Seasonal patterns of diet and ranging in two species of tamarin monkeys: Stability versus variability

From June through December, data were collected on the diet and ranging patterns of moustached (Saguinus mystax) and saddle-back (Saguinus fuscicollis) tamarin monkeys in the Amazon Basin of northeastern Peru. During this 7-month period, insects and nonleguminous fruits accounted for 83% of tamarin feeding and foraging time. Despite marked seasonal variation in rainfall and forest productivity, patterns of habitat utilization, day range, dietary diversity, resource exploitation, and activity budget remained relatively stable throughout the year. Moustached and saddle-back tamarins appear to solve problems of food acquisition and exploit patchily distributed feeding sites using a relatively limited set of foraging patterns. In general, these primates concentrate their daily feeding efforts on several trees from a small number of target plant species. These feeding sites are uncommon, produce only a small amount of ripe fruit each day, and are characterized by a high degree of intraspecific fruiting and flowering synchrony. Trees of the same species are frequently visited in succession, and individual feeding sites are revisited several times over the course of 1–2 weeks. This type of foraging pattern occurred during both dry and wet seasons and when exploiting fruit, nectar, legume, and exudate resources. Seasonal variation in the percentage of feeding and foraging time devoted to insectivory was also limited. In this investigation, there was no consistent evidence that temporal changes in overall forest fruit production had a major impact on the feeding, foraging, or ranging behavior of either tamarin species.     

A classification of subtropical riverine grassland and forest in Chitwan National Park,Nepal

Eight grassland associations with ten phases and two riverine forest associations were identified on the floodplains of Chitwan National Park in lowland Nepal. TwoThemeda arundinacea associations were primarily stable edaphic associations on mollic soils, often with aquic moisture regimes.Themeda associations were floristically similar to adjacent sal forest. Four mixed tall-grass associations primarily ofNarenga porphyrocoma, Saccharum bengalense, andSaccharum spontaneum were identified. These andThemeda arundinacea types were characterized by a very weak component of woody species. Two grass-shrub associations ofSaccharum bengalense andNarenga porphyrocoma with a strong woody species component typical of riverine forest were described.Trewia nudiflora-Bombax ceiba riverine forest and mixed riverine forest types also were identified on the basis of understory composition. Mixed tall-grass and grass-shrub associations appeared to represent early and late phases of grassland succession to riverine forest. Trajectories of succession are controlled primarily by fire and wildlife grazing. The classification refines the general classifications applied to the central Terai of Nepal and India, and should provide insight for classification of other Terai riverine grasslands.Abbreviations DS Dabadghao and Shankarnarayan's 1973 grassland classification for India - IMCY Imperata cylindrica - NAFA Narenga fallax - NAPO Narenga porphyrocoma - PHKA Phragmites karka - SABE Saccharum bengalense - SASP Saccharum spontaneum - THAR Themeda arundinacea     

基于数字标本探究绿绒蒿属植物花期的变化

近年来,随着全球气温的明显升高,气候变化引起的全球变暖受到人们的广泛关注.气候变暖会使植物物候发生改变,花期的变化能够直观地反映出植物对周围环境的适应,尤其是高山植物对气候变化更为敏感,因此探究高山植物的花期更具有代表性.为了解植物在气候变暖背景下花期的变化特征,并制定出合理的植物保护措施,该文以典型的高山植物绿绒蒿属...     

Spatial and temporal variation of benthic Cladocera (Crustacea) studied with activity traps in Lake Myvatn, Iceland

