FERTILIZATION DYNAMICS AND PARENTAL EFFECTS UPON FRUIT DEVELOPMENT IN RAPHANUS RAPHANISTRUM: CONSEQUENCES FOR SEED SIZE VARIATION

Seed weight varies significantly within and among fruits of wild radish (Raphanus raphanistrum). To determine sources of this variation, we studied fertilization and seed development following controlled pollinations. Within fruits, central ovules were fertilized prior to distal ovules and attained greater seed size. Ninety-seven percent of the variation in mean seed wt per fruit was explained by an analysis of variance incorporating parental effects, pollination date, and the number of seeds per fruit. We document strong maternal effects on the number of ovules per ovary, the number of fertilized ovules per ovary, the number of seeds per fruit, and mean individual seed wt per fruit. Across females, pollen donor had a slight but significant effect on seed wt; no paternal effects on fertilization rate, zygote number, or seed number per fruit were detected. Within females, with one exception, pollen donor had no significant effect on these components of seed development. Stronger maternal main effects may be due to donor x recipient interactions, cytoplasmic factors, the genetic inequity within triploid endosperm, and/or strict maternal control over resource allocation. The large maternal effects relative to paternal effects may limit the rate at which natural selection acts on paternal traits expressed prior to seed maturation.     

REPRODUCTIVE CAPACITY AND SEED SIZE IN LUPINUS TEXENSIS

The average number of ovules produced per individual of Lupinus texensis is much greater than the average number of seeds per plant. Each plant produces approximately 2,000 ovules but only 2.5% develop into seeds. One fourth of the seeds is lost due to abortion and 0.3% is lost due to predation on the plant. Mature seeds from this population exhibit a five-fold range in weight, from 10 to 56 mg. The distribution of seed weights in the field population is skewed and leptokurtic. Seed wt is positively correlated with both seed germination and seedling survivorship. Heritability of seed wt is 0.09. There is no correlation between average seed wt per plant and total number of seeds per plant, seeds per pod, or legumes per plant.     

Factors affecting intrafruit pattern of ovule abortion and seed production in Hormathophylla spinosa (Cruciferae)

We investigated the pattern of intrafruit seed production in Hormathophylla spinosa (Cruciferae) over a 7-yr period. H. spinosa fruit have two chambers, each chamber containing two ovules, and usually situate perpendicular to the infructescence axis with one chamber above the other. The percentage of ovules ripening to seeds is usually lower than 50%. In addition, we found a consistent position-dependence in seed ripening probability, since more than 90% of the ripe seeds are arranged in the lower chamber of the fruit. This pattern of seed production is not produced by the direct or indirect effect of seed predators, by pollen limitation or by nonrandom fertilizations. By contrast, fruit removal experiments showed that sibling rivalry can partially explain the seed production pattern, be the cause of the reduction in the seed number from the uppermost threshold of 50%. Moreover, experimental manipulations of fruit orientation suggest that the position-dependence in seed production is the cause but not the effect of seed ripening. We presume that some architectural effect is producing a significant increase in the ripening probability of the ovules arranged in the lower chamber, causing thus the observed pattern in the intrafruit seed production in H. spinosa and severely constraining the maximum number of seeds per fruit to two.     

A TEST OF SEVERAL HYPOTHESES FOR THE DETERMINATION OF SEED NUMBER IN AMELANCHIER ARBOREA,USING SIMULATED PROBABILITY DISTRIBUTIONS TO EVALUATE DATA

The number of seeds per fruit is variable within Amelanchier arborea trees. Because A. arborea flowers are five-carpellate and each carpel contains two ovules, we were able to use the pattern of seed maturation within fruits to test whether the failure of some ovules to develop into seeds is determined by mechanisms operating at the level of carpels, such as stigma-clogging, or by mechanisms operating at the level of ovules, such as ovule infertility. The presence of one-, two-, and zero-seeded carpels demonstrated that the number of ovules developing into seeds was not due entirely to carpel-level phenomena. In order to test the hypothesis of carpel independent seed development, without the assumption that all ovules have the same probability of developing into seeds, it was necessary to use simulation, since no conventional statistical models were appropriate. Analysis of this simulation allowed us to reject carpel independent processes as the only determinant of seed number. A mixed model of seed development, in which some carpels fail entirely and ovules in the remaining carpels develop equiprobably, was shown to be consistent with the data.     

