The diet and ecology of Hawaii's extinct flightless waterfowl: evidence from coprolites

At least five species of large flightless waterfowl have become extinct in the Hawaiian Islands in recent millennia. These birds are thought to have occupied the role of large herbivores in a wide range of terrestrial habitats. A collection of coprolites from one of the species ( Thambetochen chauliodous ) was obtained during excavations in Holocene cave sediments on the island of Maui. The chemical composition and pollen and spore content of the coprolites are analysed and compared with pollen/spore spectra from the cave sediments and from recent goose scats. The results support the contention that these birds were primarily folivorous, and further suggest that ferns were important in the diet. The coprolites have a very fine texture that may result from efficient hindgut fermentation and digestion of plant fibre. Our data are discussed in the light of a recent hypothesis of plant/herbivore coevolution between extinct avian herbivores and native Hawaiian lobelias. The loss of large native herbivores, as well as other changes in vertebrate trophic structure due to extinctions over the past few thousand years, may still be affecting ecological processes in areas of the Hawaiian islands with native vegetation.     

Positive effects of forest edges on plant reproduction: literature review and a case study of bee visitation to flowers of

Positive effects of fragmentation on plant reproduction are uncommon; in a literature review we found significant negative effects on fruit or seed set for 50 plant species, compared to 26 species showing no effect, and only nine affected positively. One of these is the declining New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae), and here we investigate the mechanism of this positive effect. P. tetrapetala requires visits from native bird or bee pollinators to produce fruit. Fruit set was consistently pollen limited at several South Island sites because of a shortage of pollinators, but within a site at Lake Ohau, plants on forest edges had higher fruit set than those in the forest interior. Previous work showed that this difference was not caused by a shortage of resources in interior plants, but was associated with higher bird visitation rates to flowers on edges. In this study, we tested whether native bees also show a preference for edge flowers. At two sites (Ohau and Craigieburn) edge mistletoes had higher visitation by native bees (Hylaeus agilis and Leioproctus sp.) and higher fruit set. Some, but not all, of the higher visitation to edge flowers was explained by a preference amongst bees for flowers in direct sunshine. Therefore, P. tetrapetala experiences higher fruit set on edges because both of its main groups of pollinators (endemic birds and bees) visit edge flowers more often. The other eight published cases of positive effects of fragmentation on fruit set also all reported increased visitation rates by pollinators.     

Upper-montane plant invasions in the Hawaiian Islands: Patterns and opportunities

In the Hawaiian Islands, massive volcanoes have created extreme elevation gradients, resulting in environments ranging from nearly tropical to alpine, spread across a distance of only a few dozen kilometers. Although the Hawaiian Islands are widely recognized for opportunities to study lowland tropical forest invasions, less attention has been paid to invasions of Hawaii's upper-montane forest, sub-alpine and alpine environments. This study synthesizes current knowledge of plant naturalization in upper-montane environments of the Hawaiian Islands in order to (1) determine whether patterns of tropical versus temperate species invasion change with elevation, and (2) evaluate whether upper-montane invaders are having significant impacts on native plant communities. A total of 151 naturalized plant species have been recorded at 2000 m or higher. Most species (93%) are herbaceous, and over half (52%) are native to Europe/Eurasia. Twenty-one species (14%) are reported to be disruptive in native plant communities, mainly by forming dense stands that appear to inhibit recruitment of natives, but also by altering vegetation structure or causing changes in ecosystem processes. Fourteen species (9%) were first recorded within the past 30 years, indicating that new invasions of upper-montane habitats are ongoing. At 1200 m elevation, only 38% of naturalized species are temperate in origin, but the proportion of temperate species increases linearly with elevation up to 3000 m (alpine habitat), where all naturalized species are temperate in origin and over 80% are native to Europe/Eurasia. Declining temperature along the elevation gradient probably drives this pattern. The extreme elevation gradients in the Hawaiian Islands provide specific opportunities for comparative studies on the ecology and evolution of temperate invaders while also creating a unique field environment for understanding interactions between temperate and tropical species.     

