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1.
Population size estimates are an integral part of rare plant conservation, but common abundance measurements such as cover and ramet number may not accurately index genet population size for vegetatively spreading species. Population monitoring of Kincaid’s lupine (threatened species) populations occurs through genet-anonymous leaf cover and raceme counts despite extensive, non-adventitious rhizome growth. While the current monitoring scheme provides important resource abundance measurements for the endangered Fender’s blue butterfly, whose larvae feed on Kincaid’s lupine leaves, the methods are not appropriate for estimating lupine genet number. Major axis regression revealed well supported statistical relationships between cover, raceme, and plantlet (a measurement of modular plant growth) density within six study patches (n = 3 populations) of Kincaid’s lupine (R2 > 0.90) and when all patch data were combined (R2 > 0.91). Genet population size estimates from genotype only data with ACE (an estimator used to infer species richness) were similar to estimates derived from a combination of plantlet density and genet to plantlet ratios (genotype derived) in small, more thoroughly genotyped lupine patches. However, genet number estimates from ACE were 3–5-fold greater in less intensely genotyped patches. Genet-anonymous plant abundance measurements, such as cover, can be used to estimate genet number in populations of vegetatively spreading plants provided they are calibrated with a unit of modular plant growth. Calibration of vegetative measurements, consistency of between population relationships, and closer scrutiny of highly supported statistical models may be necessary to develop more pertinent monitoring methods for rare, vegetatively spreading plants.  相似文献   

2.
Pollinator assemblages may shift as a consequence of the destruction and fragmentation of natural habitats. The scarcity of mates and pollinators can lead plant populations to suffer from pollen limitation and a decrease in reproductive performance within fragmented areas. We studied the shift in pollinator assemblages along with pollen limitation and seed production patterns in the Mediterranean shrub Myrtus communis. Our study included six populations contrasting in patch and population size (Large vs. Small) within a fragmented landscape characterized by ∼1% of potential forest coverage. The breeding system in Myrtus communis was self-compatible, but compared with natural pollination, fruit set increased with pollen addition (quantity limited), and seed set (brood size) increased with outcross pollen addition (quality limited). While the pollinator assemblage in Large patches was taxonomically diverse, it was almost monopolized by honeybees in Small patches, where visitation rates were highest and wild bee species were almost absent. In general, Small populations were less pollen limited for fruit set than Large populations, particularly those that received the highest rates of honeybee visits. However, despite differences in fragmentation and pollinators between Large and Small populations, seed production patterns (brood size and seed mass) were rather similar among them, in agreement with similar pollen limitation levels found for brood size. A higher susceptibility of native pollinators to the presence of honeybee hives was found in Small patches, suggesting that the pollinator assemblage may be severely altered when fragmentation occurs in combination with beekeeping. We discuss its implications and effects on plant reproduction in fragmented areas.  相似文献   

3.
Fragmentation of habitats has resulted in increased inbreeding for many plant species, while the introduction of foreign seed material for ecological restoration has resulted in crosses between plants from distant populations. Both processes may reduce plant fitness and increase the risk of extinction. Variation in the expression of inbreeding and outbreeding depression has been found among different genotypes and among populations, but little is known about large scale geographical patterns within species. We studied the effects of cross-proximity on seed production and offspring performance in the perennial meadow plant Hypochoeris radicata (Asteraceae) from five populations in each of three European regions (Bohemia in northwest Czechia, Northern Hesse in central Germany, and Salland in the central Netherlands). Five artificial cross types were conducted with varying proximity of mates: selfing (self), within family crosses (WF), within population crosses (WP), between population crosses (BP), and between region crosses (BR), and the offspring were grown in a common garden. Independent of the region of origin of the maternal plant, selfing, WF and BP crosses resulted in lower seed set and germination than WP crosses, indicating partial self-incompatibility, inbreeding depression and reduced performance in the F1 progeny resulting from outbreeding. However, crosses between regions resulted in similar seed set and germination as within population crosses. For late traits, the effects of inbreeding and interpopulation crosses differed among regions. WP crosses exhibited the highest survival, flowering and multiplicative fitness only in progeny from Czech maternal plants. Our results suggest that the sensitivity of populations to introgression may vary among regions and that outbreeding depression does not necessarily increase with interpopulation distance. However, the current study investigated only effects in the F1 in a common garden and outbreeding depression may be stronger in the F2 and in field populations.  相似文献   

