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1 Monocarpy in facultative biennials can be favoured by selection when there is a more than proportional increase in fitness with size. The possible contributions of larger reproductive output and higher offspring quality to such an increase were investigated in the facultative biennial plant Digitalis purpurea. Straw mass (rosette leaves and flowering stem excluding fruits and seeds) was determined for 100 individuals of varying size and correlated with the number of flowers and seeds per flower to examine whether sex-allocation is size dependent. 2 To determine whether maternal size influences offspring growth, and whether this effect is more pronounced in the presence of competition, seeds from 32 maternal plants were grown alone, and with one, two or four competitors. 3 Total seed number increased proportionally with size. Seed quality, measured as seed size, germination percentage and speed also increased with maternal size. The combined fitness measures of total seed mass (seed number x seed size), number of seedlings (seed number x germination percentage) and total female fitness (seed number x germination percentage x mean offspring dry mass after 14 weeks) all increased disproportionally with size. 4 Sex-allocation was size dependent, with large plants emphasizing the female function. 5 Offspring dry mass after both 8 and 14 weeks of growth was strongly influenced by competition, whereas the effect of maternal size was significant only at the first harvest date. Competition did not accentuate the effects of maternal size. 6 The results support that monocarpy exists in D. purpurea because of increased offspring quality rather than a disproportionate advantage in seed output of large individuals. Key-words: delayed reproduction, maternal size-effects, monocarpy, offspring quality, seed size variation

1 For 3 years, I examined the effects of fragmentation on pollination of an endemic, euglossine bee-pollinated, epiphytic orchid, Catasetum viridiflavum, on 10 islands created during the construction of the Panama Canal and at five sites in nearby large tracts of mainland forest. 2 I investigated the viability of pollinia over time, availability of pollinators and male and female reproductive success (measured as removal of pollinaria and fruit set, respectively) at different sites. 3 Viability of pollinia declined dramatically over time, although some remained at least partially viable for up to 60 days. Bees moved between trapping stations at different sites within a day, and viable pollen therefore could have been transferred between populations. 4 Although euglossine bees were equally frequent in fragments and continuous forest, those recorded on islands were visitors from mainland sites, and not island residents. 5 Neither male nor female reproductive success were significantly different between island and mainland forest types in 1997. The higher reproductive success in certain sites within both forest types throughout the flowering season could not be explained by variation in overall population floral display. Larger inflorescences had higher male and female reproductive success. 6 In 2 of 3 years, plants on islands had significantly lower fruit set than plants on mainland sites. Female reproductive success differed dramatically across years and sites. 7 The low fruit set in 1996 and 1998 on islands in comparison with mainlands, and the observation that bees are not island residents, conform with expectations of physical isolation of forest patches. In spite of the evidence of fragmentation in this system, patterns of pollinator behaviour and of reproductive success suggest significant connectedness among sites. This 3-year study shows that a single year study may not have highlighted the complexity of the system. Key-words: Barro Colorado Island, epiphytic orchid, euglossine bee, forest fragmentation, plant reproduction

1 A long-term experiment was established in 1990 in which seeds of 54 native species, not originally present at the site, were sown into a fertility x disturbance matrix established in unproductive limestone grassland at the Buxton Climate Change Impacts Laboratory (BCCIL). The objective was to examine the roles of productivity and disturbance as major factors controlling the invasibility of plant communities, and to identify the functional characteristics of successful invaders in response to different types of invasion opportunity. The results of the first 2 years of the study have already been published. 2 After 2 years, invasion was strongly promoted by disturbance and less so by increased fertility. Three years later the cover of invaders had declined over most of the matrix, and the greatest cover of sown species was where the highest levels of fertility and disturbance coincided. However, no part of the fertility--disturbance matrix was immune to invasion and the area of the matrix occupied by each of the sown species that successfully established was unique. Abundance of invaders was reduced by low soil pH. 3 The identity and distribution of the successful invaders changed as the early stages of invasion gave way to a later stage of consolidation. After 2 years regenerative traits (seed mass and germination characteristics) were the best predictors of success. After 5 years these traits were unrelated to success of the invaders, the most successful invaders were perennial grasses, and no single trait was a good predictor of invasiveness. 4 Our results are consistent with the hypothesis that invasions are promoted by an increase in the availability of resources, either through addition of extra resources or a reduction in their use by the resident vegetation. Key-words: BCCIL, disturbance, fertility, functional types, herbivory, invasibility, limestone grassland, plant traits, seed size

1 Theoretical models indicate that coexistence of diploid and polyploid individuals in sympatric populations is unlikely when mating is random among cytotypes and hybrids are inviable. However, coexistence may be facilitated by prezygotic isolating mechanisms that reduce intercytotype mating and increase assortative mating. 2 We examined the ecological factors regulating intercytotype mating in Chamerion (formerly Epilobium) angustifolium by measuring floral morphology, flowering synchrony and insect foraging preferences in a mixed population within a diploid-tetraploid contact zone. We also calculated the minimum rate of betweencytotype mating from estimates of the frequency of triploid offspring. 3 Diploids had significantly shorter and narrower petals as well as shorter styles than tetraploids. Inflorescences were significantly taller in tetraploids than diploids, but the mean number of open flowers per inflorescence did not differ. Diploid and tetraploid flowering periods overlapped by 51%, with diploid stems flowering earlier. 4 In a plot of 20 diploid and 28 tetraploid stems that were flowering simultaneously, only 26% of all bee flights were between flowers on different stems. Of the total flights between inflorescences, only 15% were between different cytotypes. The combined effects of flowering asynchrony and insect foraging reduced the opportunities for intercytotype mating from 49% expected if mating is random to about 2% of the total number of pollinator flights. 5 A computer simulation indicated that the deficiency of pollinator flights between cytotypes was due largely to the spatial structure of cytotypes and limited pollinator flight distances within the observation plot. The frequency of triploid offspring produced during the period when both cytotypes were in flower was 6.6%, similar to the proportion of flights observed between flowers on different cytotypes (4%). 6 The results indicate that flowering phenology and insect behaviour (as influenced by clonal structure) have a significant effect on prezygotic mating isolation and triploid production, and may contribute to the maintenance of mixed cytotype populations in Chamerion angustifolium. Keywords: fireweed, phenology, pollinator behaviour, polyploidy, reproductive isolation, triploids

1 We monitored flowering and fruiting of individual male and female plants of Oemleria cerasiformis over a 6-year period in a population in western Canada, and calculated fruit set (percentage of pistils maturing) and reproductive effort (RE) (gram of reproductive tissue per gram of leaf). 2 Over 6 years, male O. cerasiformis had on average much lower total RE, but much higher RE at flowering, than females. 3 In males, strong correlations between RE and light suggested that investment in reproduction was largely determined by light levels. There were strong positive correlations of RE between years, with no evidence of periodic fluctuations. 4 In females, in contrast to males, RE at flowering was not related to light. However, fruit set was strongly correlated with light. Flowering RE and fruit set were uncorrelated in females, indicating that these are affected by different factors. 5 Correlations of RE between years in females, although often significant, were lower than in males, indicating that RE fluctuates more between years in females than in males and may respond to past levels of RE. Flowering may reflect adjustments in response to past reproduction, or may be controlled by resources other than light. Fruit set was not significantly related to previous RE. 6 The greater total RE of females and their limited ability to adjust fruit set are probably major factors contributing to the greater mortality rates of females and the male-biased sex ratios in O. cerasiformis. Keywords: control of flowering, dioecious plants, fruit set, resource allocation