Microevolutionary patterns and processes of the Native Hawaiian colonizing fern Odontosoria chinensis (Lindsaeaceae)

Abstract.— The vascular‐plant flora of the Hawaiian Islands is characterized by one of the highest rates of species endemism in the world. Among flowering plants, approximately 89% of species are endemic, and among pteridophytes, about 76% are endemic. At the single‐island level, however, rates of species endemism vary dramatically between these two groups with 80% of angiosperms and only 6% of pteridophytes being single‐island endemics. Thus, in many groups of Hawaiian angiosperms, it is possible to link studies of phylogeny, evolution, and biogeographic history at the interspecific and interisland levels. In contrast, the low level of single‐island species endemism among Hawaiian pteridophytes makes similar interspecific and interisland studies nearly impossible. Higher levels of interisland gene flow may account for the different levels of single‐island endemism in Hawaiian pteridophytes relative to angiosperms. The primary question we addressed in the present study was: Can we infer microevolutionary patterns and processes among populations within widespread species of Hawaiian pteridophytes wherein gene flow is probably common? To address this broad question, we conducted a population genetic study of the native Hawaiian colonizing species Odontosoria chinensis. Data from allozyme analyses allowed us to infer: (1) significant genetic differentiation among populations from different islands; (2) historical patterns of dispersal between particular pairs of islands; (3) archipelago‐level patterns of dispersal and colonization; (4) founder effects among populations on the youngest island of Hawaii; and, (5) that this species primarily reproduces via outcrossing, but may possess a mixed‐mating system.     

Molecular biogeography and diversification of the endemic terrestrial fauna of the Hawaiian Islands

Oceanic islands have played a central role in biogeography and evolutionary biology. Here, we review molecular studies of the endemic terrestrial fauna of the Hawaiian archipelago. For some groups, monophyly and presumed single origin of the Hawaiian radiations have been confirmed (achatinelline tree snails, drepanidine honeycreepers, drosophilid flies, Havaika spiders, Hylaeus bees, Laupala crickets). Other radiations are derived from multiple colonizations (Tetragnatha and Theridion spiders, succineid snails, possibly Dicranomyia crane flies, Porzana rails). The geographic origins of many invertebrate groups remain obscure, largely because of inadequate sampling of possible source regions. Those of vertebrates are better known, probably because few lineages have radiated, diversity is far lower and morphological taxonomy permits identification of probable source regions. Most birds, and the bat, have New World origins. Within the archipelago, most radiations follow, to some degree, a progression rule pattern, speciating as they colonize newer from older islands sequentially, although speciation often also occurs within islands. Most invertebrates are single-island endemics. However, among multi-island species studied, complex patterns of diversification are exhibited, reflecting heightened dispersal potential (succineids, Dicranomyia). Instances of Hawaiian taxa colonizing other regions are being discovered (Scaptomyza flies, succineids). Taxonomy has also been elucidated by molecular studies (Achatinella snails, drosophilids). While molecular studies on Hawaiian fauna have burgeoned since the mid-1990s, much remains unknown. Yet the Hawaiian fauna is in peril: more than 70 per cent of the birds and possibly 90 per cent of the snails are extinct. Conservation is imperative if this unique fauna is to continue shedding light on profound evolutionary and biogeographic questions.     

Floral visitation patterns of two invasive ant species and their effects on other hymenopteran visitors

