Distribution and Flowering Ecology of Bromeliads along Two Climatically Contrasting Elevational Transects in the Bolivian Andes1

We compared the diversity, taxonomic composition, and pollination syndromes of bromeliad assemblages and the diversity and abundance of hummingbirds along two climatically contrasting elevational gradients in Bolivia. Elevational patterns of bromeliad species richness differed noticeably between transects. Along the continuously wet Carrasco transect, species richness peaked at mid‐elevations, whereas at Masicurí most species were found in the hot, semiarid lowlands. Bromeliad assemblages were dominated by large epiphytic tank bromeliads at Carrasco and by small epiphytic, atmospheric tillandsias at Masicurí. In contrast to the epiphytic taxa, terrestrial bromeliads showed similar distributions across both transects. At Carrasco, hummingbird‐pollination was the most common pollination mode, whereas at Masicurí most species were entomophilous. The proportion of ornithophilous species increased with elevation on both transects, whereas entomophily showed the opposite pattern. At Carrasco, the percentage of ornithophilous bromeliad species was significantly correlated with hummingbird abundance but not with hummingbird species richness. Bat‐pollination was linked to humid, tropical conditions in accordance with the high species richness of bats in tropical lowlands. At Carrasco, mixed hummingbird/bat‐pollination was found especially at mid‐elevations, i.e., on the transition between preferential bat‐pollination in the lowlands and preferential hummingbird‐pollination in the highlands. In conclusion, both richness patterns and pollination syndromes of bromeliad assemblages varied in distinct and readily interpretable ways in relation to environmental humidity and temperature, and bromeliad pollination syndromes appear to follow the elevational gradients exhibited by their pollinators.     

The importance of bees as pollinators in the short corolla bromeliad Aechmea caudata in southern Brazil

The majority of bromeliad species are pollinated by vertebrates, mainly hummingbirds and bats. However, bees are among the most frequent visitors in some short-corolla species with ornithophilous features, but only few studies identified insects as pollinators of these bromeliads. The importance of visitors for pollination success in Aechmea caudata (Bromeliaceae) was determined through the frequency and pollination effectiveness (measured as seed set/single visit) of its visitors in a secondary Atlantic forest area in southern Brazil. Aechmea caudata is self-incompatible and therefore pollinator-dependent. A total of 16 species were recorded visiting their flowers. Bees were the most rich and frequent taxon (91% of 647 visits). Bombus morio was the most frequent species (41%). Although the floral features of A. caudata, such as scentless, tubular corollas, yellow and red flowers, and nectar secretion during the whole diurnal anthesis, are related to ornithophily, the single hummingbird species Thalurania glaucopis failed to pollinate the flowers. Its low frequency (2.5%) apparently did not promote the pollen flux between conspecific bromeliads. Pollination tests showed that no seeds developed after hummingbird visits. Seeds were formed only at flowers visited by B. morio. We discuss our findings by contrasting them with the results on the similar and sympatric A. lindenii and by emphasizing the importance of bees for pollination of bromeliads with short corolla. Our results show that pollination effectiveness together with frequency data are necessary to analyze the complex interactions between plants and their flower visitors.     

Honeyeaters and the New Zealand forest flora: The utilisation and profitability of small flowers

