Pollination Vectors Research Articles

Pollination mode determines floral scent

The main objective of this study is to determine if the pollination vector influences the potential floral emissions of flowering plants. We hypothesized that flowers pollinated by insects would emit significantly higher amounts of volatile organic compounds (VOCs) and would present a higher diversity of these compounds than flowers pollinated by wind. The floral emissions of fifteen entomophilous species and eleven anemophilous species were captured by dynamic headspace sampling under field conditions and analyzed by gas chromatography–mass spectrometry. We searched for differences in the emission profiles between anemophilous and entomophilous flowers by considering the effects of phylogeny in our analysis. The floral emissions from the two groups were significantly different. Entomophilous species presented highly diverse emissions in both magnitude of emission rates and richness of compounds depending on the species, but overall, the flowers from entomophilous species had much higher VOC emission rates and VOC richness, both for terpenes and benzenoid compounds, than those from anemophilous species (two orders of magnitude higher emissions). The data thus confirm that the presence of intensely scented flowers with complex scents is strongly related to biotic pollination.

Trait-based analysis of decline in plant species ranges during the 20th century: a regional comparison between the UK and Estonia.

Although the distribution ranges and abundance of many plant species have declined dramatically in recent decades, detailed analysis of these changes and their cause have only become possible following the publication of second- and third-generation national distribution atlases. Decline can now be compared both between species and in different parts of species' ranges. We extracted data from distribution atlases to compare range persistence of 736 plant species common to both the UK and Estonia between survey periods encompassing almost the same years (1969 and 1999 in the UK and 1970 and 2004 in Estonia). We determined which traits were most closely associated with variation in species persistence, whether these were the same in each country, and the extent to which they explained differences in persistence between the countries. Mean range size declined less in Estonia than in the UK (24.3% vs. 30.3%). One-third of species in Estonia (239) maintained >90% of their distribution range compared with one-fifth (141) in the UK. In Estonia, 99 species lost >50% of their range compared with 127 species in the UK. Persistence was very positively related to original range in both countries. Major differences in species persistence between the studied countries were primarily determined by biogeographic (affiliation to floristic element) and ecoevolutionary (plant strategy) factors. In contrast, within-country persistence was most strongly determined by tolerance of anthropogenic activities. Decline of species in the families Orchidaceae and Potamogetonaceae was significantly greater in the UK than in Estonia. Almost all of the 736 common and native European plant species in our study are currently declining in their range due to pressure from anthropogenic activities. Those species with low tolerance of human activity, with biotic pollination vectors and in the families referred to above are the most vulnerable, especially where human population density is high.

Reproductive success of Acacia longifolia (Fabaceae, Mimosoideae) in native and invasive populations

The reproductive biology of exotic species affects their capacity to become naturalised and invasive in non-native areas. Selfing is a common trait in many invasive plants probably because it provides reproductive assurance under low availability of pollination vectors and sexual partners. Nonetheless, the predominantly self-incompatible Australian Acacia species are among the most aggressive plants worldwide. To address whether there have been changes in selfing ability and natural reproductive success of A. longifolia during invasion, we compared one population in the invaded area (Portugal) with one population in the native range (Australia). We specifically assessed floral traits, fruit set and offspring traits for selfing and open-pollination treatments. Within each pollination treatment, no differences were found between areas, suggesting that the level of self-compatibility has not changed during invasion. However, the number of aborted seeds and seed size were significantly different between pollination treatments in Australia but not in Portugal. There were significant differences in the number of seeds per pod and in seed weight between ranges. A lower number of aborted seeds, a higher number of fully developed seeds and a greater seed size were found in the invaded area for both pollination treatments. In spite of the low selfing ability of A. longifolia in the invaded area, there was an increase in the quantity and size of the seeds produced in the new region, even for self-pollinated fruits, which might contribute to A. longifolia invasiveness.