Abstract.  1. Floral nectar of the native Hawaiian 'ōhi'a tree, Metrosideros polymorpha , is an important food source for several native honeycreepers and yellow-faced bees, Hylaeus spp., but is also attractive to invasive ants.
2. I undertook this study to compare floral visitation patterns of two widespread invasive ants, the Argentine ant, Linepithema humile , and the big-headed ant, Pheidole megacephala , and to determine their effects on nectar volume and floral hymenopteran visitors.
3. In the first year of the study, Argentine ants visited inflorescences more frequently than big-headed ants at mid-day and in the afternoon, but did not occur in higher densities than big-headed ants at any time of day. In the following year, Argentine ants visited inflorescences both more frequently and in higher densities than big-headed ants. Argentine ant density had a stronger association with nectar concentration than big-headed ant density.
4. Nectar volume did not differ between ant-excluded and ant-visited inflorescences for either ant species. However, ant density was negatively associated with nectar volume for both species.
5.  Hylaeus spp. never visited inflorescences with big-headed ants, while non-native honeybees visited inflorescences with and without ants of either species in equal frequency.
6. Most studies of the effects of invasive ants on native arthropods have focused on interactions on the ground. Flowers should not be overlooked as microhabitats from which native arthropods may be displaced by invasive ants.     

Interspecific Pollen Transfer: Magnitude,Prevalence and Consequences for Plant Fitness

Interspecific pollen transfer (IPT) is one of the mechanisms underlying potential competition among plants for pollinators, and it refers to movement of pollen between different plant species by pollinators that visit their flowers simultaneously. Two components of IPT, related to each other, are distinguished: (a) heterospecific pollen deposition (HPD) on conspecific stigmas, which may interfere with fertilization by conspecific pollen; and (b) conspecific pollen loss (CPL) on heterospecific flowers, which may reduce the amount of pollen transferred between conspecific flowers. Thus, IPT may lead to reciprocal losses for male and female functions of the plant, with potentially important ecological and evolutionary consequences. In this review, we explore the magnitude and prevalence of IPT, examining documented mechanisms and evaluating such potential ecological and evolutionary consequences. We compiled existing evidence of interspecific pollinator sharing and interspecific pollinator switching between flowers of different species in natural communities. We evaluated the relative importance of both HPD and CPL from studies comparing these variables in pure vs. mixed floral neighborhoods, analyzing evidence for the claim that IPT is an evolutionary force promoting character displacement in habitat affinity, flowering times, and floral morphology. We also examined the findings of hand-pollination experiments carried out to reveal different mechanisms by which heterospecific pollen can affect performance of native pollen. Finally, we review evidence for impacts of alien plant species on native species' reproduction, and briefly comment on risks of crop-to-wild gene flow imposed by the release of genetically modified (transgenic) crops through IPT.     

Invasive aphids attack native Hawaiian plants

Invasive species have had devastating impacts on the fauna and flora of the Hawaiian Islands. While the negative effects of some invasive species are obvious, other species are less visible, though no less important. Aphids (Homoptera: Aphididae) are not native to Hawai’i but have thoroughly invaded the Island chain, largely as a result of anthropogenic influences. As aphids cause both direct plant feeding damage and transmit numerous pathogenic viruses, it is important to document aphid distributions and ranges throughout the archipelago. On the basis of an extensive survey of aphid diversity on the five largest Hawaiian Islands (Hawai’i, Kaua’i, O’ahu, Maui, and Moloka’i), we provide the first evidence that invasive aphids feed not just on agricultural crops, but also on native Hawaiian plants. To date, aphids have been observed feeding and reproducing on 64 native Hawaiian plants (16 indigenous species and 48 endemic species) in 32 families. As the majority of these plants are endangered, invasive aphids may have profound impacts on the island flora. To help protect unique island ecosystems, we propose that border vigilance be enhanced to prevent the incursion of new aphids, and that biological control efforts be renewed to mitigate the impact of existing species.     