New Zealand flowers are frequently considered unspecialised allowing easy access to pollen and nectar by a wide range of visitors. Most conform with a syndrome of insect pollination (entomophily). Pollination of forest flowers by birds has been described for a range of species whose flowers are morphologically ornithophilous. On Kapiti Island and Little Barrier Island, all three species of New Zealand honeyeaters have been described feeding on flowers currently assumed to be entomophilous or where the pollination system is unknown. The persistence and regularity of visits suggests that the birds are obtaining suitable rewards in the form of nectar and could be serving as pollinators. We measured the nectar energetic value from flowers of three ornithophilous and five entomophilous species. Nectar production over 24 hours was highest in ornithophilous species, but the standing crop of nectar overlapped—ornithophilous species: Metrosideros fulgens (standing crop 6.6 J), Metrosideros excelsa (22 J), and Fuchsia excorticata (1.8 J); and entomophilous: Pittosporum crassifolium (23 J), Pseudopanax arboreus (1.5 J), Dysoxylum spectabile (3.7 early flowers -6.7 J late flowers), Pittosporum eugenioides (2.7 J) and Geniostoma rupestre (1.8 J). The entomophilous species present the flowers in aggregation and as result birds can visit a large number flowers per minute. We found that the average estimated nectar consumption rate for all the entomophilous species except G. rupestre was enough to sustain the two smaller New Zealand honeyeaters (hihi energy requirements= 0.12 kJ min(-1), median energy obtained: 0.16 kJ min(-1) D. spectabile—0.57 kJ min(-1) P. crassifolium); bellbird energy requirements = 0.10 kJ min(-1), median energy obtained: 0.14 kJ min(-1) D. spectabile—0.68 kJ min(-1) P. crassifolium). However, we estimate that if the birds are able to selectively forage on the flowers with most nectar, the energetic returns of all species may be sufficient for hihi and bellbird (hihi: 0.18 kJ min(-1) G. rupestre—0.93 kJ min(-1); P. crassifolium; bellbird: 0.12 kJ min(-1) G. rupestre 1.11 kJ min(-1) P. crassifolium). If tui (energy requirements: 0.25 kJ min(-1), forages randomly, only P. crassifolium (0.80 kJ min(- 1)) and D. spectabile late in the season (0.30 kJ min(-1)) provide sufficient returns, but if selective, P. arboreus (0.45 kJ min(-1)) may also suffice. We suggest that because (a) the nectar produced by entomophilous flowers provides sufficient energy to sustain the energetic requirements of birds, and (b) these plants flower in the cooler months when insect activity is reduced, birds might have played a wider role in pollination than previously considered. This finding is of particular importance because the abundance of New Zealand honeyeaters on the mainland has decreased considerably since human colonisation and this could be affecting forest regeneration.     

Petal micromorphology and its relationship to pollination

• The characteristics of petal epidermal conical cells affect the quality of the signals perceived by various pollinators. This study aimed to identify variations in micromorphological characteristics of flower petals and their relationship to melittophily, ornithophily and chiropterophily pollination systems.
• The petals of 11 species were analysed using scanning electron microscopy and optical microscopy and the micromorphological traits were described, measured and compared using Tukey's test, PCA and cluster analysis.
• Unlike chiropterophily, all melittophilous and some ornithophilous species possessed adaxial epidermal conical cells. Cluster grouping separated chiropterophilous flowers from melittophilous and ornithophilous. PCA analysis showed that the two morphometric profile of conical cells was the attribute that most strongly influenced the grouping of species. When considering the data set of the three pollination systems, melittophilous and ornithophilous plants were more similar to each other than they were to chriopterophilous species. The distance between conical cell apices is an important parameter in interactions with pollinators.
• This study facilitated recognition of smoothing pollinator resource access through petal micromorphological characteristics. Further research regarding the biometry of micromorphological traits related to pollination is required.

     

Colour and size of flowers in relation to pollination of Erica species

Summary Data on flower colour polymorphism were recorded for 341 of some 426 species of Erica occurring in the south-western Cape, South Africa. Thirty-eight per cent of these Erica species are colour polymorphic, the incidence of polymorphism being greater than expected for ornithophilous species and lower than expected for anemophilous species. Both altitude and season of flowering are correlated with the incidence of colour polymorphism, with most polymorphs occurring in species which have relatively large altitudinal ranges and extended flowering periods. The mean corolla length for each of pink, purple and white flowers is significantly shorter than that for each of red, orange, yellow and green flowers, suggesting that these two sets of colours correspond with entomophily and ornithophily, respectively. There are no Erica species with blue flowers. We suggest that the patterns of colour polymorphism, because of their relationships with the behaviour of pollinators, may reflect patterns of speciation in the genus.     