1 The advantages of guerrilla and phalanx growth for the guerrilla Elymus lanceolatus ssp. lanceolatus and phalanx E. l. ssp. wawawaiensis were evaluated over 2 years in two taxon mixtures with a range of densities of each subspecies and under two levels of watering. 2 Ramet numbers and biomass of the guerrilla subspecies were higher than those of the phalanx grass in the first year but in the second year declined greatly, while the phalanx grass showed no change in biomass and an increase in ramet numbers. High neighbour densities affected the phalanx subspecies more strongly than the guerrilla subspecies in the first year, but in the second year there were few differences between subspecies. Biomass of the guerrilla grass remained greater than that of the phalanx grass but ramet numbers were similar in the second year. 3 For both subspecies in both years, probability of flowering decreased at higher neighbour densities, indicating adaptation for competitive ability. In the first year, biomass was more strongly reduced by densities than flowering was, but in the second year, when crowding was apparently greater, flowering was more severely affected. 4 Genet survival was high and similar for both subspecies. 5 The presumed advantage of guerrilla subspecies in exploiting open space was supported. The guerrilla grass exploited resources more quickly in the first year by faster growth and greater ramet production, but its biomass, ramet numbers and rhizome growth, and thus its advantage, were reduced in the second year. 6 The phalanx subspecies had slower growth, produced more ramets in later years, and delayed flowering until later years. Although less able to exploit open resources, it appeared adapted to more stressful conditions, and may be able to exploit temporal resource pulses more effectively. Keywords: clonal growth, competition, Elymus lanceolatus, resource patches, sexual reproduction, vegetative reproduction

1 Phenology and reproduction were studied in three populations of the cleistogamous herb Oxalis acetosella during three growing seasons, in order to see how the balance between chasmogamous (CH) and cleistogamous (CL) reproduction varies with temporal and spatial environmental variation and with plant size. The numbers of CH and CL flower buds, flowers, immature capsules and mature capsules were counted per ramet, ramet sizes were estimated, and mature capsules were collected for seed counts. 2 Both CH and CL flower numbers were positively correlated with ramet size expressed as leaf number, but the correlation was much stronger in the CL phase. CL flower production also varied significantly between years and sites. Thus, CL production in O. acetosella was not independent of resources and climatic variation. 3 When the effects of year and site were taken into account, the probability of an individual flower developing into a mature fruit was not higher in the CL phase than in the CH phase. 4 CL production was affected by fertilization success in the CH phase. Ramets with one or more CH flowers left unfertilized generally produced more CL buds than ramets with all their CH flowers fertilized. The former group also tended to have more seeds per CL capsule. 5 Since reproductive success in the two phases varies in different temporal and spatial patterns, cleistogamy in O. acetosella is considered to be a bet-hedging strategy optimizing reproductive output in fluctuating environments. 6 The findings of this study are in conflict with the general view on cleistogamy as a fail-safe mechanism for back-up seed production, unaffected by variations in resource supply and environmental conditions. Keywords: chasmogamous, reproductive rate, resources, spatial variation, temporal variation

1 The effect of supplementary feeding on growth and reproduction of three carnivorous plants species was investigated over a 6-year period. Pinguicula alpina, P. villosa and P. vulgaris populations growing at two altitudes in a subarctic environment were fed with fruit flies (Drosophila melanogaster). 2 Fed plants increased in size relative to control plants during the first years. Subsequently a stable size difference between feeding levels was established. The weight of the over-wintering part was higher in fed plants than in control plants. 3 The flowering frequency (i.e. proportion of plants in a population carrying flowers) was also higher in the fed plants. The proportion of flowering plants increased in the feeding treatment compared to control plants during more-or-less the whole experimental feeding period (5-6 years). Seed production also increased slowly in response to feeding. 4 No feeding effect on nitrogen and phosphorus concentrations in seeds and overwintering parts was found. 5 In most characteristics the high-altitude populations were less responsive than populations growing at low altitude. In the high-altitude population reproduction failed repeatedly, suggesting that seed output may be more dependent on abiotic factors than on resource availability in cold environments. 6 Pinguicula villosa and P. vulgaris used the new resources the same summer for increased leaf rosette growth and current reproduction, showing these species to be income breeders, while the third species (P. alpina) allocated a larger proportion to storage and future reproduction, characteristic of a capital breeder. Keywords: capital breeder, carnivorous plant, income breeder, nutrients, Pinguicula, resource allocation

1 We studied the relationships between population size, reproduction and population growth rate in 23 populations of the rare, short-lived plant Gentianella germanica. We also investigated a possible correlation of population size effects with environmental variation in climate, topography, soil, vegetation, and management. To ascertain whether the differences between populations have a genetic basis, we grew 20 seed families from each of the populations in a common garden experiment. 2 In 1993, population sizes ranged from 40 to 5000 flowering plants in the field populations (geometric mean 386). Plants in small populations had fewer seeds per fruit and fewer seeds per plant than plants in larger populations, whereas seed mass was independent of population size. From 1993 to 1995 population size decreased in most populations (mean annual population growth rate 0.876), and this decrease was larger in small populations than in large populations. 3 In the common garden the positive correlation between the number of surviving plants per planted seed and original population size increased steadily over time. After 17 months there were significantly more flowering plants and more flowers per planted seed for seeds from large populations than for those from small populations. 4 Although environmental variables accounted for significant variation in population growth rate and plant performance both in the field and in the common garden, effects of population size detected in stepwise multiple regressions were not confounded with environmental effects. 5 We conclude that the reduced performance observed in plants from smaller populations was explained by genetic effects rather than by habitat quality, although pollinator limitation may have contributed to fitness reductions in the field. The Observed patterns suggest further reductions of population sizes in Gentianella germanica in the future, especially in already small populations. Our study lends support to the view that genetic problems are a major concern in plant conservation. Keywords: common garden study, population size, demography, rare species, reproduction

1 We report the results from a 7-year study on the patterns of reproduction and vegetative spread of Asarum canadense, conducted in replicate plots located in the understorey of early and late successional forest. 2 We recorded the spatial location, size, demographic performance and clonal fragment identity of all. A. canadense ramets in our plots, as well as the position and fate of seedling recuits. We also collected detailed morphological data on patterns of clonal growth. 3 Recently germinated plants and the much larger, clonally produced daughter ramets had equal survivorship. Size also had little impact on rhizome production. Within sets of genetically identical ramets, flowering ramets were larger than non-flowering ramets. When there was an effect of habitat, ramets performed best in late successional forest. 4 Neither sexual nor asexual reproduction decreased the future performance of a ramet. Having connections to other ramets had little effect on survivorship or rhizome production, but often was associated with an increased probability of flowering. Clones with more ramets outperformed smaller clones and spread the risk of genet mortality. 5 Rhizome lengths were shorter in the high light, early successional forest, but no other clonal growth parameters differed between habitats. Empirically calibrated simulation and diffusion models indicated that the between-habitat differences in rhizome length were not great enough to affect the long-term expansion of clones. 6 Diffusion coefficients for the long-term spread by clonal growth or seed dispersal were compared for a number of species. Diffusion model results indicated that plants can disperse as far by clonal growth as they do by seed, although the values for A. canadense were 14 and 8895 [cm.sup.2] [year.sup.-1], respectively. 7 Asarum canadense appears to be under unusually strong selection for seedling survival. As has been observed for some other clonal plant species, few costs were found for either sexual or asexual reproduction. Keywords: clonal plants, diffusion models, dispersal, life-history data, sexual and asexual reproduction, stochastic simulation, vegetative spread