Hybridization between introduced smooth cordgrass (Spartina alterniflora; Poaceae) and native California cordgrass (S. foliosa) in San Francisco Bay, California, USA

Introduced Spartina alterniflora (smooth cordgrass) is rapidly invading intertidal mudflats in San Francisco Bay, California. At several sites, S. alterniflora co-occurs with native S. foliosa (California cordgrass), a species endemic to California salt marshes. In this study, random amplified polymorphic DNA markers (RAPDs) specific to each Spartina species were identified and used to test for hybridization between the native and introduced Spartina species in the greenhouse and in the field. Greenhouse crosses were made using S. alterniflora as the pollen donor and S. foliosa as the maternal plant, and these crosses produced viable seeds. The hybrid status of the crossed offspring was confirmed with the RAPD markers. Hybrids had low self-fertility but high fertility when back-crossed with S. foliosa pollen. Hybrids were also found established at two field sites in San Francisco Bay; these hybrids appeared vigorous and morphologically intermediate between the parental species. Field observations suggested that hybrids were recruiting more rapidly than the native S. foliosa. Previous work identified competition from introduced S. alterniflora as a threat to native S. foliosa. In this study, we identify introgression and the spread of hybrids as an additional, perhaps even more serious threat to conservation of S. foliosa in San Francisco Bay.     

Pollinator sharing between mass-flowering oilseed rape and co-flowering wild plants: implications for wild plant pollination

Pollinating insects are not only important in wild plant pollination, but also in the production of a large number of crops. Oilseed rape production is increasing globally due to demands for biofuels which may have impacts on pollinating insects which visit the crop and on the pollination services delivered to co-flowering wild plants. In this study, we tested (1) the degree of pollinator sharing between oilseed rape and native wild plants in field margins and hedgerows and (2) the effects of oilseed rape on the quality of pollination service delivered to these wild plants. We found large overlap between flower visitors of wild plants and oilseed rape, but the composition of species overlap differed with respect to each wild plant species. Nearly all individual visitors caught on both the crop and foraging on wild species carried crop pollen, but more than half the insects also carried pollen from wild plants. However, very little oilseed rape pollen was deposited on wild plant stigmas. This shows that (1) oilseed rape overlaps in pollinator niche with most co-flowering wild plants, and (2) crop pollen deposition on wild plant stigmas is low which may indicate that it is unlikely to cause reductions in seed set of wild plants, although this was not measured here. Furthermore, wild plants in field margins and hedgerows are important sources of alternative forage for pollinating insects even when a crop is mass flowering, and we suggest maintenance and augmentation of field margins and hedgerows to provide alternative forage for pollinator conservation to continue provision of pollination services to both crops and wild plants.     

A reptilian smoking gun: first record of invasive Jackson’s chameleon (<Emphasis Type="Italic">Chamaeleo jacksonii</Emphasis>) predation on native Hawaiian species

Here we report the first conclusive evidence of an introduced reptile (Chamaeleo jacksonii) feeding on Hawaiian taxa, including 11 snails in four endemic genera from two families, including four individuals of an endangered species (Achatinella mustelina), and native insects in five genera. Native Hawaiian invertebrates were discovered in the dissected stomachs of wild caught Jackson’s chameleons collected from June to November 2009 on the island of Oahu. Although Jackson’s chameleons were introduced to the Hawaiian Islands in the early 1970s, ecological impacts have never been documented. Of particular concern is the fact that chameleons have previously only rarely been found in native Hawaiian habitat, although 12 were recently collected in a mid-elevation native forest, an area that is not likely to be suitable for their long-term persistence, but that is adjacent to higher elevation pristine forest where endemic prey are abundant and favorable climatic conditions exist for chameleon persistence. One concern is that Jacksons’s chameleons may be undergoing a range expansion into upper elevation pristine forests. If chameleons reach and establish populations in these areas, devastating impacts to the native ecosystem are possible. A thorough understanding of the impacts of chameleons on Hawaiian fauna will require additional evaluation and sampling, but dissemination of this discovery in a timely fashion is important as it provides new information regarding this threat. Monitoring and collection of chameleons is ongoing, particularly in native Hawaiian forest habitats at mid and upper elevations (600–1,300 m).     

