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1.
Ovadia O  Schmitz OJ 《Oecologia》2004,140(3):398-406
Weather can have important consequences for the structure and function of ecological communities by substantially altering the nature and strength of species interactions. We examined the role of intra- and inter-annual weather variability on species interactions in a seasonal old-field community consisting of spider predators, grasshopper herbivores, and grass and herb plants. We experimentally varied the number of trophic levels for 2 consecutive years and tested for inter-annual variation in trophic abundances. Grasshopper emergence varied between years to the extent that the second growing season was 20% shorter than the first one. However, the damage grasshoppers inflicted on plants was greater in the second, shorter growing season. This inter-annual variation in plant abundance could be explained using the foraging-predation risk trade-off displayed by grasshoppers combined with their survival trajectory. Decreased grasshopper survival not only reduced the damage inflicted on plants, it weakened the strength of indirect effects of spiders on grass and herb plants. The most influential abiotic factor affecting grasshopper survival was precipitation. We found a negative association between grasshopper survival and the total yearly precipitation. A finer scale analysis, however, showed that different precipitation modalities, namely, number of rainy days and average precipitation per day, had opposing effects on grasshopper survival, which were inconsistent between years. Furthermore, our results suggest that small changes in these factors should result in changes of up to several orders of magnitude in the mortality rate of grasshoppers. We thus conclude that in this system the foraging-predation risk trade-off displayed by grasshoppers combined with their survival trajectory and relevant weather variability should be incorporated in analytical theory, whose goal is to predict community dynamics.  相似文献   

2.
Because species interactions are often context‐dependent, abiotic factors such as temperature and biotic factors such as food quality may alter species interactions with potential consequences to ecosystem structure and function. For example, altered predator–prey interactions may influence the dynamics of trophic cascades, affecting net primary production. In a three‐year field experiment, we manipulated a plant–grasshopper–spider food chain in mesic tallgrass prairie to investigate the effects of temperature and food quality on grasshopper performance, and to understand the direct and indirect tritrophic interactions that contribute to trophic cascades. Because spiders are active at cooler temperatures than grasshoppers in our system, we hypothesized that predator effects would be strongest in cooled treatments, and weakest in warmed treatments. Grasshopper spider interactions were highly context‐dependent and varied significantly with food quality, temperature treatment and year. Spiders most often reduced grasshopper survival in the cooled and ambient temperature treatments, but had little to no effect on grasshopper survival in the warmed treatments, as hypothesized. In some years, plants compensated for grasshopper herbivory and trophic cascades were not observed despite significant effects of predators on grasshopper survival. However, in the year they were observed, trophic cascades only occurred in cooled treatments where predator effects on grasshoppers were strongest. Predicting ecosystem responses to climate change will require an understanding of how temperature influences species interactions. Our results demonstrate that changes in daily temperature regimes can alter predator–prey interactions among arthropods with consequences for ecosystem processes such as primary production and the relative importance of top–down and bottom–up processes.  相似文献   

3.
The abundance and distribution of aquatic insects may be controlled by factors at any stage of the life cycle. To understand the potential role of factors affecting egg and adult stages and oviposition, basic information on egg characteristics and oviposition behaviour is required. However, published information on New Zealand Ephemeroptera, Plecoptera and Trichoptera (EPT) is scattered and very limited. This review compiles current knowledge of New Zealand EPT egg characteristics and oviposition behaviour using published information and unpublished observations. Where direct observations are lacking, information on closely related species overseas, and inferences based on female morphology, are included. Eggs show a variety of physical characteristics that may influence egg retention, transport and distribution. Oviposition behaviour is highly selective among some taxa, but appears generalist among others, though the latter may still require specific cues. Identifying and providing for adult, egg and oviposition requirements may be fundamental to re-establishing EPT populations in restored aquatic habitats.  相似文献   