The impact of study design and life history traits on genetic variation of plants determined with AFLPs

In this study, we analysed the impact of study design and life history traits on genetic variation of plants determined with amplified fragment length polymorphisms (AFLPs), a technique widely applied in all fields of molecular plant ecology. For the proper interpretation and comparison of genetic variation based upon AFLPs, a meta-analysis based upon a large number of studies of the relationship between study design and plant life history traits on the one hand and of AFLP variation on the other hand is needed but is lacking. To bridge this gap, we extracted data on study design and genetic variation from 115 AFLP studies comprising a total of 152 species. Subsequently, we ascribed the life history traits taxonomic status, life span, frequency, mating system and pollination vector to each of the species. Then, we used linear models to analyse the impact of study design and life history traits on genetic variation. In our data set genetic variation within and among populations depended neither on the number of analysed populations nor the number of analysed individuals per population. However, maximum geographic distance between populations strongly affected genetic variation. Variation within populations decreased while variation among populations increased with maximum geographic distance. Concerning the impact of life history traits, both genetic variation within and among populations depended with increasing strength on the life span, the frequency and the mating system of the species. Following the results of this study, the number of analysed populations or individuals per population is not necessarily a problem when comparing results of different studies, at least when not very low sample sizes are used. However, corresponding study ranges would be highly recommendable, since the maximum geographic distance between populations strongly affects genetic variation.

Pollen Aggregation in Relation to Pollination Vector

Premise of research. Angiosperms possess pollen dispersal units (PDUs) of varying size, from monads (single grains) to aggregates containing thousands of grains. It has been suggested that the degree of aggregation is related to the dispersal agent (in particular, animals vs. wind), but aggregation has rarely been measured, and its correlation with pollination vectors has been examined for only a few species.Methodology. Assuming a lognormal distribution, the expected distribution for a random disaggregation process, we tested the hypothesis that the distribution of PDU sizes depends on the pollination vector, using 32 anemophilous and zoophilous species. We also examined intraspecific variation in the lognormal parameter values, using 30 different individuals of the common weed Plantago lanceolata.Pivotal results. The mean and standard deviation of the lognormal distribution of PDUs and a third parameter, the proportion of solitary monads, all separated the species by pollination vector, with the mean sl...

Reproductive biology of Ranunculus weyleri (Ranunculaceae), a narrowly endemic plant from the Balearic Islands with disjunct populations

Ranunculus weyleri is a species endemic to Mallorca Island (western Mediterranean basin) that is currently threatened due to its reduced geographical distribution and disjunct, isolated populations. It is a small, perennial herb that inhabits rocky environments, together with other endemic plants with creeping life-forms. In the present study, for the first time the reproductive biology of the species was investigated in terms of its floral phenology (floral stages and times of formation), pollen/ovule (P/O) ratios, and fruit and seed setting under natural and pollen manipulation experiments, assessing the breeding system, pollination vectors and pollen limitations. Cross-pollinations among populations were performed to evaluate the levels of compatibility between populations. In addition, the floral displays and the reproductive outputs of four wild populations were determined. The observed high P/O ratios, results of the hand-pollination experiments, and flower traits indicate that this species is predominantly allogamous. Combinations of both insects (belonging to Coleoptera, Diptera, Lepidoptera and Hymenoptera) and wind (ambophily) constitute the main pollination vectors, and pollen limitation was observed. Interpopulation crossing was effective, and exogamic depression was not present, as evidenced by the fecundity levels. The predation of the floral stems by herbivores (mainly goats) severely limits the reproductive success of this endemic species in wild populations. Finally, several ways of action are proposed for R. weyleri conservation.

Altitudinal variation in the reproductive performance of the Mediterranean shrub Rhamnus lycioides L.