4.
About 32% of Antirrhinum species are considered to be endangered; however, no field studies have focused on their reproductive biology. In this work, several aspects of the reproductive biology (flowering phenology, floral biology, breeding system) and potential limits on seed quantity and quality (pollen limitation, inbreeding depression) were studied in natural populations of three endangered species of the genus (Antirrhinum charidemi, Antirrhinum subbaeticum, Antirrhinum valentinum). Results disclose that all three species need insect visitors for seed production since fruit set after autonomous self-pollination was lower than under hand cross-pollination. A. charidemi and A. valentinum were mainly self-incompatible, whereas A. subbaeticum was self-compatible but herkogamous. Supplementary pollination in open-pollinated flowers only increased fruit set and seed set relative to controls in a given population of A. valentinum. Preliminary data on inbreeding depression at early life-cycle stages of the self-compatible A. subbaeticum revealed that the cumulative level was low. Despite the three species being closely related and sharing many ecological characteristics, they show different mating systems, and different factors limit seed quantity and quality. Thus, caution should be taken when making a common conservation plan for a group of closely related taxa.  相似文献   

5.
Trillium camschatcense, a long-lived common woodland herb, has been experiencing intensive habitat fragmentation over the last century in eastern Hokkaido, Japan. We examined the genetic diversity and population genetic structure of 12 fragmented populations with different population sizes using allozyme electrophoresis. The percentage of polymorphic loci and mean number of alleles per locus were positively related to population size, probably due to the stochastic loss of rare alleles (frequency of q<0.1) in small populations. Populations with 350 flowering plants or fewer had lost almost all of their rare alleles. While the heterozygosity and inbreeding coefficient were not related to population size, some small populations showed relatively high inbreeding coefficients. In spite of the low genetic differentiation among overall populations (FST=0.130), local population structuring was recognized between the two geographically discontinuous population groups. Within groups, sufficient historical gene flow was inferred, whereas a low dispersal ability of this species and geographical separation could produce apparent differentiation between groups.  相似文献   

6.
In this study we investigate the effect of population size on the proportion of flowers that produce a fruit (fruit set), the number of seeds per fruit (seed set), seed germinability, seedling mortality and growth in a range of population fragments for the bird-pollinated mixed mating system shrub Calothamnus quadrifidus R. Br. (Myrtaceae). We found no significant linear relationship (p < 0.05) between population fragment size and fruit set in any of the three years reproduction was studied. In contrast, we found a very strong positive correlation between the number of seeds produced per fruit and increasing population fragment size for each of the three years. We found no significant linear relationships between population fragment size and seed germination, or seedling growth and mortality. The most plausible explanation for the decline in seed set is increased inbreeding in smaller populations. Although a previous mating system analysis with allozymes did not reflect the above, we present evidence from other lines of inquiry to indicate that inbreeding does increase in smaller populations, but is masked by post-zygotic lethal systems that eliminate genetically incompetent homozygous embryos. We found no evidence that highly mobile pollinators transporting pollen among fragments rescue small fragments from inbreeding. We discuss the implications of our findings for the conservation of plant diversity in fragments of species rich Mediterranean climate shrublands.  相似文献   

