Bottlenecks and spatiotemporal variation in the sexual reproduction pathway of perennial meadow plants

Sexual reproduction is important for the growth of populations and the maintenance of genetic diversity. Several steps are involved in the sexual reproduction pathway of plants: the production of flowers, the production of seeds and the establishment of seedlings from seeds. In this paper we quantify the relative importance and spatiotemporal variability of these different steps for four grassland perennials: Centaurea jacea, Cirsium dissectum, Hypochaeris radicata and Succisa pratensis. We compared undisturbed meadows with meadows where the top soil layer had been removed as a restoration measure. Data on the number of flower heads per flowering rosette, the numbers of flowers and seeds per flower head, and the seedling establishment probabilities per seed were collected by field observations and experiments in several sites and years. Combination of these data shows that H. radicata and S. pratensis have higher recruitment rates (1.9 and 3.3 seedlings per year per flowering rosette, respectively) than the more clonal C. dissectum and C. jacea (0.027 and 0.23, respectively). Seedling establishment is the major bottleneck for successful sexual reproduction in all species. Large losses also occurred due to failing seed set in C. dissectum. Comparison of the coefficients of variation per step in space and time revealed that spatiotemporal variability was largest in seedling establishment, followed closely by flower head production and seed set.     

Changes in Florets’ Vertical Direction within Inflorescence Affects Pollinator Behavior,and Fitness in <i>Trifolium repens</i>

Ecological interactions between flowers and pollinators greatly affect the reproductive success. To facilitate these interactions, many flowers are known to display their attractive qualities, such as scent emission, flower rewards and floral vertical direction, in a rhythmic fashion. However, less is known about how plants regulate the relationship between these flower traits to adapt to pollinator visiting behavior and increase reproduction success. Here we investigated the adaptive significance of the flower bending from erect to downward in Trifolium repens. We observed the flowering dynamic characteristics (changes of vertical direction of florets, flowering number, pollen grain numbers, pollen viability and stigma receptivity over time after blossom) and the factors affecting the rate of flower bending in T. repens. Then we altered the vertical direction of florets in inflorescence of different types (upright and downward), and compared the pollinator behaviors and female reproductive success. Our results showed that florets opened sequentially in inflorescence, and then bend downwards slowly after flowering. The bending speed of florets was mainly influenced by pollination, and bending angle increased with the prolongation of flowering time, while the pollen germination rate, stigma receptivity and nectar secretion has a rhythm of “low-high-low” during the whole period with the time going. The visiting frequency of all the four species of pollinators on upward flowers was significantly higher than that of downward flowers, and they especially prefer to visit flowers with a bending angle of 30°–60°, when the flowers was exactly of the highest flower rewards (nectar secretion and number of pollen grains), stigma receptivity and pollen germination rate. The seed set ratio and fruit set ratio of upward flowers were significantly higher than downward flowers, but significantly lower than unmanipulated flowers. Our results indicated that the T. repens could increase female and male fitness by accurate pollination. The most suitable flower angle saves pollinators’ visiting energy and enables them to obtain the highest nectar rewards. This coordination between plants and pollinators maximizes the interests of them, which is a crucial factor in initiating specialized plant-pollinator relationships.     

Direct and indirect effects of episodic frost on plant growth and reproduction in subalpine wildflowers

Frost is an important episodic event that damages plant tissues through the formation of ice crystals at or below freezing temperatures. In montane regions, where climate change is expected to cause earlier snow melt but may not change the last frost‐free day of the year, plants that bud earlier might be directly impacted by frost through damage to flower buds and reproductive structures. However, the indirect effects of frost mediated through changes in plant–pollinator interactions have rarely been explored. We examined the direct and pollinator‐mediated indirect effects of frost on three wildflower species in southwestern Colorado, USA, Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), and Polemonium foliosissimum (Polemoniaceae), by simulating moderate (?1 to ?5°C) frost events in early spring in plants in situ. Subsequently, we measured plant growth, and upon flowering measured flower morphology and phenology. Throughout the flowering season, we monitored pollinator visitation and collected seeds to measure plant reproduction. We found that frost had species‐specific direct and indirect effects. Frost had direct effects on two of the three species. Frost significantly reduced flower size, total flowers produced, and seed production of Erigeron. Furthermore, frost reduced aboveground plant survival and seed production for Polemonium. However, we found no direct effects of frost on Delphinium. When we considered the indirect impacts of frost mediated through changes in pollinator visitation, one species, Erigeron, incurred indirect, negative effects of frost on plant reproduction through changes in floral traits and pollinator visitation, along with direct effects. Overall, we found that flowering plants exhibited species‐specific direct and pollinator‐mediated indirect responses to frost, thus suggesting that frost may play an important role in affecting plant communities under climate change.     

