The role of sexual and vegetative reproduction in the population maintenance of a monocarpic perennial herb,Cardiocrinum cordatum var. glehnii

Because monocarpic perennial plants have only one reproductive opportunity in their entire life, they need to ensure offspring production. Some plants reproduce both sexually and vegetatively, and vegetative reproduction could possibly compensate for seed production. Therefore, the role and significance of these reproductive modes is likely to differ between monocarps and polycarps, which can reproduce many times. Cardiocrinum cordatum var. glehnii is a monocarpic perennial that reproduces both sexually and vegetatively (bulblet formation). Here, we investigated the characteristics and contribution to population maintenance of sexual and vegetative reproduction to reveal the significance of these two reproductive modes in this species. First, we found that bulblet formation occurred in plants after the three‐leaved rosette stage. Second, resource allocation experiments revealed that although resources were mainly invested in fruit maturation after the flowering season, resource allocation was switched from sexual reproduction to vegetative reproduction if seed production was insufficient. Third, the outcrossing rate in this species varied greatly according to the environment surrounding the population. However, reproductive assurance by selfing kept seed production stable even if flowers did not receive sufficient pollen for full seed set via outcross pollination, and moreover, there was no intensive inbreeding depression. Finally, genotypic identification of ramets suggested that daughter ramets derived from vegetative reproduction received the space that the mother flowering ramet had occupied until the previous year.     

Inter-populational variation,but no-annual variation within populations,in terms of reproductive size and genetic structure in a monocarpic perennial herb,Cardiocrinum cordatum var. glehnii

Cardiocrinum cordatum var. glehnii (Liliaceae) is a monocarpic perennial herb living in temperate broad-leaved deciduous forests. In the present study we examined the sizes (basal diameter of the stem and flower numbers) of flowering individuals and genetic diversity using microsatellite loci of 23 populations of C. cordatum var. glehnii in Hokkaido, Japan, over 2 years (2009 and 2010). As a result, we found both the basal stem diameter and the number of flowers varied widely among the populations. However, although the sizes of flowering individuals differed among the populations, these were very stable in each population and in each year. In addition, for genetic diversity, the same trends (i.e. wide variation among the populations but non-annual variation) were detected.     

Genetic effects of habitat fragmentation in Viola pubescens (Violaceae), a perennial herb with chasmogamous and cleistogamous flowers

The reproductive biology of a plant species is important in the response of populations to habitat fragmentation, especially if plant-pollinator interactions are disrupted. The genetic effects of forest fragmentation were examined in the common understorey herb Viola pubescens, a species that produces self-pollinated cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers. Using allozymes, we measured genetic variation in different sized populations. These were located in woodlots of various sizes (0.5-40.5 ha) and distances from one another (0.3-46 km) within the agricultural landscape of central Ohio in the Midwestern United States. Changes in forest cover of each woodlot within the past 180 years were determined from historical sources and aerial photographs. Woodlot and population sizes were significantly and positively correlated with measures of genetic variation (A, P, HO and HE), with variation highest in populations in the largest woodlot population and lowest in the smallest woodlot population. Most large woodlots resulted from fluctuations in forest cover over the past 60 years, while smaller fragments remained the same size. Overall, populations in Crawford County were genetically differentiated from one another (theta = 0.34), but there was no relationship between genetic and geographical distance. Preliminary evidence for a single year indicated a high rate of outcrossing in most populations. Despite the CH/CL reproductive advantage and apparent outcrossing, populations of V. pubescens in small woodlots remain susceptible to potentially detrimental effects of fragmentation such as genetic drift and reduced levels of genetic variation.     

Contrasting genetic responses to population fragmentation in a coevolving fig and fig wasp across a mainland–island archipelago