1 For terrestrial plants capable of both vegetative propagation and sexual seed production, we can distinguish clones from the spatial genetic pattern of plants using multi-locus measurement of allozymes, or other molecular markers. 2 The probability of clonal identity F(r) is defined as the probability that a randomly chosen pair of plants separated by a distance r belong to the same clone. It can be estimated from spatial genetic patterns of plants determined by multi-locus molecular methods. 3 If genotypes have the same competitive ability (no local adaptation), diffusion approximation shows that the equilibrium clonal identity function F(r) is proportional to exp [-cr]/[square root of r]. 4 The exponential rate of decline with distance, c, equals [square root of (2u/v[[Sigma].sup.2])], and is determined by the relative success of sexual vs. vegetative reproduction (u/v) and the mean square parent-offspring distance in successful vegetative propagation ([[Sigma].sup.2]). 5 We carried out computer simulations to confirm the usefulness of this formula in inferring demographic processes from spatial genetic data. The results hold irrespective of the dispersal range of sexual seeds. The integral of the probability of clonal identity is closely related to the average clone size. Keywords: average clone size, clonal plants, sexual reproduction, vegetative propagation

1 Strong spatial heterogeneity in male frequencies and allocation to male and female function was found within and between androdioecious populations of the wind-pollinated ruderal Mercurialis annua in south-western Spain. 2 Sex determination is largely genetic and the constancy from year to year of the frequency of males in small quadrats suggests that seed and pollen dispersal are very limited. 3 Male frequency correlated significantly with stand density in two populations in the field and varied nonrandomly between densities in a glasshouse density experiment, strongly suggesting an environmental component to sex determination. 4 In the density experiment, stand density had a strong negative effect on relative allocation to reproduction by both males and cosexes (monoecious individuals). At higher densities, cosexes were quantitatively more female than at lower densities. Also, larger males and cosexes produced more pollen per vegetative biomass than did smaller ones, while allocation to seed production by cosexes increased only proportionally with plant biomass, so that cosexual gender shifted consistently towards greater maleness in larger plants. 5 Males produced between about five and 10 times as much pollen as cosexes, indicating that cosex sex allocation is strongly female-biased. This, and inflorescence architecture, suggest that female-biased cosexuality in M. annua has evolved as a response to selection for facultative self-fertilization in a wind-pollinated species. 6 In M. annua, androdioecy appears to be maintained by a balance between selection for reproductive assurance during colonization, which favours self-fertile cosexuality with female-biased sex allocation, and frequency-dependent selection within populations, favouring increased male allocation and thus allowing the invasion and spread of males. Keywords: androdioecy, dioecy, reproductive assurance, trade-off, wind pollination

1 The dynamics of populations of Filipendula ulmaria during succession in an abandoned meadows in the centre of the Bialowieza Primeval Forest was studied over the period 1974-90. The growth and disintegration of individual genets was followed throughout succession. 2 In patches originally dominated by grasses and macroforbs, the number of genets increased rapidly to reach five to seven times the original number within about 8 years. A second increase in numbers was seen between 12 and 14 years, due to disintegration of the genets. In a patch dominated by sedges, the population grew slowly and the resulting small genets seldom disintegrated. 3 Expansion is followed by disintegration once critical size is attained. Change in size of genets and the ratio between generative and vegetative offspring resulted in the overall spatial structure changing from uniform to more clumped over the 17-year study period. 4 The number of ramets in a genet is correlated with the size and age of the genet. The growth and survivorship of new genets and genet fragments are limited by the gradually increasing necromass cover, and by the willow canopy. 5 Overall vegetation dynamics is strongly related to F. ulmaria populations in that: (a) the increase of abundance of F. ulmaria coincided with the start of succession; (b) the maximum abundance coincided with a transient stage in the succession from macroforbs to willow; (c) the decrease in abundance of F. ulmaria began when the meadow became dominated by willow. 6 The advancing senescence of Filipendula ulmaria genets, manifested in the necrosis of their senile parts, gives rise to free space within the genet area which is subsequently colonized by other species. The number of colonizers increases with the age and size of the genet, with continued species turnover taking place above 10 years of age. Senescence and disintegration of genets thus influence succession in abandoned meadows. Keywords: growth pattern, patch dynamics, senescence of genet, spatial pattern, succession, vegetative reproduction

1 The timing of appearance and the seasonal abundance of flower buds and flowers, and of green and ripe fruit of 61 species of native woody plants in the temperate rain forest of Chiloe Island (42 [degrees] 24 [minutes] S), Chile, were recorded over the course of 2 years. 2 We evaluated the effectiveness of climatic and ecological variables to predict phenological trends in this forest. 3 Unimodal yearly patterns were found both for flowering and fruiting events in the community. In some species bimodal tendencies were detected at the population and/or individual level. 4 Some species produced flowers and/or fruits all year long, but flowering was concentrated in spring and summer. Fruiting was less seasonal and more variable in the 2 years than flowering. 5 Length of flowering and fruiting, and the peak of flowering were best correlated with ecological variables such as pollination and dispersal modes, and with family membership. Phenological differences between life forms were due to associated differences in family membership and pollination and dispersal modes. No effects could be ascribed to successional status or habitat preference of species. 6 Mean monthly temperatures were strongly and positively correlated with the number of species in flower or in fruit, and flowering was negatively correlated with average air humidity and total monthly precipitation. 7 The length of the fruit ripening period showed no correlation with mean fruit size. 8 Reproductive phenology in Chiloe was largely constrained by seasonal climatic variables, but ecological variables also need to be considered to account for the observed patterns of flowering and fruiting in this temperate forest.

1 The allocation of resources among various reproductive structures and functions can suggest the relative importance of past selective pressures in moulding reproductive patterns. 2 To determine how male and female plants of the dioecious shrub Oemleria cerasiformis differ in allocation to reproductive functions, biomass was partitioned among reproductive structures for 20 plants of each sex. 3 Structures contributing to pollinator attraction (petals and hypanthium) were heavier in males than in females. In males, these structures constituted 63% of total reproductive biomass; inflorescence stems and bracts constituted 28%, and the androecium only 9%. In females at flowering, petals and hypanthium constituted 50% of reproductive biomass, inflorescence stems and bracts 37%, and the gynoecium 13%. 4 In females, fruits constituted 87% of the total reproductive biomass at average fruit set (13.7% of pistils). Even with the lowest observed fruit set (4% of pistils), fruit comprised 75% of reproductive biomass overall, and pollinator attraction no more than 4%. Fruit biomass was distributed about equally between pulp (offspring dispersal) and stone (offspring provisioning and protection). A flower can produce up to 150 times its own weight in fruit, thus fruit set is the main factor determining how biomass is distributed among reproductive structures in females. 5 These data support the view that the primary factors influencing the evolution of reproductive allocation are, in males, pollen limitation, and in females, the necessity of provisioning and dispersing offspring.

1. Light, pollen, and leaf area were manipulated to examine the role of each of these as determinants of reproductive success in the understory shrub Lindera benzoin. 2. Fruit set was significantly greater in the sun than in the shade, and was reduced in both habitats by shading branches. 3. Supplemental pollination added significantly more viable pollen to stigmas, but plants never responded with increased fruit set, even under conditions of high light availability. 4. Treatments had no effect on fruit and seed mass, but there was a significant maternal effect on these variables. 5. Treatments did result in a significant reduction in per branch flower production in the following year, especially on fruit-bearing branches in shaded sites and on artificially shaded branches. 6. Defoliations at the level of the branch significantly reduced fruit maturation. 7. The data indicate that branches within plants are somewhat physiologically autonomous; and, because light can affect fruit/seed set and flower production in this understory plant, gap dynamics may play an important role in its reproductive ecology.

