Effects of nonhost and host plants on insect herbivory covarying with plant size in the cruciferous plant <Emphasis Type="Italic">Turritis glabra</Emphasis>

Correlation between plant size and reproductive output may be modified by herbivory in accordance with host plant density and the presence of nonhost plants. To elucidate the effects of nonhost plant density and host plant density on the intensity of herbivory and reproductive output of the host plant in relation to plant size under natural conditions, we investigated the abundance of three lepidopteran insects, Plutella maculipennis, Anthocharis scolymus, and Pieris rapae the intensity of herbivory, and fruit set of their host plant, Turritis glabra (Cruciferae). To elucidate the effects of nonhost and host plant density, we selected four categories of plots under natural conditions: low density of nonhost and high density of host plants; low density of both nonhost and host plants; high density of both nonhost and host plants; and high density of nonhost and low density of host plants. The plant size indicated by stem diameter was a good predictor of the abundance of all herbivorous species. The effects of density of nonhost and host plants on the abundance of insects varied among species and stages of insects. As the abundance of insects affected the intensity of herbivory, herbivory was more apparent on larger host plants in plots with low density of both nonhost and host plants. Consequently, the correlation between plant size and the number of fruits disappeared in low plots with density of both nonhost and host plants. In this T. glabra– herbivorous insect system, the density of nonhost plants and host plants plays an important role in modifying the relationship between plants and herbivores under natural conditions. Received: July 19, 1999 / Accepted: June 15, 2000     

Intersexual mimicry and flowering phenology facilitate pollination in a dioecious habitat specialist species, <Emphasis Type="Italic">Myristica fatua</Emphasis> (Myristicaceae)

Myristica fatua is a dioecious specialist species restricted to the endangered, freshwater Myristica swamp forests in the Western Ghats, India. Earlier studies have alluded to pollination by deception in members of the Myristica genus, and thus we examined the pollination ecology comprising floral biology, flower production, flower visitors, and reproductive success in M. fatua and inferred the potential strategies that could permit such deception in this habitat specialist tree. Male flowers provide pollen rewards for an extended period of time while female flowers are rewardless and both sexes are visited by generalist insects, mainly by honeybees and stingless bees. Bee visits were significantly more frequent and longer on male than on female flowers as bees collected pollen from male flowers. We found that flower production patterns create a preponderance of males compared to females in the swamp populations. Using a model of honeybee color vision, we found the distance between the color loci of male and female flowers and based on minimum visual angle subtended by these flowers, we suggest that the two floral sexes cannot be discriminated by bees. Bees are likely deceived by the perceptual similarity of rewardless female flowers to pollen-offering male flowers and pollination is the consequence of foraging errors made by pollinators that encounter largely male–rarely female flower mosaics as they forage among clump-distributed M. fatua trees in the swamp habitat.     

Impact of floral herbivory by <Emphasis Type="Italic">Coleotechnites eryngiella</Emphasis> Bottimer (Lepidoptera: Gelechiidae) on the reproductive output of <Emphasis Type="Italic">Eryngium yuccifolium</Emphasis> Michaux (Apiaceae): a test of the reserve ovary model

The reserve ovary model is a key hypothesis proposed to explain why plants produce surplus flowers and posits that plants may utilize surplus flowers to compensate for losses from floral herbivory. We tested this hypothesis in the prairie plant Eryngium yuccifolium and its floral herbivore Coleotechnites eryngiella. At five Illinois tallgrass prairie sites, we collected central, primary lateral, and secondary lateral inflorescences from E. yuccifolium to determine whether damage by the larvae of C. eryngiella to the flowers in earlier developing inflorescences would be compensated for in later developing inflorescences. Coleotechnites eryngiella does extensive damage to the central and primary inflorescences and little damage to the secondary inflorescences. Later maturing inflorescences did not compensate for early damage by increasing seed production in later inflorescences. The secondary inflorescences of E. yuccifolium may only compensate for catastrophic damage done to the central and primary inflorescences early on in development, serve as additional advertisements for pollinators, act as pollen donors, or allow the plant to take advantage of “ecological windows” of high pollinator and low herbivore abundance. Our findings were spatially and temporally consistent and did not support the predictions of the reserve ovary model in the E. yuccifolium–C. eryngiella system suggesting that in this system, alternate, proximate, and ultimate causes need to be explored for the production of surplus flowers.     

