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1.
In this study we use a demographic approach to analyse the differing abundance of three congeneric columnar cacti: Neobuxbaumia macrocephala (the rarest), Neobuxbaumia tetetzo (intermediate), and Neobuxbaumia mezcalaensis (the most common). Populations of these species were studied in the Tehuacan Valley (Central Mexico) over a 3-year period. We employed traditional models and life table response experiments (LTRE) to explore the association between particular demographic traits and the degree of rarity of each species. Most matrices showed population growth rate () values close to unity; the only exception was N. mezcalaensis in 2001–2002 (=1.091±0.088). In the three species the highest elasticity values corresponded to entries referring to the stasis of pre-reproductive plant and small adults. However, the LTRE indicated that most important differences in the values between years and species were associated with variation in fruit production and seedling recruitment. N. mezcalaensis yielded the highest mean due to its high fecundity in 2001–2002. This result suggests that the variation in demographic behaviour observed between species is sufficient to explain the higher abundance of N. mezcalaensis compared to the rare N. macrocephala. The high fecundity values and recruitment success observed in the former, even if they occur only seldom, may result in higher average values accounting for its high population densities.  相似文献   

2.
We document the pollination biology and mating systems of Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala, two Mexican giant columnar cacti. These two species form mixed forests in the western Tehuacan Valley, Mexico. The flowers of both N. mezcalaensis and N. macrocephala exhibit nocturnal anthesis, are self-incompatible, and are pollinated primarily by three species of nectar-feeding bats (Choeronycteris mexicana, Leptonycteris curasoae, and Leptonycteris nivalis). Neobuxbaumia mezcalaensis is androdioecious, a breeding system that appears to be uncommon among Cactaceae. Neobuxbaumia macrocephala is hermaphroditic. We hypothesize that columnar cacti show a geographical dichotomy in floral biology specialization that probably can be related to predictability in pollinator abundance.  相似文献   

3.
Neobuxbaumia macrocephala is a long-lived columnar cactus endemic to the Tehuacán-Cuicatlán Valley in south-central Mexico. This plant has a very restricted distribution and few recruitment events have been detected in its populations. In this study, we analyze the N. macrocephala demographic pattern using a projection matrix in order to determine the main limiting factors of this species. To accomplish this goal, we compare our results with those obtained for another species of the same genus, N. tetetzo. Considering that both species inhabit the same valley, we believe that this comparative study will offer insights into the main demographic limitations of N. macrocephala. Results showed that these species of columnar cacti have similar demographic patterns in which survival is the process with the highest relative contribution to λ, followed by growth and reproduction. Of all the life cycle stages, seeds and seedlings have the lowest survival probabilities due to a high mortality caused by seed predation and effects of direct solar radiation on germinated seeds. The estimated growth rates indicate that populations of these species of Neobuxbaumia are in a numerical equilibrium. With respect to reproduction, N. macrocephala produce a lower number of seeds per plant than N. tetetzo. This low level of sexual reproduction may decrease the probability of establishment of new individuals in N. macrocephala populations. It is suggested that pollen limitation and pre-dispersal seed predation could be some factors that limit the distribution and abundance of this columnar cactus. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

4.
《Acta Oecologica》2007,31(3):333-341
Relatively few studies have compared invasibility and species invasiveness among microhabitats within communities, synchronously. We surveyed the abundance and performance of non-native Alternanthera philoxeroides (Mart.) Griseb. (alligator weed), its co-occurring native congener, Alternanthera sessilis (L.) DC. (sessile joyweed), and other species in a wetland community along a riparian zone in southeast China to test the hypotheses that: i) degree of invasion differs between different types of microhabitats within the community; and ii) microhabitat types that differ in invasibility also differ in soil resource availability or in sediment characteristics likely to affect resource availability; iii) phenotypic plasticity of A. philoxeroides may play a key role in its adaptation to diverse habitats as can be concluded from its extremely low genetic diversity in China. The study riparian zone comprises different types of microhabitats including wet abandoned field, swamp, marsh dunes and gravel dunes. Consistent with these hypotheses, cover of A. philoxeroides was high in abandoned fields (73 ± 2.9%) and swamps (94 ± 1.3%), which had high soil nutrients and water availability. On the contrary, cover of native A. sessilis was relatively high in marsh dunes and grave dunes, which had coarse gravel surfaces, low soil nutrients and low water availability. A. philoxeroides showed greater morphological plasticity in response to habitat variation. In abiotically harsh habitats, stems had limited growth, and were prostrate with weak adventitious roots at nodes, forming thin, scattered patches. In the two richer habitats, the highly branched plants spread over the water or soil surface, supporting dense stronger leaf-bearing stems which grew vertically. The growth pattern of A. sessilis among microhabitats did not exhibit significant variations. These results suggest that morphological plasticity and microhabitat types with high soil resources may facilitate invasions of A. philoxeroides.  相似文献   