Patterns of fruit and seed production inBauhinia ungulata (Leguminosae)

Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.     

Selective fruit filling in relation to pollen load size in Alstroemeria aurea (Alstroemeriaceae)

 We conducted an experiment in a natural population of Alstroemeria aurea, a clonal perennial, to determine (1) if reproduction was resource limited, and (2) if fruits would be selectively filled based on differences in pollination intensity when pollen loads were adequate for full seed set. Under these conditions, differences in pollination intensity are unlikely to affect seed number, but could affect seed quality, providing an interesting test of the gametophytic competition hypothesis. To test for resource limitation, percent fruit maturation, number of seeds per fruit and average seed weight were compared to paired controls for ramets in which all but one fruit was removed. To test the effect of pollination intensity on selective resource allocation, three types of pollination treatments were performed: (1) all flowers of the single inflorescence received a low pollen load, (2) all flowers received a high pollen load, (3) alternate flowers of the inflorescence received either a high or a low pollen load. We determined the percentage of fruit that reached maturity, counted the number of seeds and ovules and calculated the average seed weight for all capsules in each treatment. Resources appeared to limit reproduction in this population since seed number and weight were significantly higher than in controls when competing capsules were removed. At the whole ramet level, a four fold difference in pollen loads had no significant effect on any of the parameters measured. However, when pollination intensity varied within an inflorescence, the number of seeds per fruit increased by about 10% in flowers that received the higher pollen load. We observed the same trend in each of 2 years, but the increase was significant in only 1 year. The differences, although not great, were only slightly smaller than when all competing fruits were removed, and were consistent with selective resource allocation based on pollination intensity independent of seed set. Received: 28 September 1997 / Accepted: 30 April 1998     

PARENTAL EFFECTS ON SEED DEVELOPMENT AND SEED YIELD IN RAPHANUS RAPHANISTRUM: IMPLICATIONS FOR NATURAL AND SEXUAL SELECTION

The possibility that sexual selection operates in angiosperms to effect evolutionary change in polygenic traits affecting male reproductive success requires that there is additive genetic variance for these traits. I applied a half-sib breeding design to individuals of the annual, hermaphroditic angiosperm, wild radish (Raphanus raphanistrum: Brassicaceae), to estimate paternal genetic effects on, or, when possible, the narrow-sense heritability of several quantitative traits influencing male reproductive success. In spite of significant differences among pollen donors with respect to in vitro pollen tube growth rates, I detected no significant additive genetic variance in male performance with respect to the proportion of ovules fertilized, early ovule growth, the number of seeds per fruit, or mean individual seed weight per fruit. In all cases, differences among maternal plants in these traits far exceeded differences among pollen donors. Abortion rates of pollinated flowers and fertilized ovules also differed more among individuals as maternal plants than as pollen donors, suggesting strong maternal control over these processes. Significant maternal phenotypic effects in the absence of paternal genetic or phenotypic effects on reproductive traits may be due to maternal environmental effects, to non-nuclear or non-additive maternal genetic effects, or to additive genetic variance in maternal control over offspring development, independent of offspring genotype. While I could not distinguish among these alternatives, it is clear that, in wild radish, the opportunity for natural or sexual selection to effect change in seed weight or seed number per fruit appears to be greater through differences in female performance than through differences in male performance.     

Effects of resource availability, and fruit and ovule position on components of fecundity in Alliaria petiolata (Brassicaceae)

In four field and glasshouse experiments designed to alter the supply of resources through manipulation of nutrients, root tissue, leaf area and fruit number in Alliaria petiolata (Brassicaceae), more than 99% of ovules per plant showed signs of fertilization, suggesting that seed production in this plant was not pollen limited. However, in all treatments a significant proportion of fruits and seeds did not develop to maturity. Total fruit and seed production did not differ significantly from controls when plants were given nutrient supplements at flowering. Removal of 50–75% of the root tissue in 1-yr-old plants significantly reduced fruit set, but had no effect on individual seed development. Removal of cauline leaves significantly reduced most measures of fruit and seed production, suggesting that current photosynthate is critical for fruit and seed filling. Seed maturation was significantly affected by both fruit position within an infructescence and ovule position within a fruit. Basally located fruits and ovules (within fruits) developed more mature seeds than distally positioned fruits and ovules. Plants responded to removal of basal fruits by re-allocating resources to distal fruits that would normally have aborted. Our results suggest that fruits and seeds act as reproductive sinks competing for parental photosynthate. Patterns of resource allocation within infructescences and fruits were also modified by our experiments.     