Injured and uninjured leaf photosynthetic responses after mechanical injury on <Emphasis Type="Italic">Nerium oleander</Emphasis> leaves,and <Emphasis Type="Italic">Danaus plexippus</Emphasis> herbivory on <Emphasis Type="Italic">Asclepias curassavica</Emphasis> leaves

Insect herbivory has variable effects on plant physiology; so greater understanding is needed about how injury alters photosynthesis on individual injured and uninjured leaves. Gas exchange and light-adapted leaf chlorophyll fluorescence measurements were collected from uninjured and mechanical partial leaf defoliation in two experiments with Nerium oleander (Apocynaceae) leaves, and one experiment with Danaus plexippus herbivory on Asclepias curassavica (Asclepiadaceae) leaves. Gas exchange impairment (lower photosynthetic rate (P _n ), stomatal conductance (g _s)) indicates water stress in a leaf, suggests stomatal limitations causing injury P _n impairment. The same pattern of gas exchange impairment also occurred on uninjured leaves opposite from injured leaves in both N. oleander experiments. This is an interesting result because photosynthetic impairment is rarely reported on injured leaves near injured leaves. No photosynthetic changes occurred in uninjured A. curassavica leaves opposite from D. plexippus-fed leaves. Partially defoliated leaves that had P _n and g _s reductions lacked any significant changes in intercellular leaf [CO₂], C _i. These results neither support, nor are sufficient to reject, stomatal limitations to photosynthesis. Manually imposed midrib vein severance in N. oleander experiment #1 significantly increased leaf C _i, indicating mesophyll limitations to photosynthesis. Maximal light-adapted leaf photochemical efficiency () and also non-photochemical quenching (q _N) were reduced by mechanical or insect herbivory to both study species, suggesting leaf trouble handling excess light energy not used for photochemistry. Midrib injury on N. oleander leaves and D. plexippus herbivory on A. curassavica leaves also reduced effective quantum yield (ΦPSII) and photochemical quenching (q _P); so reduced plastoquinone pools could lead to additional PSII reaction center closure.     

Prezygotic barriers to gene flow between <Emphasis Type="Italic">Taraxacum ceratophorum</Emphasis> and the invasive <Emphasis Type="Italic">Taraxacum officinale</Emphasis> (Asteraceae)

Prezygotic reproductive barriers limit interspecific gene flow between congeners. Here, I examine the strength of floral isolation and interspecific pollen-pistil barriers between an invasive apomictic, Taraxacum officinale, and the indigenous sexual alpine dandelion, Taraxacum ceratophorum. Experimental arrays of either native inflorescences or a mixture of native and exotic inflorescences were used to examine insect preference and to track movement of a pollen analog. Using hand-pollinations, conspecific and heterospecific pollen germination success on native stigmas was compared. To additionally test for interspecific pollen competition, T. ceratophorum plants received one of three possible hand-pollinations: control conspecific pollination, concomitant conspecific and heterospecific pollination (mixed), or conspecific pollen followed by heterospecific pollen 15 min later (staggered). Floral isolation was negligible as no insect preference was detected. On a presence/absence basis, florets on native inflorescences received slightly less pollen analog from heterospecific donors than from conspecific donors; however, the amount of dye particles transferred from either Taraxacum species to stigmas on recipient T. ceratophorum inflorescences was equivalent. In contrast to weak floral isolation, strong pollen germination and pollen competition barriers should reduce the potential for hybridization. Heterospecific T. officinale pollen exhibited reduced germination success on T. ceratophorum stigmas in comparison to conspecific pollen. Furthermore, a significant pollen-competition effect on the percentage of hybrid offspring was detected only when T. officinale preceded T. ceratophorum pollen by 15 min. This result indicates that conspecific pollen out-competes heterospecific pollen but further suggests that biotic and abiotic factors reducing pollen accrual rates may partially remove barriers to natural hybridization.     