Unfortunate encounters? Novel interactions of native Mecyclothorax, alien Trechus obtusus (Coleoptera: Carabidae), and Argentine ant (Linepithema humile, Hymenoptera: Formicidae) across a Hawaiian landscape

The Hawaiian Islands support a speciose radiation of native Mecyclothorax beetles (Coleoptera: Carabidae). This lineage has undergone a classical island radiation resulting in extensive ecological specialization, flight-wing loss, and 100% single-island endemism. We report on the sympatric occurrence of several Mecyclothorax species endemic to Haleakala volcano, East Maui with the newly arrived, adventive Trechus obtusus (Coleoptera: Carabidae), a tramp species originally from Europe. Arrival of T. obtusus in afforested, non-native gymnosperm plantation forest near Polipoli, Maui was associated with subsequent decreased abundance of native Mecyclothorax beetles. Since discovery of T. obtusus on Haleakala, their populations have been transformed through subsequent increase in frequency of brachypterous individuals. Consequences of this transformation to flight-wing dimorphic populations may simultaneously include enhanced reproductive capacity of brachypterous individuals, increased local adaptation of populations, and enhanced metapopulational dynamics ultimately permitting range expansion and occupation far beyond anything observed for the monomorphically brachypterous native Mecyclothorax. Trechus obtusus and several Mecyclothorax species occur sympatrically with Argentine ant, Linepithema humile (Hymenoptera: Formicidae) in subalpine shrublands on Haleakala. Recent sampling corroborates earlier findings that localized presence of Argentine ant is associated with significantly decreased abundance of native Mecyclothorax. Conversely, abundance of the continental T. obtusus is not significantly affected by ant presence.     

6. Peat-bog Begbunar (Osogovo Mountains,south-west Bulgaria): Four millennia of vegetation history

The aim of this study was to estimate the polleniferous potential of the most common plant communities and crops across the landscape through the study of pollen loads collected by Apis mellifera. We analysed pollen load samples from hives located in Mallorca (western Mediterranean) for one year and compared the results with a phytosociological study of the foraging area. We also analysed meteorological data to evaluate the influence of some environmental factors on the pollen production phenology. We identified 74 different pollen types (66.2% from native flora, 25.7% from exotic flora, and 8.1% from crops) belonging to 33 families. The highest polleniferous potentials in the landscape were attained by sclerophyllous forests (Quercetea ilicis) in spring, crops in autumn, wild annual rangelands (Stellarietea mediae) in winter and gardens in late summer. Our results suggest that the higher the coverage present in a vegetation class, the higher the quantity and diversity of pollen that may be provided to pollinators; therefore, its polleniferous potential may be higher. Some meteorological conditions (rainfall, temperature and daily hours of sunlight) may affect this potential through their influence on flowering phenology.     

华南主要作物和蔬果类现代花粉形态及农业考古研究价值

本文对华南地区主要的19科31种作物和蔬果类花粉进行了形态学研究,包括镜下观察、拍照和特征描述与对比。本研究涉及的花粉包括粮食作物4种,蔬菜类16种,水果类8种,油料和经济作物3种等。结果表明,不同作物的花粉在形态、大小、萌发器官和外壁纹饰等方面有明显的差别,同一科植物花粉的主要形态虽有相似之处,但根据某些细微结构特征,并通过统计学方法在一定程度上可以对相近的种类进行区别。本文对十字花科芸苔属4种蔬菜花粉(油菜、芥菜、菜心和小白菜)的扁率(赤道轴长/极轴长)以及外壁网眼长轴长度分别进行测量,发现外壁网眼长轴长度对于4种蔬菜的区分不明显,而扁率则分异显著,可为十字花科花粉种属判别提供依据。对重庆阿蓬江涪碛口遗址剖面中自明清时期以来的伴人植物十字花科花粉赤道轴长与外壁网眼长轴长度进行了测量,判别出文化层中的十字花科花粉可能为菜心类型。稻田中保存的水稻花粉直径约为34—38μm,结合水稻花粉的其它特征可以应用到全新世地层的水稻花粉鉴定。     