5.
The Pendjari Biosphere Reserve located in the Sudanian zone of Bénin, is a protected area well managed, but mainly aimed at wild animal conservation. This study assessed its effectiveness to conserve habitat species composition and population structure of three endangered African tree species: Afzelia africana Sm., Pterocarpus erinaceus Poir. and Khaya senegalensis (Desv.) A. Juss. We randomly sampled 120 plots in the protected and surrounding unprotected habitats by inventorying plant species. For the three target species, we estimated adult and juvenile densities and recorded size classes. According to floristic composition four habitats groups were recognized in relation to human disturbance, vegetation type, and moisture. These were protected savannas, unprotected savannas, old fallows and gallery forests. The estimated adult densities of A. africana were similar between protected (14 ± 1.2 tree/ha) and unprotected savannas (17 ± 0.9 tree/ha) while for P. erinaceus the adult density was significantly higher in protected (12 ± 3.7 tree/ha) than in unprotected savannas (5 ± 1.9 tree/ha). Estimated adult density of K. senegalensis was also significantly higher in protected gallery forest (40 ± 5.8 tree/ha) than in unprotected one (29 ± 4.8 tree/ha). Juvenile densities of A. africana, K. senegalensis and P. erinaceus were higher in protected habitats than in unprotected ones but the difference was not significant. Skewness coefficient indicated that populations of investigated trees were declining in their protected habitats. However, in the case of A. africana and K. senegalensis populations seemed to be mostly threatened in the protected area. We concluded that although the studied protected area is effective to conserve some habitats species compositions, protection is not sufficient to guarantee future conservation of some threatened tree species.  相似文献   

6.
7.
Man made ecosystems of dry lands are key habitats due to their ecological characteristics to survey biodiversity. This study investigated bird diversity in three oases of the Northern Algerian Sahara (i.e., Biskra in 2006, Oued Souf in 2008 and Ouargla in 2009), by using the spot-mapping method. Bird density “D” (pairs/10 ha), species richness “S” (number species), diversity (Shannon index) “H′” (in bits), and evenness “E” varied from one oasis to another (Biskra: D = 98.5, S = 47, H′ = 4.49, E = 0.81; Oued Souf: D = 96, S = 33, H′ = 3.9, E = 0.77; Ouargla: D = 91.5, S = 44, H′ = 4.39, E = 0.80). Differences in bird diversity between the monitored palm groves are due to the ecological characteristics of each environment. Documented literature outlined close taxonomic similarities between bird assemblages of the study area with many Northern Saharan oases. The Hybrid Sparrow Passer domesticus x Passer. hispaniolensis and some Columbidae species including Columba livia, Streptopelia turtur, Streptopelia senegalensis, and Streptopelia decaocto were the abundant species throughout surveyed oases in which they represented more than half (55.6%) of the sum of species densities (D = 286 pairs/10 ha). These synthropic species have known a huge expansion of their distribution range throughout Algerian oases. The correspondence analysis allowed the aggregation of both families and species into oasis they belong to. One-way ANOVA was tested to analyse variations of both family and species densities between studied oases. The ANOVA revealed there was no significant variation either in family densities (p = 0.937) or in bird densities (p = 0.622) between the surveyed oases because of the small size of bird populations.  相似文献   