4.
Neotyphodium endophytes in introduced agronomic grasses are well known to increase resistance to herbivores, but little is known of interactions between Neotyphodium endophytes and herbivores in native grass populations. We investigated whether endophytes mediate plant-herbivore interactions in a native grass species, Festuca arizonica in the southwestern United States, in two ways. First, to test the prediction that the presence and frequency of endophyte-infected (E+) plants should increase with increasing herbivory, we determined endophyte frequencies over a 4-year period in six natural Arizona fescue populations. We compared Neotyphodium frequency among plants growing inside and outside long-term vertebrate grazing exclosures. Second, we experimentally tested the effects of Neotyphodium infection, plant clone, and soil nutrients on plant resistance to the native grasshopper Xanthippus corallipes. Contrary to predictions based upon the hypothesis that endophytes increase herbivore resistance, levels of infection did not increase in plants subjected to grazing outside of exclosures relative to ungrazed plants within exclosures. Instead, endophyte frequencies tended to be greater inside the exclosures, where long-term vertebrate grazing was reduced. The grasshopper bioassay experiment corroborated these long-term patterns. Survival of grasshoppers did not differ between infected (E+) and uninfected (E–) plants. Instead, mean relative growth rate of grasshoppers was higher on E+ grasses than on E– ones. Growth performance of newly hatched grasshopper nymphs varied among host plant clones, although two of six clones accounted for most of this variation. Our results suggest that Neotyphodium-grass-herbivore interactions may be much more variable in natural communities than predicted by studies of agronomically important Neotyphodium-grass associations, and herbivory is not always the driving selective force in endophyte-grass ecology and evolution. Thus, alternative hypotheses are necessary to explain the wide distribution and variable frequencies of endophytes in natural plant populations. Received: 15 February 1999 / Accepted: 19 July 1999  相似文献   

5.
We tested the ability of consumer-resource theory to predict direct and indirect interactions among species, using an experimental system of insect herbivores and herbaceous plants. Specifically, we examined interactions among three species of grasshoppers (Melanoplus femur-rubrum, Spharagemon collare, andPhoetaliotes nebrascensis; Orthoptera, Acrididae) and herbaceous plants in experimental field cages placed over existing fertilized or unfertilized vegetation in a Minnesota old field. For the conditions inside these cages, we addressed whether (1) grasshopper diet predicted the presence of competition among grasshopper species, and (2) direct effects of grasshoppers on plants produced indirect interactions among plants, grasshoppers and soil nitrogen. Overall,M. femur-rubrum ate a greater proportion of forbs in cages, while the other two species ate primarily grasses. As expected, a pair of grasshopper species competed if they had similar diets. However, there were important exceptions that could be explained from observed indirect effects, although alternative explanations were also possible. First, all three grasshopper species significantly shifted their diets in the presence of other species, and these shifts occurred most often when competition was expected or occurred. Second, the two grassfeeding species reduced the biomass of the dominant grass (Schizachyrium scoparium) and increased available soil nitrogen and biomass of forbs. This effect may explain why the grass-feedingP. nebrascensis had a positive effect on the forb-feedingM. femur-rubrum on unfertilized plots. Overall, we show that direct effects of consumers on resources can predict competition and other important indirect interactions within a community.  相似文献   

6.
The indirect effects of native generalist insect herbivores on interactions between exotic and native grassland plants have received limited attention. Crested wheatgrass ( Agropyron cristatum ) is the most common exotic rangeland grass in western North America. Crested wheatgrass communities are resistant to colonization by native plant species and have strong competitive effects on native species, imposing problems for the restoration of native grasslands. Grasshoppers are generalist herbivores that are often abundant in Crested wheatgrass–dominated sites in the northern Great Plains. We conducted two experiments in a Crested wheatgrass–dominated grassland in western North Dakota to test the hypothesis that grasshopper herbivory influences local Crested wheatgrass community composition by impeding native seedlings. Grasshopper herbivory negatively affected the species richness, abundance, and Shannon diversity of native plants in 3 of 4 years. Although additional research is needed to determine if grasshoppers actively select native plants, the effects of grasshopper herbivory may be an important consideration in the restoration of Crested wheatgrass areas. Our findings illustrate the importance of understanding the impact of native generalist invertebrate herbivores on the relationships between exotic and native plants.  相似文献   

