Naturalization of alien plants in China

Naturalization (the establishment of a self-sustaining population for at least a decade) is a fundamental precondition for plant invasion and so compiling a complete inventory of naturalized alien species is necessary for predicting and hence preventing such invasion. However, nationwide information on naturalized plants in China is still lacking. We compiled a nationwide list of the naturalized plant species of China, based on various literature reports. The list comprised a total of 861 naturalized plant species belonging to 110 families and 465 genera. The three most dominant families were Compositae, Poaceae, and Leguminosae, accounting for 16, 13 and 12% of naturalized plants, respectively. Among genera, Euphorbia and Solanum had the most naturalized species, followed by Ipomoea, Amaranthus, Oenothera, and Trifolium. Over half of all aliens were of American origin (52%), followed by those with European (14%) and Asian (13%) origins. Annuals and perennial herbs were prevalent among naturalized species; comparison to other studies suggests however that the invasive potential is higher among plants with longer life cycles than those of annuals. The taxonomic pattern of plant naturalization in China is similar to patterns worldwide. However, the low proportion of naturalized plants within the Chinese flora overall suggests that the potential for plant invasions in China may be high. Therefore, greater attention should be focused on naturalization of alien plants in China, especially concerning species of dominant families or genera, and those with a perennial life cycle.     

Traits explain invasion of alien plants into tropical rainforests

• 1. The establishment of new botanic gardens in tropical regions highlights a need for weed risk assessment tools suitable for tropical ecosystems. The relevance of plant traits for invasion into tropical rainforests has not been well studied.
• 2. Working in and around four botanic gardens in Indonesia where 590 alien species have been planted, we estimated the effect of four plant traits, plus time since species introduction, on: (a) the naturalization probability and (b) abundance (density) of naturalized species in adjacent native tropical rainforests; and (c) the distance that naturalized alien plants have spread from the botanic gardens.
• 3. We found that specific leaf area (SLA) strongly differentiated 23 naturalized from 78 non‐naturalized alien species (randomly selected from 577 non‐naturalized species) in our study. These trends may indicate that aliens with high SLA, which had a higher probability of naturalization, benefit from at least two factors when establishing in tropical forests: high growth rates and occupation of forest gaps. Naturalized aliens had high SLA and tended to be short. However, plant height was not significantly related to species'' naturalization probability when considered alongside other traits.
• 4. Alien species that were present in the gardens for over 30 years and those with small seeds also had higher probabilities of becoming naturalized, indicating that garden plants can invade the understorey of closed canopy tropical rainforests, especially when invading species are shade tolerant and have sufficient time to establish.
• 5. On average, alien species that were not animal dispersed spread 78 m further into the forests and were more likely to naturalize than animal‐dispersed species. We did not detect relationships between the measured traits and estimated density of naturalized aliens in the adjacent forests.
• 6. Synthesis: Traits were able to differentiate alien species from botanic gardens that naturalized in native forest from those that did not; this is promising for developing trait‐based risk assessment in the tropics. To limit the risk of invasion and spread into adjacent native forests, we suggest tropical botanic gardens avoid planting alien species with fast carbon capture strategies and those that are shade tolerant.

     

Plant introduction,naturalization, and invasion in French Guiana (South America)

Continental tropical ecosystems are generally viewed as less vulnerable to biological invasions than island ones. Their apparent resistance to invasive alien species is often attributed to their higher native biota diversity and complexity. However, with the increase of human activities and disturbances and the accelerate rate of introductions of plant species, these apparently resilient continental ecosystems are now experiencing alien plant naturalization and invasion events. In order to illustrate this emergent phenomenon, we compiled a list of all known introduced and naturalized plant species in French Guiana (Guiana Shield, South America). A total of 490 alien plants were recorded, about 34% of which are currently naturalized, mainly species belonging to the Acanthaceae and Fabaceae (Faboideae) in the Eudicotyledons, and Poaceae (grasses) and Arecaceae (palms) in the Monocotyledons. The coastal dry and wet savannas appears to be vulnerable to plant invasion (with 165 naturalized species, about 34% of the alien flora), especially by Acacia mangium (Mimosaceae) and Melaleuca quinquenervia (Myrtaceae) which are forming localized but dense monotypic stands. Both tree species, intentionnally introduced for reforestation, rehabilitation, and as garden ornamentals and have the potential to spread with increasing human disturbances The number and abundance of naturalized alien plants in the relatively undisturbed tropical lowland rainforests and savannas remains still very low. Therefore, surveillance, early detection, and eradication of potential plant invaders are crucial; moreover collaboration with neighbouring countries of the Guiana Shield is essential to prevent the introduction of potentially invasive species which are still not present in French Guiana.     