8.
Woody vegetation dynamics and Dracaena cinnabari regeneration have been studied for five years in the conditions of Socotra Island. Woody plants were measured regularly inside and outside the exclosure area, and the growth and survival of D. cinnabari seedlings were observed. In the exclosure of about 1000 m2 a total of 49 species were identified, including 23 endemics, growing in the average density of 3.82 specimens per m2. The fenced area was overgrown relatively rapidly by dense grass cover – reaching approx. 2.7 t/ha. Species growth dynamics inside and outside the exclosure shows that grazing had a marked impact, leading to the elimination of trees and shrubs. All grazed species grew noticeably in the exclosure, in the average of 50 cm in 5 years. D. cinnabari as the dominant flagship species of Socotra has been studied with regards to regeneration dynamics. Observations indicate that probability of its seedlings survival increases with their age. No seedlings germinated from the seeds sown in the experiment, however, outplanted seedlings performed relatively well. Field observations show that D. cinnabari seed germination is triggered when the seed reaches a protected micro-habitat with a developed humus layer and high relative humidity in the soil lasts for at least two days.  相似文献   

9.
10.
《Ecological Engineering》2007,29(3):232-244
Urban wetlands typically have few plant species. In wetlands designed to improve water quality, nutrient-rich water and highly variable water levels often favor aggressive, flood-tolerant plants, such as Typha × glauca (hybrid cattail). At Des Plaines River Wetlands Demonstration Site (Lake Co., IL), we assessed T. × glauca dominance and plant community composition under varying hydroperiods in a complex of eight constructed wetlands. Plots flooded for more than 5 weeks during the growing season tended to be dominated by T. × glauca, while plots flooded fewer days did not. Plots with high cover of T. × glauca had low species richness (negative correlation, R2 = 0.72, p < 0.001). However, overall species richness of the wetland complex was high (94 species), indicating that wetlands in urbanizing landscapes can support many plant species where T. × glauca is not dominant. T. × glauca-dominated areas resisted the establishment of a native plant community. Removing T. × glauca and introducing native species increased diversity initially, but did not prevent re-invasion. Although 12 of the 24 species we seeded became established in our cleared plots, T. × glauca rapidly re-invaded. In year 1, T. × glauca regained an average of 11 ramets m−2, and its density doubled in year 2. The likelihood of planted species surviving decreased as duration of inundation increased, and in both seeded and planted plots, graminoids had greater survivorship through year 2 than forbs across a range of water levels. Within 4 years, however, T. × glauca was the most common plant, present in 92% of the cleared plots. Simply removing T. × glauca and adding propagules to an urban wetland is not sufficient to increase diversity.  相似文献   

11.
The objective was to identify legume shrub species for development of agroforestry technologies based on seed and forage (leaves and twigs < 10 mm diameter) yield, and determinants of forage quality. Ten individual plants of Bituminaria bituminosa ‘Ecotypes 1’, B. bituminosa ‘Ecotypes 2’, Medicago citrina, and M. arborea from Spain; Colutea istria and Onobrychis aurantiaca from Syria; C. istria from Jordan; Chamaecytisus mollis from Morocco; and Coronilla glauca from France were randomly selected from plots established in a non-tropical dryland environment in northwest Syria in 2000. Five individual plants of each species were cut back to 0.5 m above ground in March 2004. Coppice regrowths were pruned in December 2004 and April 2005 to determine forage yield and proportion of forage in the total above ground biomass (PEFB). Forage samples were analyzed for concentrations of crude protein (CP), lignin(sa), acid detergent fibre (ADFom), neutral detergent fibre (aNDFom), in vitro organic matter (OM) digestibility (IVOMD), and in vitro 24 h gas production (IVGP24h). Matured seeds were hand harvested from the remaining five plants of each species to estimate seed yield. Forage (21–250 kg DM/ha) and seed (0–200 kg DM/ha) yields; PEFB (0.22–0.96); and concentrations of CP (85–115 g/kg DM), lignin(sa) (14–42 g/kg DM), ADFom (94–170 g/kg DM), aNDFom (122–217 g/kg DM), IVOMD (456–617 g/kg OM), and IVGP24h (27–42 ml 200 mg/DM) varied (P<0.05) among shrub species. The IVOMD and IVGP24h were positively correlated (r = 0.75, P<0.032), whereas IVOMD and IVGP24h were negatively correlated with ADFom, lignin(sa) and aNDFom. In terms of forage and seed yields and determinants of forage quality, C. istria from Jordan, M. arborea, B. bituminosa ‘Ecotype-2’, C. istria and O. aurantiaca have higher potential than C. mollis, C. glauca and B. Bituminosa ‘Ecotype-1’ for the development of agroforestry technologies in non-tropical dry areas.  相似文献   