Benthic Cladocera were studied with a modified type of an activity trap in Lake Myvatn in 1990–1992. After feasibility experiments, the operation time and the distance of the traps from the benthic substrate were adjusted in order to minimize the effects of diurnal variation and the trapping of planktonic organisms. The trap catches of Eurycercus lamellatus were positively correlated with their abundance at the bottom as estimated by grab sampling (r = 0.910, P < 0.001). The usefulness of the activity trap was demonstrated by: (1) a lake-wide survey of the benthic Cladocera; (2) a study of the seasonal variation in the size distribution, abundance and sex ratio of E. lamellatus; and (3) a study of the seasonal succession of Chydorus sphaericus and Alona affinis. The variation of benthic Cladocera among 21 trap sites distributed on a 1–2-km scale across the lake exceeded the within-site variation. The sampling sites could be divided into five main groups based on cluster analysis. Eurycercus lamellatus was the most common species in the mat of filamentous green algae (Cladophorales). Alonella nana dominated the area of spring water inflow in the north basin and Macrothrix hirsuticornis the area of spring water inflow in the southeastern part of the lake. In other parts of the lake either Chydorus sphaericus or Alona quadrangularis tended to dominate. The size distribution and sex ratio of E. lamellatus was followed at two sites through one summer. In early summer most individuals were females less than 1.45 mm long. Around mid-summer they had grown to 0.69–3.1 mm. By the end of August the size distribution had become bimodal, with a large number of small males and a smaller number of much larger females. The seasonal succession in the abundance of E. lamellatus, A. affinis and C. sphaericus was followed at four sites over two seasons. With some exceptions the abundance of a species followed a similar seasonal trajectory on the different stations in any one year. There was, however, a marked difference between the two years (1991 and 1992), probably related to different temperatures.     

Phenology of nine common woody species in semi-arid,deciduous Kalahari Sand vegetation

The phenological patterns of 9 woody species that are common components of Kalahari Sand communities were observed over a period of 32 months. The observations were made on plants adjacent to the soil moisture study sites which have been described earlier (Childes & Walker 1987). A pre-rain flush was noted in the 2 shrub/small tree species Ochna pulchra and Terminalia sericea. Leaf fall in all species was related to a decrease in soil moisture and minimum temperature. The rooting habits and other adaptations of the species resulted in a sequential leaf fall in the communities. Open woodland and scrub species such as Pterocarpus angolensis showed a generally synchronised pre-rain flowering, while the closed woodland species e.g. Baikiaea plurijuga had protracted asynchronous flowering periods. Fruit ripening generally occurred in the dry season when conditions were ideal for fruit and seed dispersal.     

Endogenous and environmental factors influence 35S promoter methylation of a maize A1 gene construct in transgenic petunia and its colour phenotype

Summary 30000 transgenic petunia plants carrying a single copy of the maize A1 gene, encoding a dihydroflavonol reductase, which confers a salmon red flower colour phenotype on the petunia plant, were grown in a field test. During the growing season plants with flowers deviating from this salmon red colour, such as those showing white or variegated phenotypes and plants with flowers exhibiting only weak pigmentation were observed with varying frequencies. While four white flowering plants were shown at the molecular level to be mutants in which part of the A1 gene had been deleted, other white flowering plants, as well as 13 representative plants tested out of a total of 57 variegated individuals were not mutants but rather showed hypermethylation of the 35S promoter directing A1 gene expression. This was in contrast to the homogeneous fully red flowering plants in which no methylation of the 35S promoter was observed. While blossoms on plants flowering early in the season were predominantly red, later flowers on the same plants showed weaker coloration. Once again the reduction of the A1-specific phenotype correlated with the methylation of the 35S promoter. This variation in coloration seems to be dependent not only on exogenous but also on endogenous factors such as the age of the parental plant from which the seed was derived or the time at which crosses were made.     

浙江低山地区多用途植物无患子的开花物候特征

无患子(Sapindus mukorossi Gaertn.)是我国长江以南地区传统的重要绿化树种,其果皮富含皂苷,种仁富含油脂,是国家林业局审定的新型木本油料树种之一。为研究多用途树种无患子在浙江低山地区的开花特征,2012年和2013年连续两年对位于浙江省天台县9年生无患子人工林在群体、个体、花序和单花水平进行开花物候观测和比较,并运用开花日期、相对开花强度和同步性等指数研究了无患子开花物候特征。观察结果显示:无患子花呈浅黄白色,花的类型有雄花和两性花,没有发现雌花。雄花较两性花大(花径分别为5.09 mm和3.72 mm),雄蕊多为8枚,个别7或9、10枚;雌蕊退化仅留下浅绿色凸起。两性花花萼稍抱拢,花药藏于花被片下,雄蕊大多8枚,极少数7枚或9枚,柱头高于花药并伸出花苞,子房一般具3室,极少数4室或仅2室。无患子2012年的开花进程略早于2013年,其花期集中在在5月中旬至6月上旬,单花从花蕾膨大到花朵凋谢一般为8—9 d。在2012年和2013年,无患子在群体、个体和花序水平的花期约为30 d、20 d、11 d和28 d、19 d、13 d。个体水平的开花振幅均呈单峰曲线,年际间相似性较高;开花同步性在个体水平同步性较高(同步指数为0.868),表现出一种大量、集中的开花式样;相对开花强度在单株间分布范围相对宽泛,但主要分布在30%—40%,在年际间和年际内均呈现极显著差异。花期同步指数在两年的变异范围分别是0.81—0.97和0.70—0.98,不同单株开花同步性在年际内差异极显著,但在年际间差异性则不显著。由此可见,无患子的生殖资源分配存在明显的时空差异,较长的花期可以减少非法花粉的干扰、保持其种群基因多样性,遗传因子是决定无患子开花物候的主要因素,生态环境对无患子开花物候的影响还需进一步研究,本研究以期为探索无患子开花的主要限制因子奠定基础。     