Native and naturalized range size in Pinus: relative importance of biogeography,introduction effort and species traits

Aim Pine trees (genus Pinus) represent an ancient lineage, naturally occurring almost exclusively in the Northern Hemisphere, but introduced and widely naturalized in both hemispheres. As large trees of interest to forestry, they attract much attention and their distribution is well documented in both indigenous and naturalized ranges. This creates an opportunity to analyse the relationship between indigenous and naturalized range sizes in the context of different levels of human usage, biological traits and the characteristics of the environments of origin. Location Global. Methods We combined and expanded pre‐existing data sets for pine species distributions and pine species traits, and used a variety of regression techniques (including generalized additive models and zero‐inflated Poisson models) to assess which variables explained naturalized and indigenous range sizes. Results Indigenous and naturalized range sizes are positively correlated but there are many notable exceptions. Some species have large indigenous ranges but small or no naturalized ranges, whereas others have small indigenous ranges, but have naturalized in many regions. Indigenous range is correlated to factors such as seed size (?), age at first reproduction (?), and latitude (+, supporting Rapoport's rule), but also to the extent of coverage of species in the forestry literature (+). Naturalized range size is strongly influenced by the extent of coverage of species in the forestry literature (+), a proxy for propagule pressure. Naturalization was also influenced by average elevation in the indigenous range (?) and age at first reproduction (?). Main conclusions The macroecological and evolutionary pressures facing plant groups are not directly transferable between indigenous and naturalized ranges. In particular, there are strong biases in species naturalization and expansion in invasive ranges that are unrelated to factors determining indigenous range size. At least for Pinus, a new set of macroecological patterns are emerging which are profoundly influenced by humans.     

Variation of food spectra of tube-nosed goby <Emphasis Type="Italic">Proterorhinus marmoratus</Emphasis> (Perciformes,Gobiidae)—a new species in the Rybinsk Reservoir

Size-age structure and food composition of tube-nosed goby Proterorhinus marmoratus in the Rybinsk Reservoir have been studied. It was shown that food spectra changed in the process of dispersal of this species over the water body and considerably vary during the season. In the period of naturalization, feeding of the tube-nosed goby is characterized by group specialization; the object of specialization is Gmelinoides. Having dispersed over the water body and naturalized, it manifested itself as a generalist; its food composition became diverse and was determined by the seasonal dynamics of the population and biomass of food items.     

Investment in seed dispersal structures is linked to invasiveness in exotic plant species of south-eastern Australia

Naturalized plant species disperse their populations over considerable distances to become invasive. We tested the hypothesis that this shift from naturalization to invasion is facilitated by increased investment of resources in seed dispersal appendages, using an assemblage of naturalized plants of south-eastern Australia. Compared with non-invasive species, we found in both cross-species and independent-contrasts analyses that invasive species invested more heavily in seed dispersal appendages, regardless of the structure present on the seed associated with the mode of dispersal (e.g., wings versus fleshy fruits). Invasive species such as Lonicera japonica, Hedera Helix and Acetosa sagittata were found to invest as much as 60–70% of total diaspore mass in dispersal appendages. The positive relationship between dispersal investment and invasion success was still prevalent after controlling for the effects of plant growth form, seed mass and capacity for vegetative growth. Our findings demonstrate that a plant’s investment in dispersal appendages helps to overcome the dispersal barrier in the shift from naturalization to invasion.     

Niche based distribution modelling of an invasive alien plant: effects of population status, propagule pressure and invasion history

Forecasting the spatial spread of invasive species is important to inform management planning. Niche-based species distribution models offer a well-developed framework for assessing the potential range of species. However, these models assume equilibrium between the species’ distribution and its ecological requirements. During range expansion, invasive species are not in such equilibrium due to both dispersal limitation and frequent casual occurrence in sites unsuitable to persistent populations. In this article we use the example of the invasive annual plant Ambrosia artemisiifolia in Austria to evaluate if model accuracy can be enhanced in such non-equilibrium situations by taking account of propagule pressure and by restricting model calibration to naturalized populations. Moreover, we test if model accuracy increases during invasion history using distribution data from 1984 to 2005. The results suggest that models calibrated with naturalized populations are much more accurate than those based on the total set of records. Proxies of propagule pressure slightly but significantly improve goodness of fit, accuracy, and Type I and II error rates of models calibrated with all available records but have less consistent effects on models of naturalized populations. Model accuracy did not increase during the recent invasion history, probably because the species is still far from an equilibrium distribution. We conclude that even a coarse assessment of population status with records of invasive species delivers important information for predictive modelling and that proxies of propagule pressure should be included into such models at least during early to intermediate stages of the invasion history.     