Rhamnus lycioides L. subsp. Oleoides (Rhamnaceae) is a perennial shrub native to the Mediterranean Basin distributed along an altitudinal gradient, from sea level up to 1 000 m a.s.l. The specific goals of our study were (i) to compare plant morphology between two contrasting populations, (ii) to determine the reproductive system of R. lycioides, quantifying the relative importance of insects and wind as pollen vectors, (iii) to test if pollen limitation differs between populations, (iv) to study the main factors influencing fruit set and (v) to compare plant reproductive performance (mass allocation to flowers, fruits and seeds) between the two habitats. In the present study, we examined plant morphology and the reproductive performance of R. lycioides L. in contrasting environments in two populations located at the extremes of its altitudinal range in the island of Mallorca (Balearic Islands, Western Mediterranean Basin) along a 3-year period. Plant morphology, the relative importance of insects and wind as pollen vectors, the pollen limitation to seed production and the plant reproductive performance (mass allocation to flowers, fruits and seeds) were determined. Rhamnus lycioides individuals showed a higher plant surface/plant height ratio at the mountain than at the coast. This species appeared to be ambophilous despite its inconspicuous flowers, although the relative importance of wind as a pollination vector was higher at the mountain than at the coastal site. Fruit set was much higher at the mountain, where pollen appeared to be a limiting factor. By contrast, fruit set was not limited by pollen availability at the coastal population, where resource (water and nutrients) limitation seemed to be more determining. Flower size was greater at the coast, in contrast to fresh fruit weight that was higher at the mountain. Despite the relatively few differences between sites in precipitation patterns along the study period, water availability appeared to be the key factor explaining not only fruit set but also the reproductive performance of this species in the study populations.

Reproductive biology of a threatened Australian saltmarsh plant –Wilsonia backhousei

The reproductive biology of a threatened saltmarsh plant, Wilsonia backhousei Hook.f., was investigated with a view to improving conservation and restoration outcomes for the species. Population phenology was studied every two weeks, over two consecutive flowering seasons, in three to six 0.25m2 quadrats set in monocultures of the species at each of eight sites in New South Wales, Australia. Floral density (flowersm−2) ranged from 0 to 5800±1400m−2 and varied significantly among sites (P<0.05). Peak flowering occurred in mid-late October, during a period of no tidal inundation; fruit maturation coincided with inundation by extreme high tides in December, January and February. Sediment samples collected from each quadrat post-flowering were analysed for water content, salinity, texture (clay content) and pH. Ordinal logistic regression (OLR) of floral density against foliage volume and sediment variables showed a significant positive response to increasing foliage volume and negative responses to increasing salinity and clay content (P<0.05). Foliage volume, in turn, showed a significant positive response to sediment water content and again negative responses to increasing salinity and clay content (P<0.05). Fruit development occurred at all sites; however, little to no seed was produced at five of the sites. When quadrats not producing seed were excluded (to limit the influence of self-incompatibility), OLR of seed yield against floral density and sediment variables indicated sediment water content was the only significant predictor of yield (P=0.015). The morphology and phenology of individual flowers, potential pollination vectors, and general seed biology were also investigated. A combination of floral characteristics indicated that W. backhousei is wind-pollinated, likely to be outbreeding, and may be self-incompatible. The fruit is buoyant and, as maturation coincides with inundation by extreme high tides, may be dispersed within and among sites by tidal flow. The seed was found to be viable and long-lived (>70% germination in both fresh seed and seed aged for 6 years); however, seed germination is limited by physical dormancy and is significantly reduced by salinity levels ≥40dSm−1 (6±2.4% after 28 days, P<0.001). Based on these outcomes, recommendations are made for maximising the reproductive potential of remnant and restored populations.

Effects of forest fragmentation on the effective and realized gene flow of Neotropical tree species: implications for genetic conservation

Effects of forest fragmentation on the effective and realized gene flow of Neotropical tree species: implications for genetic conservation

Does pollen aerodynamics correlate with pollination vector? Pollen settling velocity as a test for wind versus insect pollination among cycads (Gymnospermae: Cycadaceae: Zamiaceae)