Sources of variation in pollinator contribution within a guild: the effects of plant and pollinator factors

Among plants visited by many pollinator species, the relative contribution of each pollinator to plant reproduction is determined by variation in both pollinator and plant traits. Here we evaluate how pollinator movement among plants, apparent pollen carryover, ovule number, resource limitation of seed set, and pollen output affect variation in contribution of individual pollinator species to seed set in Lithophragma parviflorum (Saxifragaceae), a species visited by a broad spectrum of visitors, including beeflies, bees and a moth species. A previous study demonstrated differences among visitor species in their single-visit pollination efficacy but did not evaluate how differences in visitation patterns and pollen carryover affect pollinator efficacy. Incorporation of differential visitation patterns and pollen carryover effects —commonly cited as potentially important in evaluating pollinator guilds — had minor effects (0–0.6% change) on the estimates of relative contribution based on visit frequency and single-visit efficacy alone. Beeflies visited significantly more flowers per inflorescence than the bees and the moth. Seed set remained virtually constant during the first three visited flowers for beeflies and larger bees, indicating that apparent pollen carryover did not reduce per-visit efficacy of these taxa. In contrast, Greya moth visits showed a decrease in seed set by 55.4% and the smaller bees by 45.4% from first to second flower. The larger carryover effects in smaller bees and Greya were diminished in importance by their small overall contribution to seed set. Three variable plant traits may affect seed set: ovule number, resource limitation on seed maturation, and pollen output. Ovule number per flower declined strongly with later position within inflorescences. Numbers were much higher in first-year greenhouse-grown plants than in field populations, and differences increased during 3 years of study. Mean pollen count by position varied 7-fold among flowers; it paralleled ovule number variation, resulting in a relatively stable pollen:ovule ratio. Resource limitation of seed set increased strongly with later flowering, with seed set in hand-pollinated flowers ranging from 66% in early flowers to 0% in the last two flowers of all plants. Variation in ovule number and resource limitation of seed maturation jointly had a strong effect on the number of seeds per flower. Visitation to early flowers had the potential to cause more seed set than visitation to later flowers. Overall, the most important sources of variation to seed production contribution were differences among pollinators in abundance and absolute efficacy (ovules fertilized on a single visit) and potentially differential phenology among visitor species. These effects are likely to vary among populations and years.     

Reproduction of beetle‐pollinated Anaxagorea dolichocarpa (Annonaceae) is resilient to habitat disturbance in rainforest fragments

Strong evidence exists that fragmentation negatively affects pollination and plant reproduction, but little research has been conducted with regards to tropical trees. Specifically, effects of forest fragmentation on reproduction of plants with beetle‐pollinated flowers are poorly understood, and there are no data on the impact of fragmentation on reproduction in the structurally important tropical family Annonaceae. We examined the relationship between fragment size, pollinator abundance and seed set of beetle‐pollinated Anaxagorea dolichocarpa (Annonaceae) in a disturbed Brazilian Atlantic rainforest. Flower and fruit production and abundance of pollinators were quantified over ten months in three large (306–388 ha) and three small (6–14 ha) forest fragments. We recorded per flower pollinator abundance, resulting fruit set (fruits per flower) and seed set (monocarps per fruit) for a total of 209 individually marked flowers, and compared pollinator abundance in 186 flowers across all fragments. Flower and fruit production differed among fragments, but were similar for the combined large and small fragments. Between 64.8% (large fragments) and 66.3% (small fragments) of flowers received at least one pollinator. We found no significant difference in pollinator numbers between large and small fragments, and no correlation between pollinator abundance and fruit and seed set. A single visitor had a high probability of pollinating a flower. We conclude that 1) fragment size had no influence on pollinator number and plant reproductive success, and 2) generalist behavior of the pollinating beetles mitigate the risk of pollination failure for the reproductively specialized plant. However, further research may yet reveal genetic impoverishment of populations in small fragments due to restricted pollinator movements.     