Effects of grazing intensity on growth,reproduction, and abundance of three palatable forbs in Kansas tallgrass prairie

The effects of different intensities of cattle grazing on theaboveground growth, reproduction, and abundances of three palatable forbs werestudied in native tallgrass prairie. Populations of Asterericoides, Ruellia humilis, andAmorpha canescens were sampled at peak flowering duringthe1993–1995 growing seasons in four annually-burned sites varying incattle stocking density [ungrazed, low, moderate, high]. The threeforbs exhibited reduced shoot growth and/or reproduction under moderate toheavy grazing, and in no case did grazing increase any measure of plantperformance. Ruellia showed reduced shoot height andbiomass, percentage of stems flowering, and reproductive biomass in response tograzing. Aster showed decreases in shoot biomass andheightwith grazing. Amorpha showed no change in shoot orreproductive biomass, but a decrease in percent of flowering stems and inreproductive allocation with grazing. Patterns in the percentage of stemsgrazedindicated generally high but variable palatability among these species. Bycontrast, the three species showed inconsistent population response to grazing.Abundance (frequency) of all three species indicated no short-term changebetween years in response to grazing intensity. Responses of these speciesdiffer considerably from those of most other perennial tallgrass prairie forbsthat are unpalatable, unconsumed, and increase in performance (e.g. size,abundance) due to release from competition from the dominant grasses underungulate grazing. The results demonstrate that immediate aboveground growth andreproductive responses of established adults to grazing are not good predictorsof grazer effects on population abundances in tallgrass prairie.     

斗竹的开花生物学特性研究

通过野外观测及光学解剖,观察了斗竹(Oligostachyum spongiosum)开花林相、开花动态、花器官构造、结实情况,以及花后林相更新等生物学特性,采用光学显微技术结合石蜡制片,对斗竹的大、小孢子的发生及雌、雄配子体的发育过程进行研究。结果表明：(1)斗竹为一次性整体开花竹类,花期为4月下旬～5月下旬,花期约持续45 d,成花量大。(2)花序为圆锥状混合花序,每花序由4枚小穗构成;小穗细长,每枚小穗由5～17枚小花组成;小花为颖花,顶部小花不发育,外稃、内稃各1枚;浆片3枚,卵圆形;雄蕊4～6枚(多为6),每枚花药具有4个花粉囊,花药壁发育为基本型,绒毡层为腺质型,小孢子四分体为左右对称型,成熟花粉粒为2 细胞型,球形,表面纹饰颗粒状,具单个萌发孔,花粉发育过程中部分花药出现异常收缩及空腔的败育花粉粒;雌蕊1枚,柱头3叉,羽毛状,子房1室,胚珠倒生,厚珠心,胚囊为蓼型,成熟胚囊结构及发育过程均正常;雌雄同熟,异花授粉,果实为颖果。(3)斗竹花后全林死亡,结实率低,自然条件下结实率为8.1%。研究结果为研究竹子系统分类、开花机制,开展杂交育种及竹林更新复壮工作等提供基础性资料。     

Clonal growth of <Emphasis Type="Italic">Typha domingensis</Emphasis> Pers., subject to drawdowns and interference of <Emphasis Type="Italic">Eleocharis mutata</Emphasis> (L.) Roem. et Schult. in a tropical coastal lagoon (Brazil)

