Avian Pollinators Research Articles

Floral pigments and their perception by avian pollinators in three Chilean Puya species.

The Chilean Puya species, Puya coerulea var. violacea and P. chilensis bear blue and pale-yellow flowers, respectively, while P. alpestris considered to be their hybrid-derived species has unique turquoise flowers. In this study, the chemical basis underlying the different coloration of the three Puya species was explored. We first isolated and identified three anthocyanins: delphinidin 3,3',5'-tri-O-glucoside, delphinidin 3,3'-di-O-glucoside and delphinidin 3-O-glucoside; seven flavonols: quercetin 3-O-rutinoside-3'-O-glucoside, quercetin 3,3'-di-O-glucoside, quercetin 3-O-rutinoside, isorhamnetin 3-O-rutinoside, myricetin 3,3',5'-tri-O-glucoside, myricetin 3,3'-di-O-glucoside and laricitrin 3,5'-di-O-glucoside; and six flavones: luteolin 4'-O-glucoside, apigenin 4'-O-glucoside, tricetin 4'-O-glucoside, tricetin 3',5'-di-O-glucoside, tricetin 3'-O-glucoside and selagin 5'-O-glucoside, which is a previously undescribed flavone, from their petals. We also compared compositions of floral flavonoid and their aglycone among these species, which suggested that the turquoise species P. alpestris has an essentially intermediate composition between the blue and pale-yellow species. The vacuolar pH was relatively higher in the turquoise (pH 6.2) and pale-yellow (pH 6.2) flower species, while that of blue flower species was usual (pH 5.2). The flower color was reconstructed in vitro using isolated anthocyanin, flavonol and flavone at neutral and acidic pH, and its color was analyzed by reflectance spectra and the visual modeling of their avian pollinators. The modeling demonstrated that the higher pH of the turquoise and pale-yellow species enhances the chromatic contrast and spectral purity. The precise regulation of flower color by flavonoid composition and vacuolar pH may be adapted to the visual perception of their avian pollinator vision.

Conspicuous, green flowers are an honest signal of nectar rewards in a bird-pollinated tree (Fuchsia excorticata, Onagraceae)

Bird-pollinated flowers typically appear ‘red’. Fuchsia excorticata (Onagraceae), a gynodioecious tree species endemic to New Zealand, is a notable exception. It produces ‘green’, cauliflorous flowers at early stages in flower ontogeny, when pistils are receptive. Flowers later turn ‘red’ as they lose their receptivity. We conducted field observations and spectrographic analyses to test whether: (1) receptive, green-phase flowers are actually more conspicuous to avian pollinators against their natural backgrounds than unreceptive, red-phase flowers, (2) green-phase flowers produce more nectar, and (3) relationships between flower conspicuousness and nectar production are similar in females and hermaphrodites. Results showed that the reflectance properties of green-phase flowers sharply contrast ‘orange’ tree bark, their natural visual background, rendering them more conspicuous to the avian eye than red-phase flowers. Green-phase flowers also produced more nectar than red-phase flowers as an honest signal of rewards. Similar results were observed in both female and hermaphrodite plants. Overall results provide an unusual example of reversed flower-background colour contrasts, with ‘reddish’ hues being incorporated into the visual backgrounds of floral displays rather than being associated with the flowers themselves. They also illustrate that flower conspicuousness can serve as an honest signal of nectar rewards to pollinators.

Moving with your mutualist: Predicted climate‐induced mismatch between Proteaceae species and their avian pollinators