1. The contribution of seed rain to the seed bank and to the seedling cohort was evaluated for three species, Abies balsamea, Acer saccharum and Betula alleghaniensis, in a deciduous forest near Quebec, Canada. Through experimental manipulations, seed-bank turnover time and rate of seed incorporation into the soil were estimated for these tree species. The forest floor was also modified in small quadrats to simulate various natural microsites; seedling emergence and early survival, and microsite characteristics were then monitored. 2. All Abies and Acer seedlings, and most Betula seedlings, originated from the previous year's seed rain. Abies and Acer were characterized by a winter-transient seed bank, but Betula maintained a persistent reserve of seeds in the soil. Turnover time of the Betula seed bank was c. 2 years in humus, but

1. Modules are important to plant growth because they have the meristems needed to produce daughter units. The module dynamics of single plants are examined in a model developed to evaluate the relative importance of seasonality and reproductive effort. The model is a logistic system in which K is the maximum number of modules per plant and r(t), the instant growth rate, is the capacity of modules to multiply under optimal conditions minus the costs of seasonality and flowering. 2. Simulations included adverse seasons varying in severity and frequency, different timings of births and deaths of modules, different flowering times and reproductive efforts, different performances under optimal conditions, and different maximum plant sizes. 3. Of all the parameters in the model, only the capacity to multiply and the combined costs of flowering and climatic severity had a substantial impact on early plant size. The rate of module accumulation slowed when plants got close to maximum size. Mathematically complex frequencies, timing and delays in mortality, growth and flowering can be disregarded. 4. The capacity to multiply vegetatively (r.sub.v) should be measured in newly emerged seedlings growing under optimal conditions. before the onset of negative size-dependent factors. Producing daughter modules early in the life of modules should be favoured when rapid growth is crucial. The value of [r.sub.v] limits the amount of reproductive effort, [Phi), and seasonal severity, [Sigma], that a plant can sustain. Plants should show increased reproductive effort at the climatically benign end of their range. Key-words: module demography, seasonality, reproductive episodes, reproductive effort Journal of Ecology, 1992, 80, 123-130

(1) Time of reproduction in Oenothera biennis was controlled experimentally by gibberellic acid applications in a glasshouse experiment. Performance of vegetative plants and plants reproducing at various ages was compared by means of growth analysis. (2) Regardless of age, reproduction increased stem allocation and decreased root and leaf allocation. Early reproduction reduced growth relative to vegetative plants, while late reproduction had no effect on growth in the long term and enhanced growth in the short term. Seed output increased with age at reproduction up to a point after which there was little change. (3) The reduced growth of plants reproducing at an early age was due to a decrease in leaf area ratio, and the enhanced growth of older plants to a temporary increase. Specific leaf area in older plants increased with reproduction, temporarily over-compensating for the decrease in leaf allocation. There was a temporary increase in unit leaf rate in plants reproducing at a young age but not in plants reproducing at a late age. (4) Changes in specific leaf area were the result of a switch in leaf morphology between vegetative and reproductive plants. Vegetative plants produced leaves with petioles which increased in length with age. This morphology minimized self-shading in the vegetative rosettes. Leaves produced after reproduction had short petioles and, consequently, a higher specific leaf area. Plants reproducing at an early age produced few new leaves and exhibited little change in specific leaf area. (5) It is suggested that the beneficial effects of reproduction on canopy structure and photosynthesis that are observed in many species can compensate for the cost of reproduction, providing the accumulated nutrient reserves are sufficient to supply the reproductive structures.

SUMMARY (1) Clonal replicates of Anthoxanthum odoratum were reciprocally transplanted between a relatively wet (mesic) and a relatively dry xeric) site in a northern California grassland. The survival, reproductive output and growth of the transplants was followed for three growing seasons. Flowering times were measured in the first two years. (2) Variation in mortality and total three-year reproductive output was almost completely determined by phenotypic plasticity. Total mortality over the study period was 80% at the xeric site and 30% at the mesic site. Most mortality at the xeric site occurred during the summer. Total reproductive output was over three times higher at the mesic site than at the xeric site. (3) Clones of xeric origin had a higher reproductive output in the first year and an earlier average age of first reproduction than clones of mesic origin. Mortality, reproductive output and growth for the mesic clones were more strongly size-dependent than for the xeric ones. Flowering time was earlier at the xeric site and for the xeric clones. No significant site-origin interactions were found.

SUMMARY 1) This paper reports the results of an investigation of spatial, temporal and individual variability of survivorship, growth rates and reproductive behaviour of a dioecious palm, Chamaedorea tepejilote, in a high evergreen tropical forest in Mexico. Mortality, number of leaves, stem height increment, number of inflorescences and probability of reproduction were observed for 810 individuals over four years on three permanent plots, each 20 m x 30 m in area. (2) Seedlings had the highest mortality. Mature plants that did not reproduce in four years had a higher mortality than those which reproduced. Sexes of C. tepejilote did not differ in mortality among plots. (3) The mean stem height increment of male and female (mature) plants ranged from 6 to 12 cm [year.sup.-1]. Individual variation in height increment over four years varied from 0 to c. 80 cm. Male plants showed spatial variation in growth rate but not females. Males produced significantly more leaves [year.sup.-1](2-3) than females (2-0). Both sexes had different rates of production of leaves among years. (4) Number of inflorescences produced [plant.-1] was positively correlated with the height of the plants in both male and female plants, but males produced significantly more inflorescences than females. The sexes did not show spatial variation in the production of inflorescences among plots. (5) The reproductive behaviour between years varied more in female than in male plants. Males were more constant than females in the probability of reproduction and in the number of inflorescences produced in four years. A few individuals contributed to the majority of the inflorescences produced in the four years studied: seventeen males of forty-seven plants and thirteen females of thirty-five plants produced more than 70% of the total inflorescences in one plot, and twenty males of forty-five plants and fourteen females of forty-five plants produced also more than 70% of the inflorescences in another one.

1 In gender dimorphic species, reproductive allocation (RA, the ratio of reproductive to vegetative biomass) is predicted to be greater in female plants than in male plants. Empirical research on dimorphic plant species supports this hypothesis. To date, of 44 dimorphic angiosperms for which RA has been reported in the literature, RA is greater in females than males in 40 species, is equal in four, and in no species is it greater in males. 2 In many instances where differential RA occurs, sexual dimorphism in morphological or physiological traits has been reported. This dimorphism is often attributed to the differing costs of reproduction or to selection to counteract such costs. 3 We investigated RA and other morphological and physiological characters in Gynatrix pulchella, a dimorphic species that we found ranges from dioecious to subdioecious or gynodioecious, depending on season and locality. Our results showed that contrary to our predictions functionally male plants allocated significantly more biomass to reproduction than female plants across three populations. Greater male RA was due to a combination of larger, more numerous flowers and lower leaf biomass per branch than females. 4 There were no detectable costs of greater RA in males in terms of decreased overall growth or increased mortality. Additionally, leaf nitrogen content was greater in males than in females and there were no between-sex differences in gas exchange. 5 The finding that male plants allocate significantly more resources to reproduction than females in G. pulchella is apparently a unique case. However, equivalent RA for the sexes does occur in gynodioecious species and we suggest that higher male RA in gynodioecious plants may be more common than predictions based on sexual systems involving pure males. 6 Our results challenge accepted theory that allocation to reproduction should be greater in female plants than in males. In light of these findings, predictions regarding which sex should allocate more to reproduction need to be revised to accommodate the diversity of plant sexual systems.