Flowering phenology,pollen flow and fruit production in the andean shrub Befaria resinosa

Summary In the eastern Andes of Colombia, the shrub Befaria resinosa (Ericaceae) has peaks of flowering that are separated by extended periods of low flower production. The effect that these fluctuations in flower production have on pollen flow was investigated by using fluorescent dye as a pollen analog. Dye applied to open flowers was dispersed over long distances more often during low flower production than during high flower production. Whether enhanced pollen dispersal during flowering lows is of benefit to individual plants is not clear. The proportion of flowers that set fruit is positively correlated with flower abundance, negating the possibility that increased pollen dispersal results in a higher rate of fruit production due to outbreeding effects. It is also difficult to attribute the pattern of fruit production to changes in pollinator visitation rates, which are negatively correlated with flower abundance in the case of hummingbirds and not correlated at all with flower abundance in the case of insects. An opportunistic, large-bodied hummingbird (Colibri coruscans) visits B. resinosa during high flowering and may be a particularly effective pollinator, accounting for some of the increase in the proportion of flowers setting fruit. Rainfall is positively correlated with flower production and may be an important factor in shaping flowering phenology, but it is not significantly correlated with the proportion of flowers setting fruits. The possibility that low-level flowering may counteract inbreeding that results from peak flowering is discussed.     

Pollinator preference and pollen viability mediated by flower color synergistically determine seed set in an Alpine annual herb

Gentiana leucomelaena manifests dramatic flower color polymorphism, with both blue‐ and white‐flowered individuals (pollinated by flies and bees) both within a population and on an individual plant. Previous studies of this species have shown that pollinator preference and flower temperature change as a function of flower color throughout the flowering season. However, few if any studies have explored the effects of flower color on both pollen viability (mediated by anther temperature) and pollinator preference on reproductive success (seed set) in a population or on individual plants over the course of the entire flowering season. Based on prior observations, we hypothesized that flower color affects both pollen viability (as a function of anther temperature) and pollen deposition (as a function of pollinator preference) to synergistically determine reproductive success during the peak of the flowering season. This hypothesis was tested by field observations and hand pollination experiments in a Tibetan alpine meadow. Generalized linear model and path analyses showed that pollen viability was determined by flower color, flowering season, and anther temperature. Anther temperature correlated positively with pollen viability during the peak of the early flowering season, but negatively affected pollen viability during the peak of the mid‐ to late flowering season. Pollen deposition was determined by flower color, flowering season (early, or mid‐ to late season), and pollen viability. Pollen viability and pollen deposition were affected by flower color that in turn affected seed set across the peak of the flowering season (i.e., when the greatest number of flowers were being pollinated). Hand pollination experiments showed that pollen viability and pollen deposition directly influenced seed set. These data collectively indicate that the preference of pollinators for flower color and pollen viability changed during the flowering season in a manner that optimizes successful reproduction in G. leucomelaena. This study is one of a few that have simultaneously considered the effects of both pollen viability and pollen deposition on reproductive success in the same population and on individual plants.     

Anthropogenic edges,isolation and the flowering time and fruit set of Anadenanthera peregrina,a cerrado savanna tree

Fragmentation exposes plants to extreme environmental conditions with implications for species phenology and reproduction. We investigated whether isolation and edge effects influence size, flowering time, fruit set, and seedling establishment of Anadenanthera peregrina var. falcata. We compared trees in the interior (n?=?85), and on the edge (n?=?74) of a cerrado savanna fragment as well as in a pasture (n?=?26) with respect to size, flowering phenology, flower and fruit production, fruit and seed set, predispersal seed predation, and seedling establishment. Trees in the pasture were larger and produced a higher number of flowers and fruits than trees on the edge and interior, yet seed set did not differ across environments. The plant size structure explained the flower and fruit production, and the self-compatibility breeding system caused a similar seed set regardless of the environment. First flowering was later and fruit set higher in the interior. We argue that time of first flower influenced the fruit set of Anadenathera. Edge and isolated trees started to flower earlier as a response to microclimatic conditions—mainly temperature—reducing the fruit set. Predispersal seed predation was lower among pasture trees. Conversely, we found seedlings only on the edge and in the interior of cerrado, suggesting that the pasture was of poor quality habitat for Anadenanthera recruitment. Isolation affected the plant size structure and reproduction of Anadenanthera trees. Studies comparing plant phenology under contrasting environmental conditions may offer clues on how global change may affect plant reproduction in the tropics.     