AbstractAimClimate change influences species distribution in space and time, but predicting the overlap in the range of interacting species under different climate scenarios remains a challenge. Here, we explore how climate change influences shifts in species ranges among mutualists.LocationCape Floristic Region (CFR), South Africa.TaxonProteaceae and Passeriformes.MethodsWe used machine‐learning algorithms (random forest and boosted‐regression trees) and regression model (generalized additive models) to predict range shifts of 11 bird‐pollinated Proteaceae species, combined occurrence prediction of 71 bird‐pollinated Proteaceae and their two most important, endemic, pollinator bird species. We determined the degree of overlap in geographical ranges of nectar‐feeding birds and Proteaceae under different climate scenarios. Species ranges were projected to the years 2050 and 2070 using representative concentration pathways (RCP) 4.5 and 8.5 and three global climate models.ResultsThe majority of Proteaceae species in our model are predicted to experience range contractions, which ranged from 1% under 2050 RCP 4.5 CCSM4 to 79% under 2070 RCP 8.5 CNRM‐CM5 climate scenarios, leading to 55% and 62% range loss for Cape sugarbird and orange‐breasted sunbird, respectively, under extreme climate scenarios. Proteaceae species are predicted to experience least overlap with nectar‐feeding birds in the northern and eastern range under future climate scenarios.Main ConclusionClimate change threatens species occupying the mountain range of the northern limit and other regions of the CFR. Reduced range overlap of mutualists may have significant implications for the reproduction and persistence of Proteaceae. We suggest active monitoring of Proteaceae populations in regions where species are predicted to lose their range, particularly so for threatened species with small ranges.

Citizen science data reveal altitudinal movement and seasonal ecosystem use by hummingbirds in the Andes Mountains

Ensuring connectivity is crucial to protect landscapes but it requires knowledge about how animals use ecosystems throughout the year. However, animal movements remain largely unknown in biodiversity hotspots, even for species that fulfill key ecological roles, as is the case of hummingbirds in the Andes. In the complex topography of mountain slopes, movement of these avian pollinators may occur either between habitat patches with asynchronous plant blooms or across ecosystems that are located within the same elevation bands or along altitudinal gradients. Here, we used two decades (2000–2020) of records from citizen science data and boosted regression trees to predict monthly distributions for 55 hummingbird species in the Andes. We identified shifts in altitudinal distribution between contiguous months and calculated changes in the proportion of predicted distributions occupied by ecosystem types. Our findings reveal substantial altitudinal movement and differences in the proportion of ecosystem types utilized throughout the year that had not been previously reported for several species. Yet the magnitude of altitudinal and ecosystem shifts varies between hummingbird clades, and in some cases changes in the proportion of ecosystem types within estimated distributions occurs with little variation in altitude. All ecosystems across the Andes show temporal changes in hummingbird occurrence, but these are higher in natural landscapes compared to croplands or urban areas. Finally, we used phylogenetic logistic regression to test whether altitudinal and ecosystem shifts affect population trends. We found that higher ecosystem seasonality is more strongly associated with decreasing populations in comparison to altitudinal shifts. Altogether, our study reveals complex patterns of movement in hummingbirds and highlights the importance of ecological connectivity across different ecosystem types. More generally, it demonstrates the opportunity of using citizen science data to increase understanding about species' seasonal occurrences, so that landscapes can be better managed to protect animal movement.Keywords: boosted regression trees, eBird, ecological connectivity, species distribution models

Post-secretory synthesis of a natural analog of iron-gall ink in the black nectar of Melianthus spp.

The black nectar produced by Melianthus flowers is thought to serve as a visual attractant to bird pollinators, but the chemical identity and synthesis of the black pigment are unknown. A combination of analytical biochemistry, transcriptomics, proteomics, and enzyme assays was used to identify the pigment that gives Melianthus nectar its black color and how it is synthesized. Visual modeling of pollinators was also used to infer a potential function of the black coloration. High concentrations of ellagic acid and iron give the nectar its dark black color, which can be recapitulated through synthetic solutions containing only ellagic acid and iron(III). The nectar also contains a peroxidase that oxidizes gallic acid to form ellagic acid. In vitro reactions containing the nectar peroxidase, gallic acid, hydrogen peroxide, and iron(III) fully recreate the black color of the nectar. Visual modeling indicates that the black color is highly conspicuous to avian pollinators within the context of the flower. Melianthus nectar contains a natural analog of iron-gall ink, which humans have used since at least medieval times. This pigment is derived from an ellagic acid-Fe complex synthesized in the nectar and is likely involved in the attraction of passerine pollinators endemic to southern Africa.