1 Demographic studies in natural habitats are important for understanding the life history and mechanisms of population persistence of particular species. For plants living in high-alpine habitats, it is of significant importance to what extent sexual or clonal reproduction contribute to population growth, but respective data are scarce. 2 We studied the demography of Geum reptans, an alpine plant which reproduces by seeds and by vegetative rosettes formed at the ends of above-ground stolons. In three consecutive years, growth, survival, and reproduction were measured in two populations with 579 and 301 individuals, respectively. The two resulting transition matrices per population were used to calculate population growth rates (?) and elasticities, and to perform stochastic simulations to assess the relative importance of sexual vs. clonal reproduction for population growth. 3 Population growth rates (?) varied from 0.999 to 1.074 among years and populations. The frequency of seed and stolon production was relatively constant over the years. However, there was interannual variation in seed germination (0.7u2.4%) and in establishment of clonal offspring (53u74%). 4 Elasticity analysis showed that changes in the survival of adults had the largest effect on ?, confirming the importance of longevity and persistence in the life history of G. reptans. 5 Stochastic simulations showed that in G. reptans, independently of location and year, both sexual and clonal reproduction did not significantly differ in their contribution to the population growth rate ?. Establishment from seeds contributes to population growth particularly in favourable years, while the more regularly occurring reproduction by clonal offspring may ensure population growth in less favourable years. 6 Sexual reproduction in clonal plants is frequently explained by the short- and long-term benefits of genetic variation and the need for dispersal and colonization, for which seeds are better suited than vegetative organs. Our results, however, show the importance of sexual reproduction in a clonal plant for local dynamics as well, and prove the power of matrix models to evaluate the relative contributions of the two reproductive modes.

1 We assessed the effects of population density and the spatial arrangement of genetically compatible mates on the seed set and pollen flow of a heterostylous, bumblebee-pollinated perennial, Primula sieboldii E. Morren (Primulaceae), by using an experimental population under natural pollination conditions. 2 We also examined the intermorph differences in the pollen dispersal distance and the frequency of self- and intramorph fertilization. 3 Seed set was significantly correlated with the number of opposite-morph flowers within 2 m in short-styled genets, and within 3 m in long-styled genets. 4 Mean pollen dispersal distance within the experimental population was 5.4 m, which was slightly shorter than that in a low-density population measured in a previous study (7.2 m). 5 The proportions of seedlings sired by the same morph or selfed were 10.2% and 3.0%, respectively, in long-styled mothers, compared with 1.9% and 0.0% among short-styled mothers. However, these differences were not statistically significant and no marked differences in pollen dispersal distances were observed between the two morphs. 6 Our results suggest that the presence of opposite-morph genets within several metres is essential for success of seed reproduction in P. sieboldii, irrespective of population density, and that stochastic deviation of the morph ratio in small populations is therefore likely to cause considerable reduction in seed set.

1 The series of steps used to regulate a plant's investment in reproduction in response to environmental stresses is a life-history strategy critical to maximizing fitness. We investigated how the andromonoecious herb Solanum carolinense regulates its maternal investment in response to stress from foliar and floral herbivory. 2 Most of the variation among S. carolinense individuals (ramets) in maternal investment occurred during the initiation of flower-bud primordia, with ramets initiating between 9 and 167 flower buds. 3 In response to simulated floral herbivory, S. carolinense regulated maternal investment by decreasing the abortion rate of flower buds, increasing the ratio of perfect to male flowers and decreasing the rate of fruit abortion. 4 In response to foliar herbivory, the plants increased the rate of fruit abortion and decreased allocation to perennial root growth. 5 Some individuals specialized at regulating during early phenological stages, others specialized at later regulation, and there appeared to be trade-offs between these strategies. 6 Because most plants must cope with multiple stresses that occur at different times in their phenology, such trade-offs suggest the presence of adaptive constraints. In particular, a plant's ability to tolerate damage by one species of herbivore may be constrained by the cost of lower tolerance of the damage caused by the other herbivores that feed on the plant.

1 We tested the hypothesis that the competitive ability of a plant changes during its lifetime, by evaluating variations in the relative influence of standing biomass and litter on plant performance. 2 Seedlings of two annual herbaceous species ('targets'), of contrasted life-forms (Crepis foetida and Bromus madritensis) were transplanted into an old-field. The competitive ability of seedlings, vegetative and reproductive plants towards neighbours was recorded over one growing season. 3 Fourteen traits related to plant morphology, growth and reproduction were measured to assess the competitive ability of targets. Relationships among traits were characterized to identify a set of traits as a surrogate of target competitive ability. 4 The two target species responded similarly. Early growth was facilitated by litter and, to a greater degree, by vegetative biomass. Thereafter, the effect of neighbouring vegetation on target performance was negative, with a maximum depressing effect on reproduction (especially seed number and date of flowering) despite a weak facilitative effect of litter. Plant basal diameter, measured at peak growth period, and total number of inflorescences per plant, were found to predict growth and reproductive components of competitive ability, respectively. 5 Assessing the effects of competition for population success from the response of vegetative plants will underestimate its importance because competition appears to exert its maximal impact on seed production.

1 Ecological context can significantly affect plant reproduction: in particular, differences in the relative allocation of resources to male and female function can contribute to gender variation. 2 We quantified variation in sex expression among populations of Antirhea borbonica, a sexually dimorphic woody pioneer species found both on young lava flows and in later stages of primary succession on the volcanic island of La Reunion. We also tested whether environmental conditions influence maternal fertility by experimentally manipulating resource levels in natural populations. 3 The polliniferous morph showed significant gender variation, from almost zero fruit production in pioneer populations to high fruit set, albeit of less than females, in late-succession. Repeated observations over 4 years showed that, even in pioneer populations, most polliniferous plants are capable of producing fruits. 4 A significant increase in fruit production by the polliniferous morph was observed after 2 years of resource supplementation in a pioneer population. 5 Sex ratios were close to 1 : 1 in all but one of 12 populations. Seeds and seedlings produced by the polliniferous morph in a late-succession population had significantly lower viability than those from females. These results indicate that there is strong selection against the maternal offspring produced by polliniferous plants and that, regardless of successional status, A. borbonica possesses a functionally dioecious sexual system. 6 The combination of multi-year surveys and experimental manipulation of resource availability provides evidence of phenotypic gender plasticity. This provides a novel illustration of how the heterogeneous environment of primary succession can influence trait variation.

1 Species attributes have been used to explain invasion patterns assuming the prevalence of biological mechanisms, although this approach often suffers several methodological and conceptual limitations, such as local idiosyncrasies, differences among habitats, phylogenetic constraints and insufficient sample size. 2 The relative importance of 15 species traits for explaining the abundance over 350 naturalized alien plant species was assessed across five Mediterranean islands (Corsica, Crete, Majorca, Malta and Sardinia). A comparative analysis accounting for phylogeny was used to examine variation in semi-quantitative estimates of species abundance in comparable habitats across the five island floras. 3 Species were divided into those with affinity for semi-natural, agricultural and ruderal habitats. Both vegetative and reproductive attributes were evaluated for individual islands and averaged across all islands. 4 Vegetative propagation, large leaf size, summer flowering, long flowering period and dispersal by wind or vertebrates were positively associated with average alien abundance across all five islands. Fewer significant trends were found in island-specific patterns. 5 The relative importance of a few reproductive traits is reflected in over-representation of Caryophyllales, Asterales and Poales (late flowering, large seed size and anemochory). Although significant covariation in traits was found there was no evidence for well-defined invasive syndromes. 6 Succulence was important in ruderal habitats, long flowering period in agricultural habitats and vertebrate seed dispersal in semi-natural habitats, suggesting that empty niches, avoidance of competitors and exploitation of mutualists, respectively, are important. 7 The study highlights the importance of estimating invasion success across a wide region, but analyses of specific invasion stages are also needed. Reproductive traits, which may be more relevant for long-distance colonization, and vegetative traits, which determine local dominance and persistence, were, nevertheless, both related to abundance within islands.