Impact of volcanic activity on a plant-pollinator module in an island ecosystem: the example of the association of <Emphasis Type="Italic">Camellia japonica</Emphasis> and <Emphasis Type="Italic">Zosterops japonica</Emphasis>

Volcanic activity provides an indispensable opportunity to study the ecological responses of organisms to environmental devastation. We examined the reproductive success of Camellia trees to identify how volcanic activity affects the processes of leaf survival, flowering activity, fruit and seed production, pollinator abundance, pollinator visitation frequency, pollination rate, and fruit and seed maturation at different damage sites on Miyake-jima, which experienced an eruption in the summer of 2000. Volcanic gases negatively affect leaf survival and reduce flowering activity in heavily damaged areas. Pollen transfer was sufficient to ensure that higher pollination rates (83%) occurred in heavily damaged areas than in less damaged areas (26–45%), but pollinator densities were lower in response to reduced flower resources. Fruit abortion rates were greater in heavily damaged sites (78%) than in less-damaged sites (53–63%). Consequently, fruit-set rates (16–29%) did not differ significantly among sites. Seed set rates tended to increase with increasing volcanic damage. The negative correlation between seed-set rates and seed mass suggests that the decreased seed mass in severely damaged sites was attributable to the better pollination rates observed there. These results indicate that compensation mechanisms ensure better reproductive success at sites that are more strongly affected by volcanic activity.     

Effects of herkogamy and inbreeding on the mating system of <Emphasis Type="Italic">Mimulus luteus</Emphasis> in the absence of pollinators

Self-pollination mechanisms are often invoked to explain plant reproduction in environments devoid of pollinators. However, populations may evolve a diverse variety of strategies depending on the ecological context of pollination. In this study we examined the pollination environment, inbreeding depression, and herkogamy of Mimulus luteus (Phrymaceae) in two consecutive years in an attempt to evaluate the extent to which these factors determine the current level of autogamy in this population. Results indicate that pollinators were almost absent in the study site in 2005 and 2006. Likewise, no evidence of significant inbreeding depression for seed production and seed germination was detected in the 2 years. Because M. luteus presents hermaphrodite flowers with ‘movement herkogamy’ (touch-sensitive stigmata that close upon contact), and anther–stigma separation, we evaluated the role of these traits in self-fertilization. First, we assessed the effects of pollen source (self- and xenogamous pollen, and control solution) on stigmata dynamics after pollen deposition, and seed production. We observed that stigmata that received pollen (self- and xenogamous hand-pollinated) remained closed for a longer time than flowers that received no pollen (control flowers). Seed production, however, was unaffected by pollen source, indicating that movement herkogamy does not prevent self-fertilization in this population. Second, a phenotypic selection analysis revealed that seed production increased with a reduction of anther–stigma separation in absence of pollinators (bagged flowers), suggesting that low herkogamy levels are promoted in this population. Our results indicate that lack of inbreeding depression, ineffective movement herkogamy, and selection against anther–stigma separation are factors that may contribute to the prevalence of autogamous reproductive mechanisms when M. luteus faces environments with scarce mating opportunity.     

Benzyladenine Promotes Flowering in <Emphasis Type="Italic">Doritaenopsis</Emphasis> and <Emphasis Type="Italic">Phalaenopsis</Emphasis> Orchids

Two experiments were performed to determine how application of the cytokinin benzyladenine (BA) influenced flowering in Doritaenopsis and Phalaenopsis orchid clones. In the first experiment, two vegetative orchid clones growing in 15-cm pots were transferred from a 28°C greenhouse that inhibited flowering to a 23°C greenhouse for flower induction (day 0). A foliar spray (0.2 L m⁻²) containing BA at 100, 200, or 400 mg L⁻¹ or 25, 50, or 100 mg L⁻¹ each of BA and gibberellins A₄ + A₇ (BA+GA) was applied on days 0, 7, and 14. Plants treated with BA alone at 200 or 400 mg L⁻¹ had a visible inflorescence 3–9 days earlier and had a mean of 0.7–3.5 more inflorescences and 3–8 more flowers per plant than nontreated plants. The application of BA+GA had no effect on inflorescence number and total flower number at the rates tested. In the second experiment, three orchid clones received a single foliar spray of BA at 200 mg L⁻¹ at six time points relative to time of transfer from 29°C to 23°C (−1, 0, +1, +2, +4, or +6 weeks). A separate group of plants received a BA application at week 0 but was maintained at 29°C. Inflorescence number was greatest in all three orchid clones when plants were treated with BA 1 week after the temperature transfer. Plants that were sprayed with BA and maintained at 29°C did not initiate inflorescences. The promotion of flowering by the application of BA suggests that cytokinins at least partially regulate inflorescence initiation of Doritaenopsis and Phalaenopsis, but its promotion is conditional and BA application cannot completely substitute for an inductive low temperature.     