7.
The relative importance of ecological and genetic factors in regulating the demographic processes of small populations is unknown for most rare plants. Dithyrea maritima (beach spectacle pod; Brassicaceae) is a rare, rhizomatously spreading, and self-incompatible herbaceous perennial endemic to coastal sand dunes of southern California. Low seed production in this species may be caused by insufficient pollinator visits, which may be exacerbated by competition for pollinator visits from non-native plants that have invaded the coastal dunes. I tested this ‘ecological’ hypothesis by removing flowers of Cakile maritima and Carpobrotus spp. from three experimental plots on San Nicolas Island. A second possible limitation on seed set is low diversity of genets within subpopulations, which could lead to scarcity of compatible mates. I tested this ‘genetic’ hypothesis by assigning ramets to clones using isozymes, and by relating clonal diversity within populations to seed set. Removal of non-native plants had no detectable effect on pollination service to D. maritima or on seed set, and seed set was unrelated to natural variation in pollination service among populations within a single year. In contrast, clonal diversity within a 10 m2 patch was a strong predictor of seed set. Hence a genetic factor explains spatial variation in seed set on San Nicolas Island. On larger spatial and temporal scales, however, pollination service also affects patterns of seed set: a shift in pollination from flies in 1998 to bees in 1999 probably caused a corresponding increase in seed set across San Nicolas Island, while extremely low seed set at another site (San Miguel Island) is probably caused by a virtual absence of pollinators there.  相似文献   

8.
Larger clonal sizes observed in abandoned than in managed grassland could result in increased geitonogamy in Knautia arvensis. The species was investigated for self-compatibility, seed set without pollinators, and inbreeding depression in a greenhouse experiment. Seed set was equivalent in hand-selfed and hand-outcrossed plants (c. 53%), indicating full self-compatibility. Seed set was low (2.8%) in caged, unmanipulated flower heads. There was no significant difference in seed weight, germination, and survival between selfed and outcrossed progeny. Juvenile biomass was significantly lower in selfed than in outcrossed progeny (on average 45% lower). Cumulative fitness calculations for germination, survival, and juvenile biomass showed that the mean inbreeding depression was 58% in offspring produced by selfing. The results suggest that in K. arvensis, which is protected against self-pollination within flower heads through protandry, the likely mechanism for selfing is via geitonogamy among flower heads. Geitonogamy among ramets within the larger clones observed in abandoned grassland could reduce offspring viability in K. arvensis since the fitness of selfed offspring was low. Inbreeding depression could therefore add to the recruitment problems experienced by plants in abandoned grassland, both in K. arvensis and probably in other clonal grassland species, depending on their growth structure and breeding system.  相似文献   

9.
Morphological and functional characteristics of flowers may have major effects on their reproductive success. Here, we report a study on the characteristics of flowers of Petrocoptis viscosa, a herb species endemic to the northwest Iberian Peninsula, restricted to crevices in limestone outcrops, and currently occurring in only three populations within an area of less than 30 km2. We also investigated the effects of pollen source on indicators of reproductive success. The results show that Petrocoptis viscosa flowers are well adapted to autogamy. Inbreeding depression (as determined by comparison of results obtained after selfing and outcrossing) was negligible for fruit production (δ=−0.05) and mean seed number (δ=−0.11), low for seed germination percentage (δ=0.08), but relatively high for mean seed weight (δ=0.23). The spatial structure and small size of population of Petrocoptis viscosa may mean that inbreeding is frequent in natural habitats. Adaptation of plants to autogamy may therefore be energetically beneficial (i.e. less wasted expenditure on rewards and flowers).  相似文献   

10.
About twenty-five percent of all southern African Oxalis species are rare/endangered and highly localized, making them especially vulnerable to extinction through inbreeding, low genetic variation, disrupted biological interactions and stochastic events; all consequences of small population sizes. Moreover, Oxalis displays tristyly, which is a rare and specialized sexual system that includes a strong self-incompatibility component between three floral morphs to promote out-crossing within populations. As tristyly requires the availability of plants with different floral morphs as well as effective pollinators for seed production, this breeding system can affect small populations when fully expressed. Factors that may have an effect on rarity in Oxalis were investigated by focusing on the expression of tristyly, levels of natural seed production, clonality and the ecology of eight rare/highly localized Oxalis species. Field experiments revealed that the reproductive success of some Oxalis species may be hampered by tristyly, resulting in extremely low levels of natural seed production. Other species display a more relaxed expression of self-incompatibility, which in combination with the possibility of cross-pollinations provides reproductive assurance regardless of population structure and pollinator availability. Others are rare and endangered, but appear not to be negatively affected by the tristylous breeding system. Most species are limited by their highly specific habitat requirements and are particularly vulnerable to variation in rainfall patterns.  相似文献   