1 Male steriles (MS) must have a fitness advantage relative to hermaphrodites (H) if they are to be maintained in gynodioecious species. We report experiments in which we disentangle the relative contributions of seed size, inbreeding and maternal sex to the fitness advantage of male steriles in Plantago coronopus L. 2 Seed size effects were observed throughout growth experiments in the glasshouse and were reflected in all biomass measurements. In the field, seed size effects resulted in a fourfold increase in standardized seed production per initial buried seed after 2 years between small (mean weight = 0.13 mg) and large (0.20 mg) seeds. 3 Inbreeding depression, calculated from seed to seed was (delta) = 0.37 after one generation of selfing and (delta) = 0.93 after the second generation of selfing. Regression of log(1-delta ) on inbreeding level suggested synergistic epistasis in fitness. 4 Even after taking into account the effects of seed size and inbreeding level, the offspring of a male sterile mother had a 16% advantage over a hermaphrodite, but this disappeared when the progeny sex ratio (the ratio of MS : H individuals among the offspring) was taken into account. 5 In the field, offspring of large seeds had both a higher overall incidence of flowering, and a higher probability of flowering in their first year, thus generating an extra cohort of individuals. The high inbreeding depression in fitness after two generations of selfing was also due to a very low incidence of flowering among the S2 individuals. Flowering probability therefore appears to be a critical trait in this system. 6 In the field, the contributions of seed size variation (15%) and inbreeding (9%) combine with 48% higher seed production to give a total fitness advantage of 70% of male steriles relative to hermaphrodites. This is probably sufficient for maintenance of gynodioecy under nuclear-cytoplasmic inheritance of male sterility. 7 Both inbreeding effects (as a consequence of the sexual system) and pleiotropic effects (of the genes coding for male sterility) play a role in the maintenance of gynodioecy in this species, with an apparently greater role for the latter.

1 Patterns of biomass allocation to sexual and vegetative reproduction were examined in a perennial stoloniferous clonal plant, Potentilla anserina (L.) Rydb. ssp. egedii (Wormsk.) Hiitonen, in relation to intraspecific competition between monoclonal and multiclonal ramets. 2 We predicted that a lack of competition would generate allocation to rapid, short-distance spread (vegetative propagation), while the presence of competition would increase allocation to long-distance dispersal (sexual reproduction), and that the allocation shift would be more pronounced where the competing ramets were related. 3 P. anserina ramets were grown in a glasshouse in small pots, either alone (no competition) or with a size-matched ramet that originated from the same clone (within-genet competition) or a different one (between-genet competition). 4 Competition suppressed both growth and reproduction, but there was no treatment response in relative investment at the level of a whole genet, although both mother ramets and their daughters showed clear effects when analysed separately. 5 When experiencing competition, the mother ramet allocated relatively more to flowers, whereas allocation to vegetative growth was more intense when competition was absent. Allocation patterns were independent of the relatedness of competitors. 6 The results imply that P. anserina can modify the allocation of resources to different life-history traits according to competitive stress. Such flexibility is likely to reflect a shift in the optimal allocation strategy during the life cycle of a plant with a guerilla growth form with rapid exploitation of free space in a new patch by vegetative spread favoured. When spread becomes limited by competition, long-distance dispersal in space (seeds) or time (persistence) becomes beneficial.

1 Theory predicts that hermaphrodites adjust sex allocation in relation to the relative fitness contributions of male and female functions. Few studies have, however, focused on temporal variation in sex allocation within individuals. 2 We quantified temporal variation in allocation to male and female function of hermaphrodites of gynodioecious Thymus vulgaris across a single flowering season, in families from four natural populations grown in an experimental garden. 3 Allocation to pollen production and to seed set and germination varied significantly among sample dates, with male function highest when female function was lowest, and a significant negative correlation between pollen production and seed set among families indicated a trade-off between male and female function. 4 Females and hermaphrodites showed gender-specific flowering phenology: female plants achieved peak flowering later and flowered for a significantly shorter period than hermaphrodites. 5 The number of open female flowers was significantly positively correlated with pollen production by hermaphrodites. Hermaphrodite male function was maximized at the time of peak flowering by females in all four populations. 6 These results fit theoretical predictions that across-season variation in the mating environment could select for a temporal variation in hermaphrodite sex allocation, but other factors (e.g. variation in the selfing rate or resource levels) may also contribute to the observed pattern.

1 Habitat fragmentation and the resulting decline in population size can affect biotic interactions and reproductive success of plant species. We investigated the impact of habitat type, population size, morph type and frequency, plant density, floral display and predation on different reproductive components in 16 populations of the distylous self-incompatible perennial herb, Primula vulgaris, a rare, declining species in Belgium. 2 Although habitat type accounted for significant variation in population size, we did not find any relation between habitat type and either reproductive and vegetative characteristics. Population size, however, strongly affected reproductive success, such that plants in small populations produced significantly fewer fruits per plant and seeds per fruit, and therefore fewer seeds per plant. 3 No significant difference was found between morph types for any reproductive characteristic, nor an interaction with population size. However, when morph frequency was strongly biased (? 1 : 3), the proportion of flowers setting fruit and the number of seeds per fruit were significantly lower in individuals of the common morph type. 4 Within populations, individual plants varied tremendously in size and floral display. Total number of fruits per plant significantly increased with floral display, but the highest fruit set per flower was found at intermediate flower number. 5 The proportion of fruit suffering pre-dispersal predation per plant significantly increased with floral display, but this did not offset the potential fitness gains of producing a large display. Furthermore, the absolute number of predated fruits per plant was significantly and positively affected by the interaction of the total number of fruits per plant and the density of the population. Journal of Ecology (2004) 92, 5u14

1 We assessed the influence of the spatial pattern of leaf damage on growth and reproduction (through both male and female functions) of the wild gourd, Cucurbita pepo L. ssp. texana at three structural levels of the plant (nodes, primary branches and entire branch systems). 2 We applied concentrated or dispersed leaf damage treatments (removing 5% of original leaf area in both), and compared their effects on 12 traits, ranging from the production of new nodes through flower production to pollen performance and seed number/size. 3 Only one of the traits was affected by the spatial pattern of damage, and then only at the primary branch level, where pollen performance was greater in the concentrated than in the dispersed treatment. 4 Regardless of the spatial pattern of damage, we found that low to moderate levels of foliar damage significantly affected very few traits. This indicates a high tolerance of simulated herbivory. Overcompensation for one trait (pollen performance) occurred at the node and primary branch levels. 5 The results suggest that compensatory resources can be translocated within damaged branches.

1 Salinization is a growing environmental stress in wetland ecosystems world-wide. Several models have been proposed that predict clonal plant responses to stress, including that environmental stress stimulates sexual reproduction. 2 We conducted a common-garden experiment to investigate the effects of salinity on 10 natural populations of Iris hexagona, a clonal perennial endemic to freshwater and brackish wetlands of the North American Gulf Coast. 3 Salinity reduced vegetative growth but either increased or had neutral effects on sexual reproduction, consistent with the clonal stress hypothesis. Salinity of 4 [micro]g g-1 more than doubled the number of seeds produced compared with freshwater controls, but flower number and seed mass were unaffected. 4 Salinity reduced total below-ground mass by nearly 50% compared with controls, with no significant change in rhizome numbers. 5 Plants from 10 randomly selected I. hexagona populations differed dramatically in growth and reproduction, independent of salinity. Total biomass that accumulated over the 20-month experiment ranged across all treatments from 52 to 892 g, and flower numbers varied from 2.3 to 11.3 per replicate. 6 Populations did not respond differently to salinity, except with respect to above- : below-ground ratios, thus providing no conclusive evidence for local adaptation to salinity stress. 7 Our results concur with published models of plant reproductive strategies in variable environments, in that environmental stress stimulated sexual reproduction at the expense of growth. However, these models do not predict the observed sharp decline in seed production at near lethal salinity levels.