Naturalization of ornamental plant species in public green spaces and private gardens

Ornamental horticulture is the most important pathway for alien plant introductions worldwide, and consequently, invasive spread of introduced plants often begins in urban areas. Although most introduced ornamental garden-plant species are locally not naturalized yet, many of them have shown invasion potential elsewhere in the world, and might naturalize when climate changes. We inventoried the planted flora of 50 public and 61 private gardens in Radolfzell, a small city in southern Germany, to investigate whether local naturalization success of garden plants is associated with their current planting frequency, climatic suitability (as assessed with climatic niche modelling) and known naturalization status somewhere in the world. We identified 954 introduced garden-plant species, of which 48 are already naturalized in Radolfzell and 120 in other parts of Germany. All currently naturalized garden plants in Radolfzell have a climatic suitability probability of ≥ 0.75 and are naturalized in ≥ 13 out of 843 regions globally. These values are significantly higher than those of garden plants that have not become locally naturalized yet. Current planting frequencies, however, were not related to current naturalization success. Using the identified local naturalization thresholds of climatic suitability and global naturalization frequency, and climate projections for the years 2050 and 2070, we identified 45 garden-plant species that are currently not naturalized in Radolfzell but are likely to become so in the future. Although our approach cannot replace a full risk assessment, it is well-suited and applicable as one element of a screening or horizon scanning-type approach.     

Photic induction of locomotor activity is correlated with photic habitat in <Emphasis Type="Italic">Anolis</Emphasis> lizards

A variety of ecologically important behaviors, including circadian rhythms and seasonal reproduction, are influenced by non-visual responses to light, yet very little is known about the relationship between photic habitat and non-visual photoreception. Puerto Rican Anolis lizards have diverged into multiple photic niches, making them a good model for non-visual photosensory ecology. We investigated the photic induction of locomotor activity, a non-visual response to light, in four species of Anolis comprising two pairs of closely related, ecomorphologically similar species whose microhabitats differ in solar irradiance. We developed a device for continuous, automated detection and recording of anole locomotor activity, and used it to characterize activity under 12:12 h light–dark cycles. Next, we administered a series of 2-h light pulses during the dark period of the light–dark cycle and measured the increase in locomotor activity relative to baseline dark activity. Five different irradiances (ranging from very dim to daytime levels) were given to each individual lizard on separate nights. As expected, light caused an irradiance-dependent increase in locomotor activity in all four species. The responses at the highest irradiances were significantly greater in species occupying relatively more shaded habitats, suggesting that non-visual photoreception may be adapted to habitat light in Anolis lizards.     

Does adaptive radiation of a host lineage promote ecological diversity of its bacterial communities? A test using gut microbiota of Anolis lizards

Adaptive radiations provide unique opportunities to test whether and how recent ecological and evolutionary diversification of host species structures the composition of entire bacterial communities. We used 16S rRNA gene sequencing of faecal samples to test for differences in the gut microbiota of six species of Puerto Rican Anolis lizards characterized by the evolution of distinct ‘ecomorphs’ related to differences in habitat use. We found substantial variation in the composition of the microbiota within each species and ecomorph (trunk‐crown, trunk‐ground, grass‐bush), but no differences in bacterial alpha diversity among species or ecomorphs. Beta diversity analyses revealed subtle but significant differences in bacterial composition related to host phylogeny and species, but these differences were not consistently associated with Anolis ecomorph. Comparison of a trunk‐ground species from this clade (A. cristatellus) with a distantly related member of the same ecomorph class (A. sagrei) where the two species have been introduced and are now sympatric in Florida revealed pronounced differences in the alpha diversity and beta diversity of their microbiota despite their ecological similarity. Comparisons of these populations with allopatric conspecifics also revealed geographic differences in bacterial alpha diversity and beta diversity within each species. Finally, we observed high intraindividual variation over time and strong effects of a simplified laboratory diet on the microbiota of A. sagrei. Collectively, our results indicate that bacterial communities are only weakly shaped by the diversification of their lizard hosts due to the strikingly high levels of bacterial diversity and variation observed within Anolis species.     