Fitness consequences of infection of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> with its natural bacterial pathogen <Emphasis Type="Italic">Pseudomonas viridiflava</Emphasis>

Variation in plant resistance to pathogen infection is commonly observed in interactions between wild plants and their foliar pathogens. Models of host–pathogen interactions indicate that a large cost of infection is generally necessary to maintain this variation, yet there is limited evidence that foliar pathogens cause detectable fitness reductions in wild host plants. Most published work has focused on fungal pathogens. Pseudomonas viridiflava, a common bacterial pathogen of the annual weed Arabidopsis thaliana across its range, comprises two distinct genetic clades that cause disease symptoms of different severity. Here we measured the extent of infection of wild A. thaliana populations in the Midwest, USA, and examined the effect on seed production, in field and growth-chamber experiments, of experimental inoculation with isolates from the two clades. We found infection with P. viridiflava varied from 0 to 56% in Midwest A. thaliana populations, with the possibility of several leaves per plant infected later in the growing season. In the growth chambers, experimental inoculation reduced seed set by averages of 15 and 11% for clades A and B, respectively. In the field experiment, only clade A affected plant fitness significantly, reducing seed set by an average of 38%. Underlying these average effects we observed both negative and positive effects of infection, and variation in both fitness among plant genotypes and sensitivity to environmental conditions.     

The effects of nutrient addition on floral characters and pollination in two subalpine plants, <Emphasis Type="Italic">Ipomopsis aggregata</Emphasis> and <Emphasis Type="Italic">Linum lewisii</Emphasis>

The availability of soil and pollination resources are main determinants of fitness in many flowering plants, but the degree to which each is limiting and how they interact to affect plant fitness is unknown for many species. We performed resource (water and nutrients) and pollination (open and supplemental) treatments on two species of flowering plants, Ipomopsis aggregata and Linum lewisii, that differed in life-history, and we measured how resource addition affected floral characters, pollination, and reproduction (both male and female function). We separated the direct effects of resources versus indirect effects on female function via changes in pollination using a factorial experiment and path analysis. Resource addition affected I. aggregata and L. lewisii differently. Ipomopsis aggregata, a monocarp, responded to fertilization in the year of treatment application, increasing flower production, bloom duration, corolla width, nectar production, aboveground biomass, and pollen receipt relative to control plants. Fertilization also increased total seed production per plant, and hand-pollination increased seeds per fruit in I. aggregata, indicating some degree of pollen limitation of seed production. In contrast, fertilization had no effect on growth or reproductive output in the year of treatment on L. lewisii, a perennial, except that fertilization lengthened bloom duration. However, delayed effects of fertilization were seen in the year following treatment, with fertilized plants having greater aboveground biomass, seeds per fruit, and seeds per plant than control plants. In both species, there were no effects of resource addition on male function, and the direct effects of fertilization on female function were relatively stronger than the indirect effects via changes in pollination. Although we studied only two plant species, our results suggest that life-history traits may play an important role in determining the reproductive responses of plants to soil nutrient and pollen additions.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of <Emphasis Type="Italic">Melastoma malabathricum</Emphasis> and <Emphasis Type="Italic">Tibouchina semidecandra</Emphasis> with sense and antisense dihydroflavonol-4-reductase (DFR) genes

Genetic engineering of a wide variety of plant species has led to the improvement of plant traits. In this study, the genetic transformation of two potentially important flowering ornamentals, Melastoma malabathricum and Tibouchina semidecandra, with sense and antisense dihydroflavonol-4-reductase (DFR) genes using the Agrobacterium-mediated method was carried out. Plasmids pBETD10 and pBETD11, each harbouring the DFR gene at different orientations (sense and antisense) and selectable marker nptII for kanamycin resistance, were used to transform M. malabathricum and T. semidecandra under the optimized transformation protocol. Putative transformants were selected in the presence of kanamycin with their respective optimized concentration. The results indicated that approximately 4.0% of shoots and 6.7% of nodes for M. malabathricum regenerated after transforming with pBETD10, whereas only 3.7% (shoots) and 5.3% (nodes) regenerated with pBETD11 transformation. For the selection of T. semidecandra, 5.3% of shoots and 9.3% of nodes regenerated with pBETD10 transformation, while only 4.7% (shoots) and 8.3% (nodes) regenerated after being transformed with pBETD11. The presence and integration of the sense and antisense DFR genes into the genome of M. malabathricum and T. semidecandra were verified by polymerase chain reaction (PCR) and nucleotide sequence alignment and confirmed by southern analysis. The regenerated putative transformants were acclimatized to glasshouse conditions. Approximately 31.0% pBETD10-transformed and 23.1% pBETD11-transformed M. malabathricum survived in the glasshouse, whereas 69.4% pBETD10-transformed and 57.4% pBETD11-transformed T. semidecandra survived. The colour changes caused by transformation were observed at the budding stage of putative T. semidecandra transformants where greenish buds were produced by both T. semidecandra harbouring the sense and antisense DFR transgenes. Besides that, the production of four-petal flowers also indicated another morphological difference of putative T. semidecandra transformants from the wild type plants which produce five-petal flowers.     