7.
1. The dynamics of parasitic organisms depend critically upon the frequency distribution of parasite individuals per host. However, the processes giving rise to this frequency distribution have rarely been modelled and tested for organisms with complex host selection behaviour. 2. In this study Microrhopala vittata, a chrysomelid beetle, was used to investigate how oviposition behaviour, movement and density of host plants interact in shaping the frequency distribution of egg clusters per host in the field. 3. Enclosures were stocked with two different host species and different beetle densities and various stochastic process models were fitted to egg cluster count data obtained from these enclosures. The different models were derived considering different scenarios, in particular whether or not plant density limits oviposition rate, whether or not ovipositing females actively seek out the most attractive plant within their perception radius and whether a female's oviposition rate is determined by plant intrinsic factors, the plant's egg cluster load or the surrounding beetle density. 4. The model parameters fitted to cage data were used to describe the frequency distribution of egg cluster counts obtained in a release experiment in the field. A total of 220 beetle pairs were released at five locations in a field where this beetle was not observed previously. Each release point was at a border between the two host species. 5. One model predicted for the preferred host species the egg cluster count frequencies in the field from parameters estimated in the cages. This model assumed that egg clusters present on a plant increased subsequent oviposition on this plant. All other models could not describe the distribution of egg cluster counts for either of the two host species. 6. The results suggest that females seek out attractive hosts actively and the attractiveness of a plant increases with its egg cluster load. This behaviour creates a frequency distribution of egg clusters per host that depends only on beetle density but not on plant density. This conclusion has important implications for modelling insect-plant interactions.  相似文献   

8.
Abstract.  1. Few entomological studies include soil-dwelling insects in mainstream ecological theory, for example the preference–performance debate. The preference–performance hypothesis predicts that when insect herbivores have offspring with limited capacity to relocate in relation to a host plant, there is a strong selection pressure for the adult to oviposit on plants that will maximise offspring performance.
2. This paper discusses the proposition that insect herbivores that live above ground, but have soil-dwelling offspring, should be included in the preference–performance debate. Twelve relevant studies were reviewed to assess the potential for including soil insects in this framework, before presenting a preliminary case study using the clover root weevil ( Sitona lepidus ) and its host plant, white clover ( Trifolium repens ).
3. Maternal S. lepidus preferentially oviposited on T. repens plants that had rhizobial root nodules (which enhance offspring performance) rather than T. repens plants without nodules, despite plants having similar foliar nutritional quality. This suggests that adult behaviour above ground was influenced by below-ground host-plant quality.
4. A conceptual model is presented to describe how information about the suitability for offspring below ground could underpin oviposition behaviour of parental insects living above ground, via plant- and soil-mediated semiochemicals. These interactions between genetically related, but spatially separated, insect herbivores raise important evolutionary questions such as how induced plant responses above ground affect offspring living below ground and vice versa.  相似文献   

9.
刘慧  廉振民  常罡  孔光耀 《昆虫知识》2007,44(2):214-218
应用种-多度分布模型、多样性指数、相似性分析、主成分(PCA)分析及多元逐步回归等方法比较了洛河流域不同生境的蝗虫群落结构。结果显示:洛河流域各生境的蝗虫分布基本上服从Preston对数正态分布,其中以森林拟合的最好。各多样性指数的变化趋势均为森林>森林草原>河滩和农田>典型草原。在相似性分析中,典型草原、森林草原和森林这3种生境相似性很高,而河滩和农田则是完全不同的另一种生境。对各生境植被因素和蝗虫群落所进行的主成分分析,结果非常理想,两维主成分的累计方差贡献率分别达到了92.558%和78.566%。通过多元逐步回归发现,影响蝗虫种类和数量变化的植被因有草本植物高度多样性、树木盖度、豆科优势度、禾本科优势度和其他科优势度等。  相似文献   