This paper presents the results of a study on the clonal growth of Typha domingensis Pers. in the Imboassica lagoon, in the intervals between four drawdowns. Sampling was performed over a period of two years, from permanent quadrats, in the four months after each of the drawdowns. The high mortality of the macrophytes after each drawdown is followed by a period in which the stands recover by producing ramets. The results have shown that the growth areas around the boundary of the stand (boundary band, BB) and one further towards the middle (innermost zone, IZ) show different recovery characteristics. The BB area recovered more quickly after the first drawdown, but both areas had the same accumulated biomass after the third drawdown. At the contact boundary, (CB) with stand of Eleocharis mutata, a decrease in the growth of T. domingensis occurred with a progressive invasion of E. mutata in its stand. After 10 months with no drawdown, T. domingensis produced a large quantity of inflorescences, which indicates recovery. It can therefore be concluded that successive drawdowns may decrease the regeneration ability of T. domingensis, favoring the expansion of E. mutata in the lagoon.     

Significance of intra-inflorescence variation on flowering time of a spring ephemeral, <Emphasis Type="Italic">Gagea lutea</Emphasis> (Liliaceae), under seasonal fluctuations of pollinator and light availabilities

I studied the relationship between seed-set patterns within inflorescences and temporal variations in light and pollinator availabilities for 2 years in the spring ephemeral species Gagea lutea in a deciduous forest. Timing of canopy closure and seasonal trend of pollinator frequency did not synchronize with the annual fluctuation in flowering phenology. In the early snowmelt year, seed-set success reflected the seasonal pollinator abundance from early to middle flowering periods. In the late snowmelt year, however, seed-set rates were independent of pollinator activity and decreased with canopy closing even after hand pollination. The restricted seed production by defoliation and the increase in seed-set rates at the forest edge suggested that seed production was supported by current photosynthetic carbon gain. Thus, annual fluctuations of reproductive success can explain the variation in flowering phenology within a population although seasonal light deterioration would serve as a selective force for flowering in the early season.     

Succession of microfungal assemblages in decomposing peatland plants

We investigated the microfungal assemblages in the decomposing tissues of dominant plant species in two peatlands in southern boreal Alberta, Canada, to determine if distinct patterns of succession of microfungi occurred throughout the first two years of decomposition. These plant species were Sphagnum fuscum from a bog and Carex aquatilis leaves and rhizomes and Salix planifolia leaves and roots from a riverine, sedge-dominated fen. Canonical correspondence analyses, a multivariate statistical analysis used infrequently in mycological research, revealed distinct patterns of fungal species succession in two of the five litters (S. fuscum and C. aquatilis leaves). Furthermore, our analyses showed that substantially different microfungal assemblages were associated with these litters within the first two years of decomposition. Litter quality variables, such as total nitrogen, total phosphorus, and total carbon tissue nutrient concentrations, explained most of the succession patterns and differences in the microfungal assemblages of these five litters. Our data did not reveal the classical taxonomic zygomycete – ascomycete/fungi imperfecti – basidiomycete pattern of succession during organic matter decomposition. Similarly, a succession of functional groups of microfungi, i.e., cellulose-degraders preceding lignin-degraders, generally was not apparent. Instead, microfungi with broad spectra of enzymatic abilities co-existed over the first two years of decomposition in these peatland plant litters. These microfungi have a limited ability to decompose complex phenolic polymers, such as lignin, resulting in the accumulation of peat in these ecosystems. Some microfungal taxa were not affected by changes in litter quality, environmental variables, or surface water chemistry and were present at all stages of decomposition.     

Seasonal variation in phytoplankton composition and physical-chemical features of the shallow Lake Doïrani,Macedonia, Greece

Phytoplankton species composition, seasonal dynamics and spatial distribution in the shallow Lake Doïrani were studied during the growth season of 1996 along with key physical and chemical variables of the water. Weak thermal stratification developed in the lake during the warm period of 1996. The low N:P ratio suggests that nitrogen was the potential limiting nutrient of phytoplankton in the lake. In the phytoplankton of the lake, Chlorophyceae were the most species-rich group followed by Cyanophyceae. The monthly fluctuations of the total phytoplankton biomass presented high levels of summer algal biomass resembling that of other eutrophic lakes. Dinophyceae was the group most represented in the phytoplankton followed by Cyanophyceae. Diatomophyceae dominated in spring and autumn. Nanoplankton comprised around 90% of the total biomass in early spring and less than 10% in summer. The seasonal dynamics of phytoplankton generally followed the typical pattern outlined for other eutrophic lakes. R-species (small diatoms), dominant in the early phase of succession, were replaced by S-species (Microcystis, Anabaena, Ceratium) in summer. With cooling of the water in September, the biomass of diatoms (R-species) increased. The summer algal maxima consisted of a combination of H and M species associations (sensu Reynolds). Phytoplankton development in 1996 was subject to the combined effect of the thermal regime, the small depth of mixing and the increased sediment-water interactions in the lake, which caused changes in the underwater light conditions and nutrient concentrations.     