Using Pop-GUIDE to Assess the Applicability of MCnest for Relative Risk of Pesticides to Hummingbirds

Hummingbirds are charismatic fauna that provide important pollination services, including in the continental US, where 15 species regularly breed. Compared to other birds in North America, hummingbirds (family Trochilidae) have a unique exposure route to pesticides because they forage on nectar. Therefore, hummingbirds may be exposed to systemic pesticides borne in nectar. They also may be particularly vulnerable to pesticide exposure due to their small size and extreme metabolic demands. We review relevant factors including hummingbird life history, nectar residue uptake, and avian bioenergetic considerations with the goal of clearly identifying and articulating the specific modeling challenges that must be overcome to develop and/or adapt existing modeling approaches. To help evaluate these factors, we developed a dataset for ruby-throated hummingbirds (Archilochus colubris) and other avian species potentially exposed to pesticides. We used the systemic neonicotinoid pesticide imidacloprid as an illustration and compared results to five other common current use pesticides. We use the structure of Pop-GUIDE to provide a conceptual modeling framework for implementation of MCnest and to compile parameter values and relevant algorithms to predict the effects of pesticide exposure on avian pollinators. Conservative screening assessments suggest the potential for adverse effects from imidacloprid, as do more refined assessments, though many important limitations and uncertainties remain. Our review found many areas in which current USEPA avian models must be improved in order to conduct a full higher-tier risk assessment for avian pollinators exposed to neonicotinoid insecticides, including addition of models suitable for soil and seed treatments within the MCnest environment, ability to include empirical residue data in both nectar and invertebrates rather than relying on existing nomograms, expansion of MCnest to a full annual cycle, and increased representation of spatial heterogeneity. Although this work focuses on hummingbirds, the methods and recommendations may apply more widely to other vertebrate pollinators.

Evaluating the success of functional restoration after reintroduction of a lost avian pollinator.

Conservation translocation is a common method for species recovery, for which one increasingly frequent objective is restoring lost ecological functions to promote ecosystem recovery. However, few conservation translocation programs explicitly state or monitor function as an objective, limiting the ability to test assumptions, learn from past efforts, and improve management. We evaluated whether translocations of hihi (Notiomystis cincta), a threatened New Zealand passerine, achieved their implicit objective of restoring lost pollination function. Through a pollinator‐exclusion experiment, we quantified, with log response ratios (lnR), the effects of birds on fruit set and seed quality in hangehange (Geniostoma ligustrifolium), a native flowering shrub. We isolated the contributions of hihi by making comparisons across sites with and without hihi. Birds improved fruit set more at sites without hihi (lnR = 1.27) than sites with hihi (lnR = 0.50), suggesting other avian pollinators compensated for and even exceeded hihi contributions to fruit set. Although birds improved seed germination only at hihi sites (lnR = 0.22–0.41), plants at sites without hihi had germination rates similar to hihi sites because they produced 26% more filled seeds, regardless of pollination condition. Therefore, although our results showed hihi improved seed quality, they also highlighted the complexity of ecological functions. When an important species is lost, ecosystems may be able to achieve similar function through different means. Our results underscore the importance of stating and monitoring the ecological benefits of conservation translocations when functional restoration is a motivation to ensure these programs are achieving their objectives.

Restored and remnant Banksia woodlands elicit different foraging behavior in avian pollinators.