Interacting species of pollinator–host systems, especially the obligate ones, are sensitive to habitat fragmentation, due to the nature of mutual dependence. Comparative studies of genetic structure can provide insights into how habitat fragmentation contributes to patterns of genetic divergence among populations of the interacting species. In this study, we used microsatellites to analyse genetic variation in Chinese populations of a typical mutualistic system – Ficus pumila and its obligate pollinator Wiebesia sp. 1 – in a naturally fragmented landscape. The plants and wasps showed discordant patterns of genetic variation and geographical divergence. There was no significant positive relationship in genetic diversity between the two species. Significant isolation‐by‐distance (IBD) patterns occurred across the populations of F. pumila and Wiebesia sp. 1 as whole, and IBD also occurred among island populations of the wasps, but not the plants. However, there was no significant positive relationship in genetic differentiation between them. The pollinator populations had significantly lower genetic variation in small habitat patches than in larger patches, and three island pollinator populations showed evidence of a recent bottleneck event. No effects of patch size or genetic bottlenecks were evident in the plant populations. Collectively, the results indicate that, in more fragmented habitats, the pollinators, but not the plants, have experienced reduced genetic variation. The contrasting patterns have multiple potential causes, including differences in longevity and hence number of generations experiencing fragmentation; different dispersal patterns, with the host's genes dispersed as seeds as well as a result of pollen dispersal via the pollinator; asymmetrical responses to fluctuations in partner populations; and co‐existence of a rare second pollinating wasp on some islands. These results indicate that strongly interdependent species may respond in markedly different ways to habitat fragmentation.     

Conservation of old individual trees and small populations is integral to maintain species' genetic diversity of a historically fragmented woody perennial

Historically fragmented and specialized habitats such as granite outcrops are understudied globally unique hot spots of plant evolution. In contrast to predictions based on mainstream population genetic theory, some granite outcrop plants appear to have persisted as very small populations despite prolonged geographic and genetic isolation. Eucalyptus caesia Benth. is a long‐lived lignotuberous tree endemic with a naturally fragmented distribution on granite outcrops in south‐western Australia. To quantify population to landscape‐level genetic structure, we employed microsatellite genotyping at 14 loci of all plants in 18 stands of E. caesia. Sampled stands were characterized by low levels of genetic diversity, small absolute population sizes, localized clonality and strong fine‐scale genetic subdivision. There was no significant relationship between population size and levels of heterozygosity. At the landscape scale, high levels of population genetic differentiation were most pronounced among representatives of the two subspecies in E. caesia as originally circumscribed. Past genetic interconnection was evident between some geographic neighbours separated by up to 20 km. Paradoxically, other pairs of neighbouring stands as little as 7 km apart were genetically distinct. There was no consistent pattern of isolation by distance across the 280 km range of E. caesia. Low levels of gene flow, together with strong drift within stands, provide some explanation of the patterns of genetic differentiation we observed. Individual genet longevity via the ability to repeatedly resprout and expand from a lignotuber may enhance the persistence of some woody perennial endemic plants despite small population size, minimal genetic interconnection and low heterozygosity.     

How climate,migration ability and habitat fragmentation affect the projected future distribution of European beech

Recent efforts to incorporate migration processes into species distribution models (SDMs) are allowing assessments of whether species are likely to be able to track their future climate optimum and the possible causes of failing to do so. Here, we projected the range shift of European beech over the 21st century using a process‐based SDM coupled to a phenomenological migration model accounting for population dynamics, according to two climate change scenarios and one land use change scenario. Our model predicts that the climatically suitable habitat for European beech will shift north‐eastward and upward mainly because (i) higher temperature and precipitation, at the northern range margins, will increase survival and fruit maturation success, while (ii) lower precipitations and higher winter temperature, at the southern range margins, will increase drought mortality and prevent bud dormancy breaking. Beech colonization rate of newly climatically suitable habitats in 2100 is projected to be very low (1–2% of the newly suitable habitats colonised). Unexpectedly, the projected realized contraction rate was higher than the projected potential contraction rate. As a result, the realized distribution of beech is projected to strongly contract by 2100 (by 36–61%) mainly due to a substantial increase in climate variability after 2050, which generates local extinctions, even at the core of the distribution, the frequency of which prevents beech recolonization during more favourable years. Although European beech will be able to persist in some parts of the trailing edge of its distribution, the combined effects of climate and land use changes, limited migration ability, and a slow life‐history are likely to increase its threat status in the near future.     