Studies of cycad pollination globally have revealed obligate pollination mutualisms with insects, typically hostspecific beetles. Some cycads in the genus Cycas have floating seeds allowing oceanic dispersal, and have colonized remote islands such as Fiji, Guam, and Madagascar. This seems to contradict the expected requirement that specific beetle pollinators be present in order for cycads to establish in remote localities. We therefore postulated that these ‘island’ cycads are wind pollinated. We tested for adaptations associated with wind pollination in a laboratory study of pollen aerodynamics. The pollen from a range of (non-cycad) wind-pollinated plants was not relatively ‘buoyant’: the settling velocities of wind-pollinated species exceeded those of insect-pollinated cycads and some animal-pollinated angiosperms. We attributed this result to settling velocity being, in part, correlated with pollen size, as cycad pollen was consistently smaller. A better predictor for pollination vector was the tendency of pollen to aggregate during a vertical fall. Pollen of wind-pollinated plants separated into single grains, whereas cycad pollen and pollen of animal-pollinated angiosperms adhered in large aggregations, the settling velocity of which increased rapidly with aggregate size. The pollen of cycads known to be insect pollinated was similar in morphology, settling speed, and clumping behaviour to pollen of ‘island’ cycads of unknown pollination biology. Based on these aerodynamics, we predict that cycad species on oceanic islands have insect pollinators. More broadly, we propose that pollen aggregation during a vertical fall provides a sound test for wind versus animal pollination when the pollination vector is unknown.

Twenty-five years of progress in understanding pollination mechanisms in palms (Arecaceae).

With more than 90 published studies of pollination mechanisms, the palm family is one of the better studied tropical families of angiosperms. Understanding palm-pollinator interactions has implications for tropical silviculture, agroforestry and horticulture, as well as for our understanding of palm evolution and diversification. We review the rich literature on pollination mechanisms in palms that has appeared since the last review of palm pollination studies was published 25 years ago. Visitors to palm inflorescences are attracted by rewards such as food, shelter and oviposition sites. The interaction between the palm and its visiting fauna represents a trade-off between the services provided by the potential pollinators and the antagonistic activities of other insect visitors. Evidence suggests that beetles constitute the most important group of pollinators in palms, followed by bees and flies. Occasional pollinators include mammals (e.g. bats and marsupials) and even crabs. Comparative studies of palm-pollinator interactions in closely related palm species document transitions in floral morphology, phenology and anatomy correlated with shifts in pollination vectors. Synecological studies show that asynchronous flowering and partitioning of pollinator guilds may be important regulators of gene flow between closely related sympatric taxa and potential drivers of speciation processes. Studies of larger plant-pollinator networks point out the importance of competition for pollinators between palms and other flowering plants and document how the insect communities in tropical forest canopies probably influence the reproductive success of palms. However, published studies have a strong geographical bias towards the South American region and a taxonomic bias towards the tribe Cocoseae. Future studies should try to correct this imbalance to provide a more representative picture of pollination mechanisms and their evolutionary implications across the entire family.

Duplicated C-Class MADS-Box Genes Reveal Distinct Roles in Gynostemium Development in Cymbidium ensifolium (Orchidaceae)

The orchid floral organs represent novel and effective structures for attracting pollination vectors. In addition, to avoid inbreeding, the androecium and gynoecium are united in a single structure termed the gynostemium. Identification of C-class MADS-box genes regulating reproductive organ development could help determine the level of homology with the current ABC model of floral organ identity in orchids. In this study, we isolated and characterized two C-class AGAMOUS-like genes, denoted CeMADS1 and CeMADS2, from Cymbidium ensifolium. These two genes showed distinct spatial and temporal expression profiles, which suggests their functional diversification during gynostemium development. Furthermore, the expression of CeMADS1 but not CeMADS2 was eliminated in the multitepal mutant whose gynostemium is replaced by a newly emerged flower, and this ecotopic flower continues to produce sepals and petals centripetally. Protein interaction relationships among CeMADS1, CeMADS2 and E-class PeMADS8 proteins were assessed by yeast two-hybrid analysis. Both CeMADS1 and CeMADS2 formed homodimers and heterodimers with each other and the E-class PeMADS protein. Furthermore, transgenic Arabidopsis plants overexpressing CeMADS1 or CeMADS2 showed limited growth of primary inflorescence. Thus, CeMADS1 may have a pivotal C function in reproductive organ development in C. ensifolium.