Pollinators and the pollination services they provide are critical for seed set and self‐sustainability of most flowering plants. Despite this, pollinators are rarely assessed in restored plant communities, where their services are largely assumed to re‐establish. Bird–pollinator richness, foraging, and interaction behavior were compared between natural and restored Banksia woodland sites in Western Australia to assess their re‐establishment in restored sites. These parameters were measured for natural communities of varying size and degree of fragmentation, and restored plant communities of high and low complexity for three years, in the summer and winter flowering of Banksia attenuata and B. menziesii, respectively. Bird visitor communities varied in composition, richness, foraging movement distances, and aggression among sites. Bird richness and abundance were lowest in fragmented remnants. Differences in the composition were associated with the size and degree of fragmentation in natural sites, but this did not differ between seasons. Restored sites and their adjacent natural sites had similar species composition, suggesting proximity supports pollinator re‐establishment. Pollinator foraging movements were influenced by the territorial behavior of different species. Using a network analysis approach, we found foraging behavior varied, with more frequent aggressive chases observed in restored sites, resulting in more movements out of the survey areas, than observed in natural sites. Aggressors were larger‐bodied Western Wattlebirds (Anthochaera chrysoptera) and New Holland Honeyeaters (Phylidonyris novaehollandiae) that dominated nectar resources, particularly in winter. Restored sites had re‐established pollination services, albeit with clear differences, as the degree of variability in the composition and behavior of bird pollinators for Banksias in the natural sites created a broad completion target against which restored sites were assessed. The abundance, diversity, and behavior of pollinator services to remnant and restored Banksia woodland sites were impacted by the size and degree of fragmentation, which in turn influenced bird–pollinator composition, and were further influenced by seasonal changes between summer and winter. Consideration of the spatial and temporal landscape context of restored sites, along with plant community diversity, is needed to ensure the maintenance of the effective movement of pollinators between natural remnant woodlands and restored sites.

Flower abundance and defendability at two mass-blooming understory plants structure nectar-feeding bird guilds in garúa forest of western Ecuador

Mutualistic interactions, such as animal pollination, structure biodiversity in the Neotropics. In coastal montane garúa (fog) forests of Ecuador, 2 mass-blooming plants attract up to 17 species of nectar-feeding birds, especially hummingbirds. We describe avian guilds and behavior at the 2 mass bloomers and use mist-netting capture rates to test 3 predictions: (1) capture rates of territorial hummingbirds will increase with flower abundance on the mass bloomer they defend, (2) hummingbirds known to mainly use other flowers will show no change in capture rate during mass blooms, and (3) field observations of interspecific interactions will be reflected in capture rates. We statistically modeled capture rates of bird species, species richness, and Shannon Diversity Index in response to flower abundance on the 2 mass bloomers during 16 flowering seasons (1996–2013). Capture rates of 8 nectar-feeding species increased significantly with increased abundance of white-flowered Psychotria hazenii blooms, while only one species, Speckled Hummingbird (Adelomyia melanogenys), increased significantly in response to red-flowered Stenostephanus clarkii flower abundance, and aggressively defended these flower patches. Violet-bellied Hummingbird (Damophila julie) showed the strongest capture rate response to increased abundance of P. hazenii flowers, and was the dominant territorial hummingbird around these shrubs. Endangered Esmeraldas Woodstars (Chaetocercus berlepschi) and Little Woodstars (Chaetocercus bombus) visited both mass bloomers, but had a statistically significant increase only with P. hazenii highest flower abundance suggesting that restoration to recover endangered woodstars will benefit more from plantings of P. hazenii than S. clarkii. We conclude that flower abundance and defendability structure avian pollinator networks at these mass bloomers more so than nectar quality, quantity, or secretion rates, all of which were similar.

Neonicotinoid pesticides exert metabolic effects on avian pollinators

Neonicotinoids are neurotoxic systemic insecticides applied extensively worldwide. The impacts of common neonicotinoids like imidacloprid on non-target invertebrate pollinators have been widely studied, however effects on vertebrate pollinators have received little attention. Here, we describe the first study evaluating the effects of short-term (3 d) exposure to a range of environmentally relevant concentrations ({0.2},upmu hbox {g g}^{-1} to {2.5},upmu hbox {g g}^{-1}cdotBody Weight) of imidacloprid on wild-caught ruby-throated hummingbirds. Within 2 h of exposure, hummingbirds exhibited a significant depression in energy expenditure (up to 25% pm 11%). We did not observe significant effects on foraging behaviour measured in the subsequent 2 h to 4 h, although the effect size estimate was large (0.29). We also analyzed tissues collected 24 h after the final dose and did not observe significant effects on immune response or cholinesterase activity, although this may be related to our small sample size. We determined that hummingbirds excrete imidacloprid quickly (elimination half-life of 2.1hbox { h} pm 0.1hbox { h}) relative to other bird species. Hummingbirds have high energetic demands and store relatively little energy, especially during migration and breeding seasons. Therefore, changes in their metabolism following exposures to imidacloprid observed herein could bear important survivorship consequences for hummingbirds.