12.
We devised a probability distribution model that best expressed species richness per quadrat in grassland communities, and clarified the mechanism by which the mean richness per quadrat was always larger than the variance among quadrats. Our model will aid in the understanding of community structures, and allow comparisons among different communities. The model was constructed based on relatively simple theoretical assumptions about the mechanisms in play in target communities. We assumed in the model that the number of species occurring in an actual quadrat, j, is the sum of “the fundamental number of species”, k (constant), and “a fluctuating number of species”, i (a Poisson variate with the mean of μ); that is, j = k + i, where i, j and k are non-negative integers. The probability that j species occur in a quadrat is given by a Poisson-like distribution (extended Poisson), with two parameters k and μ. The mean species richness in the probability distribution is expressed by λ (= k + μ), and the variance is λ  k. The proposed model afforded a good fit for the observed frequency distribution of species richness per quadrat. If even one species is common among many quadrats, the mean number of species per quadrat is greater than the variance. The greater the number of common species among quadrats is, the larger is the value of k, and then the more pronounced is the difference between the mean and the variance (although the variance does not change). We fitted the model to 55 datasets collected by ourselves from grasslands in various locations (Tibet, Inner Mongolia, Slovakia, or Japan), with varying quadrat size (0.25, 0.0625, or 0.01 m2), and under differing management status (various stocking densities).  相似文献   

13.
The legumes (Fabaceae) Genista monspessulana and Spartium junceum are major invaders in several other parts of the world, but not yet so in South Africa. We determine their current distributions in South Africa at different spatial scales, assess population structure (soil seed banks and size at reproduction) evaluate current management activities, and provide recommendations for control (including assessing the feasibility of nation-wide eradication). G. monspessulana occurs at nine localities in three quarter-degree cells, covering a total of 22.7 ha. S. junceum is much more widespread, occurring in 33 quarter-degree cells and is frequently cultivated in private gardens. All naturalised or invasive populations are in disturbed areas, mostly along roadsides. Once established, G. monspessulana and S. junceum accumulate large, persistent soil-stored seed banks, ranging in size between 909 and 22,727 (median 1970) seeds/m2 and 0 and 21,364 (median 455) seeds/m2 for the two species respectively. Both species resprout vigorously after cutting and stump herbicide application (60% of G. monspessulana and 43% of S. junceum plants resprouted) which necessitates regular follow-ups. We estimate that over 10 years, at a cost of about ZAR 81,000 (1 ZAR = 0.114 US$ as on 6 October 2012), G. monspessulana could be extirpated from South Africa. S. junceum is far more widespread and coupled with low effectiveness of control, abundance of seeds and seed longevity, eradication is unfeasible. We recommend that control methods used for S. junceum be improved to prevent resprouting, and that areas are managed to limit the movement of seeds and avoid further spread and establishment. Further studies are required to understand why these two species have failed to replicate the invasiveness shown in other parts of the world.  相似文献   

14.
《Small Ruminant Research》2007,67(1-3):64-69
Wheat (Triticum aestivum L.) pastures are increasingly being used for cool-season forages to complement range-based goat production systems in southern USA. Because goats are more selective than cattle, ideal nitrogen (N) fertilizer rates already established for wheat grazed by cattle may be different for goats. Weight gains of Boer X Spanish doe kids (average 17 kg) as well as forage yields and crude protein (CP), acid detergent fiber (ADF) and acid detergent lignin (ADL) concentrations were measured for two winter seasons on replicated wheat paddocks fertilized with 0, 56, 112 and 224 kg N/ha per season in split autumn/spring applications at Stephenville, TX, USA. Animals were stocked in the pasture at 20 head/ha from January to April 2003 (478 mm rainfall from September to March) and 2004 (355 mm rainfall). Available forage ranged from 50 to 200 kg/ha in January and from 2300 to 6300 kg/ha in April in the 0 and 224 kg N/ha paddocks, respectively. Crude protein dry matter (DM) concentration ranged from 25 to 34% (0 and 224 kg N/ha, respectively) in January, but down to 13 and 22% across treatments in April. Average daily gains (ADG) over the 90-day trial were similar both years, 68 g per head per day for the 0 N treatment and undifferentiated among the fertilized paddocks, all near 90 g per head per day. Results indicate that N fertilizer rates above 56 kg/ha per season do not increase ADG/kid, but will increase ADG/ha if stocking rates are adjusted for forage production.  相似文献   