Pollination of the heterostylous Galápagos native, <Emphasis Type="Italic">Cordia lutea</Emphasis> (Boraginaceae)

The hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination due to greater insect activity at night typical of hot, arid regions. Cordia lutea, a heterostylous member of the Galápagos flora, was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen-ovule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. There was a significant difference in fruit set between flowers experiencing legitimate cross-pollinations (pin × thrum) and those experiencing all other pollination treatments except facilitated autogamy. There was no significant difference in seed set among any of the treatments, but there was a trend toward greater seed set for flowers experiencing open-pollination, legitimate cross-pollination, and nocturnal pollination. There was no significant difference in fruit set or seed set between flowers experiencing diurnal pollination and nocturnal pollination, although there was a trend toward greater seed set resulting from nocturnal pollination. Carpenter bees were the most effective diurnal pollinators, whereas moths were the most effective nocturnal pollinators. Of the two, moths are more efficient at transporting pollen from plant to plant. Results indicate that an overall low productivity of this species is due to pollen limitation exacerbated by nectar robbing. Cordia lutea exhibits a mixed mating system, producing a relatively low level of fruits through a combination of self- and cross-pollination, facilitated by the relatively few insects that are available.     

Comparative ecophysiology of CAM and C3 bromeliads. I. The ecology of the Bromeliaceae in Trinidad

Abstract This article deals with the physiological ecology of the Bromeliaceae, a large neotropical family containing both terrestrial and epiphytic forms, as well as many species with crassulacean acid metabolism (CAM). The article is in two parts. In the first, we review what is known of the occurrence of CAM and C₃ species in the Bromeliaceae. The photosynthetic pathways are discussed in the context of the major taxonomic divisions within the family and the great diversity of bromeliad life-forms. Of the three subfamilies, the Pitcairnioideae contain both C₃ and CAM species and are essentially all terrestrial. In contrast, the Tillandsioideae are entirely epiphytic or saxicolous, with CAM species being restricted to the genus Tillandsia, And in the Bromelioideae all species show CAM, but terrestrial and epiphytic forms are found in about equal numbers. The evidence suggests that both CAM and the epiphytic habit arose more than once in the family's evolutionary history. In the second part we consider the photosynthetic ecology of the various bromeliad life-forms in more detail using the specific example of Trinidad (West Indies). CAM bromeliads tend to be centred on the drier regions of the island and C₃ forms on the wetter areas. However, at any one site there is a marked vertical stratification of species within the forest profile. Based on the known habitat preferences of the bromeliads, six contrasting sites were selected for field studies in Trinidad. These ranged from arid coastal scrub to montane rain forest, the vegetational and climatic characteristics of which are described here. The constancy of δ¹³C values (carbon-isotope ratios) for individual CAM species in these markedly different habitats emphasized the need for ecophysiological studies to characterize environmental effects on CO₂ assimilation and transpiration. The following papers in this series present the results of a comparative investigation of gas exchange and leaf water relations of CAM and C₃ bromeliads in situ at the various sites.     

Species richness and ecophysiological types among Bolivian bromeliad communities

The relationship between diversity and composition of neotropicalbromeliad communities and abiotic and autecological factors is still poorlyunderstood. In this study, I related point diversity (mean species number per400 m² plot), diversity (total species number persite), representation of life-forms (epiphytes, terrestrials, saxicoles), andsix ecophysiological types of bromeliads at 74 forest sites in the BolivianAndes and adjacent lowlands to 12 environmental factors reflecting mostlyclimatic conditions. A total of 192 species, including 108 epiphytes, 106saxicoles, and 49 terrestrials, were recorded. Extrapolation revealed that theactual total species number in the region is at least 24% higher than recorded,especially among terrestrial (71%) and saxicolous (40%) species. Epiphytes weremore fully sampled because of their tendency towards larger range size andbecause they are distributed more evenly where they occur. Overall, theenvironmental factors explained up to 61% of the observed variance, reflectingall expected relationships such as the increase of tank bromeliads in wethabitats and of atmospheric bromeliads in arid regions. Point diversity almostalways showed higher regression coefficients than diversity, possibly as aresult of more complete sampling in small plots and because the abundance ofindividual species (which influences point diversity) may be more closelyrelated to abiotic factors than species richness. Despite somewhat lower diversity in arid areas, point diversity peaked in dry habitats,presumably due to the scarcity of competing epiphytic orchids, ferns, and aroidsthat lack the extreme adaptation of bromeliads to drought stress and lownutrient availability. The decline of epiphytic bromeliad diversity at highelevations appears to be linked to low temperatures, particularly increasingfrost frequency. It is hypothesized that the low diversity of bromeliads inhumid tropical lowland forests is caused by low photosynthetic rates due to highwater stress and low light availability combined with high respiration losses.In combination, these factors would impede the maintenance of a positive carbonbalance.     