Pollination biology of <Emphasis Type="Italic">Disanthus cercidifolius</Emphasis> var. <Emphasis Type="Italic">longipes</Emphasis>, an endemic and endangered plant in China

Disanthus cercidifolius Maxim. var. longipes H.T. Chang usually has two inflorescences growing in opposite directions in the axillae, but occasionally three inflorescences grow paratactically. The typical flowering process could be divided into 4 periods: “Pre-dehiscence”, “Initial dehiscence”, “Full dehiscence” and “Withering”. Both the natural population and the planted population had a flowering peak of 15–35 days after the first flower bloomed. There were significant differences between the time courses of flowering of the two populations. Out-crossing is the main breeding system in this species. And autogamy decreases the risk of reproductive failure of this species. The main insect pollinators of D. cercidifolius var. longipes are Episyrphus balteatus de Geer, Scaptodrosophila coracina Kikkawa and Peng, Polistes olivaceus de Geer, Apis cerana Fabricius, Nezara viridula L. and Coccinella septempunctata L., and so on. Among the insects, S. coracina and E. balteatus are the most important and efficient pollinators, but others are inefficient pollinators. Though wind pollination is not efficient, it guarantees reproduction when insect pollinators are not available. “Mass flowering” is an adaptive behavior and reproductive strategy of this species, and “few fruiting” could be caused by the lack of pollinators.     

Effects of low-efficiency pollinators on plant fitness and floral trait evolution in <Emphasis Type="Italic">Campanula americana</Emphasis> (Campanulaceae)

Floral visitors vary in their pollination efficiency and their preferences for floral traits. If low-efficiency pollinators decrease the amount of pollen available to higher efficiency visitors, then low-efficiency visitors may actually have negative fitness consequences for the plants that they visit. We used experimental arrays in two populations to determine the floral preferences and the fitness effects of low-efficiency (or ugly) pollinators on Campanula americana. These ugly pollinators (halictid bees) preferentially visited flowers with pollen over flowers that had had their pollen removed. C. americana pollen color varies quantitatively from light tan to dark purple, and we found that natural variation in pollen color influenced the magnitude of halictid preferences for flowers with pollen. In general, preferences for flowers with pollen were stronger when the ugly pollinators foraged in arrays of flowers with tan-colored pollen than in arrays with purple-colored pollen. When plants received few visits by efficient Bombus pollinators, visits by ugly pollinators significantly decreased siring success relative to plants where visits by ugly pollinators were prevented. In contrast, ugly pollinators did not influence siring success when higher efficiency pollinators were more abundant. Thus, the relationship between low-efficiency pollinators and the plants that they visit varies from commensalistic to antagonistic depending on the presence of other pollinators in the community. Our findings suggest that the negative fitness effects and floral preferences of low-efficiency or ugly pollinators may contribute to the maintenance of a pollen color polymorphism in C. americana.     

<Emphasis Type="Italic">Xanthomonas gardneri</Emphasis> exoenzymatic activity towards plant tissue

