazed 1‐ha plots, we recorded density of adult trees, pollinator visitation frequency to inflorescences and seeds per inflorescence in focal trees. Adult tree density was higher in protected plots than in cattle grazed plots. Density of reproductive trees was positively correlated with seed production, suggesting positive density dependence for reproduction (Allee effect). Pollinator visitation to inflorescences and seed production was higher in protected plots compared with plots under cattle grazing. Suppression of anthropogenic degradation has resulted in higher adult tree density in protected plots, indirectly higher pollinator visitation to inflorescences and higher reproductive success of trees. Increased frequency of plant‐pollinator interactions and tree reproduction suggest success of management practices aimed at protecting P. flexuosa woodlands.     

Introduced populations of <Emphasis Type="Italic">Genista monspessulana</Emphasis> (French broom) are more dense and produce a greater seed rain in California,USA, than native populations in the Mediterranean Basin of Europe

Some invasive plants perform better in their area of introduction than in their native region, and this is often attributed either to phenotypic responses and/or to adaptive evolution following exposure to new environmental conditions. Genista monspessulana (French broom) is native to Europe, but highly invasive and abundant along the Pacific Coast of the USA. In this study, the population density and age structure, plant growth and reproductive traits, and seed bank characteristics of 13 native (Mediterranean Basin) and 15 introduced (California, USA) field populations of G. monspessulana were compared. Mean population density, plant height and stem diameter were greater in introduced populations, with the latter two traits explained by a greater mean plant age. Age structure also showed a greater percentage of seedling plants in introduced populations. Fecundity was higher in introduced populations when measured in terms of mature seeds per pod, but lower when comparing seed production per plant (number of pods and mature seeds). Thus, seed rain and seed bank size was considerably higher in introduced populations. Results from this study indicate that G. monspessulana performs better in its introduced region. We hypothesize that release from natural enemies and competitors together with more favorable environmental conditions in the introduced region may explain the invasion success of G. monspessulana. As a result, an integrated management approach using introduced seed predators to suppress seed production and selected management practices to reduce seed banks may be needed for effective long-term control in California.