Breeding systems of Bromeliaceae species: evolution of selfing in the context of sympatric occurrence

Co-occurring congener plant species in the highly diverse Atlantic forests of southeastern Brazil may act as natural laboratories for evaluating evolution of reproductive shifts. We assessed the breeding systems in a sympatric assemblage of bromeliad species and compiled literature available for the family to compare our experiments with available information. We performed controlled experiments of autonomous selfing, self- and cross-pollination in 40 species of 11 genera of two subfamilies that, in general, overlap their blooming period and share the same pollination vectors. We also tested for differences between self-compatible (SC) and self-incompatible (SI) species with regard to ecological factors such as abundance, co-flowering and co-occurrence. Most species experimentally tested and surveyed in the literature (75%) were SC. Species from the subfamily Tillandsioideae were predominantly SC, while Bromelioideae showed greater variation in breeding systems. About 43% of the species studied set fruits spontaneously in the absence of pollinator vectors. We found that SC species were the more abundant, were more frequently associated with other relatives and overlapped their blooming period with other species more than SI species. Thus, our results suggest that self-compatibility is common for Bromeliaceae and do not support the traditional hypothesis of reproductive assurance used to explain the evolution of selfing. We discuss self-compatibility as a reproductive isolating mechanism in the presence of pollen flow among sympatric congener species.

Extended phylogeny of Aquilegia: the biogeographical and ecological patterns of two simultaneous but contrasting radiations

Studies of the North American columbines (Aquilegia, Ranunculaceae) have supported the view that adaptive radiations in animal-pollinated plants proceed through pollinator specialisation and floral differentiation. However, although the diversity of pollinators and floral morphology is much lower in Europe and Asia than in North America, the number of columbine species is similar in the three continents. This supports the hypothesis that habitat and pollinator specialisation have contributed differently to the radiation of columbines in different continents. To establish the basic background to test this hypothesis, we expanded the molecular phylogeny of the genus to include a representative set of species from each continent. Our results suggest that the diversity of the genus is the result of two independent events of radiation, one involving Asiatic and North American species and the other involving Asiatic and European species. The ancestors of both lineages probably occupied the mountains of south-central Siberia. North American and European columbines are monophyletic within their respective lineages. The genus originated between 6.18 and 6.57 million years (Myr) ago, with the main pulses of diversification starting around 3 Myr ago both in Europe (1.25–3.96 Myr ago) and North America (1.42–5.01 Myr ago). The type of habitat occupied shifted more often in the Euroasiatic lineage, while pollination vectors shifted more often in the Asiatic-North American lineage. Moreover, while allopatric speciation predominated in the European lineage, sympatric speciation acted in the North American one. In conclusion, the radiation of columbines in Europe and North America involved similar rates of diversification and took place simultaneously and independently. However, the ecological drivers of radiation were different: geographic isolation and shifts in habitat use were more important in Europe while reproductive isolation linked to shifts in pollinator specialisation additionally acted in North America.

Perianth organization and intra-specific floral variability

Floral symmetry and fusion of perianth parts are factors that contribute to fine-tune the match between flowers and their animal pollination vectors. In the present study, we investigated whether the possession of a sympetalous (fused) corolla and bilateral symmetry of flowers translate into decreased intra-specific variability as a result of natural stabilizing selection exerted by pollinators. Average size of the corolla and intra-specific variability were determined in two sets of southern Spanish entomophilous plant species. In the first set, taxa were paired by family to control for the effect of phylogeny (phylogenetically independent contrasts), whereas in the second set species were selected at random. Flower size data from a previous study (with different species) were also used to test the hypothesis that petal fusion contributes to decrease intra-specific variability. In the phylogenetically independent contrasts, floral symmetry was a significant correlate of intra-specific variation, with bilaterally symmetrical flowers showing more constancy than radially symmetrical flowers (i.e. unsophisticated from a functional perspective). As regards petal fusion, species with fused petals were on average more constant than choripetalous species, but the difference was not statistically significant. The reanalysis of data from a previous study yielded largely similar results, with a distinct effect of symmetry on variability, but no effect of petal fusion. The randomly-chosen species sample, on the other hand, failed to reveal any significant effect of either symmetry or petal fusion on intra-specific variation. The problem of low-statistical power in this kind of analysis, and the difficulty of testing an evolutionary hypothesis that involves phenotypic traits with a high degree of morphological correlation is discussed.