Pollination-related characteristics in the mimosoid legumeAcacia terminalis (Leguminosae)

Intraspecific variation has been found for several pollination-related characteristics in two isolated populations of the self-incompatible treeAcacia terminalis: floral characteristics including colour and flowering time; style length; size and colour of extrafloral nectaries on the leaf petioles; chemical components of the extrafloral nectar; different taxa of bee pollinators; and frequency differences in bird pollinators. These differences possibly reflect the evolution of two different pollination syndromes within this species.     

Succession in the southern part of the Canadian boreal forest

Forest succession following fire in a forest mosaic of northwestern Quebec has been studied in order to: (1) describe the successional pathways using communities of different ages and (2) evaluate convergence of successional pathways and possible effect of fire suppression on the establishment of steady-state communities. As a first step, ordination and classification techniques were used in order to remove changes in forest composition which are related to abiotic conditions. Then, ordinations based on tree diameter distributions were used to study shifts in species composition in relation to time since the last fire.Even under similar abiotic conditions, successional pathways are numerous. However, regardless of forest composition after fire, most stands show convergence toward dominance of Thuja occidentalis and Picea mariana on xeric sites and dominance of Abies balsamea and Thuja occidentalis on more mesic sites. Stable communities of >300 yr occur on xeric sites while on mesic sites directional succession still occurs after 224 yr. Nearly all species involved in succession are present in the first 50 yr following fire. Only Abies balsamea and Thuja occidentalis increase significantly in frequency during succession. Following initial establishment, successional processes can generally be explained by species longevity and shade tolerance. Early successional species may be abundant in the canopy for more than 200 yr while the rapid decrease of Picea glauca, a late successional species could be related to spruce budworm outbreaks. Considering the short fire rotation observed (about 150 yr), a steady-state forest is unlikely to occur under natural conditions, though it may be possible if fire is controlled.     

A six-year study of fire-related flowering cues and coexistence of two perennial grasses in a wet longleaf pine (<Emphasis Type="Italic">Pinus palustris</Emphasis>) savanna

Integrating population and community ecology can improve our understanding of the impacts of natural disturbances. Fire-stimulated flowering occurs in many long-lived herbaceous species of fire-maintained grasslands and savannas. Coexistence of these long-lived species may be affected in part by interspecific differences in the effect of fire-stimulated flowering on resource conservation, clonal growth, and longevity. This study comprised two parts. The first part investigated the effectiveness of different fire-related cues on fire-stimulated flowering in two cooccurring dominant grass species in a wet longleaf pine (Pinus palustris) savanna in southeastern Mississippi, USA. The second part investigated the immediate effects of the most important of these cues (damage and removal of aboveground vegetation and surface litter in May) along with nutrient addition on several measures of fitness and abundance over 6 years. Despite being a very effective inductive cue, when repeated frequently over 6 years, clipping plus surface litter removal significantly reduced flowering in both species. This negative effect was reduced to some extent by nutrient addition in Muhlenbergia expansa (which exhibited higher reproductive investment following clipping and fire than did Ctenium aromaticum). Frequent clipping resulted in an increasing numerical advantage of C. aromaticum over M. expansa with time. There was evidence of a modest release of C. aromaticum from competition with M. expansa in response to annual clipping. Responses suggest that suppressing flowering until after fire reduces the cost of flowering and maintains shoot densities, at least in M. expansa. Differences in the responses of these two species to repeated clipping and nutrient addition suggest that, despite their both exhibiting fire-stimulated flowering, each species is favored by slightly different fire frequencies. Moderate variation in fire frequency could maintain their coexistence in the long term.     