10.
1. Adaptive phenotypic plasticity has been a major subject in evolutionary ecology, but how a species' behaviour may respond to certain environmental change is still not clear. In grasslands worldwide, large herbivores are increasingly used as a tool for grazing management, and occur to interact with grasshoppers that dominate grassland insect communities. Previous studies have been well-documented about grazing effects on diversity and abundance of grasshoppers. Yet, how grazing may alter grasshopper behaviour, and potential effects on their abundance remains elusive. 2. We conducted a field experiment by manipulating grazing using sheep, cattle, and their mix to examine the behavioural responses and abundance of the grasshoppers (Euchorthippus unicolor) to grazing in a Leymus chinensis-dominated grassland. 3. Results showed that the grasshoppers spent less time on feeding and resting on grasses, but more time on switching and resting on forbs under cattle grazing and mixed grazing with cattle and sheep. In contrast, the grasshoppers spent more time on feeding but less time on switching and resting on forbs under sheep grazing. The behavioural changes were also potentially linked to grasshopper abundance in the context of grazing management. 4. The responses of grasshopper behaviour and abundance to grazing may be largely triggered by altered vegetation and microclimates. Such behavioural flexibility of grasshoppers must be considered when large herbivores are recognised as a management tool for influencing grasshopper abundance, and grazer species should be paid more attention both individually and jointly for better grassland conservation.  相似文献   

11.
Interactions between above‐ and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above‐ and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial‐feeding and 3) reduce plant‐feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species‐rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni‐carnivorous nematodes were evaluated in relation to plant community composition. Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom‐up control of the nematodes. However, our results show that above‐ and belowground insect herbivores may facilitate root‐feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores.  相似文献   

12.
To examine the relative importance and interactions of trophic and non-trophic effects of plant invasions on herbivores, we investigated how the invasion of weeping lovegrass Eragrostis curvula impacted Eusphingonotus japonicus, a food generalist grasshopper endemic to gravelly floodplains with sparse vegetation in Japan. Field observations and laboratory experiments showed that the grasshopper fed mainly on herbs endemic to the gravelly floodplains, which were negatively impacted by the alien grass. The alien grass was not consumed as food. Field censuses also showed that the abundance of the grasshopper was positively correlated with the coverage of endemic herbs in a plot where weeping lovegrass was not dominant. Dominance of the grass (i.e., habitat modification for E. japonicus) negatively impacted the grasshopper and weakened the positive relationship between the grasshopper and endemic herbs. These results suggest that an understanding of the relationship between non-trophic and trophic effects is essential to predict the impacts of plant invasions on herbivores.  相似文献   

13.
植物表皮蜡质中的饱和链烷作为内源指示剂广泛用于评价放牧家畜的食性和食量, 但用于天然草原蝗虫食性的评价研究较少。为了探讨天然草原蝗虫的食性及其生态位变化, 本研究以内蒙古天然草原为研究对象, 于2003年7-8月沿降水梯度选择3种典型植物群落(小针茅Stipa klemenzii、 羊草Leymus chinensis和大针茅Stipa grandis群落), 在每个植物群落不同放牧压力下小区随机做20个植被样方, 样方内植物齐地面刈割, 测定其地上生物量和物种多样性, 取主要植物种测定其链烷模式, 同时采集放牧小区优势蝗虫种亚洲小车蝗Oedaleus asiaticus的粪便, 测定其链烷模式, 运用链烷技术评价蝗虫的食性及其营养生态位。结果表明: 不同植物群落中优势牧草种类及其比例不同, 其链烷模式存在种间差异, 链烷技术可以评价亚洲小车蝗的食性。亚洲小车蝗的食性在不同植物群落及不同放牧压力下存在显著的差异, 在羊草和大针茅群落中, 亚洲小车蝗是禾草采食者, 主要采食羊草和糙隐子草Cleistogenes squarrosa, 且与绵羊的营养生态位重叠指数较低, 分别为0.0619和0.0172; 在小针茅群落中亚洲小车蝗是杂类草采食者, 主要采食无芒隐子草Cleistogenes songorica、 猪毛菜Salsola collina和小针茅, 且与绵羊的营养生态位重叠指数较高, 达到0.1815。因此, 放牧不仅改变了群落的植物种类组成, 而且直接影响了亚洲小车蝗的食物组成, 二者对食物资源利用存在一定程度的竞争。  相似文献   