Seed-set evaluation of four male-sterile, female-fertile soybean lines using alfalfa leafcutting bees and honey bees as pollinators

SUMMARYMale-sterile, female-fertile plants were used to produce hybrid soybean seed. Manual cross-pollination using male-sterile plants to produce large quantities of hybrid seed is difficult and time-consuming because of the low success rate in cross-pollination. Insect pollinators may be suitable vectors to transfer pollen, but the most suitable vector for pollen transfer from the male parent to the female parent has not been identified for soybean. The objective of the present study was to evaluate seed-set on four male-sterile, female-fertile soybean lines by using alfalfa leafcutting bees (Megachile rotundata (F.)) and honey bees (Apis mellifera (L.)) as pollinators. Seed-set was evaluated in summers 2003 and 2005 near Ames, Iowa, USA and in summers 2003, 2004, and 2005 near Wooster, Ohio, USA. Neither the effect of pollinator species nor the interaction effect of pollinator species×location was significant for any year. Honey bees performed similarly to alfalfa leafcutting bees at both locations. The results indicated significant differences for seed-set among male-sterile lines, suggesting preferential pollination. Male-sterile lines, ms1 (Urbana) and ms2 (Ames 2), had higher cross-pollinated seed-set compared to ms6 (Ames 1), and ms6 (Corsoy 79). At the Ames location, ms1ms1 (Urbana) plants had the highest seed-set (50·16 seeds per male-sterile plant in 2005). At the Wooster location, ms1ms1 (Urbana) plants also had the highest seed-set (92·04 seeds per male-sterile plant) in 2005. Costs and local conditions need to be addressed to support the choice of either pollinator species as a pollination vector to produce hybrid soybean seed.

Fruit type, life form and origin determine the success of woody plant invaders in an urban landscape

The spread of alien plant species is a critical ecological event worldwide, but the forces that control this spread are not well documented. Alien plant species are well known to disrupt ecological services of native ecosystems, change the composition of native habitats, and often lead to the extirpation of native flora and fauna. Here, we report on life history patterns of plant species with rapidly spreading and declining ranges in North America’s major urban region. We tested for differences in life history traits between the 466 native and alien woody flora of the New York metropolitan area. We also examined the relationship between life history traits and change in distribution in the New York metropolitan area between 1900 and 2000. Native and alien species of the New York metropolitan area differ with respect to pollination vector and breeding system. However, pollination vector and breeding system are not associated with success, defined here as increasing range spread in the urban environment; instead, fruit type (dispersal), life form and origin are important determinants of success. Alien species that are deciduous trees, shrubs or vines with fleshy fruit are the most successful in increasing their distribution in this urban landscape. Newly introduced species with these characteristics are expected to have a better chance at establishing in similar urban landscapes and should be targets for intensive management. The ability to predict which alien species will become invasive is also a valuable tool for the prevention of invasions by newly introduced plant species.