11.
Habitat fragmentation is a major threat to species survival worldwide due to genetic isolation, inbreeding depression, genetic drift and loss of adaptive potential. However the data on how gene-flow changes following habitat fragmentation is contradictory. If there is significant gene-flow between spatially isolated populations then limited conservation resources could be directed away from projects to ‘establish genetic connectivity’ and used to address other consequences of habitat fragmentation.This research focused on an endangered tree species Gomortega keule (Gomortegaceae) in a fragmented landscape in the Central Chile Biodiversity Hotspot and addressed three questions: (1) How far does pollen move between pollen donors and seed trees and what is the shape of the dispersal curve? (2) Do insect pollinators travel outside of forest patches? (3) Do small populations and single trees contribute to genetic connectivity across the landscape?Paternity analysis results show that G. keule’s insect pollinators travel outside of forest patches, over distances of 6 km, beyond the scale of population fragmentation or genetic structure. Pollen moved from small sites and single trees into large sites, as well as in the other direction, indicating these sites play a key role as functioning elements of the wider population and as stepping stones between sites. Fragmentation at the scale investigated has not led to genetic isolation, thus genetic connectivity per se is not a conservation priority. Other consequences of land-use change, specifically continuing habitat loss and population reduction, still threaten the survival of the species.  相似文献   

12.
Loss of genetic variation in populations may have other effects than inbreeding depression and loss of adaptive potential. In the case of the numerous gynodioecious plant species having cytonuclear systems of sex determination with dominant nuclear restorers of the male function, reduced genetic variation and increased inbreeding would increase the proportion of non-restorer recessive genes found in homozygosity, and therefore that of female plants producing pistillate flowers. This could have opposite effects on the extinction risk of the population. Female plants produce no pollen and may cause pollen limitation, but at the same time they may reduce average homozygosity and inbreeding depression because they are forced outcrossers. We observed that inbreeding indeed increased the frequency of female plants and pistillate flowers in the population, and that this effect was accompanied by reductions in population recruitment independent of inbreeding depression and likely due to pollen limitation. These results suggest that dominant nuclear restorers of pollen production speed up the extinction of small populations of Silene littorea, and that sex determination mechanisms might be an important factor to consider in the conservation of many plant species.  相似文献   

13.
The earthworm Lumbricus terrestris has relatively low dispersal rates. This can represent a challenge for the internal gregarine parasite Monocystis, the dispersal of which often depends on the host. Mating of Monocystis can also be restricted to parasite stages within the current host individual. Adaptations, including host behavioural modification, that improve parasite transmission and simultaneously avoid inbreeding within a single host individual should be favoured by selection. We used a correlative approach to investigate the question of parasitic manipulation in this Gregarine-Lumbricid system. We observed mature earthworms (n=24) for 3 weeks while recording various measures of activity (surface activity, burrowing activity, surfacing delay, number of surface visits) and correlated parasite load with these activity measures. We found a significant positive correlation between surface activity and midden (or cast) production, which suggests a simple method for assessing the overall activity of local earthworm populations. However, we found no evidence of behavioural manipulation of any measure of host activity. We discuss these results in the context of inbreeding depression and host-parasite coevolution.  相似文献   

14.
We investigated how genetic factors and pollen shortage affect seed production in a small population of Magnolia stellata, a threatened insect-pollinated tree. We used microsatellite and manual pollination techniques, and compared a small population to a large one. Compared to the large population, the small population showed low allelic variation and had an FIS significantly greater than 0 in adults, indicating that genetic deterioration, including genetic drift and inbreeding, may have occurred in adults. Manual self-pollination lowered seed production relative to manual cross-pollination to a different extent between populations: δ (the magnitude of inbreeding depression due to self-fertilization) was lower in the small population than in the large population. However, under natural pollination, the estimated embryo mortality rates after ovules self-fertilized were similar between the two populations because the primary selfing rate was higher in the small population. The ovule mortality rate due to pollen shortage and that due to factors independent of pollen shortage and selfing were both approximately 10% higher in the small population, suggesting that pollen transfer may have decreased and genetic deterioration effects may have increased in that population. These factors reduced seed production in the small population (female reproductive success = 0.3%) compared to the large population (2.6%). Our results suggest that seed production in the small population of M. stellata is strictly limited by elevated pollen shortage, selfing, and genetic deterioration in adults, which accelerate the risk of extinction.  相似文献   