Patagonian glacial effects on the endemic Green-backed Firecrown, Sephanoides sephaniodes (Aves: Trochilidae): evidence from species distribution models and molecular data

Climate changes during the late Pleistocene influenced the demography and distribution of species in Patagonia. During the last glacial maximum (LGM), ice sheets covered a great extent of the temperate rainforest in the western Patagonian Andes. The persistence of forest species in refugia during the LGM has been debated for many vertebrates, but rarely for birds. The Green-backed Firecrown (Sephanoides sephaniodes) is an important avian pollinator distributed from the south of the Atacama Desert (28°S) to Tierra del Fuego (54°S) in South America. We evaluated the species’ evolutionary history, combining molecular data and models for past and current species distribution. Our results show two distinct haplogroups: the genetically diverse North–South clade (NS) restricted to the Mediterranean and coastal temperate regions that exhibits a signature of population expansion after LGM, and the Austral-East clade (AE) confined to the temperate intermountain range, eastern temperate, and sub-Antarctic regions, with lower genetic diversity and evidence of a more recent population expansion. This AE clade and the past distribution models support the species survival in valleys and lowlands south of the ice sheets limit during LGM until the present. A secondary contact zone was observed with haplotypes from the AE clade distributed in low frequency along with the northern areas. Our results support the paleorefugia hypothesis during the LGM with postglacial secondary contact.

Hummingbirds and bumble bees exposed to neonicotinoid and organophosphate insecticides in the Fraser Valley, British Columbia, Canada.

To measure exposure to neonicotinoid and other pesticides in avian pollinators, we made novel use of cloacal fluid and fecal pellets from rufous (Selasphorus rufus) and Anna's (Calypte anna) hummingbirds living near blueberry fields in the Fraser River Valley and Vancouver Island, British Columbia, Canada. To examine on-farm exposure to pesticides in invertebrate pollinators, we also collected bumble bees native to Canada (Bombus mixtus, Bombus flavifrons, and Bombus melanopygus), their pollen, and blueberry leaves and flowers from within conventionally sprayed and organic blueberry farms. By sites and sample type, the results reported in the present study represent pooled samples (n = 1). In 2015 to 2016, the combined concentration of the neonicotinoid insecticides imidacloprid, thiamethoxam, and clothianidin detected in hummingbird cloacal fluid from sites near conventionally sprayed blueberry fields was 3.63 ng/mL (ppb). Among the 18 compounds measured in fecal pellets, including one neonicotinoid (imidacloprid), only piperonyl butoxide was detected (1.47-5.96 ng/g). Piperonyl butoxide is a cytochrome P450 inhibitor applied with some insecticides to increase their toxic efficacy. Only diazinon was detected in bumble bees (0.197 ng/g), whereas diazinon (1.54-1.7 ng/g) and imidacloprid (up to 18.4 ng/g) were detected in pollen collected from bumble bees including the bees from organic sites located near conventionally sprayed blueberry farms. Imidacloprid was also detected at 5.16 ng/g in blueberry flowers collected 1 yr post spray from 1 of 6 conventionally sprayed blueberry farms. Environ Toxicol Chem 2018;37:2143-2152. © 2018 SETAC.

Indigenous plants and artificial nectar sources facilitate urban adjustment of avian pollinators in Cape Town

Indigenous plants and artificial nectar sources facilitate urban adjustment of avian pollinators in Cape Town

A bird pollinator shows positive frequency dependence and constancy of species choice in natural plant communities.