Population genetic effects of urban habitat fragmentation in the perennial herb Viola pubescens (Violaceae) using ISSR markers

BACKGROUND AND AIMS: Fragmentation of natural habitats can negatively impact plant populations by leading to reduced genetic variation and increased genetic distance as populations become geographically and genetically isolated from one another. To test whether such detrimental effects occur within an urban landscape, the genetic structure of six populations of the perennial herb Viola pubescens was characterized in the metropolitan area of Greater Cincinnati in southwestern Ohio, USA. METHODS: Using three inter-simple sequence repeat (ISSR) markers, 51 loci amplified across all urban populations. For reference, four previously examined agricultural populations in central/northern Ohio and a geographically distant population in Michigan were also included in the analysis. KEY RESULTS: Urban populations retained high levels of genetic variation (percentage of polymorphic loci, P(p) = 80.7 %) with similar genetic distances among populations and an absence of unique alleles. Geographic and genetic distances were correlated with one another, and all populations grouped according to region. Individuals from urban populations clustered together and away from individuals from agricultural populations and from the Michigan population in a principle coordinates analysis. Hierarchical analysis of molecular variance (AMOVA) revealed that most of the genetic variability was partitioned within populations (69.1 %) and among groups (22.2 %) of southwestern Ohio, central/northern Ohio and Michigan groups. Mean F(st) was 0.308, indicating substantial population differentiation. CONCLUSIONS: It is concluded that urban fragmentation does not appear to impede gene flow in V. pubescens in southwestern Ohio. These results are consistent with life history traits of this species and the possibility of high insect abundance in urban habitats due to diverse floral resources and nesting sites. Combined with the cleistogamous breeding system of this species, pollinator availability in the urban matrix may buffer populations against detrimental effects of habitat fragmentation, at least in larger forest fragments. Consequently, it may be inappropriate to generalize about genetic effects of fragmentation across landscapes or even across plant species with different pollination systems.     

Spatially variable habitat quality contributes to within‐population variation in reproductive success

Variation in habitat quality is common across terrestrial, freshwater, and marine habitats. We investigated how habitat quality influenced the reproductive potential of mud crabs across 30 oyster reefs that were degraded to different extents. We further coupled this field survey with a laboratory experiment designed to mechanistically determine the relationship between resource consumption and reproductive performance. We show a >10‐fold difference in average reproductive potential for crabs across reefs of different quality. Calculated consumption rates for crabs in each reef, based on a type II functional response, suggest that differences in reproductive performance may be attributed to resource limitation in poor quality reefs. This conclusion is supported by results of our laboratory experiment where crabs fed a higher quality diet of abundant animal tissue had greater reproductive performance. Our results demonstrate that spatial variation in habitat quality can be a considerable contributor to within‐population individual variation in reproductive success (i.e., demographic heterogeneity). This finding has important implications for assessing population extinction risk.     

Strong dispersal in a parasitoid wasp overwhelms habitat fragmentation and host population dynamics

The population dynamics of a parasite depend on species traits, host dynamics and the environment. Those dynamics are reflected in the genetic structure of the population. Habitat fragmentation has a greater impact on parasites than on their hosts because resource distribution is increasingly fragmented for species at higher trophic levels. This could lead to either more or less genetic structure than the host, depending on the relative dispersal rates of species. We examined the spatial genetic structure of the parasitoid wasp Hyposoter horticola, and how it was influenced by dispersal, host population dynamics and habitat fragmentation. The host, the Glanville fritillary butterfly, lives as a metapopulation in a fragmented landscape in the Åland Islands, Finland. We collected wasps throughout the 50 by 70 km archipelago and determined the genetic diversity, spatial population structure and genetic differentiation using 14 neutral DNA microsatellite loci. We compared the genetic structure of the wasp with that of the host butterfly using published genetic data collected over the shared landscape. Using maternity assignment, we also identified full‐siblings among the sampled parasitoids to estimate the dispersal range of individual females. We found that because the parasitoid is dispersive, it has low genetic structure, is not very sensitive to habitat fragmentation and has less spatial genetic structure than its butterfly host. The wasp is sensitive to regional rather than local host dynamics, and there is a geographic mosaic landscape for antagonistic co‐evolution of host resistance and parasite virulence.     