POLLINATION AND SEED SET IN DIERVILLA LONICERA (CAPRIFOLIACEAE): TEMPORAL PATTERNS OF FLOWER AND OVULE DEPLOYMENT

Ovule development in Diervilla lonicera (Caprifoliaceae) is limited by insufficient pollination early in the blooming period and during extensive rainy periods. Production of flowers is skewed in time; an initial burst of flowering is followed by a long period of sparse flower production. Ovule number per flower increases through the blooming period. I discuss the interactions of fruit and seed set, ovule number, and bumble bee pollinator visitation patterns. When certain flowers have a higher a priori probability of successful pollination, it may be advantageous for plants to put more ovules in those flowers. Selective ovule deployment may be a general adaptive phenomenon that has received little attention.     

Factors affecting pollinator movement and plant fitness in a specialized pollination system

The rate of pollen exchange within and among flowers may depend on pollinator attraction traits such as floral display size and flowering plant density. Variations in these traits may influence pollinator movements, pollen receipt, and seed number. To assess how floral display size and flowering plant density affect parameters of pollinator visitation rate, pollen receipt per flower, seed number per fruit and the between-plant pollinator movements, we studied the self-incompatible plant, Nierembergia linariifolia. Per-flower pollinator visitation rate and bout length increased linearly with increasing floral display size. Pollen receipt per flower increased linearly with increasing flowering plant density. For seed number per fruit, a polynomial model describing an increased seed number per fruit at low density and a decreased seed number per fruit at high density provided a significant fit. Per-flower pollinator visitation rate was not associated with pollen receipt per flower and seed number per fruit. Bees visited plants located near to the center of the population more frequently than plants located at the periphery. Increases in both floral display size and flowering plant density led to an increased chance of a plant being chosen as the center of the pollinator foraging area. These results suggest that even though large floral displays and high flowering plant density are traits that attract more pollinators, they may also reduce potential mate diversity by restricting pollen movement to conspecific mates that are closely located.     

Within-population spatial variation in pollinator visitation rates, pollen limitation on seed set, and flower longevity in an alpine species

Pollen limitation through insufficient pollen deposition on stigmas caused by too infrequent pollinator visitation may influence the reproductive outcome of plants. In this study we investigated how pollinator visitation rate, the degree of pollen limitation, and flower longevity varied spatially among three sites at different altitudes within a population of the dwarf shrub Dryas octopetala L. in alpine southern Norway. Significant pollen limitation on seed set only occurred at the mid-elevation site, while seed set at the other sites appeared to be mainly resource limited, thus indicating a spatial variation in pollen limitation. There was no association between the spatial variation in the extent of pollen limitation and pollinator visitation rate to flowers. However, pollinator visitation rates were related to flower longevity of Dryas; sites with low visitation rates had long-lived flowers and vice versa. Thus, our results suggest within-population spatial co-variation between pollinator visitation rates, pollen limitation, and a developmental response to these factors, flower longevity.     

Flower heliotropism in an alpine population of Ranunculus acris (Ranunculaceae): effects on flower temperature,insect visitation,and seed production

Some plants in arctic and alpine habitats have heliotropic flowers that track the sun. This results in a heating of the flower's interior, which may improve the possibilities for insect pollination and seed production. Here, I examine whether flower heliotropism in an alpine population of the self-incompatible Ranunculus acris L. (Ranunculaceae) enhances pollinator visitation and seed production. Flowers of Ranunculus acris tracked the sun during the day. Tracking accuracy was greatest during the middle of the day. The temperature elevation in flowers was negatively correlated with the flower's angle of deviation from the sun. Despite the increased temperature, insects did not discriminate among flowers on the basis of their angle of deviation from the sun, or tend to stay longer in the flowers aligned closest towards the sun. A tethering experiment was conducted on three groups of plants flowering at different times in the 1993 season and on one group the following season. Manipulation plants were constrained not to track the sun, whereas control plants tracked the sun naturally. Solar tracking had no effect on seed:ovule ratio, seed mass, or abortion rate in any of the groups. There is probably a very narrow range of weather conditions (cold, sunny, and calm) where flower heliotropism may enhance visitation rate to flowers and their seed production.     