Bacterial spot caused by Xanthomonas spp. is an important tomato and pepper disease worldwide. Recent outbreaks of bacterial spot disease in Central Brazil and Canada have been attributed to Xanthomonas gardneri, which is also recognized as group D of Xanthomonas campestris pv. vesicatoria. Carotenoid-like pigments called xanthomonadins, which are diagnostic for yellow Xanthomonas spp., were extracted from X. gardneri. It was shown that the model plant Arabidopsis thaliana, member of the Brassicaceae family, can develop disease symptoms in response to different isolates of X. gardneri. Secretion of enzymes has been shown to play an important role in pathogenicity for different pathogens, and to begin to understand the interaction of X. gardneri and A. thaliana, a biochemical analysis of secreted proteins in the presence of A. thaliana leaves was performed. Different enzymatic activities such as for cellulase, α-arabinofuranosidase, pectinase, invertase and xylanase were assayed. In the presence of leaves, cellulase activity was highest after 60 and 72 h of growth and α-arabinofuranosidase activity was detected between 12 and 72 h of growth. Pectinase, invertase and xylanase activities were not detected. Cellulase and α-arabinofuranosidase activities may be important for X. gardneri acquisition of plant nutrients through degradation of cellulose fibers and hemicellulose of the cell wall, respectively, to the invasion of the host tissue and/or may generate signal molecules that are recognized by the plant. This is the first study to address how X. gardneri responds to host plant tissue.     

The floral biology and reproductive system of <Emphasis Type="Italic">Mauritia flexuosa</Emphasis> (Arecaceae) in a restinga environment in northeastern Brazil

Studies of the floral biology of the buriti palm, Mauritia flexuosa, have presented conflicting results with respect to the mechanism of pollination, indicating either cantharophily or anemophily. To resolve this question, the floral biology of M. flexuosa was studied in a coastal restinga environment in northeastern Brazil. The reproductive system was studied experimentally, and floral visitors were collected by bagging inflorescences. In this environment, M. flexuosa, a dioecious species, has several gender-specific floral features that function to attract pollinators, especially beetles. The male flowers produce large amounts of pollen as a reward, and male and female inflorescences produce similar odors that attract pollinators to female flowers, which offer only a nectar secretion as a reward. When feeding on the female flowers, the visitors frequently come into contact with the stigmata. To increase the chances of pollination, the female flowers persist longer than the male ones, and the viability of the pollen grain is very high. A curculionid beetle species of the genus Grasidius was found to be an effective pollinator. We suspect that wind also contributes to the pollination of M. flexuosa in the study area, but in a relatively minor way.     

Visual discrimination between two sexually deceptive <Emphasis Type="Italic">Ophrys</Emphasis> species by a bee pollinator

Almost all species of the orchid genus Ophrys are pollinated by sexual deception. The orchids mimic the sex pheromone of receptive female insects, mainly hymenopterans, in order to attract males seeking to copulate. Most Ophrys species have achromatic flowers, but some exhibit a coloured perianth and a bright, conspicuous labellum pattern. We recently showed that the pink perianth of Ophrys heldreichii flowers increases detectability by its pollinator, males of the long-horned bee Eucera berlandi. Here we tested the hypothesis that the bright, complex labellum pattern mimics the female of the pollinator to increase attractiveness toward males. In a dual-choice test we offered E. berlandi males an O. heldreichii flower and a flower from O. dictynnae, which also exhibits a pinkish perianth but no conspicuous labellum pattern. Both flowers were housed in UV-transmitting acrylic glass boxes to exclude olfactory signals. Males significantly preferred O. heldreichii to O. dictynnae flowers. In a second experiment, we replaced the perianth of both flowers with identical artificial perianths made from pink card, so that only the labellum differed between the two flower stimuli. Males then chose between both stimuli at random, suggesting that the presence of a labellum pattern does not affect their choice. Spectral measurements revealed higher colour contrast with the background of the perianth of O. heldreichii compared to O. dictynnae, but no difference in green receptor-specific contrast or brightness. Our results show that male choice is guided by the chromatic contrast of the perianth during the initial flower approach but is not affected by the presence of a labellum pattern. Instead, we hypothesise that the labellum pattern is involved in aversive learning during post-copulatory behaviour and used by the orchid as a strategy to increase outcrossing.     

Phylogenetic Community Context Influences Pollen Delivery to <Emphasis Type="Italic">Allium cernuum</Emphasis>