Animal pollinators mediate reproduction of many plant species. Foraging theory suggests that animal pollinators exhibit preferences for common plant species in natural communities (positive frequency-dependent foraging) and temporary single-species specialization (flower constancy) during foraging bouts. Positive frequency dependence may favor common plant species; flower constancy may enhance conspecific pollen transfer particularly in rare plant species. Previous experimental studies suggest that avian pollinators are unlikely to exhibit these behaviors. We studied foraging behavior of Cape Sugarbirds (Promerops cafer), the main avian pollinator of many Protea species, using focal-plant and focal-bird sampling, assisted by high-resolution maps of the spatiotemporal distribution of Protea individuals and their flowering status. We found that Sugarbird's visitation preference increased with species' relative floral abundance, and that individual Sugarbirds tended to visit single species in sequence. Flower constancy during foraging bouts was significantly higher than expected from random plant-animal encounters at the scale of pollinator movements. Positive frequency dependence may favor the reproduction of abundant plant species while flower constancy may be particularly important for rare plant species. This first simultaneous study of both behaviors in a natural plant-pollinator system shows that bird pollinators exhibit both types of behavior and, in this way, possibly influence plant community structure.

Inbreeding, low genetic diversity, and spatial genetic structure in the endemic Hawaiian lobeliads Clermontia fauriei and Cyanea pilosa ssp. longipedunculata

The endemic lobeliad genera Cyanea and Clermontia (Campanulaceae) are among the largest in the native Hawaiian flora, and contain large numbers of endangered and threatened taxa. As a baseline for future studies of rare species in this group, we used RAD markers to estimate genetic variation and spatial genetic structure in single populations of two common species, Cyanea pilosa ssp. longipedunculata on Hawai`i and Clermontia fauriei on Kaua`i. We found low to moderate levels of genetic diversity (He ≈ 0.13 and πall ≈ 0.0013 for both species), consistent with studies of several other island plant species, and substantial inbreeding (Fis ≈ 0.17). There was no evidence for spatial genetic structure in Cyanea, and in Clermontia SGS was weak and restricted to small spatial scales (<10 m). The relative dearth of genetic diversity and high levels of inbreeding in these common lobeliads may reflect pre-existing conditions in this group or selfing in response to a decline in native avian pollinators, raising concerns that inbreeding and loss of genetic variation may be even more severe in rare species of this highly diverse but endangered group.

Field of Dreams: Restitution of Pollinator Services in Restored Bird‐Pollinated Plant Populations

AbstractEcosystem functionality is an increasingly important objective of ecological restoration. Despite this, a few studies have rigorously assessed reproductive functionality within restored plant populations, and it is largely assumed that pollinators follow restoration of plant communities—“build it and they will come.” Here, we applied an ecological genetic approach to determine the impact of spatial separation on mating in Banksia menziesii (Proteaceae), a dominant bird‐pollinated species of Banksia woodlands of Western Australia. All plants at three post‐mining restored sites (n = 72 [13 years old], n = 21 [8 years old], and n = 20 [9 years old]), as well as a sample from an adjacent natural reference site (n = 42), were genotyped at nine microsatellite loci. Seed set, mating system parameters, realized pollen dispersal through the assignment of paternity to seed, and avian pollinator species composition, abundance and behavior, were assessed. All patches displayed equivalent heterozygosity (He = 0.53–0.59) and very weak genetic divergence (FST ≤ 0.01). Seed of plants within restored sites showed complete outcrossing and relatively high seed set, 26% of which were sired by pollen donors located beyond the local patch. Similar abundance and movement of nectar‐feeding birds was observed in restored and natural sites, despite lower bird species diversity in the restored site, where a smaller, less aggressive species was dominant. Our results demonstrate the restitution of wide outcrossing in these restored Banksia patches within an active mine‐site, and suggest that restored bird‐pollinated Banksia populations are resilient to human impacts, due largely to their generalist pollinator requirements and highly‐mobile avian pollinators.

Eocene fossil is earliest evidence of flower-visiting by birds.

Birds are important pollinators, but the evolutionary history of ornithophily (bird pollination) is poorly known. Here, we report a skeleton of the avian taxon Pumiliornis from the middle Eocene of Messel in Germany with preserved stomach contents containing numerous pollen grains of an eudicotyledonous angiosperm. The skeletal morphology of Pumiliornis is in agreement with this bird having been a, presumably nectarivorous, flower-visitor. It represents the earliest and first direct fossil evidence of flower-visiting by birds and indicates a minimum age of 47 million years for the origin of bird-flower interactions. As Pumiliornis does not belong to any of the modern groups of flower-visiting birds, the origin of ornithophily in some angiosperm lineages may have predated that of their extant avian pollinators.