14.
Abstract.  1. It is commonly assumed that arthropod species living or hibernating in the soil would not be affected by grassland fires, even though burning results in elevated surface and below-ground soil temperatures. The importance of elevated below-ground soil temperatures during fires on the survival of grasshopper eggs had not been examined.
2. The effects of simulated autumn grassland fires of varying intensities on below-ground egg mortality were examined with grasshopper species laying shallow egg pods ( Ageneotettix deorum ) and deeper egg pods ( Melanoplus sanguinipes ) to test the hypothesis that exposure to heat during fires was the mechanism responsible for population reductions in A. deorum following fire.
3. Species-specific oviposition characteristics mediated the effects of fire intensity on below-ground egg mortality. The results indicate that fires occurring in areas with at least 3100 kg ha−1 standing crop biomass would be expected to significantly reduce populations of A. deorum , but not M. sanguinipes . No A. deorum eggs hatched in 12 of the 14 oviposition containers subjected to simulated fires approximating a standing crop biomass of 4500 kg ha−1. This is the first study to link field observations of rangeland insect populations following fire to mechanisms related to below-ground egg mortality.  相似文献   

15.
H. G. Robertson 《Oecologia》1987,73(4):601-608
Summary Oviposition by Cactoblastis cactorum on Opuntia ficus-indica and O. aurantiaca was assessed from the positioning of egg sticks on plants in the field. The number of egg sticks laid on O. ficus-indica plants was affected by: (1) plant size; (2) moth emergence near the plant; (3) cladode condition; and (4) plant conspicuousness. These factors contributed towards the clumping of egg sticks on plants. There was no apparent oviposition preference for one of the two host plant species despite the fact that egg predation was higher and fecundity lower on O. aurantiaca. The selection of a site for oviposition on the host plants was influenced by: (1) cladode condition; (2) height above ground; and (3) shelter from wind during oviposition. Succulent cladodes were the favoured sites for oviposition. The evidence suggests that in C. cactorum, oviposition site selection is largely the net result of a compromise between oviposition behaviour selected for increasing the probability of juvenile survival and oviposition behaviour selected for increasing the probability of laying the full complement of eggs. In addition, environmental and physiological factors such as wind and wing-loading, are thought to place constraints on the range of sites available for oviposition.  相似文献   

16.
To clarify factors causing mortality of Leptocorisa chinensis Dallas (Hemiptera: Alydidae) eggs in rice fields, sentinel egg masses were exposed for seven days in two rice, Oryza sativa L. (Poaceae), fields. An insecticide was sprayed to remove natural enemies in one-half of each field before exposing egg masses to predation. An egg mass containing 14 eggs was glued to a plastic label, and 21 egg masses each were placed in the sprayed and unsprayed control plots. During exposure, the number of hatched and missing eggs was observed daily. Egg predators were sampled in the fields before and after insecticide application. After the egg masses were retrieved from the fields, mortality factors of the unhatched eggs were assessed in the laboratory. The mean number of hatched and missing eggs was not significantly different between the sprayed and control plots in field A. In field B, however, the numbers were significantly different. The percentage of missing eggs in damaged egg masses ranged from 80 to 100%. In the laboratory, we observed that feeding marks caused by the grasshopper Conocephalus chinensis (Redtenbacher) were similar to those on the eggs exposed in the rice fields. The density of C. chinensis was low in control plots of field A. In contrast, the density was high in those of field B. These observations suggest that the density of egg predators, e.g., C. chinensis, is a mortality factor of L. chinensis eggs in rice fields.  相似文献   