15.
《Journal of Asia》2014,17(4):647-651
The veiled polypore, Cryptoporus volvatus, is distributed widely in North America and East Asia and is believed to have a mutualistic relationship with coleopteran species—the fungus providing food and shelter in basidiocarps and beetle helping disperse spores.Seventy fresh basidiocarps of C. volvatus were collected from the Japanese red pine (Pinus densiflora) in the spring season of 2013 from two sites in Korea. A total of 251 insects (101 adult and 150 larvae) were collected from the inside of basidiocarps and identified using morphology and mitochondrial cytochrome c oxidase subunit I (COI) sequences. Six species belonging to five coleopteran families were identified. The number of spores attached to the bodies of adult insects was counted and average spore counts for each of the six species ranged between 1.0 × 104 and 5.2 × 105 spores/individual. Across localities, three species were shared (Aethina suturalis, Trogossita japonica and Parabolitophagus felix) and carried spores at high densities on their bodies, making them more likely to aid in spore dispersal.  相似文献   

16.
Leptadenia reticulata (Retz.) Wight. & Arn. is an important medicinal plant, belongs to the family Asclepiadaceae. This plant is known for its medicinal uses since 4500 BC. Presently this is an endangered species (Arya et al., 2003). Six shoots (2–4 cm long) per node differentiated on MS medium + 5.0 mg/l of BAP + additives. Incorporation of additives in the culture medium promoted growth of cultures. The shoots differentiated per explant were repeatedly transferred on to fresh MS + 1.0 mg/l of BAP + 0.1 mg/l of NAA and additives. The regenerated shoots were subcultured for further multiplication on MS + 1.0 mg/l BAP + 0.5 mg/l Kin + 2-iP (0.5 mg/l) and 0.1 mg/l of NAA + additives regularly after an interval of 3 weeks. Addition of ammonium sulphate in the medium resulted in increase in shoot number and promoted elongation also growth of cultures was sustained even if subculturing was delayed (26 ± 2 days). Success was also achieved in defining protocol for in vitro regeneration of shoots from petiole derived callus. Shoots regenerated in vitro by both processes were rooted in vitro on 1/4 strength of MS medium + 3.0 mg/l of IBA after 15–20 days. Cent percent of the shoots rooted ex vitro, if the in vitro regenerated shoots were treated with 200 mg/l of IBA. The in vitroex vitro rooted plantlets were hardened under different regimes of temperature and humidity in a greenhouse. The hardened plantlets were transferred to soil in polybags. More than 95% plants survived in field conditions. Total dry biomass harvested per year was 2800 kg/acre.  相似文献   

17.
Despite of the generalized expansion of wild ungulates in Europe, roe deer (Capreolus capreolus) is experiencing contrasted population trends; it is expanding in some regions while declining in others likely due to the expansion of other deer species. In both extremes, reliable methods to estimate population abundance are required. We evaluated different methods of estimating deer abundance in Mediterranean woodlands based on pellet group counts. Distance Sampling applied to pellet counts and a new easier and cost-effective method based on strip-variable transect counts (FST) were assessed comparing their estimates (pellet group density) with the abundance indices obtained from traditionally used reference methods (faecal standing crop) in 61 localities (n = 183 surveys). The average roe deer density estimated from faecal standing crop was 5.56 ± 0.75 (range 0.01–20.74) deer per 100 ha. Distance Sampling and FST estimates correlated with reference methods. As a first conclusion it may be noted that all indirect methods used here can be used to estimate roe deer abundance. The selection of a given method based on pellet counts to estimate roe deer population abundance should take into account the specific objectives of the research, resources available, and the timescale in which the information is required. Among them, Distance Sampling may be used when human resources and skills are enough but FST is a rapid and efficient alternative to estimate pellet group density when they are not.  相似文献   