Oviposition by mutualistic seed-parasitic pollinators and its effects on annual fitness of single- and multi-flowered host plants

The balance of intimate relationships between plants and seed-eating pollinators can depend on pollinator behaviour in relation to floral characters, such as flower size and flower number. Here, we examined how pollinator oviposition in relation to these traits affected annual fitness (seed output) of single- and multi-flowered Trollius europaeus along altitudinal gradients in subarctic Sweden and the French Alps. Small flies (Chiastocheta spp.) pollinate T. europaeus and their larvae feed on developing seeds. Assuming that late flowers in multi-flowered plants attracted flies to the earliest flower on the same plant, we expected more eggs and higher seed predation in early multiple flowers than in single flowers. Relative seed predation would thereby increase with flower number. Both in Sweden and the Alps, more eggs were placed on large flowers. Early multiple flowers were slightly larger than single flowers, and about twice the size of secondary flowers. As a result, and possibly combined with the effects of secondary flowers, early multiple flowers attracted more ovipositing flies and experienced relatively higher seed predation. However, this did not generally result in higher seed predation of multi-flowered hosts. Multiple flowers had greater seed output than single flowers at all altitudes, also in the high alpine and subarctic sites, where single flowers were more abundant. We hypothesise that the distribution of multiple flowers generally is enforced by environmental factors, rather than by fly-host plant interactions, because only very rarely (in triple-flowered alpine plants) was seed predation disproportionate, and the relationship skewed to the disadvantage of the host. The outcome of the mutualistic interaction was often similar in alpine and subarctic populations, but the underlying factors were different. Subarctic flowers had high abortion and low predation rates, while alpine flowers experienced the reversed situation. The higher fly abundance in the Alps suggests a more intense mutualistic interaction than in Sweden. Despite varying ecological and environmental conditions at these sites, the mutualistic relationship was generally in balance. However, when it was unbalanced, this could be explained by fly behaviour in response to floral traits, and by differences in fly abundance. Received: 4 January 1999 / Accepted: 5 May 1999     

Effectiveness of ants as pollinators of<Emphasis Type="Italic"> Lobularia maritima</Emphasis>: effects on main sequential fitness components of the host plant

The effectiveness of ants as pollinators of Lobularia maritima (Cruciferae) was experimentally analyzed by assessing (1) their quantitative importance at flowers; (2) their effect on host plant seed production; (3) their effect on the performance of host plant progeny, estimated as seed germination, seedling emergence, seedling survival to flowering, and (4) the overall effect of ants on a cumulative, more realistic measure of plant fitness related to the recruitment probability. Flowers of L. maritima were visited during the 2 years of study (1996 and 1997) by more than 50 pollinator species belonging to about 30 families of disparate taxonomic affiliation, notably ants and flies. There was significant seasonal variability in insect abundance and type. Ants, especially Camponotus micans (Formicidae), visited the flowers of L. maritima in summer, representing 81.2% of the visits during this season. This ant species acted as a pollinator of L. maritima, with flowers visited exclusively by ants producing significantly more seeds than flowers from which all pollinators were excluded, whereas flowers visited by only winged insects did not differ from self-pollination. Ant-pollinated flowers produced seeds with a germination rate comparable to the other treatments. Moreover, seedlings from these seeds emerged as fast, and survived at the same rate as controls. Consequently, both ants and winged insects had similar overall effects on host plant recruitment probability (0.6 and 0.7% of initial ovules produced flowering offspring, respectively), a result similar to that of open-pollinated flowers (1.0%). This study demonstrated that the overall effectiveness of the ant C. micans as a summer pollinator of L. maritima was as high as that of other winged insects, contributing not only to the seed production of this crucifer but also to the recruitment of new flowering offspring. Received: 17 February 1999 / Accepted: 26 August 1999     

The ontogeny of flowering and sex expression in divergent populations of Lomatium grayi