作物花粉高温应答机制研究进展

随着全球气候变暖加剧, 农作物面临更加严峻的高温威胁。高温胁迫影响作物生长发育各个阶段, 其中花粉发育过程对高温胁迫最为敏感, 因此花粉高温应答机制成为当前植物学研究热点。研究表明, 花粉可以通过质膜上的钙离子通道、内质网中的未折叠蛋白反应、活性氧积累以及H2A.Z等机制感知高温胁迫, 并通过调控热激蛋白表达、糖代谢、激素水平及活性氧清除能力适应高温胁迫。该文从高温对花粉发育的影响、花粉高温胁迫应答机制以及花粉高温胁迫研究的实验设计等方面进行综述, 旨在为相关研究提供借鉴。     

Determinants of thermal balance in the Hawaiian giant rosette plant,Argyroxiphium sandwicense

The effects of leaf pubescence and rosette geometry on thermal balance were studied in a subspecies of a Hawaiian giant rosette plant, Argyroxiphium sandwicense. This species, a member of the silversword alliance, grows above 2000 m elevation in the alpine zone of two Hawaiian volcanoes. Its highly pubescent leaves are very reflective (absorptance in the 400–700 nm waveband=0.44). Temperature of the expanded leaves was very similar to, or even lower than, air temperature during clear days, which was somewhat surprising given that solar radiation at the high elevation sites where this species grows can exceed 1100 W m^–2. However, the temperature of the apical bud, which is located in the center of the parabolic rosette, was usually 25°C higher than air temperature at midday. Experimental manipulations in the field indicated that incoming solar radiation being focussed towards the center of the rosette resulted in higher temperatures of the apical bud. Attenuation of wind speed inside the rosette, which increased the thickness of the boundary layer surrounding the apical bud, also contributed to higher temperatures. The heating effect on the apical bud of the large parabolic rosette, which apparently enhances the rates of physiological processes in the developing leaves, may exclude the species from lower elevations by producing lethal tissue temperatures. Model simulations of apical bud temperatures at different elevations and laboratory estimates of the temperature threshold for permanent heat injury predicted that the lower altitude limit should be approximately 1900 m, which is reasonably close to the lower limit of distribution of A. sandwicense on Haleakala volcano.     

Outcrossing potential between 11 important genetically modified crops and the Chilean vascular flora

The potential impact of genetically modified (GM) crops on biodiversity is one of the main concerns in an environmental risk assessment (ERA). The likelihood of outcrossing and pollen‐mediated gene flow from GM crops and non‐GM crops are explained by the same principles and depend primarily on the biology of the species. We conducted a national‐scale study of the likelihood of outcrossing between 11 GM crops and vascular plants in Chile by use of a systematized database that included cultivated, introduced and native plant species in Chile. The database included geographical distributions and key biological and agronomical characteristics for 3505 introduced, 4993 native and 257 cultivated (of which 11 were native and 246 were introduced) plant species. Out of the considered GM crops (cotton, soya bean, maize, grape, wheat, rice, sugar beet, alfalfa, canola, tomato and potato), only potato and tomato presented native relatives (66 species total). Introduced relative species showed that three GM groups were formed having: a) up to one introduced relative (cotton and soya bean), b) up to two (rice, grape, maize and wheat) and c) from two to seven (sugar beet, alfalfa, canola, tomato and potato). In particular, GM crops presenting introduced noncultivated relative species were canola (1 relative species), alfalfa (up to 4), rice (1), tomato (up to 2) and potato (up to 2). The outcrossing potential between species [OP; scaled from ‘very low’ (1) to ‘very high’ (5)] was developed, showing medium OPs (3) for GM–native relative interactions when they occurred, low (2) for GMs and introduced noncultivated and high (4) for the grape‐Vitis vinifera GM–introduced cultivated interaction. This analytical tool might be useful for future ERA for unconfined GM crop release in Chile.     