Macroecological drivers of alien conifer naturalizations worldwide

Understanding the factors that drive the global distribution of alien species is a pivotal issue in invasion biology. Here, we used data on naturalized conifers (Pinaceae, Cupressaceae) from sixty temperate and subtropical regions and five continents to test how environmental and socio‐economic conditions of recipient areas as well as introduction efforts affect naturalization probabilities. We collated 18 predictor variables for each region describing environmental, biogeographic and socio‐economic conditions as well as a measure of the macro‐climatic match with the species' native ranges, and the extent to which alien conifers are used in commercial forestry. Naturalization probabilities across all species and regions were then related to these predictor variables by means of generalized linear mixed models. For both Pinaceae and Cupressaceae, naturalization probabilities were generally higher in the Southern Hemisphere, and increased with indicators of habitat diversity of the recipient region. The match in macro‐climatic conditions between the native and introduced regions was a significant predictor of conifer naturalization, but socio‐economic variables were less powerful predictors. Only for Cupressaceae did a socio‐economic variable (human population density) affect naturalization probabilities. Key attributes facilitating naturalization were related to introduction effort. Moreover, usage in commercial forestry generally fostered naturalization, although the actual size of alien conifer plantations in a region was only correlated with the naturalization of Pinaceae. Our results suggest that climate matching, habitat diversity and introduction effort co‐determine the probability of naturalization, which additionally, is modulated by biogeographic features of the recipient area, such as incidence of natural enemies or competitors. To date, the most widely used tools for invasive plant risk assessment only account for climate match and rarely factor in other attributes of the recipient environment. Future tools should additionally consider biotic environment and introduction effort if risk assessment is to be effective.     

Soil-borne seed pathogens: contributors to the naturalization gauntlet in Pacific Northwest (USA) forest and steppe communities?

Soil-borne seed pathogens are omnipresent but are often overlooked components of a community’s biotic resistance to plant naturalization and invasion. Using multi-year greenhouse experiments, we compared the seed mortality of single invasive, naturalized, and native grass species in sterilized and unsterilized soils collected from Pacific Northwest (USA) steppe and forest communities. Native Pseudoroegneria spicata displayed the greatest seed mortality, naturalized Secale cereale displayed intermediate seed mortality, and invasive Bromus tectorum was least affected by soil pathogens. Seed mortality across all three species was consistently greater in soils collected from steppe than soils collected from forest; seeds sown into sterilized steppe soil experienced half the overall seed mortality compared to seeds sown into unsterilized steppe soil. Soil sterilization did not affect grass seed mortality in forest soils. We conclude that (1) removing soil-borne pathogens with sterilization does increase native and non-native grass seed survival, and (2) soil-borne pathogens may influence whether an introduced species becomes invasive or naturalized within these Pacific Northwest communities as a result of differential seed survival. Soil-borne pathogens in these communities, however, have the greatest negative effect on the survival of native grass seeds, suggesting that the native microbial soil flora more effectively attack seeds of native plants than seeds of non-native species.     

Patterns of ecomorphological convergence among mainland and island Anolis lizards

Differing selective pressures on islands versus the mainland may produce alternative evolutionary outcomes among closely related lineages. Conversely, lineages may be constrained to produce similar outcomes in different mainland and island environments, or mainland and island environments may not differ significantly. Among the best‐studied island radiations are Caribbean Anolis lizards. Distinct morphotypes, or ‘ecomorphs’, have been described, and the same ecomorphs have evolved independently on each Greater Antillean island. The mainland Anolis radiation has received much less attention. We use a large morphological data set and a novel phylogenetic hypothesis to show that mainland Anolis did not evolve the same morphotypes as island Anolis, despite some island species being more closely related to mainland species than to island species that share their morphotype. A maximum of four of the six Caribbean ecomorphs were found to exist on the mainland, and just 15 of 123 mainland species are assignable to a Caribbean ecomorph. This result was insensitive to differing taxon samples and alternative phylogenetic hypotheses. Mainland convergence to a Caribbean ecomorph occurs only among species assigned to the grass‐bush ecomorph. Thus, the ecomorphs that have evolved convergently multiple times in the Caribbean have not evolved in parallel on the mainland. These results are consistent with the hypothesis that mainland and island environments offer different selective pressures. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 852–859.     