Summary Populations of Lomatium grayi (Umbelliferae), an andromonoecious, perennial herb, differe in growth rates, flowering frequency, and survivorship. Effects of these different life histories on the ontogeny of sex expression were analyzed for plants from two populations grown from seedlings in a common garden and monitored for six years. Plants from Smoot Hill, Washington grew faster, had a higher probability of flowering at each age and size after the first year of growth, and a higher probability of flowering repeatedly among years than did plants from Clarkston, Washington. The proportion of plants producing some hermaphroditic flowers increased with plant size in both populations. Smoot Hill plants, however, were more likely to begin flowering as small, staminate plants than Clarkston plants. Clarkston plants did not begin flowering until they were older and larger, and most of these plants produced some hermaphroditic flowers when they began reproduction. The positive association between production of hermaphroditic flowers and both plant size and age was consistent with the hypothesis that hermaphroditic flowers are more costly to produce than staminate flowers.Although the populations did not differ in the total number of flowers per plant produced at any age or size, Smoot Hill plants consistently produced a lower percentage of hermaphroditic flowers than Clarkston plants at larger sizes and later ages. Consequently, selection for faster growth rates and higher flowering frequency at small sizes and early ages may have favored the more staminate-biased sex ratios in the Smoot Hill population.     

Seed set variation in wild Clarkia populations: teasing apart the effects of seasonal resource depletion,pollen quality,and pollen quantity

In habitats where resource availability declines during the growing season, selection may favor early‐flowering individuals. Under such ephemerally favorable conditions, late‐blooming species (and individuals) may be particularly vulnerable to resource limitation of seed production. In California, a region prone to seasonal drought, members of the annual genus Clarkia are among the last to flower in the spring. We compared pollen limitation (PL) of seed set and outcrossing rates between early‐ and late‐flowering individuals in two mixed‐mating Clarkia taxa to detect whether flowering time is associated with changes in seed set due to resource depletion, PL, or increased selfing. In 2008–2010, we hand‐pollinated one flower on a total of 1855 individual plants either Early (near the onset of flowering) or Late (near the end of flowering) in the flowering season and compared seed set to adjacent, open‐pollinated flowers on the same stem. To assess the contribution of pollen quality to reproduction, we first (2008) used allozymes to estimate outcrossing rates of seeds produced by Early and Late open‐pollinated flowers. Second (2009), we conducted an anther‐removal experiment to estimate self‐pollen deposition. Seed set in Clarkia unguiculata was not pollen‐limited. Clarkia xantiana ssp. xantiana was pollen‐limited in 2008 and 2010, but not 2009. PL did not differ between Early and Late treatments. In both taxa, seed set of Early flowers was greater than Late flowers, but not due to PL in the latter. Reproduction was generally pollinator‐dependent. Most pollen deposition was xenogamous, and outcrossing rates were >0.7 – and similar between Early and Late periods. These results suggest that pollen receipt and pollen quality remain seasonally consistent. By contrast, the resources necessary to provision seeds decline, reducing the fitness benefits associated with resource allocation to ovules.     

Spatiotemporal Variability in the Reproductive Success of the Continually Flowering Shrub Dillenia suffruticosa in Borneo

Continually flowering plants bloom continuously throughout the year, as often seen in plants distributed along the roadsides or in the understory layers in Southeast Asia's tropical rain forests. Dillenia suffruticosa (Griff. ex Hook. f. & Thomson) Martelli (Dilleniaceae) is one such continually flowering shrub that flowers during periods of community‐wide mass flowering, general flowering (GF), and non‐GF. During irregularly occurring GF periods, when species of all forest layers flower synchronously for several months, some pollinators migrate to the canopy layer, where GF promotes the pollination success of participating plants. Continually flowering plants share the available pollinator community with GF plants, and the reproductive success of continually flowering plants may be affected during the GF period. To assess the effects of GF on the reproductive success of a diverse range of continually flowering plants, we examined the differences in pollinator density and reproductive success between GF and non‐GF periods in D. suffruticosa at four different research sites. Although the seed set differed among the four research sites, pollinator density and fruit set did not differ between GF and non‐GF periods or research sites. Our results suggest that the reproductive success of D. suffruticosa was maintained at an approximately constant level, regardless of the flowering phenology of the canopy layer or other vegetation components.     