A DNA Barcoding Approach to Characterize Pollen Collected by Honeybees

In the present study, we investigated DNA barcoding effectiveness to characterize honeybee pollen pellets, a food supplement largely used for human nutrition due to its therapeutic properties. We collected pollen pellets using modified beehives placed in three zones within an alpine protected area (Grigna Settentrionale Regional Park, Italy). A DNA barcoding reference database, including rbcL and trnH-psbA sequences from 693 plant species (104 sequenced in this study) was assembled. The database was used to identify pollen collected from the hives. Fifty-two plant species were identified at the molecular level. Results suggested rbcL alone could not distinguish among congeneric plants; however, psbA-trnH identified most of the pollen samples at the species level. Substantial variability in pollen composition was observed between the highest elevation locality (Alpe Moconodeno), characterized by arid grasslands and a rocky substrate, and the other two sites (Cornisella and Ortanella) at lower altitudes. Pollen from Ortanella and Cornisella showed the presence of typical deciduous forest species; however in samples collected at Ortanella, pollen of the invasive Lonicera japonica, and the ornamental Pelargonium x hortorum were observed. Our results indicated pollen composition was largely influenced by floristic local biodiversity, plant phenology, and the presence of alien flowering species. Therefore, pollen molecular characterization based on DNA barcoding might serve useful to beekeepers in obtaining honeybee products with specific nutritional or therapeutic characteristics desired by food market demands.     

Small numbers of bee and non-bee pollinators detected moving between on-farm native plantings and neighbouring grass cropland

On-farm native plantings support insect pollinator diversity, however, they must move between this habitat and crops grown elsewhere on the farm if they are to have any possibility of delivering pollination services that benefit growers. To determine whether pollinator movement occurs, sticky traps to capture verified crop pollinating insects (bees and non-bees species) were placed at distances of 0, 50, 100, 150 and 250 m from 5 year old native plantings into adjacent grass crops on three farms in New Zealand. These were activated twice for 48 h in Dec 2017 and Jan 2018. Captured pollinators were examined for pollen originating from the native plantings. A total of 993 individuals from 13 crop pollinating species were counted of which 506 were examined for pollen. Eight individuals representing three pollinator species were found with pollen sourced from the plantings. Of these, the native bee Lasioglossum sordidum (n = 4) was found to have travelled up to 250 m, while the native flies Melangyna novaezelandiae (n = 3) and Odontomyia sp. (n = 1) travelled up to 150 m. Despite finding few pollinators moving between these habitats, we recommend further studies to assess (1) whether the current study is truly indicative of limited pollinator movement across these habitats at broader temporal (e.g. seasonal and yearly), spatial and system scales (e.g. a broader range of agriculture systems and regions). Such knowledge can inform farmers on whether or not it is worthwhile establishing on-farm native plantings to support pollinators.     

Impact of invasions by alien plants on soil seed bank communities: Emerging patterns

Much of our current understanding of the impact of invasive species on plant communities is based on patterns occurring in the above-ground vegetation, while only few studies have examined changes in soil seed banks associated with plant invasions, despite their important role as determinants of vegetation dynamics. Here, we reviewed the literature on the impact of plant invasions on the seed bank and we provide a quantitative synthesis using a meta-analysis approach. Specifically, (1) we quantified the impact of 18 invasive alien plants on (i) species richness and (ii) density of the seed banks of invaded communities, based on 58 pair-wise invaded-uninvaded comparisons (cases); we identified (2) the invasive taxa that are responsible for the largest changes in the seed bank; and (3) the habitats where substantial changes occur. Our study showed three major findings: (1) species richness (68% of cases) and density (58% of cases) were significantly lower in native seed banks invaded by alien plants; (2) species richness and density of native and alien species were remarkably lower in seed banks invaded by large, perennial herbs compared to uninvaded sites; and (3) invaded seed banks were often associated with a larger richness and/or abundance of alien species. This study indicates a need for additional seed bank data in invasion ecology to characterize species-specific and habitat-specific impacts of plant invasions, and to determine whether changes in the seed banks of native and alien species are a symptom of environmental degradation prior to a plant invasion or whether they are its direct result. The findings of this study help improve our capacity to predict the long-term implications of plant invasions, including limitations in the recruitment of native species from the seed bank and the potential for secondary invasions by seeds of other alien species.