17.
Abstract.  1. Predation risk to insects is often size- or stage-selective and usually decreases as prey grow. Any factor, such as food quality, that accelerates developmental and growth rates is likely to reduce the period over which prey are susceptible to size-dependent predation.
2. Using field experiments, several hypotheses that assess growth, development, and egg production rates of the rangeland grasshopper Ageneotettix deorum (Scudder) were tested in response to combinations of food quality and predation risk from wolf spiders to investigate performance variation manifested through a behaviourally mediated path affecting food ingestion rates.
3. Grasshoppers with nutritionally superior food completed development ≈ 8–18% faster and grew 15–45% larger in the absence of spiders, in comparison with those subjected to low quality food exposed to spider predators. Growth and development did not differ for grasshoppers feeding on high quality food when predators were present in comparison with lower quality food unimpeded by predators. Responses indicated a compensatory relationship between resource quality and predation risk.
4. Surviving grasshoppers produced fewer eggs compared with individuals not exposed to spiders. Because no differences were found in daily egg production rate regardless of predation treatment, lower egg production was attributed to delayed age of first reproduction. Results compare favourably with responses observed in natural populations.
5. Risk of predation from spiders greatly reduced growth, development, and ultimately egg production. Increased food quality counteracts the impact of predation risk on grasshoppers through compensatory responses, suggesting that bottom-up factors mediate effects of spiders.  相似文献   

18.
The population dynamics of two grasshoppers (Melanoplus femurrubrum and M. sanguinipes) were studied using experimental microcosms over 8 years at a Palouse prairie site in Montana. Grasshopper density, survival and reproduction in the experimental populations responded in a density-dependent fashion to natural and experimental changes in food availability for all grasshopper developmental stages, both within and between all years. We observed that field populations of the grasshoppers at the site exhibited density, survival and reproductive responses similar to the experimental populations over the period of the study. Because we could not identify any differences between the field and microcosm environments or the grasshopper individuals in them, we contend that field populations were ultimately limited by food within and between years. Density-dependent food limitation occurred for all age categories over the entire summer, because food abundance declined relative to grasshopper food requirements over the summer. Food limitation occurred between years, because in years with the lowest food abundance, the populations produced more hatchlings for the next year than could be supported by the highest observed food abundance. Finally, the observed annual changes in food abundance were correlated with the annual variation in weather (rainfall and temperature), which indicated that the long established relationship between grasshopper densities and weather conditions does not imply population limitation by density-independent processes.  相似文献   

19.
Most members of the superfamily Acridoidea (Orthoptera) oviposit in the soil, but some species oviposit directly on or in tissue of host plants. Oviposition in association with host plants has been reported for only 6% of acridoid species for which oviposition behaviour is known, hut the behaviour is systematically and geographically widespread, including members of two families and seven acridid subfamilies on three continents. This distribution suggests that host plant oviposition by grasshoppers has evolved independently at least eleven times in the world's grasshoppers fauna. A comparative approach to investigating oviposition on host plants shows that it tends to occur in species of inundated habitats and tropical forests, in species with narrow diets, and is correlated with a reduction in clutch size.  相似文献   

20.
In East Africa, traditional pastoralists increase landscape heterogeneity by creating traditional livestock corrals (bomas). When these bomas are abandoned, they serve as long‐term hot spots of increased nutrients and unique vegetation. However, the effect of bomas on insect populations is unclear. Grasshopper (Suborder Caelifera) assemblages are thought to reflect vegetation, and within Caelifera, the subfamily Oedipodinae is known to be associated with degraded areas. We sampled vegetation and collected grasshoppers inside of abandoned bomas, 50 m from abandoned bomas and 250 m from abandoned bomas. Bomas had significantly lower grass abundance than background vegetation. Total grasshopper abundance was positively correlated with grass and forb abundance, while the proportion of grasshoppers in the subfamily Oedipodinae was negatively correlated with grass abundance. Grasshopper abundance was significantly lower inside of bomas than outside of them, but the proportion of grasshoppers in the subfamily Oedipodinae was significantly higher inside of bomas than outside of them. This suggests that the decreased vegetation in abandoned bomas supports fewer grasshoppers, but a higher fraction of the grasshopper assemblage in abandoned bomas is composed of Oedipodinae. Thus, traditional pastoralists can have long‐term effects on the size and composition of grasshopper assemblages through the use of bomas.  相似文献   

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