How strongly do interactions with closely‐related native species influence plant invasions? Darwin's naturalization hypothesis assessed on Mediterranean islands

Aim Recent works have found the presence of native congeners to have a small effect on the naturalization rates of introduced plants, some suggesting a negative interaction (as proposed by Charles Darwin in The Origin of Species), and others a positive association. We assessed this question for a new biogeographic region, and discuss some of the problems associated with data base analyses of this type. Location Islands of the Mediterranean basin. Methods Presence or absence of congeners was assessed for all naturalized alien plants species at regional, local and habitat scales. Using general linear models, we attempted to explain the abundance of the species (as measured by the number of islands where recorded) from their congeneric status, and assessed whether the patterns could be alternatively accounted for by a range of biological, geographical and anthropogenic factors. A simulation model was also used to investigate the impact of a simple bias on a comparable but hypothetical data set. Results Data base analyses addressing Darwin's hypothesis are prone to bias from a number of sources. Interaction between invaders and congenerics may be overestimated, as they often do not co‐occur in the same habitats. Furthermore, intercorrelations between naturalization success and associated factors such as introduction frequency, which are also not independent from relatedness with the native flora, may generate an apparent influence of congenerics without implying a biological interaction. We detected no true influence from related natives on the successful establishment of alien species of the Mediterranean. Rarely‐introduced species tended to fare better in the presence of congeners, but it appears that this effect was generated because species introduced accidentally into highly invasible agricultural and ruderal habitats have many relatives in the region, due to common evolutionary origins. Main conclusions Relatedness to the native flora has no more than a marginal influence on the invasion success of alien plants in the Mediterranean, although apparent trends can easily be generated through artefacts of the data base.     

A phylogenetic approach towards understanding the drivers of plant invasiveness on Robben Island,South Africa

Invasive plant species are a considerable threat to ecosystems globally and on islands in particular where species diversity can be relatively low. In this study, we examined the phylogenetic basis of invasion success on Robben Island in South Africa. The flora of the island was sampled extensively and the phylogeny of the local community was reconstructed using the two core DNA barcode regions, rbcLa and matK. By analysing the phylogenetic patterns of native and invasive floras at two different scales, we found that invasive alien species are more distantly related to native species, a confirmation of Darwin's naturalization hypothesis. However, this pattern also holds even for randomly generated communities, therefore discounting the explanatory power of Darwin's naturalization hypothesis as the unique driver of invasion success on the island. These findings suggest that the drivers of invasion success on the island may be linked to species traits rather than their evolutionary history alone, or to the combination thereof. This result also has implications for the invasion management programmes currently being implemented to rehabilitate the native diversity on Robben Island. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 142–152.     

Patterns of plant invasions in China: Taxonomic,biogeographic, climatic approaches and anthropogenic effects

This study was aimed to determine the patterns as well as the effects of biological, anthropogenic, and climatic factors on plant invasions in China. About 270 volumes of national and regional floras were employed to compile a naturalized flora of China. Habit, life form, origin, distribution, and uses of naturalized plants were also analyzed to determine patterns on invasion. Correlations between biological, anthropogenic and climatic parameters were estimated at province and regional scales. Naturalized species represent 1% of the flora of China. Asteraceae, Fabaceae, and Poaceae are the dominant families, but Euphorbiaceae and Cactaceae have the largest ratios of naturalized species to their global numbers. Oenothera, Euphorbia, and Crotalaria were the dominant genera. Around 50% of exotic species were introduced intentionally for medicinal purposes. Most of the naturalized species originated in tropical America, followed by Asia and Europe. Number of naturalized species was significantly correlated to the number of native species/log area. The intensity of plant invasion showed a pattern along climate zones from mesic to xeric, declining with decreasing temperature and precipitation across the nation. Anthropogenic factor, such as distance of transportation, was significantly correlated to plant invasions at a regional scale. Although anthropogenic factors were largely responsible for creating opportunities for exotic species to spread and establish, the local biodiversity and climate factors were the major factors shaping the pattern of plant invasions in China. The warm regions, which are the hot spots of local biodiversity, and relatively developed areas of China, furthermore, require immediate attentions.     