The colorful language of Australian flowers

The enormous increase in phylogenetic information in recent years has allowed many old questions to be reexamined from a macroevolutionary perspective. We have recently considered evolutionary convergence in floral colors within pollination syndromes, using bird-pollinated species in Australia. We combined quantitative measurements of floral reflectance spectra, models of avian color vision, and a phylogenetic tree of 234 Australian species to show that bird-pollinated flowers as a group do not have colors that are significantly different from the colors of insect-pollinated flowers. However, about half the bird-pollinated flowers have convergently evolved a narrow range of colors with dominant long-wavelength reflection far more often than would be expected by chance. These convergent colors would be seen as distinctly different from other floral colors in our sample when viewed by honeyeaters (family Meliphagidae), birds with a phylogenetically ancestral type of color vision and the dominant avian pollinators in Australia. Our analysis shows how qualitative ideas in natural history, like the concept of pollination syndromes, can be given more precise definition and rigorous statistical testing that takes into account phylogenetic information.

Investigating the pollination syndrome of the Hawaiian lobeliad genus Clermontia (Campanulaceae) using floral nectar traits

Floral nectar sugar compositions have, for several decades, been used to predict a plant species' pollinator guild. Plants possessing a generalist ornithophilous pollination syndrome produce nectar that is dilute (8-12% w/v sugars) with a low sucrose to hexose (glucose and fructose) ratio. The Hawaiian lobeliad genus Clermontia contains 22 endemic species of shrubs and small trees that are believed to have evolved flowers adapted for pollination by now mostly extinct or endangered endemic passerines in the Drepanidinae and Mohoidae. We analyzed the nectar sugar compositions, concentration, and nectar standing crop of 23 taxa to test the assumption that Clermontia taxa have evolved floral traits in response to selection pressures from these avian pollinators. All Clermontia taxa produced nectar with sugar concentrations (mean: 9.2% w/v ± 1.8 SD) comparable to the nectar of other plant species with a generalized bird pollination system. Nectar sugars were overwhelmingly composed of hexoses in all taxa (mean sucrose/hexose ratio: 0.02 ± 0.02). Nectar standing crop volumes varied widely among taxa, ranging from 9.7 µL ± 7.1 to 430.5 µL ± 401.8 (mean volume: 177.8 ± 112.0). Collectively, the nectar traits indicate that Clermontia species possess a generalist passerine pollination syndrome.

Adaptive radiation, correlated and contingent evolution, and net species diversification in Bromeliaceae

We present an integrative model predicting associations among epiphytism, the tank habit, entangling seeds, C3 vs. CAM photosynthesis, avian pollinators, life in fertile, moist montane habitats, and net rates of species diversification in the monocot family Bromeliaceae. We test these predictions by relating evolutionary shifts in form, physiology, and ecology to time and ancestral distributions, quantifying patterns of correlated and contingent evolution among pairs of traits and analyzing the apparent impact of individual traits on rates of net species diversification and geographic expansion beyond the ancestral Guayana Shield. All predicted patterns of correlated evolution were significant, and the temporal and spatial associations of phenotypic shifts with orogenies generally accorded with predictions. Net rates of species diversification were most closely coupled to life in fertile, moist, geographically extensive cordilleras, with additional significant ties to epiphytism, avian pollination, and the tank habit. The highest rates of net diversification were seen in the bromelioid tank-epiphytic clade (Dcrown=1.05My−1), associated primarily with the Serra do Mar and nearby ranges of coastal Brazil, and in the core tillandsioids (Dcrown=0.67My−1), associated primarily with the Andes and Central America. Six large-scale adaptive radiations and accompanying pulses of speciation account for 86% of total species richness in the family. This study is among the first to test a priori hypotheses about the relationships among phylogeny, phenotypic evolution, geographic spread, and net species diversification, and to argue for causality to flow from functional diversity to spatial expansion to species diversity.