15.
Inbreeding depression constitutes a significant threat to the viability of small populations. In addition to small size and isolation of populations, short distance dispersal may elevate risk of inbreeding, but empirical evidence is scarce. Inbreeding depression has been demonstrated in the highly endangered red-cockaded woodpecker Picoides borealis. It has been suggested that conservation efforts to support extant populations should aim at spatially aggregating territories to enhance dispersal success. This however may aggravate inbreeding risk because distance between territories and hence dispersal distances become short. We analysed empirical data from a long-term study of the demography of the red-cockaded woodpecker and found that inbreeding risk varied inversely with natal dispersal distance of the mother. Using an individual-based, spatially explicit population model that incorporates simulations of environmental and demographic stochasticity and an empirically derived, species-specific estimate of inbreeding costs, we demonstrated that inbreeding depression significantly elevated extinction risk in this species. On the other hand, even though dispersal distances in populations with spatially aggregated territories were shorter and the proportion of inbred individuals was higher than in other populations of the same size, such populations were still more persistent. Despite the overall adverse effect of inbreeding depression on viability of red-cockaded woodpecker populations, lowering interterritorial distances can be viewed as a valuable conservation tool. Given the small size and isolated location of most extant red-cockaded woodpecker populations however, our findings suggest that inbreeding depression represents a significant threat to the survival of this species.  相似文献   

16.
An increasing number of invasive species are changing ecosystems around the world. Road verges have commonly become the first footholds of non-native species in the new environments. Regularly mown road verges also offer habitats for meadow flora and fauna, which in Europe have suffered from the radical decline of semi-natural biotopes due to the agricultural modernization. We studied impacts of an invasive plant Lupinus polyphyllus on the plant and Lepidoptera species composition along road verges. The plant species composition was studied on 15 sites (with 1 m2 quadrats) and butterflies and diurnal moths along 15 transects (with weekly censuses) in SE Finland, each site and transect representing equally lupine invaded verge and an adjacent non-lupine verge. The species richness and diversity of flora and the cover and species richness of low growing (<20 cm) species, in particular, was lower in lupine verges compared to non-lupine verges. Also, the abundance of butterflies was lower in lupine verges. As the lupine cover approached 100%, fewer butterflies were observed in lupine transects compared to the adjacent non-lupine transects and a higher proportion of individuals were flying. Our results suggest that the changes in plant species assemblages and lower plant species richness in lupine invaded areas had “bottom-up” effects on higher trophic levels. Further studies on the control of lupine are urgently needed, but meanwhile we suggest regular mowing before the lupines have shed their seeds, together with the removal of the cuttings, to be the best management option.  相似文献   

17.
The two brown frogs Rana arvalis and Rana temporaria were monitored at 57 localities (that contained a total of 120 ponds) for up to 17 years each during the years 1989-2005. The analysis summarized below only accounts for trends within sites actually usable for frogs during the analysis period, large scale habitat losses are thus not accounted for. R. arvalis populations tended to increase over the study period. R. temporaria populations displayed no significant change. However, both species displayed significant fluctuations from year to year. These were not correlated between the two species. Localities with permanent ponds tended to display more positive population trends than localities with temporary ponds and ponds in pastures tended to display more positive trends than those in forests. For ponds in cropped fields, where only R. temporaria were found, the trend were also generally negative. Thus, long-term trends suggest that neither species is in decline. Nevertheless, the population trends observed in more exploited habitats are less positive than those in relatively unexploited habitats. We conclude frog populations in agricultural habitats should be more carefully studied to identify the factors behind the decline. The negative trend in temporary ponds are cause for a closer analysis of the effects of weather factors on frog population dynamics.  相似文献   