Bimodal pollination system of the bromeliad Aechmea nudicaulis involving hummingbirds and bees

In order to compare the effectiveness of birds and insects as pollinators, we studied the floral biology of the bromeliad Aechmea nudicaulis (L.) Grisebach in the biome of the Atlantic rain forest, southern Brazil. On Santa Catarina Island, flowering extends from mid-September to the end of December, with diurnal anthesis. The reproductive system is obligatory xenogamy, thus pollinator-dependent. Flowers secrete 31.84 μl of nectar per day, with a mean sugar concentration of 23.2%. Highest nectar volume and sugar concentration occur at the beginning of anthesis. Most floral traits are characteristic for ornithophily, and nectar production appears to be adapted to the energy demand of hummingbirds. Continued secretion of the sucrose-dominated nectar attracts and binds visitors to inflorescences, strengthening trapline foraging behaviour. Experiments assessing seed set after single flower visits were performed with the most frequent visitors, revealing the hummingbird Thalurania glaucopis as the most effective pollen vector. In addition, bees are also functional pollinators, as substantiated by their high visitation frequency. We conclude that this pollination system is bimodal. Thus, there is redundancy in the pollination service provided by birds and bees, granting a high probability of successful reproduction in Ae. nudicaulis.     

Evolutionary disruption in the pollination system of Vanilla (Orchidaceae)

• Pollination of the pantropical Vanilla has been linked to melittophily and food deception.
• Here we investigated the role of flower traits on the reproduction of Neotropical Vanilla. We also studied the evolution of pollination systems in order to understand the origin of production of flower resources and the diversification of pollinators in this orchid genus. Our study was founded on data of adaptations in flower morphology, production of resources, scent release, pollinators and breeding systems of Vanilla and presenting new data on reproductive biology of V. palmarum. Data on reproductive biology of Vanilla were mapped onto a phylogeny to address our queries on the evolution of pollination systems in this genus.
• Vanilla palmarum shows a mixed mating system, with its facultative autogamous flowers being pollinated by hummingbirds. Its yellow flowers are scentless and produces nectar. Mapping of the pollination system onto trees resulted in one origin for bird pollination and at least two origins for autogamy in Vanilla. Nectar secretion has a single origin in the Neotropical thick-leafed lineage.
• Bird pollination of Vanilla is shown for the first time. The origin of ornithophily within a bee-pollinated clade is supported by flower morphology. Floral transitions to ornithophily have been favoured by the occupation of a distinct niche from that of the other thick-leafed Vanilla species. Despite its specialized pollination, V. palmarum is autogamous. A mixed mating system can promote reproductive assurance in the case of a decline in pollinator populations, or in areas where pollinator services are irregular or absent.

     

Heterogeneity of terrestrial bromeliad colonies and regeneration of Acacia praecox (Fabaceae) in a humid-subtropical-Chaco forest, Argentina