Loci under selection during multiple range expansions of an invasive plant are mostly population specific,but patterns are associated with climate

Identifying the genes underlying rapid evolutionary changes, describing their function and ascertaining the environmental pressures that determine fitness are the central elements needed for understanding of evolutionary processes and phenotypic changes that improve the fitness of populations. It has been hypothesized that rapid adaptive changes in new environments may contribute to the rapid spread and success of invasive plants and animals. As yet, studies of adaptation during invasion are scarce, as is knowledge of the genes underlying adaptation, especially in multiple replicated invasions. Here, we quantified how genotype frequencies change during invasions, resulting in rapid evolution of naturalized populations. We used six fully replicated common garden experiments in Brazil where Pinus taeda (loblolly pine) was introduced at the same time, in the same numbers, from the same seed sources, and has formed naturalized populations expanding outward from the plantations. We used a combination of nonparametric, population genetics and multivariate statistics to detect changes in genotype frequencies along each of the six naturalization gradients and their association with climate as well as shifts in allele frequencies compared to the source populations. Results show 25 genes with significant shifts in genotype frequencies. Six genes had shifts in more than one population. Climate explained 25% of the variation in the groups of genes under selection across all locations, but specific genes under strong selection during invasions did not show climate‐related convergence. In conclusion, we detected rapid evolutionary changes during invasive range expansions, but the particular gene‐level patterns of evolution may be population specific.     

Mating system shifts a species’ range

Understanding the ecological and evolutionary mechanisms that shape a species’ range is an important goal in evolutionary biology. Evidence indicates that mating system is an effective predictor of the global range of native species or naturalized alien plants, but the mechanisms underlying this predictability are not elaborated. Here, we develop a theoretical model to account for the ranges of plants under different mating systems based on migration‐selection processes (an idea proposed by Haldane). The model includes alternation of gametophyte and sporophyte generations in one life cycle and the dispersal of haploid pollen and diploid seeds as vectors for gene flow. We show that the interaction between selfing rates and gametophytic selection determines the role of mating system in shaping a species’ range. Selfing restricts the species’ range under gametophytic selection in nonrandom mating systems, but expands the species’ range under the absence of gametophytic selection in any mating system. Gametophytic selection slightly restricts the species’ range in random mating. Both logarithmic and logistic models of population demography yield similar conclusions in the case of fixed or evolving genetic variance. The theory also helps to explain a broader relationship between mating system and range size following biological invasion or plant naturalization.     

Naturalized Orchid Bee Pollinates Resin‐reward Flowers in Florida: Novel and Known Mutualisms

Females of an orchid bee, Euglossa viridissima, recently naturalized in southern Florida, routinely collect resin to construct their brood cells from the flowers of two Clusia (Clusiaceae) and two Dalechampia (Euphorbiaceae) species. We demonstrated that the bee pollinates three of these species including: (1) the newly naturalized D. scandens, which it pollinates in Mexico; (2) the ornamental D. aristolochiifolia native to Peru; and (3) the ornamental C. lanceolata native to Brazil, but not the apomictic Clusia rosea native to Florida. Field observations indicated that the bee promotes outcrossing in a naturalized D. scandens population. Comparisons of fruit set between unmanipulated control flowers and flowers supplemented with additional pollen indicated that the presence of bee eliminates pollen limitation for cultivated C. lanceolata. The orchid bee's pollination of ornamental resin‐reward plants may promote their naturalization.     

Diploid male production in a rare and locally distributed bumblebee, Bombus florilegus (Hymenoptera, Apidae)

The European bumblebee B. terrestris was recently introduced in Japan for agricultural purposes and has now become naturalized. The naturalization of this exotic species may have great detrimental effects on closely related native Japanese bumblebees. The Japanese bumblebee Bombus florilegus is a rare and locally distributed species found in the Nemuro Peninsula of Hokkaido, Japan. In order to assess its population genetics, we estimated the genetic structure of B. florilegus in 16 breeding colonies (queen, workers, and males) and 20 foraging queens by analyzing microsatellite DNA markers. Of the 36 queens analyzed by genotyping and dissection, 32 had been inseminated by a male. The remaining 4 had not been inseminated at all. Of the 4 nonmated queens, one was triploid. Diploid males were found in 4 breeding colonies. Based on the microsatellite data, it appears that B. florilegus has low reproductive success. Since matched mating and nonmating within local populations are high, the extinction risk is correspondingly higher. Our results suggest that conservation of the Japanese B. florilegus is required in order to protect it from both habitat destruction and the naturalization of alien species. Received 19 July 2007; revised 13 October 2007; accepted 15 October 2007.