Fruit mass variability in Vaccinium myrtillus as a response to altitude,simulated herbivory and nutrient availability

Variability in fruit mass may respond to environmental conditions, in addition to the genetic effect that has been reported in several reproductive features. We first analyzed fruit traits in 15 localities along an altitudinal gradient (300–2000 m a.s.l.) in the berries of Vaccinium myrtillus. We then tested whether changes in natural conditions, such as nutrient availability and herbivory by ungulates, affected fruit features in this species. Therefore, nitrogen (N) addition and clipping were applied in plots situated in six of the 15 localities. In these plots, we later collected fruits in two consecutive years in order to obtain fruit mass, seed number and initial number of ovules per flower ovary. Data along the altitudinal gradient showed that fruit mass was determined by both ovule number and seed number, although these factors only explained approximately half of the variation. Fruit mass and number of ovules and seeds followed a similar pattern with altitude, increasing until reaching a maximum at around 1700 m. Regarding the effect of the experimental treatments, fertilized non-clipped plants produced the heaviest fruits but clipping alone had no significant effect on fruit mass. Moreover, high soil pH had a positive influence on fruit mass. In addition, whereas the original number of ovules per ovary was not affected by the experimental treatments, the number of seeds per fruit increased and the abortion rate decreased in fertilized non-clipped plots, which means that the effect of simulated herbivory on these fruit traits depended on N addition. In conclusion, fruit mass was clearly affected by nutrient availability and this effect is attributed to an increase in the production of seeds rather than to an increase in module size and number of ovules per ovary. This outcome suggests that fruit mass is a plastic trait influenced by environmental factors like nutrient availability.     

Seed germination patterns of Salvia mellifera in fire-prone environments

Summary I examined the effects of pollen loads containing pollen from one, three and five donors on fruit production and fruit quality in Campsis radicans. Number of pollen donors had no significant effect on % fruit production, seed number, seed weight or seed germination. In singledonor pollinations the identity of the donor did have a strong effect on the above parameters. Furthermore, the best single donor sired fruits with more seeds and heavier seeds than any mixture containing this donor. This pattern indicates interference of pollens or preemption of some ovules by the inferior pollen. In Campsis, therefore, the number of pollen donors contributing to a pollen load is less important than the identity of these donors in determining fruit production and fruit quality. Seeds from fruits resulting from mixed pollination were slightly more variable than seeds from fruits resulting from single-donor pollinations.     

EFFECT OF OVULE POSITION ON SEED PRODUCTION,SEED WEIGHT,AND PROGENY PERFORMANCE IN PHASEOLUS COCCINEUS L. (LEGUMINOSAE)

We examined the effect of ovule position within the ovary on the probability of seed maturation, on seed weight, and on progeny performance in the outbreeding legume Phaseolus coccineus. Ovaries of P. coccineus possess six linearly arranged ovules (ovule position one = stylar end). We found that in both 1987 and 1988, ovule position had a significant effect on the probability of seed maturation under field conditions. In 1987, ovule positions one. two, and three had a higher probability of maturing seeds than the three most basal ovule positions. In 1988, the probability of producing a mature seed in ovule position one was more similar to the three most basal ovule positions than to ovule positions two and three. The position of the ovule in the ovary had no significant effect on seed weight in 1987, but it had a significant effect in 1988. Overall, seeds from ovule positions one, two, and three tended to produce heavier seeds than the three most basal ovule positions. The effects of ovule position on progeny performance were determined in a greenhouse and a field study. In the greenhouse study, we found no significant overall effect of the position of the ovule that produced the seed on progeny performance. In the field study, we did find a significant ovule position effect on several measures of reproductive performance as well as an overall effect on reproductive performance. In addition, we found a significant interaction between ovule position and number of seeds per fruit. Progeny from the stylar end of the fruit outperformed the progeny from the peduncular end in fruits containing many seeds, whereas there were no significant differences between progeny produced in the stylar and peduncular ends of fruits containing few seeds. Causes of position effects are unknown but hypotheses abound.     