Pollen‐Ovule Ratio and Gamete Investment in Pedicularis (Orobanchaceae)

AbstractThe Pedicularis species provides ideal materials to study floral evolution because of their substantial flower variation based on a narrow genetic basis, even though they are almost exclusively pollinated by bumblebee. These traits allow us to detect the evolutionary trends of floral parameters without considering genetic background and the difference of pollination vectors. The pollen‐ovule ratio is widely used to estimate the pattern of resource investment in two sexual functions in flowering plants. Forty species representing all of the corolla types in Pedicularis were used to study pollen‐ovule ratio, gamete investment, and their correlations. Results show that pollen‐ovule ratio does not differ among both different corolla types and taxonomic groups. It is therefore suggested that pollen‐ovule ratio should be a parallel evolution. The correlations between pollen‐ovule ratio and pollen size (−), and ovule size (+) can be successfully explained in terms of sex allocation theory. The biological significance of such relationships was also discussed. Additionally, we analyzed the pattern of resource investment into female gamete, which has been somewhat neglected, and found that plants have different patterns of gamete investment between the two sexual functions.

Potential Risk of Hybridization in Ex Situ Collections of Two Endangered Species of Sinojackia Hu (Styracaceae)

AbstractSpontaneous hybridization in ex situ facilities can undermine the genetic integrity of ex situ collections and potentially contaminate open‐pollinated seeds or seedlings destined for the reintroduction of endangered plant species into the wild. In the present study, the potential risk of hybridization between two endangered Chinese endemic species, namely Sinojackia xylocarpa Hu and S. rehderiana Hu, which are naturally allopatric species but were conserved ex situ in Wuhan Botanical Garden (WBG), Wuhan, China, were investigated over three consecutive years from 2003 to 2005. The entire overlapping flowering period of the two species was 14–20 d and the two species shared the same pollinator insects during the entire flowering season in WBG. The floral isolation between the two species was not an issue in the ex situ collection at WBG. The results suggest an opportunity for pollen transfer between species and a potential risk of genetic introgression and loss of genetic identity of open‐pollinated seeds produced in the ex situ collection of these two endangered species. An artificial reciprocal cross between S. xylocarpa and S. rehderiana confirmed that the two congener species could readily set seeds, indicating no post‐pollination barriers to hybridization and the importance of spatial isolation as a barrier to inter‐specific crossing. Therefore, to manage these crossable species with overlapping flowering times and shared pollination vectors in ex situ facilities, spatial isolation should be carefully considered to minimize the possibility of spontaneous hybridization.(Managing editor: Wei Wang)

Ecological correlates of range structure in rare and scarce British plants

Summary The distribution patterns of 391 rare and scarce British plants (species recorded in 100 or fewer 10 × 10 km squares) were characterized by their distributional area (area of occupancy at 1‐km scale: AOO1) and levels of aggregation (as reflected in fractal dimensions measured across two scales: D1−10 and D10−100). Eighteen plant traits were tested for relationships to AOO, and to fractal dimension while controlling for AOO. These included both directly heritable traits (e.g. life‐form) and emergent properties that are, at most, indirectly heritable (e.g. typical local density). The latter set included an index of net distributional change and an index of range dynamism. Only two traits, habitat preference and local abundance, were significantly related to AOO1, but about half were associated with fractal dimension. Relatively aggregated fine‐scale distributions (high D1−10) were related to high local abundance, lack of specialized, long‐distance dispersal mechanisms, habitat preference and an increasing range size with relatively few local extinctions (i.e. a positive index of change with low dynamism). Relatively aggregated coarse‐scale distributions (high D10−100) were related to the use of insect pollinators, obligate outcrossing, habitat preference and relatively stable ranges (low dynamism). Multivariate analyses of subsets of conceptually related variables showed that few variables interacted to affect distributional variables. A highly significant negative relationship between dynamism and fractal dimension appears to be driven primarily by high rates of local extinction, leading to relatively scattered, diffuse range structures. Furthermore, it suggests that recent population trends may be inferred from snapshots of contemporary distribution patterns. The role and interpretation of phylogenetically informed analyses in studies such as this are debatable. However, we found similar relationships in both phylogenetically informed and conventional analyses for all variables except pollination vector (a strongly conserved trait). The spatial pattern of plant species distributions is associated with a range of ecological traits, particularly those describing past changes in distribution. The analysis of distribution patterns therefore has the potential to inform future conservation effort.