18.
《Ecological Indicators》2008,8(5):454-461
In order to evaluate the dispersal pattern of airborne fluoride emissions, from a single source in the city of Ouro Preto, Brazil, the fluoride impact on some herbaceous plant species was studied using the plants as passive bioindicators. Foliar fluoride contents of eight species collected at different distances from an aluminium smelter were analyzed. The plant species were: Baccaharis dracunculifolia, Bidens pilosa, Borreria verticillata, Calopogonium mucunoides, Erigeron bonariensis, Hedychium coronarium, Ipomoea purpurea and Ipomoea cairica. In all species the fluoride accumulation decreased exponentially with the distance from the emission source. There was specific and distinct variation in fluoride accumulation among the species, a group of high-accumulator species (B. dracunculifolia and Bidens pilosa) and a group of low-accumulator species (I. cairica, H. coronarium and Borreria verticillata). C. mucunoides and E. bonariensis occupied an intermediate position. There was a pattern of plant contamination response during the periods analyzed. The plants nearest to the emission source, between 0.4 km northwest and 1.1 km east, showed fluoride contamination traits in leaves reaching values between 100 and 500 μg g−1. Moreover, fluoride contents higher than 1000 μg g−1 were found in these plants. At the most distant stations, situated 2.9 km northwest and 6 km east from the factory, the fluoride content of the dry matter was less than 10 μg g−1 showing that plants at those distances were submitted to minimum contamination. There were different patterns of tolerance among the species analyzed. While B. dracunculifolia accumulated fluoride up to 1500 μg g−1 in dry matter without any signs of injury, Borreria verticillata showed severe necrosis in leaves, but the fluoride content found was not higher than 120 μg g−1.  相似文献   

19.
Foraging efficiency of Lysiphlebus fabarum Marshall, the most abundant and effective parasitoid of the black bean aphid, Aphis fabae Scopoli, in terms of functional and numerical responses and mutual interference, was studied on broad bean plants in a growth chamber at 21 °C, 70 ± 5% RH and a photoperiod of 16:8 (L:D) h. Using logistic regression, a type II functional response was determined for L. fabarum. Nonlinear least-square regression was used to estimate the searching efficiency (a') and handling time (Th). Numerical response of L. fabarum to cumulative host densities was partially linearly increasing. Nicholson's model and linear regression were used to determine the per capita searching efficiency and interference coefficient, respectively. In general, the per capita parasitism and, consequently, the per capita searching efficiency decreased significantly as parasitoid density increased. Mutual interference and quest constants were ? 0.508 and ? 0.697, respectively. The results of this study suggest that both the host and parasitoid densities have no significant impact on the progeny sex ratio. The information provided here will be useful in assessing the efficiency of L. fabarum as a biological control agent of A. fabae, devising mass-rearing protocols and implementing release programs for this parasitoid.  相似文献   

20.
The Iberian wild goat (Capra pyrenaica) is an endemic species of the Iberian Peninsula. Of the four generally accepted subspecies (Capra pyrenaica victoriae, C.p. hispanica, C.p. pyrenaica, C.p. lusitanica) only two subsist (C.p. victoriae, C p. hispanica). The subspecies once found in Portugal, C. p. lusitanica, became extinct in the 19th century. However, the reintroduction of the C. p. victoriae in north-west Spain, led to the natural recolonization of this subspecies into Portugal. Knowledge of the Iberian wild goat in Portugal is still limited, making it difficult to evaluate the major conservation/management needs. To fill this gap, here we describe the historical distribution of the Iberian wild goat in Portugal and summarize the available information on the reintroduction and recolonization process of this species. Additionally, we used line itinerary survey (2011–2012), coupled with Distance Sampling, to estimate current densities, range and population structure of the Iberian wild goat distribution in Portugal. The Iberian wild goat density is 2.78/100 ha (95% CI: 1,72–4,50; CV: 18,36%) and the abundance is of 576 (CI 95%: 356–930; CV: 18,36%). The distribution data shows that the population is divided in three nuclei: 1- Serra do Gerês (13,840 ha); 2–Serra Amarela (1235 ha); 3–Castro Laboreiro (343 ha), in a total area of 15,418 ha. Iberian wild goat population in Portugal has greatly increased in the last years, both in number and distribution range. The demographic data shows a potential for increase in the next years but our current ecological background knowledge still remains limited. Iberian wild goat management will benefit from a long-term project including public awareness, scientific research and management solutions.  相似文献   

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