Effect of pollen load size and source (self, outcross) on seed and fruit production in highbush blueberry cv. 'Bluecrop' (VACCINIUM CORYMBOSUM; Ericaceae)

Reproductive fitness of a plant is ultimately determined by both number and quality of seed offspring. This is determined by sexual selection of pollen microspores and ovules during pollination and fertilization. These processes may include pollen competition and seed abortion, which reduce the number of microspores and ovules available for final seed production. Thus, even an excess of pollen microspores to ovules does not result in fertile seeds equal to ovule number. We investigated pollen requirements of highbush blueberry (Vaccinium corymbosum cultivar 'Bluecrop') for maximal seed production and how fertile seed number translates into fruit quality, since fruit quality would ultimately determine the dispersal of its offspring. We demonstrate that individual blueberry flowers with a mean of 106 ovules reach their maximum fruit set and mass and minimum time to ripen when 125 outcross pollen tetrads pollinate a flower, compared to 10 or 25. Three hundred tetrads resulted in the increase of fertile seeds, but did not result in a further increase of fruit mass or fruit set, or decrease in time to ripen. We also examined the effect of pure and mixed loads of self and outcross pollen (25 and 125 tetrads), and found no differences in fertile seed number, fruit mass, or percentage fruit set when pollen loads were either 25 self or outcross pollen tetrads, although number of days to ripen was significantly shorter by 8 d with 25 outcross tetrads. When the pollen load of 125 tetrads consisted of self or a 50:50 mixture of self and outcross pollen, fruit mass, days to ripen, and percentage fruit set were not different from loads of 125 outcross pollen. In addition, a pollen load of 25 outcross tetrads resulted in fertile seed number and fruit quality in between that of 25 self, and 125 self, 125 mixed, or 125 outcross tetrads. Large, small, and flat seed types were identified, and only large seeds (length = 1.7 mm) were fertile. These results improve our understanding of pollen load size and source requirements of a crop plant and the limits to pollen transfer when translated to fruit growth.     

Ovule abortion in white clover (Trifolium repens L.)

Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20^oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.     

Pollination intensity and potential seed set in Passiflora vitifolia

Summary Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200–350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25–50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.     

From flowering to dispersal: reproductive ecology of an endemic plant,Astragalus australis var. olympicus (Fabaceae)

Astragalus australis var. olympicus is an endemic plant of the Olympic Mountains, Washington. It is considered a Species of Concern by the U.S. Fish and Wildlife Service. This study focused on the reproductive biology of the plant from flower production through seed germination to identify possible weak points that might contribute to its rarity and impede its conservation. Most plants produced a large mean number of flowers and ovules (314.8 and 4106, respectively), but relatively few of these formed fruits and seeds (25.8 and 3.8%, respectively). In decreasing importance, ovules in fruits were lost to predation, seed abortion, and lack of fertilization. The percentages of these fates differed among sites and years. Excluding pollinators by bagging flowers reduced fruit set by ∼50%, but seed set per fruit and seed mass were unaffected. Germination was affected by scarification, temperature, and moisture availability. About 11% of seeds damaged by predispersal seed predators (weevil larvae) remained viable and were released from dormancy. I hypothesize that predispersal seed predation (over 80% at one site) has a negative effect on population growth. Conservation of this species could benefit from improved fruit set and decreased seed predation.     

Plasticity of reproductive components at different stages of development in the annual plant Thlaspi arvense L.

Summary This study examines the effect of different densities and the removal of all neighbours at different stages of development on all components of reproduction in the inbreeding annual Thlaspi arvense L. A 64-fold increase in density significantly reduced all repooductive components. The number of flower buds per plant was decreased most strongly; the order of decreasing plasticity among the other components was number of capsules per flower, individual seed weight, ovule number per capsule, flowers per flower bud and seeds per ovule. Removing neighbours at all stages of development increased seed yield of plants in comparison to the control without density reduction, but patterns of plasticity depended strongly on time of treatment. The main effect of the removal of neighbours at the vegetative stage was to increase the number of flowers per plant, but the number of ovules per capsule and seed weight increased also, and abortion of capsules decreased. Removing neighbours at the onset of flowering initially failed to affect flower number per plant, instead it resulted in a strong reduction of capsule abortion and an increase in seed weight. However, several weeks after flowering had initially ceased, fresh lateral inflorescences were produced, resulting in a second flush of reproduction. Removing neighbours at the stage of fruit ripening resulted at first only in an increase in seed witht, but later a second reproductive phase occurred. Fresh lateral branches were produced, but the apical meristem was also reactivated. The overall pattern of plasticity among all reproductive components in response to a removal of neighbours was the same as in response to density. The position of a capsule along the inflorescence influenced its number of ovules, the rate of seed abortion and the mean weight of seeds, with the type of effect depending on the developmental stage at which neighbours were removed. Significant negative correlations were found between the mean weight of seeds and the number of seeds in a capsule under all treatments.     