Survival ofSclerotinia minor Jagger sclerotia in solarized soil

Calcium, magnesium and potassium dynamics in decomposing litter of three tree species were measured over a two-year period. The speices studied were flowering dogwood (Cornus florida), red maple (Acer rubrum) and chestnut oak (Quercus prinus). The order of decomposition was:C. florida>A. rubrum>Q. prinus.Calcium concentrations increased following any initial leaching losses. However, there were net releases of Ca from all three litter types since mass loss exceeded the increases in concentration. Net release of Ca by the end of two years from all three species combined was 42% of initial inputs in litterfall. Magnesium concentrations increased in the second year, following decreases due to leaching during the first year inC. florida andA. rubrum litter. Net release of Mg by the end of two years was 58% of initial inputs. Potassium concentrations decreased rapidly and continued to decline throughout the study. Net release of K by the end of two years was 91% of initial inputs.These data on cation dynamics, and similar data on N, S and P dynamics from a previous study, were combined with annual litterfall data to estimate the release of selected nutrients from foliar litter of these tree species at the end of one and two years of decomposition. The relative mobility of all six elements examined in relation to mass loss after two years was; K>Mg>mass>Ca>S>P>N.     

Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

This study examined whether the daily rhythms of locomotor activity and behavioural thermoregulation that have previously been observed in Australian sleepy lizards (Tiliqua rugosa) under field conditions are true circadian rhythms that persist in constant darkness (DD) and whether these rhythms show similar characteristics. Lizards held on laboratory thermal gradients in the Australian spring under the prevailing 12-hour light : dark (LD) cycle for 14 days displayed robust daily rhythms of behavioural thermoregulation and locomotor activity. In the 13-day period of DD that followed LD, most lizards exhibited free-running circadian rhythms of locomotor activity and behavioural thermoregulation. The predominant activity pattern displayed in LD was unimodal and this was retained in DD. While mean levels of skin temperature and locomotor activity were found to decrease from LD to DD, activity duration remained unchanged. The present results demonstrate for the first time that this species’ daily rhythm of locomotor activity is an endogenous circadian rhythm. Our results also demonstrate a close correlation between the circadian activity and thermoregulatory rhythms in this species indicating that the two rhythms are controlled by the same master oscillator(s). Future examination of seasonal aspects of these rhythms, may, however, cause this hypothesis to be modified.     

Neighborhood size in a beetle pollinated tropical aroid: effects of low density and asynchronous flowering

Summary Genetic neighborhood size and area were estimated from pollinator movements over 3 years in a scarab beetle-pollinated clonal herb, Dieffenbachia longispatha (Araceae) at the La Selva Biological Station, Costa Rica. This species was characterized by low densities of reproductive individuals and asynchronous flowering within the population. The pollinator flight distributions were characterized by relatively long mean distances between consecutive visits to inflorescences (83 m) and movements to the nearest neighboring inflorescence in the appropriate phase of flowering. Pollinator movement distributions between consecutive visits to inflorescences were significantly leptokurtic in 2 of the 3 years. I calculated neighborhood sizes incorporating the levels of kurtosis and found minimal estimates of N _e to be 227–611 ramets and neighborhood area to be 88 000–180 000 m². The three beetle species that made 94% of the visits (Cyclocephala gravis, C. amblyopsis, and Erioscelis columbica) varied in their flight distributions and in their contributions to the estimates of neighborhood size. Cyclocephala amblyopsis exhibited the greatest degree of kurtosis in its movement patterns, and neighborhood size based on its movement was large relative to N _e calculated from movement distributions of the other two beetle species. Long-distance movements of C. amblyopsis (>300 m) accounted for 68% of the neighborhood size.     

Sex expression,female frequency,and reproductive output in a gynodioecious clonal herb, <Emphasis Type="Italic">Glechoma longituba</Emphasis> (Lamiaceae)

We investigated the sex morphs and frequency of females in 24 natural populations of the clonal, gynodioecious species Glechoma longituba. In addition to the presence of hermaphrodites and females, there were some individuals with intermediate sex expression that could not be categorized as either morph. The majority of populations contained a predominance of hermaphrodites, although female frequency varied from 0 to 100%. The sexual expression of individual ramets did not change over three consecutive years or when ramets were transplanted to different populations, but it did change over the course of a flowering season. Seeds from females weighed more than those from hermaphrodites. The seed set of hermaphrodites was relatively constant across populations; the seed set of females was higher than that of hermaphrodites in most populations, but lower in populations in which females occurred at a very high frequency because of pollen limitation. This led to a negative correlation being detected between the seed set of females and the frequency of females in a population. We postulated that the adjustment of sex expression within seasons could be an adaptive mechanism of reproductive assurance in this system.