Habitat fragmentation influences genetic diversity and differentiation: Fine‐scale population structure of Cercis canadensis (eastern redbud)

Forest fragmentation may negatively affect plants through reduced genetic diversity and increased population structure due to habitat isolation, decreased population size, and disturbance of pollen‐seed dispersal mechanisms. However, in the case of tree species, effective pollen‐seed dispersal, mating system, and ecological dynamics may help the species overcome the negative effect of forest fragmentation. A fine‐scale population genetics study can shed light on the postfragmentation genetic diversity and structure of a species. Here, we present the genetic diversity and population structure of Cercis canadensis L. (eastern redbud) wild populations on a fine scale within fragmented areas centered around the borders of Georgia–Tennessee, USA. We hypothesized high genetic diversity among the collections of C. canadensis distributed across smaller geographical ranges. Fifteen microsatellite loci were used to genotype 172 individuals from 18 unmanaged and naturally occurring collection sites. Our results indicated presence of population structure, overall high genetic diversity (H_E = 0.63, H_O = 0.34), and moderate genetic differentiation (F_ST = 0.14) among the collection sites. Two major genetic clusters within the smaller geographical distribution were revealed by STRUCTURE. Our data suggest that native C. canadensis populations in the fragmented area around the Georgia–Tennessee border were able to maintain high levels of genetic diversity, despite the presence of considerable spatial genetic structure. As habitat isolation may negatively affect gene flow of outcrossing species across time, consequences of habitat fragmentation should be regularly monitored for this and other forest species. This study also has important implications for habitat management efforts and future breeding programs.     

Plant reproductive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis

The loss and fragmentation of natural habitats by human activities are pervasive phenomena in terrestrial ecosystems across the Earth and the main driving forces behind current biodiversity loss. Animal-mediated pollination is a key process for the sexual reproduction of most extant flowering plants, and the one most consistently studied in the context of habitat fragmentation. By means of a meta-analysis we quantitatively reviewed the results from independent fragmentation studies throughout the last two decades, with the aim of testing whether pollination and reproduction of plant species may be differentially susceptible to habitat fragmentation depending on certain reproductive traits that typify the relationship with and the degree of dependence on their pollinators. We found an overall large and negative effect of fragmentation on pollination and on plant reproduction. The compatibility system of plants, which reflects the degree of dependence on pollinator mutualism, was the only reproductive trait that explained the differences among the species' effect sizes. Furthermore, a highly significant correlation between the effect sizes of fragmentation on pollination and reproductive success suggests that the most proximate cause of reproductive impairment in fragmented habitats may be pollination limitation. We discuss the conservation implications of these findings and give some suggestions for future research into this area.     

Spatial and demographic population genetic structure in Catasetum viridiflavum across a human-disturbed habitat

Spatial and temporal genetic structures were examined across sites on islands and mainland (continuous forest) populations of an epiphytic orchid, Catasetum viridiflavum, using 17 polymorphic allozyme loci. I tested whether patches on islands or at mainland sites comprised small local populations or a large population. Low among population differentiation was observed across the landscape suggesting that the species-specific pollinator and tiny wind-dispersed seeds maintain interconnections among distant patches. Temporal genetic structure among stage classes, and among breeding individuals are important components of the maintenance of genetic variation in this orchid. The natural history of this species including small breeding populations, probable high frequency of mating among relatives, and the high rates of seed movement among sites contribute to the high FIS. These data show that physically isolated patches in this epiphytic orchid comprise a single larger genetic population, which is independent of the physical distances among sites. Although quite different in ecological and life history characteristics, the genetic structure of this orchid demonstrates a pattern similar to temperate and tropical trees in fragmented landscapes.     

Estimation of effective population size and detection of a recent population decline coinciding with habitat fragmentation in a ground beetle

We assess the impact of habitat fragmentation on the effective size (N(e)) of local populations of the flightless ground beetle Carabus violaceus in a small (<25 ha) and a large (>80 ha) forest fragment separated by a highway. N(e) was estimated based on the temporal variation of allele frequencies at 13 microsatellite loci using two different methods. In the smaller fragment, N(e) estimates ranged between 59 and a few hundred, whereas values between 190 and positive infinity were estimated for the larger fragment. In both samples, we detected a signal of population decline, which was stronger in the small fragment. The estimated time of onset of this N(e) reduction was consistent with the hypothesis that recent road constructions have divided a continuous population into several isolated subpopulations. In the small fragment, N(e) of the local population may be so small that its long-term persistence is endangered.     