Spatial and temporal dispersion patterns of pollinators and their relationship to the flowering strategy of Yucca whipplei (Agavaceae)

Summary A field investigation of the mutualistic interaction between a monocarpic perennial plant, Yucca whipplei, and its host-specific pollinator and seed predator, Tegeticula maculata (Lepidoptera: Prodoxidae), was conducted to determine how the resource utilization pattern and population dynamics of the pollinator have influenced the evolution of the flowering and fruiting pattern of the plant. Although the temporal pattern of emergence of pollinators results in a relatively close tracking of flower abundance within a season, the ratio of pollinators to open flowers does vary significantly within a season, as well as between seasons. At any point in time during the flowering season, the population of adult yucca moths is distributed evenly among the available flowers, so that the number of pollinators on an inflorescence is directly proportional to the number of open flowers available. The relative isolation of individual flowering plants appears to have little effect on the distribution of pollinators among inflorescences. The number of fruits initiated on a plant is directly proportional to the number of flowers produced, and is also partially determined by the time of flowering. Yucca whipplei always produces many more flowers than fruits. Most flowers are not fertilized, and the plants also generally abort and abscise immature fruits after flowering. Fruit production of at least some plants, however, appeared limited by pollination. It is also expected that in some years the relative abundance of pollinators will be low enough that most plants will be pollinator-limited. It is suggested that the pattern of flowering and fruiting of this species has evolved in response to the unpredictability of pollinator availability, both within and between seasons. Resource uncertainty and selection acting on the male component of fitness may also be involved.     

Determinants of seed production in Geranium maculatum

Summary We experimentally examined factors limiting seed production in two populations of the perennial woodland herb Geranium maculatum in central Illinois, USA. To test the pollinator-limitation hypothesis, we compared the seed production of plants whose flowers were supplementarily pollinated with outcross pollen to that of control plants receiving natural pollination only. To test if fruit production by early flowers suppresses fruit and seed formation by late flowers, a third group of plants was prevented from producing seed from the first 50% of the flowers to open (stigmas were excised at flower opening). Finally, to test if seed maturation and flower initiation are correlated with photosynthetic capacity, we performed a defoliation experiment in which either the stem leaves within the inflorescence, the stem leaves below the inflorescence, or the rosette leaves were removed during late flowering. Plants that reccived supplemental pollination produced 1.5–1.6 times more seeds than control plants. We found no difference between hand-pollinated plants and controls in mortality, flowering frequency or number of flowers produced in the year following the experiment. In both control and hand-pollinated plants, the fruit set and total seed production of early flowers were more than twice as high as those of late flowers. In one of the two populations, plants whose early flowers were prevented from setting seed produced significantly more seeds from their late flowers than did control plants. Seed predation was low and did not differ between early and late flowers. Leaf removal did not affect seed number or size in the year of defoliation, nor did it reduce survival or flower production in the subsequent year. This suggests that the plants were able to compensate for a partial defoliation by using stored resources or by increasing photosynthetic rates in the remaining leaves. Taken together, the results demonstrate that both pollinator activity and resource levels influence patterns of seed production in G. maculatum. While seed production was pollinatorlimited in both populations, a seasonal decline in resource availability was apparently responsible for the low seed production by late flowers.     

Dissecting components of flowering pattern: size effects on female fitness

Flowering synchrony is essential for plant reproductive success, especially in the case of small‐sized populations of self‐incompatible species. Closely related to synchrony, flowering intensity influences pollinator attraction and pollinator movements. Thus, a high flowering intensity may increase pollinator attraction but, at the same time, may also increase the probability of geitonogamous pollinations. Depending on the mating system, the female fitness of plants in small populations may be affected by both the positive effects of higher flowering synchrony and pollinator attraction and the negative effects of geitonogamous pollinations induced by a high flowering intensity. It was hypothesized that different‐sized plants in a population would show contrasting flowering patterns, resulting in differences in pollinator behaviour. These influences could result in differences in mating and female reproductive success. This hypothesis was tested by studying the flowering pattern of Erodium paularense (Geraniaceae), a rare and endangered endemic of central Spain. The temporal distribution of flower production was explored throughout the reproductive season, and the probability of xenogamy and geitonogamy and their relationship to plant size and fitness components were calculated. The analysis of this partially self‐compatible species showed diverse flowering patterns related to different plant sizes. Small plants produced a larger number of seeds per fruit in spite of having lower values of flowering synchrony. By contrast, large plants produced a larger number of seeds from geitonogamous pollinations. The effect of different flower displays and outcrossing rates on seed set varied throughout the season in the different groups. Our findings highlight the relevance of individual plant size‐dependent phenology on female reproductive success and, in particular, on the relationship between flowering synchrony and fitness. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156 , 227–236.