In several tropical and subtropical forests, plants of the understorey act as an ecological filter that differentially affects woody species regeneration. In convex sectors of the Schinopsis balansae (Anacardiaceae) forests of the Southeastern Chaco there are dense colonies of terrestrial bromeliads. These may influence forest regeneration by intercepting rain water and propagules in their tanks. Within colonies, the spatial distribution of bromeliads is clumped because their clonal growth leaves numerous internal gaps. In this study we describe the internal heterogeneity of three bromeliad colonies (plots) and analyze how this heterogeneity affects Acacia praecox regeneration (i.e. seedling recruitment and survival). In January 1996, we randomly placed three transects with 150 contiguous quadrats of 100 cm(2) in each plot. For each quadrat we recorded the type of floor cover (i.e. bromeliads, herbs, litter, or bare soil) and the presence of A. praecox seeds or seedlings. In July 1996 we relocated the transects and recorded seedling survival. Bromeliad colonies showed a high internal heterogeneity. Almost half of the 450 quadrats were covered by two terrestrial bromeliads. Aechmea distichantha was recorded in 81% of all quadrats with bromeliads, and Bromelia serra in the others. All quadrats with bromeliads were covered by litter. Half of them were occupied by the bases of bromeliads and the others were covered by their leaves. In contrast, where bromeliads were not present, soil surface was covered by litter in 83% and by herbaceous vegetation in 11% of the quadrats; very few quadrats were covered by bare soil. In January 1996, we recorded 127 seeds and 176 seedlings of A. praecox. Seed and seedling densities of A. praecox were similar in quadrats with and without bromeliads, but variability in seedling density of A. praecox was higher within than among plots. Seed density was higher in quadrats covered by bromeliad leaves than inside the tanks. Seedling survival of A. praecox was slightly higher in quadrats with bromeliads in only one of the three plots. No seedling survived inside the bromeliad tanks. Apparently. bromeliad colonies have no effect on seedling regeneration of A. praecox.     

Two bromeliad species with contrasting functional traits partition the understory space in a South American xerophytic forest: correlative evidence of environmental control and limited dispersal

We examined the spatial distribution of two bromeliad species with contrasting functional traits in the understory of a xerophytic South American Chaco forest. Aechmea distichantha is a facultative terrestrial species with well-developed phytotelma and short rhizomes, whereas Bromelia serra is a strictly terrestrial species with soil-exploring roots and long rhizomes. Both bromeliads develop colonies on relatively elevated patches in Schinopsis balansae forests. We evaluated the roles of environmental controls, limited dispersal, and interspecific competition as drivers of the different distribution of these bromeliads. We mapped the overstory, understory and topography of 16 forest plots with bromeliads (400 m² each, subdivided in 100 4-m² subplots). We sampled soil characteristics on sectors dominated by each bromeliad species. We used structural equation modeling to assess direct and indirect associations of each bromeliad species cover with environmental conditions, abundance of conspecifics in the vicinity, and local abundance of the other species. A. distichantha cover increased on elevated subplots with high tree/shrub basal area, whereas B. serra cover showed the opposite pattern. In addition, A. distichantha cover was negatively associated with B. serra cover, but not vice versa, and cover of both species increased with the abundance of nearby conspecifics, suggesting that limited vegetative dispersal partly accounted for their distribution. Sectors dominated by A. distichantha had lower soil bulk density and higher organic matter content than those dominated by B. serra. According to our model, influences of competition and limited vegetative dispersal reinforce the association between distribution of these bromeliads and environmental heterogeneity of the forest understory.     

Mixed hummingbird: Long‐proboscid‐fly pollination in ‘ornithophilous’Embothrium coccineum (Proteaceae) along a rainfall gradient in Patagonia,Argentina

Abstract The pollination ecology of eight populations of the tree Embothrium coccineum was studied along a steep rainfall gradient in NW Patagonia, Argentina. The showy red flowers suggest an ornithophilous pollination syndrome and they have been reported to attract hummingbirds in Argentina and hummingbirds and passerines in Chile. At each population, flower visitors were recorded and floral rewards were analysed. We found a highly significant increase in nectar concentration towards the drier end of the gradient, but this change was not related to the turnover of species in the flower‐visitor assemblage of E. coccineum. In addition to the hummingbird Sephanoides sephaniodes (Green‐Backed Firecrown, Trochilidae) which is widespread throughout the temperate forest at this latitude, other species seem to be locally important as pollinators of E. coccineum in some sites in Argentina (e.g. two long‐tongued tanglewing flies (Nemestrinidae) of the genus Trichophthalma). The long‐dated occurrence of tanglewing flies in South America, relative to the more modern hummingbirds, suggests that ornithophily may be a derived character in E. coccineum, the ancestral condition being pollination by Nemestrinidae.     

Do cloud forest tree species differ in their suitability as a substrate for epiphytic bromeliads?