18.
We provide a brief review of practices and relevant studies for restoration of Nymphoides peltata (yellow floating heart, Asaza), a distylous floating-leaf clonal plant, in Lake Kasumigaura, Japan to develop a model of integrated genetic and demographic conservation for threatened plants. Several theoretically expected issues, such as sudden extinction of small populations with low genetic diversity, limited seed production in small-sized local populations, and significantly high heterozygosity in adults that have survived environmental change, were ascertained through integrated studies on demography with discrimination of genets and genetics using highly polymorphic genetic markers. Investigation of genetic properties of the remnant soil seed bank suggested that the seed bank could potentially restore genetic diversity, although the fitness reduction of seed banks caused by inbreeding could affect the success of restoration. As a result of restoration efforts, increases in the number of local populations and genets in the Lake Kasumigaura metapopulation have led to population recovery.  相似文献   

19.
We discuss the population biology of two calcareous grassland gentians, Gentianella germanica and Gentianopsis ciliata, in relation to the habitat management currently practiced in The Netherlands. There, at the margin of their range, both species are rare. Gentianella germanica persists on six remaining locations, whereas Gentianopsis ciliata, with two populations, is nearly extinct. Gentianella germanica is a strict biennial, Gentianopsis ciliata an iteroparous perennial. Both species depend on insects for seed production and suffer from low insect visitation. Pollination experiments in one Dutch population demonstrated that Gentianopsis ciliata is self-compatible, but hardly sets any seed under natural conditions due to pollen limitation. The low reproductive success of both species is partly due to the low pollinator densities at their late flowering time, partly caused by the small population size of the gentians themselves, and partly a result of mowing too early. The latter has destroyed the seed crop of several subsequent years in one population of Gentianopsis ciliata and some of Gentianella germanica. In Gentianella germanica, the early mowing and low insect visitation seems to have resulted in selection of less herkogamous and consequently more autofertile individuals. The perspectives for Gentianopsis ciliata are currently extremely poor in The Netherlands. Under the present circumstances, extinction will most likely occur within 10-20 years. Population reinforcement (seeding, artificial cross-pollination with nearby populations) should be considered if we want to conserve this species. For both gentians, but also of other flagship species of nutrient-poor calcareous grasslands, the total grassland area needs to be enlarged and must constitute an interconnected network of reserves. The traditional management method, sheep grazing, is to be preferred over mowing, but only if the flock visits each grassland patch or reserve for only a short time of less than a day, and with intervals of more than 2 weeks between visits. If mowing is preferred for other reasons, it should be done rotationally, and not before October.  相似文献   

20.
Sowing with seed mixtures is a common practice in restoring species-rich communities in areas with impoverished species pools. The potential genetic consequences of using these mixtures, however, are poorly understood and often not considered in practical restoration. We investigated genetic diversity, inbreeding and genetic structure of samples collected from 26 populations of the common wetland plant species Lychnis flos-cuculi in an agricultural region in Switzerland. Some of these populations were natural, while others had been sown several years ago. This enabled us to compare the genetic composition of populations of indigenous origin with those originating from commercially produced seed mixtures. Gene diversity and allelic richness were similar in natural and sown populations. In contrast, inbreeding coefficients were three times higher in sown than in natural populations. The sown populations were genetically distinct from the native populations. We distinguished two homogeneous gene pools that presumably originated from different source populations used to produce seed mixtures. The use of commercially produced seeds may alter the genetic diversity and structure of plant populations. The observed higher inbreeding coefficients of sown populations could lead to reduced population viability. To restore genetically diverse populations, the seeds for further propagation should be collected from numerous individuals in large and non-isolated populations nearby restored sites. Ex situ stocks for the production of commercial seed mixtures should only be propagated for a few generations to avoid negative effects such as inbreeding or loss of local adaptation.  相似文献   

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