1 Life history theory predicts that reproduction incurs costs in terms of future growth and survival. In infertile environments reproductive events may accelerate nutrient turnover such that losses of limiting nutrients cannot be replenished by uptake from the soil. 2 We compared the effect of reproduction on nitrogen (N) turnover and N use-efficiency, i.e. the annual dry matter produced per unit N lost, of three carnivorous species of the genus Pinguicula on an infertile subarctic heath. We hypothesized that reproduction should increase N turnover, unless a larger N pool or improved N resorption can compensate for the losses associated with reproduction. 3 These carnivorous herbs showed a nitrogen use strategy similar to that of noncarnivorous plants (herbs and grasses) with a relatively low mean residence time (MRT) of N and a large dry matter productivity per unit N in the plant (annual N productivity). N pool size and the efficiency of N resorption from senescent leaves were similar in reproductive and non-reproductive individuals. Reproductive individuals had significantly larger annual N losses and thus a lower average MRT (0.8 vs. 1.8 years), with values [is less than] 1 indicating that the annual N losses are greater than the annual average N pool. Unless plants can enhance their nutrient acquisition, flowering may therefore impact on future growth and survival. 4 This study presents evidence for a direct link between reproduction, reflected in a higher relative allocation to inflorescences, turnover and N use-efficiency; the latter being reduced because of increased N turnover. The ranking of species in terms of reproductive allocation was the reverse of their ranking in terms of their N use-efficiency. Key-words: carnivorous plants, costs of reproduction, life-history, mean residence time, nitrogen productivity, nitrogen use-efficiency, Pinguicula, plant strategies, reproductive allocation, subarctic.

1 Patterns of fruit production in the subdioecious plant Astilbe biternata were used to test whether sex ratio is correlated with relative fruit production by females and males; whether males that produce large inflorescences also produce proportionally more fruit; whether male fruit production is correlated with habitat type; and whether pollen limitation could affect fruiting. 2 Inflorescence length, a good predictor for flower production, was surveyed along with percentage fruit production and sex ratio in 22 populations from throughout the species range, including eight populations where plants were growing in both roadside and understorey habitats. In one population, the percentage fruit production of males and females was assessed in relation to the distance from to the nearest pollen source. 3 There was significant variation in sex ratios among populations, but this was not correlated with relative (female:male) total fruit production. Fruiting males produced smaller inflorescences than either females or non-fruiting males, and within fruiting males, individuals with large inflorescences produced proportionally fewer fruits than those with small inflorescences. The proportion of males that produced fruit was higher in roadside than understorey habitats whereas all females produced fruit in both habitats. Female, but not male, percentage fruit production decreased with distance from the nearest potential pollen source. 4 Allocation patterns to fruiting differed between males and females. Percentage fruit production declined as inflorescence size increased for both males and females. Astilbe biternata males with a genetic propensity to produce fruit might produce smaller inflorescences, or fruit production might be determined by resource availability within the inflorescence after the inflorescence is produced. Key-words: dioecy, fruit set, gynodioecy, reproductive compensation, sex allocation

1 A trade-off between current and future reproduction, often referred to as the cost of reproduction, is a fundamental assumption in life history theory. In long-lived plants, large absolute differences in size between individuals, storage of resources between reproductive events and organ preformation may make such costs difficult to demonstrate, especially when only natural variation is considered. 2 The long-lived legume Lathyrus vernus shows large size differences compared with variation in carbon resource allocation, and is known to store resources in below-ground rhizomes. We therefore followed individual plants over a period of 4 consecutive years. We examined the cost of reproductive investment by comparing the performance of untreated plants that differed in size and herbivore damage. We also compared controls with plants where we experimentally reduced flowering in terms of fitness measured as: survival, growth, flower number, fruit:flower ratio and storage. 3 Natural patterns of flowering and fruiting provided no evidence of a negative relationship between current and future reproduction. Individuals that produced fruits did not experience a lower probability of surviving and producing fruits the following season compared with flowering individuals that failed to produce any fruits, even when differences in above-ground size and herbivore damage were taken into account. 4 Flower removal in a single season increased the allocation to the rhizome but the size of shoot buds for the next season was not increased. Experimental manipulation of reproductive effort by repeated removal of flowers during 3 consecutive years, however, resulted in a significant increase in vegetative size and the probability of flowering and setting fruit compared with control plants. 5 While long-term data on natural variation in fruit production and short-term experimental data provided no evidence of a cost of reproduction, such a cost is still present, although detectable only after repeated flower removal. Key-words: delayed response, flower removal, fruit production, long-term flowering pattern, organ preformation Journal of Ecology (2001) 89, 237-246

1 The expansion histories of two South American species of Cortaderia, similar in morphology but differing profoundly in their breeding systems, were compared in California, USA. 2 Both species were introduced to California in the mid-1800s, but herbarium records indicate that the sexual C. selloana has expanded spatially at twice the rate of the asexual C. jubata. 3 The invasiveness of C. selloana has increased over time, whereas that of C. jubata has remained relatively constant. Populations of C. selloana now occupy more vegetation types and more non-ruderal habitats than C. jubata. 4 Populations of C. selloana have experienced directional morphological change, whereas the morphology of C. jubata has been constant over the 90 years for which preserved specimens are available. 5 The invasion of an alien species appears to be a malleable process, rather than a singular event. Species traits, such as inbreeding, can be advantageous at some stages but disadvantageous at others. Alien species also adjust over time to the novel and diverse selective regimes that they encounter as they expand spatially. Sexual species may have a greater ability to adjust to diverse selective landscapes relative to asexual species. Key-words: evolution, history, inbreeding, invasion, invasive plants, pampas grass. Journal of Ecology (2001) 89, 88-98

1 Achnatherum calamagrostis (L.) Beauv. is a perennial, tussock forming grass which is conspicuously successful as a pioneer in badlands in submediterranean areas. We analysed its population dynamics using a matrix population model that is intermediate between traditional demographic models and fully spatially explicit models. 2 Tussocks are considered as a set of spatial units, each classified according to the number and state (seedling, juvenile or adults) of the tillers it contains. The growth rate ([[Lambda].sub.i]) determined from the model estimates the spatial spread of A. calamagrostis as a rate of increase in the number of occupied quadrats. 3 We constructed six projection matrices from data for populations on two substrate types, in 2 years with differing climatic conditions and considering the whole life cycle or eliminating sexual reproduction or vegetative multiplication. 4 All the matrices predicted growth rates greater than one. Sexual reproduction was an important process for spatial spread in A. calamagrostis, unlike many other perennial grasses. In contrast, new colonization by vegetative reproduction contributed little to spatial growth of populations, although some expansion may still be possible in the absence of sexual reproduction. 5 A. calamagrostis, like other tussock-forming plants, exhibits a conservative tactic of slow spread. Tiller dynamics serve mainly for consolidation and maintenance of the plant in already occupied space and sexual reproduction is the main way to ensure colonization of new safe-sites. Climatic conditions influenced growth rates which increased during non-drought years above the near maintenance value seen in drought years. Key-words: clone, elasticity analysis, matrix models, sexual reproduction, temporal variability Journal of Ecology (2000) 88, 950-963