Intra-inflorescence variation in floral traits and reproductive success of the hermaphrodite Silene acutifolia

BACKGROUND AND AIMS: Intraspecific variation in floral components and reproductive success is often located at the intra-individual level. The arrangement of flowers within inflorescences may explain a great deal of this variation. The variation in number of ovules, fruit set, number of seeds per fruit, seed set, seed weight and seed germination is investigated at different positions within the inflorescence of Silene acutifolia. METHODS: Data were obtained in natural populations, and germination experiments were conducted in a germination chamber. KEY RESULTS: The number of ovules, fruit set, number of seeds, seed set and seed weight, showed a significant decline from early (primary) position to later (tertiary) position. The patterns of intra-inflorescence variation were consistent in different populations and years of study. Seed germination showed an opposite pattern, seeds from primary position showed the lowest germination percentages and seeds from tertiary position the highest, although the effect of position on germination was only marginally significant. There was significant among-population variation in number of ovules per flower. Fruit set also varied significantly among populations, with lower fruit set in the smaller and more isolated population. No significant among-population differences were detected in number of seeds per fruit and seed set. Seeds from the smallest and more isolated population (Arnado) were the lightest. Seed germination showed strong differences between populations, seeds from Arnado started to germinate later, and showed the lowest final germination percentages. CONCLUSIONS: Architectural effects or resource competition are the most commonly proposed hypothesis to explain these patterns. Data suggest that there is less pollen available to pollinate tertiary flowers, and that there is not enough outcross pollen in Arnado. The germination percentages suggest that there is variation in the source of pollen within inflorescences, with high probability of receiving outcross pollen in flowers from primary position, and higher probability of geitonogamous crosses in tertiary flowers.     

POLLINATION OF THE ARROYO WILLOW,SALIX LASIOLEPIS: ROLE OF INSECTS AND WIND

We studied the relative roles of insects and wind as pollen vectors for the arroyo willow, Salix lasiolepis Benth. through insect exclosure studies at two elevational sites. Insect pollination resulted in production of 99.9% of seeds at a low elevation site (2,130 m) and at a high elevation site (2,450 m) with wind playing an exceedingly small role. Few pollen grains reached individual pistillate catkins despite the presence of abundant airborne willow pollen near male plants. In flowers that showed evidence of receipt of wind transferred pollen, due to their swollen appearance, we found only 1.74 fertilized ovules per flower and that 90.9% of these fertilized ovules were aborted by the maternal plant. In contrast, flowers open to insect visitation possessed 7.00 fertilized ovules per flower, 83.3% of which became filled seeds. We tested for the existence of apomictic seed production through use of closed bags that excluded both insect-and wind-transferred pollen but found no evidence of seed produced in this treatment. Additional control studies documented that wind treatment bags did not impede pollen flow while neither wind or closed bags influenced seed set in our treatments.     

Effects of fruit thinning on fruit and seed features of <Emphasis Type="Italic">Cistus ladanifer</Emphasis>

Fruit and seed features are the result of reproductive allocation decisions which ultimately depend on both plant availability of resources and total number of developing fruits. In this study, we manipulated fruit load in Cistus ladanifer plants by removing 0, 25 or 75% of developing fruits. Fruit features (total fruit weight, fruit-wall weight, total seed weight per fruit and seed number per fruit) were unaffected by fruit thinning, nevertheless mean seed weight increased in treated plants independently of thinning intensity. This reduced compensation was unrelated to plant size and had no consequences on fruit predation by insects. From these results it could be suggested that not only availability of resources but also morphological constraints could affect seed size in Cistus ladanifer. On the other hand, this change in seed weight could have important consequences since in this species heavy seeds perform better after fire events but light ones are advantageous in between fire recruitments.     

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

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