Few studies have examined how the number and identity of species in the neighbouring community influences the reproductive success of particular focal species. Pollen delivery, an important component of fitness of sexual plants, is a function of not just the floral traits of any particular individual, but of features of the population and community as it depends on pollinator abundance and preferences. Many pollinators in flowering communities will prefer patches with high floral abundance or diversity yet may exhibit lower floral constancy when more flowering species are present. Thus, pollination efficiency could increase or decrease with increased species richness and this will alter the selection pressures placed upon the floral traits (such as floral colour or reward) of any member of a particular community. Moreover, recent studies have indicated that plant-pollinator networks are phylogenetically structured (pollinators visit related plant species more than expected by chance) and this may be an important factor structuring flowering plant communities. Thus, the sheer number of species within a patch may be less important than the number of closely-related species. We investigate whether species richness or phylogenetic proximity of coflowering species influences the amount and proportion of conspecific pollen delivered to nodding onion, Allium cernuum, in fragment patches of Garry Oak meadows in South Western British Columbia, Canada. We find that pollen delivery depended upon the presence of close relatives far more than on species richness or population density, indicating a central role of the community structure on pollination in flowering plant communities. Insofar as pollen delivery relates to the relative number of seeds produced by members of the community, pollination may in turn determine the community structure of the next generation.     

Effects of browsing in relation to vegetation cover on common yew (<Emphasis Type="Italic">Taxus baccata</Emphasis> L.) recruitment in Mediterranean environments

Common yew (Taxus baccata L.) stands are recognized as prioritary habitats for biodiversity conservation within the European Union. The effects of browsing on the regeneration capacity and spatial dispersal of T. baccata recruits at the European southern limit of the species in the Mediterranean Basin have been herein studied. The efficacy of T. baccata recruitment has been evaluated at six localities in the Northern Sardinia mountains, which have similar altitude, climate, soil, and vegetation but have different types of uses (three were grazed by livestock and three were not). At each site, five habitats have been identified for T. baccata seed dispersal: reproductive female T. baccata canopy, reproductive female Ilex aquifolium canopy, non-fleshy-fruited tree canopy, fleshy-fruited shrubs, and open areas. The density of seedlings was found to be greater under fleshy-fruited trees (reproductive female T. baccata and I. aquifolium) than under shrubs, whereas the sapling density was higher in shrubby habitats, especially at grazed sites due to the mechanical protection afforded by the spiny shrubs against herbivores. Land use (LU) has been found to be the most important factor in determining the spatial distribution of seedlings and saplings in relation to forest habitats. Although browsers had an ephemeral but positive effect on seed germination through their trampling and the resultant scarification, this process eventually became ineffective as was shown by the occurrence of the lowest density of saplings in those habitats where the density of seedlings was the highest. The ultimate and most important effect of browsing was the sharp decrease in the density of saplings, and their almost complete extinction, in non-shrubby habitats. This study highlights the result that, in Mediterranean ecosystems, browsing constitutes the main negative factor on T. baccata seedling-sapling transition and furthermore confirms the necessity to preserve shrubby patches in the vicinity of reproductive female T. baccata and I. aquifolium to permit the regeneration of T. baccata in the presence of livestock. Moreover, at ungrazed sites, T. baccata is able to colonize non-shrubby shady habitats. The application of different management strategies to ungrazed and grazed sites should therefore be the main direction in the management and preservation of T. baccata stands in the Mediterranean region.     

What We Think We Know vs. What We Need to Know About Orchid Pollination and Conservation: <Emphasis Type="Italic">Cypripedium</Emphasis> L. as a Model Lineage

While Darwin (1862, 1877) showed that reproductive success in orchid populations depended on adaptive floral morphology coupled with pollinator visitation a more recent review of the literature (Tremblay et al., 2005) confirmed that many out-breeding species are pollinator-limited because most orchid species showing low fecundity also lack rewards. The absence of rewards depresses both pollinator fidelity and the frequency of pollinator visits to an orchid population even though orchid flowers that lack rewards retain the same interlocking floral structures for precise pollinia removal and deposition found in related species that offer rewards. Using the genus, Cypripedium, as a model lineage of non-rewarding flowers this study also shows that the correlation between low fruit set in a Cypripedium sp. and its specific pollinator(s) is insufficient to predict specific frequencies of low fecundity. Annual rates of fruit set often vary broadly between populations of the same species and within the same population over several seasons. We speculate that fruit-set rates also decline when orchid demography and additional biotic and abiotic factors interrupt rates of pollinator activity (pre-zygotic) and fertilization/fruit maturation (post-zygotic). We suggest that that traditional field studies on pollination ecology and breeding systems be combined with data sets recording genetic variation and orchid flower demography in relation to seasonal variation in climate. We also propose that the same information be collected in regard to genetic variation, demography and phenology of populations of known orchid pollinators and co-blooming angiosperm species native to orchid habitats.