(1) This study evaluates the role of vegetative reproduction in the genet-level demography of Oenocarpus mapora ssp. mapora, a clump-forming subcanopy palm. Both genet and ramet dynamics were studied over a six-year period on Barro Colorado Island, Panama, within permanent plots in three sites: 'mature forest', advanced 'secondary forest', and windthrow-prone 'disturbed forest'. (2) All ramets develop through a fixed sequence of morphological stages; a genet's stage-class is determined by the stage and size of its largest ramet, which defines genet functional status within the population. A genet establishing from seed develops through two single-ramet stages (seedling and non-clonal juvenile), followed by three clonal stages (clonal juvenile, subadult and reproductive adult). (3) Both ramet growth rates and ramet survivoship increase with ramet size and developmental stage. High within-stage variation in ramet growth suggests tolerance of understorey suppression but opportunistic response to higher light levels. Higher ramet growth rates were observed in the 'secondary forest' site following several large treefall events in the first year of the study. (4) Rates of daughter ramet production by clonal genets average < 1 per genet [year.sup.-1]. A genet appears to produce daughter ramets when environmental conditions also favour vigorous growth and sexual reproduction by existing ramets. In contrast to non-clonal stages, survivorship of clonal genets is very high because treefalls and windthrows, a major mortality factor for all stage-classes, rarely kill all ramets within a genet. Genet flowering frequency increases with adult clone size, and flowering is stimulated by high light levels. (5) A static population structure in the 'mature forest' site is evident in its low genet population density, high dominance of large adult clones and poor seedling recruitment. In contrast, high genet population density, high juvenile dominance and good seedling recruitment in the 'disturbed forest' site suggest that O. mapora may be especially favoured in habitats prone to canopy disturbance. A year of very high seedling recruitment in the 'disturbed forest' site followed a severe dry-season drought that opened the canopy by killing many canopy-level O. mapora stems. (6) In O. mapora, the clonal habit spreads mortality risk to the genet among ramets capable of independent existence. Other benefits may also occur. Genet-level study supports a view of vegetative reproduction as a growth process that enhances genet survival and reproductive value.

(1) Factors affecting the germination, survival and reproduction of field populations of a hemiparasitic summer annual (Euphrasia pseudokerneri) and two strict biennials (Linum catharticum and Gentianella amarella) were examined at two chalk grassland sites. Data are also provided on a second annual (E. nemorosa). (2) In the field, germination of E. pseudokerneri, Linum and Gentianella was restricted to a narrow 'window' of germination sites where mean turf height was only 1-3 cm. All three species germinated poorly in longer turf, and E. pseudokerneri and Linum also germinated less well in very short areas. Survival of E. pseudokerneri, Linum and Gentianella, and reproductive output of Gentianella, were higher in areas of short turf. Overall, Gentianella was the most sensitive to turf height and Linum the least. (3) Mortality rates of E. nemorosa, Linum, and (especially) E. pseudokerneri were higher during dry periods even over three years of normal rainfall, but Gentianella was not affected. (4) Experimental treatments, applied in the field, showed that E. pseudokerneri survival was decreased by adding nitrate, and increased by clipping the turf, by adding water and by excluding rabbits; E. pseudokerneri fecundity was increased by excluding rabbits and by adding phosphate; and Linum survival and fecundity were increased by regular applications of snail poison. (5) The performance of each species was affected by a unique suite of factors which varied between years.

(1) Larvae of the two tortricid lepidopterans, Synnoma lynosyrana and Synalocha gutierreziae, form silk cases that tie together a significant proportion of the photosynthetic stems and leaves of the common rangeland perennial, Gutierrezia sarothrae, which are toxic to cattle. (2) These insects were significantly more abundant in cattle-grazed plots than in ungrazed plots of the Sevilleta National Wildlife Refuge, located in central New Mexico, USA. (3) Using these herbivores as the experimental manipulation of the plant, measurements were made of photosynthetic area and proximate reproduction of plants with both tied and control (non-tied) branches. In within-plant comparisons, tied branches had significantly less photosynthetic area than control branches. The number of flowers/branch, flowers/capitulum, seeds/branch and seeds/capitulum were all significantly greater for control than for tied branches. However, seeds produced by tied branches germinated more rapidly and at a higher percentage than seeds from control branches over the same time period. (4) The onset of senescence occurred on smaller volume plants in the ungrazed, high larval abundance plots than in the grazed, low larval abundance plots. (5) The results suggest that, at natural levels of tissue loss, Synnoma and Synalocha can seriously affect both the photosynthetic area and the reproduction of individual plants, and can thus potentially affect Gutierrezia population dynamics.

1 Using a combination of observational and experimental approaches, both allocation of resources to reproduction (often called the direct cost of reproduction) and the subsequent long-term costs (the indirect, delayed or demographic cost) associated with reproductive allocation to male and female function in Siparuna grandiflora (Siparunaceae), a tropical dioecious shrub, were examined. 2 The objectives were to determine whether females allocate more biomass or nitrogen per reproductive episode than males, and whether there is a long-term cost of reproduction in terms of subsequent growth or reproduction for either sex. If there is no long-term cost of reproduction, then reproduction may be viewed as free in an evolutionary sense. 3 As is generally the case in dioecious species, females allocated more biomass and nitrogen to reproduction than males. Females also showed delayed costs of reproduction in terms of decreased growth and subsequent reproduction, whereas males did not. 4 The lack of measurable delayed costs in males suggests that with the evolution of dioecy, selection has reduced delayed costs of reproduction in S. grandiflora males. In contrast, females that were prevented from reproducing were able to re-allocate resources to growth, and produced more stem length on average than males. This reallocation response may have evolved to reduce delayed costs of reproduction in females over time frames longer than that considered in the present study. Keywords: demographic costs of reproduction, direct costs of reproduction, fruit production, sexual dimorphism

1 The clonal cactus Opuntia rastrera shows predominantly sexual reproduction in grasslands (GH) and clonal propagation in nopaleras (NH). We assessed the effects of light, herbivory, water availability and the habitat an offspring came from on the survival and growth of sexual or clonal offspring (i.e. seedlings and cladodes), through 3- and 4-year common garden and short-term greenhouse experiments. 2 Shading by nurse plants increased seedling survival in the field by an order of magnitude, and a small additional advantage due to predator protection by grasses was observed. Strong herbivory transforms a facultative nurse-protege relationship for seedlings into an obligatory one. 3 In the greenhouse seedlings grew better under shade, but in the field the production of the first cladode was delayed in seedlings in the more shaded GH. Competition for soil resources may be more intense under a dense grass tussock than under a open shrub, thus affecting the nurse-protege relationship. Seedling survival under nurse plants was similar in GH and NH, but higher plant cover suggests that a larger number of seedlings will establish in GH in the long term. 4 Cladode survival was higher in NH. Cladodes were more successful than seedlings at establishing in intercanopy areas, possibly due to physiological differences as well as their ability to survive partial predation. Cladode survival in intercanopy areas may explain the enhanced clonal propagation in the more open NH scrubland, together with their susceptibility to the flooding which affects GH. 5 The high seedling and cladode survival in the greenhouse experiments contrasted with that observed in the field, indicating that survival is determined by the interaction between herbivores, plants and abiotic conditions rather than the physiological aptitude of the plants. Keywords: Cactaceae, clonal vs. sexual recruitment, herbivory, nurse plants, Opuntia rastrera