There is evidence for the existence of varying degrees of host preference in vascular epiphytes; certain tree species can be positively, neutrally, or negatively associated with epiphytes. The objective of this study was to evaluate whether tree species of the cloud forest differ in their suitability as a substrate for epiphytic bromeliads. To evaluate the association between epiphytic bromeliad cover and host tree species, we sampled 62 plots (each of 200 m²) in four cloud forest fragments in Veracruz, Mexico. For all trees ≥10 cm in diameter at breast height (DBH), we recorded species name, DBH, and percentage cover of bromeliads in categories of tree coverage. In total, 587 trees belonging to 52 species were recorded. All of the 10 tree species used to assess differences in epiphyte cover (each with a minimum of nine individuals) supported bromeliads, but mean bromeliad cover differed significantly among the tree species. The tree species that concentrated the highest bromeliad cover were Quercus sartorii (29.86%) and Liquidambar styraciflua (21.72%). Our results indicate that, while none of the tree species analyzed was a limiting host for epiphytic bromeliads in general, varying levels of bromeliad cover occur depending on the host species in tropical montane cloud forest fragments suggesting that certain tree species are better hosts than others. The implications for conservation efforts of differential tree species suitability as epiphyte hosts are discussed.     

Environmental patterns and ecological correlates of range size among bromeliad communities of Andean Forests in Bolivia

The abiotic, historical, and autecological factors determining the range sizes of tropical plant species and the distribution of endemism are still poorly understood. In this study, the variation of range-size rarity was analyzed among the bromeliad communities of 74 forest sites in the Bolivian Andes and adjacent lowlands with respect to 14 environmental factors reflecting mostly climatic conditions and to species attributes such as life-form, ecophysiological type, pollination mode, and fruit type. The global ranges of all 192 recorded bromeliad species were mapped on a 1° grid, quantified as the number of 1° grids occupied by a species, and range-size rarity indices were calculated as the mean inverse range size of all species at a given study site. At the community level, range-size rarity increased with elevation, most notably among epiphytic taxa. Range-size rarity of terrestrial forest species increased with decreasing habitat area, presumably reflecting the agglomeration of endemic species in isolated dry forest valleys with restricted area. Epiphytes showed higher range-size rarity in the most humid areas, which are also geographically isolated. At the species level, range size revealed a limited relationship to pollination mode or ecophysiological type but differed significantly between epiphytic species (large ranges) and terrestrial and saxicolous taxa (small ranges). However, this pattern was outweighed by differences among fruit types, with berries corresponding to large ranges, winddispersed seeds with flight appendages to intermediate ranges, and wind-dispersed seeds without appendages to small ranges. It is hypothesized that the tendency toward larger ranges among epiphytes (of any plant group) is due at least partly to the prevalence of taxa with adaptations to long-distance dispersal, ensuring efficient colonization of canopy habitats while preventing the differentiation of populations.     

Insect Pollination in the Cycad Genus Bowenia Hook, ex Hook. f. (Stangeriaceae)1

All confirmed records of entomophilic pollination in cycads are for species in the Zamiaceae. This paper presents details of entomophily in both species of Bowenia in the Stangeriaceae. Seed set in female cones from which wind and water‐borne pollen, but not insects, was excluded, indicates that pollination is obligately entomophilous. The pollination vectors are Miltotranes weevils and the relationships are species‐specific and possibly coevolutionary.     

Flowering phenologies of hummingbird plants from the temperate forest of southern South America: is there evidence of competitive displacement?

Plant species sharing pollinators may compete through pollination. This type of competition may lead to overdispersed flowering phenologies. However, phenological segregation is difficult to detect in seasonal climates. We compared patterns of phenological overlap in assemblages of ornithophilous plants from three localities of the temperate forest of southern South America with those generated by four different null models. These species were all visited and presumably pollinated by a single species, the hummingbird Sephanoides sephaniodes, which makes this situation ideal to evaluate the role of pollination‐mediated competition. For one site, we compiled data on flowering phenologies for three different years. Three models considered the flowering period of the whole assemblage of ornithophilous plants as the phenological window within which flowering phenologies were randomized, but made no further assumptions on how species should be distributed within that temporal frame. The fourth model assigned differential probabilities to different time intervals based on the flowering onset of non‐ornithophilous plant species. Observed mean pairwise overlaps for all localities and years were well within the interval defined by the 2.5 and 97.5% percentiles of the randomized distribution of expected mean pairwise overlaps according to models 1–3. However, model 4 showed a consistent trend towards overdispersion of ornihophilous phenologies, which show a shift towards mid‐ to late‐summer flowering. Thus, to the extent that the distribution of flowering of non‐ornithophilous species reflects the constraints imposed by a highly seasonal climate, our results provide support to the proposal that pollinator sharing may cause evolutionary displacement or ecological sorting of flowering phenologies. Other factors, such as phylogenetic inertia, could also contribute to explain extant phenological patterns in the highly endemic ornithophilous flora of the temperate forest of southern South America.     