Landscape genetics of the self-compatible forest herb Geum urbanum: effects of habitat age, fragmentation and local environment

To investigate the role of habitat fragmentation, fragment age and local environment in shaping the genetics of plant populations, we examined the genetic structure of the self-compatible forest herb Geum urbanum using microsatellite markers. A historical land-use reconstruction assigned the studied populations to two age classes: populations in primary forest fragments, and populations in secondary fragments. Local environmental conditions were quantified on the basis of the herb-layer community composition. A stepwise general linear model revealed that levels of within-population genetic diversity were best explained by population size, landscape connectivity and the interaction between both. Connectivity was positively correlated with the genetic diversity of small populations, but did not significantly affect the diversity of large populations. Contrary to what we expected, secondary-forest populations showed lower divergence relative to populations located in primary patches. Small populations were genetically more diverged compared to large populations. Mantel tests showed no significant isolation by distance and no significant correlation between habitat similarity and genetic differentiation. We conclude that gene flow has probably prevented founder events from being reflected in the present genetic structure of G. urbanum. Gene flow towards low-connectivity populations, however, seemed to be insufficient to counteract the effects of drift in small populations.     

黑龙江省完达山地区马鹿生境破碎化及其影响因子

应用景观生态学原理和地理信息系统技术,分析黑龙江省完达山地区马鹿生境相关因子重要性、对景观连接度进行模糊相对赋值,建立了景观连接度评价模型及景观斑块指数,研究了黑龙江省完达山地区关于马鹿生境的景观连接度水平、生境的适宜性以及景观的空间结构。结果表明:(1)在155.6km2的面积中,适宜地区的总面积仅为14.81km2,占研究地区的9.52%;次适宜地区的总面积为9.57km2,占研究地区的6.15%;一般适宜地区的总面积为130.05km2,占研究地区的83.58%;不适宜地区的总面积为1.17km2,占研究地区的0.75%;(2)研究地区马鹿各类适宜地区呈多个斑块且相互隔离,在空间分布上处于破碎状态,而且不适宜地区斑块(人为活动景观)的面积比例虽小,在生态系统中形态上的破碎化程度较小,但对马鹿的生境的生态功能的丧失起到重要作用。     

Evolutionary consequences of habitat fragmentation: population size and density affect selection on inflorescence size in a perennial herb

Habitat fragmentation is considered to be one of the major threats to biological diversity worldwide. To date, however, its consequences have mainly been studied in an ecological context, while little is known about its effects on evolutionary processes. In this study we examined whether habitat fragmentation affects selection on plant phenotypic traits via changes in plant-pollinator interactions, using the self-incompatible perennial herb Phyteuma spicatum. Specifically, we hypothesized that limited pollination service in small or low-density populations leads to increased selection for traits that attract pollinators. We recorded mean seed production per capsule and per plant as a measure of pollination intensity and assessed selection gradients (i.e., trait-fitness relationships) in 16 natural populations of varying size and density over 2 years. Mean seed production was not related to population size or density, except for a marginal significant effect of density on the mean number of seeds per capsule in 1 year. Linear selection for flowering time and synchrony was consistent across populations; relative fitness was higher in earlier flowering plants and in plants flowering synchronously with others. Selection on inflorescence size, however, varied among populations, and linear selection gradients for inflorescence size were negatively related to plant population size and density in 1 year. Selection for increased inflorescence size decreased with increasing population size and density. Contrary to our expectation this appeared not to be related to changes in pollination intensity (mean seed production was not related to population size or density in this year), but was rather likely linked to differences in some other component of the abiotic or biotic environment. In summary, our results show that habitat fragmentation may influence selection on plant phenotypic traits, thereby highlighting potential evolutionary consequences of human-induced environmental change.     

Home range size scales to habitat amount and increasing fragmentation in a mobile woodland specialist

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Development of microsatellite markers in a large perennial herb, Veratrum album ssp. oxysepalum

We developed 11 polymorphic microsatellite [simple sequence repeat (SSR)] loci from genomic DNA of Veratrum album ssp. oxysepalum using a dual-suppression polymerase chain reaction technique and an improved method. These markers, with four to 17 alleles per locus, identified 47 genotypes in 48 samples collected from a population in Hokkaido, Japan. The observed and expected heterozygosities ranged from 0.042 to 0.938 and from 0.448 to 0.909, respectively. These SSR markers will be available to identify genets and evaluate genetic diversity of V. album ssp. oxysepalum.