Micro-environmental factors and the endemism of bromeliad aquatic fauna

Tank bromeliads harbour aquatic microcosms with many endemic species among their leaves. We performed a set of experiments to determine which factors maintain the bromeliad aquatic fauna in isolation from neighbouring ponds. We cultivated three invertebrates species (an ostracod, an annelid and a cladoceran) from a pond surrounded by terrestrial bromeliads in Southeastern Brazil and introduced them inside cleaned bromeliads, using recipients with the same volume as controls. The pH, conductivity and organism densities were monitored in the bromeliad samples and controls for 41 days. The samples introduced inside the cleaned bromeliads showed a significant decrease in pH and conductivity compared to the controls. The pond organism populations introduced in the bromeliads presented a high extinction rate and a significant population decrease when compared to the ones introduced in the controls. We attributed the population decline experienced by the pond organisms to the oligotrophic conditions generated inside the tanks by the bromeliads due to the nutrient absorption. We suggest that the changes in water chemistry induced by the bromeliads could play an important role in isolating their microcosm communities from other freshwater systems. Other mechanisms that could produce the high rates of endemism in bromeliad fauna are discussed. Handling editor: K. Martens     

A preliminary study on pollination biology of Omphalogramma souliei Franch. (Primulaceae), a species endemic to China

The pollination biology of Omphalogramma souliei Franch., a species endemic to southwestern China, was investigated. Floral phenology, flower visitors, pollen/ovule ratio, attractants and rewards to the visitors were observed, measured, and recorded. Bagging experiments to exclude pollinators were carried out in the wild for two years. Our results revealed five important aspects of the reproductive biology of Omphalogramma souliei. 1) The pollen-ovule ratio was 1748±233. The breeding system was self-compatible, with facultative xenogamy. 2) The pollination syndrome is entomophily, and this species could not be pollinated by wind if the pollinators were unavailable. 3) Six insect species were observed visiting the flowers of Omphalogramma souliei in the wild, of them, three species of hymenoptera, Lasioglossum sp., Heriades parvula Cockerell and Micrapis florae Fabricius, are the principal floral visitors and effective pollinators. 4) The visual attractants to the visitors are floral color and shape, the large yellow anthers, and the rewards for visitors are pollen and nectar. 5) Cleistogamy may also occur, since the anthers of some flowers dehisced before opening of the corolla. The results of floral biology and pollination characters suggest that xenogamy predominated and autogamy played an assistant role in the evolution of reproduction and breeding system of O. souliei.     

Nocturnal and diurnal pollination of Clerodendrum molle (Verbenaceae) in the Gal��pagos Islands

The primary hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination because of the greater insect activity at night typical of hot, arid regions. Clerodendrum molle, a widespread member of the Galápagos flora was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen?Covule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. Results indicate no significant difference in fruit set. Cross-pollinated flowers showed a significant increase in seed set over all treatments except facilitated autogamy. Nocturnal and diurnal fruit and seed set did not differ significantly. Nocturnal visitors included ants, spiders, hawk moths, and roaches whereas diurnal visitors included carpenter bees and ants. Galápagos members of C. molle exhibit incomplete protandry and set fruit via autonomous autogamy as a result of natural selection in an environment with few faithful pollinators. Overall low fruit and seed set are likely because of a combination of pollen and resource limitation, the latter exacerbated by nectar robbing. Studies of island angiosperms are crucial for complete understanding of the population dynamics of indigenous plants, which can assist conservation officials in protecting these species.