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1.
谈冰畅  朱小龙  宁晓雨  谷娇  安苗  李宽意 《生态学报》2015,35(10):3199-3203
在室外受控实验条件下,研究了不同密度(0,150,450个/m2)纹沼螺(Parafossarulus striatulus)对沉水植物苦草(Vallisneria spiralis)生长的影响。结果表明,螺类牧食活动促进了苦草生长,与无螺对照组相比,低密度螺处理组中苦草的相对生长率、株高均增加了20%;高密度组中苦草的相对生长率、叶片数和株高分别增加了28%、15%和27%。分析表明,纹沼螺通过牧食活动降低植物叶片上附着生物干重,从而促进了苦草生长。丰富了螺-草互利关系的研究内容,有助于加深理解水生态系统中生物之间的生态关系。  相似文献   

2.
Heller  Joseph  Abotbol  Avi 《Hydrobiologia》1997,344(1-3):65-73
The freshwater snail Melanopsis praemorsa is veryabundant inoases of the Judean Desert. To determine its role as littershredder, experiments were carried out in Nahal Arugot. Boxeswereplaced in the stream (29 °C), each containing 1 g ofdrywillow leaves together with one snail; or six snails.With one snail per box, dry leaf weight after two daysdeclined to72% of the initial dry weight, after twelve days to 58% andaftereighteen days to only 40%. During this period thesnails in the experiment increased by 12% in shell-height, by20%in snail weight (including the shell), by 33% in live freshbiomass. Each snail consumed about 10 mg litter per day.With six snails per box, dry leaf weight after two daysdeclined to62% of the initial dry weight and after twenty days to only15%.In natural populations where density was 44 snails per quadrat(of25×25 cm), 1 g of dry leaves was reduced to 25%theinitial weight within three days. Overall plant cover along a600×10 m stretch of the stream was found to be45%, ofwhich 65% was willow. During one year about 1 kg litter wasshedper m2 willow; by extrapolation, this would be about1800 kglitter throughout the stretch. Much of this vast amount oflitteris consumed by the snails, who thereby reduce summer dammingof theoasis. Our study suggests that M. praemorsa, a generalistfeeder, may be a major litter shredder in certain desert oasisecosystems.  相似文献   

3.
  • 1 The effects of epiphyton grazing and nutrient recycling by the freshwater snail Planorbis planorbis on the growth of the macrophyte Ceratophyllum demersum were examined in laboratory experiments.
  • 2 Ceratophyllum plants grown in the presence of snails, or in water chemically conditioned by snails, were significantly longer, had more healthy nodes of leaves, and more growing tips than Ceratophyllum plants grown in isolation. There were no significant differences between the growth of plants that were grazed by snails, and those plants which received water chemically conditioned by snails.
  • 3 Adult P. planorbis released 3.74 × 10?4μg phosphate, 23.9 × 10?4μg nitrate, 4.38 × 10?4μg ammonia, and 0.79 × 10?4μg of urea mg?1 wet weight of snail h?1. Measurements of these chemicals in the experimental systems suggested that ammonia was an important nutrient in stimulating the growth of Ceratophyllum.
  • 4 Removal of epiphyton by grazing snails significantly prolonged the life of individual Ceratophyllum leaves compared to ungrazed leaves.
  相似文献   

4.
“螺-草”的互利关系   总被引:15,自引:2,他引:13  
水生态系统中存在螺-草互利现象。然而,植食性螺类与水生植物之间是否存在这种互利关系目前尚无定论。椭圆萝卜螺(肺螺亚纲)与铜锈环棱螺(前腮亚纲)是常见的淡水螺类,其中,椭圆萝卜螺能牧食多种水生植物的活体。通过室外实验,研究了这两种螺类在不同密度条件下对沉水植物(苦草)生长的影响。实验结果表明,低密度的椭圆萝卜螺促进了苦草的生长,螺、草之间存在明显的互利关系,高密度时螺类对苦草植株本身的大量牧食则显著限制了植物的生长。对铜锈环棱螺而言,不同密度的螺类均明显促进了受附生生物胁迫的苦草的生长,螺-草互利关系成立。分析认为,螺-草互利关系的存在是有其限制条件的,对植食性螺类而言,只有在较低的螺类密度条件下才存在这种互利关系。  相似文献   

5.
The dried peripheral area of pond Idumban (62 ha) increased from 3.2 ha in January to 3 1.9 ha in April. Pila globosa, which were abundant in the littoral area, did not commence aestivation during this period, perhaps due to low temperature and/or high dissolved oxygen content. The number of aestivating snails averaged 0.5/m2 in May, 1973 (3.6% of the total population) and it increased to 1.1/M2 in September (26.2%). Biomass of the snail increased from 3.5 to 19.9 g dry weight (including shell)/M2. Number of aestivating snails increased from 0.4/m2 (5.2% of the total population) in May 1974 to 0.8/m2 (11.1%) in July and the biomass from 4.1 g/m2 to 10.7 g/m2. Availability of dried area for aestivation increased from 5.3 to 23.7 ha in 1973 and from 13.5 to 30.2 ha in 1974.Monthly observations made on the marked snails forced to aestivate at 7.5, 15.0, 22.5 and 30.0 cm depth in the pond during May, revealed that temperature above 35°C and moisture below 5% were critical. Mortality and weight loss decreased in the snails forced to aestivate at increasing depth. Random observations indicated that 83% of the aestivating snails buried themselves at 15 cm depth in the pond. On the whole, 98,480 snails (592 Kg) and 115,270 (758 Kg) died during aestivation in 1973 and 1974 respectively. Of the total weight loss, the energy lost via metabolism contributed only a small fraction of 2.2% (12 Kg) and 2.1% (15 Kg) during these years. Considering the total aestivation area, the snails which succumbed averaged only 0.4/m2/year (2.5 g/m2/year). On an average, dry substance equivalent to about 2.6 mg dry weight/ g dry weight of snail/ day (3.7 gcal/ g live snail/ day) was lost on metabolism by the aestivating snails, i.e. the metabolic level of the aestivating snail was about 1 / 18th of that of the actively feeding snail.  相似文献   

6.
1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g−1 snail DW d−1. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m−2, forming a spongy pond scum in the no‐apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out‐competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out‐competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co‐dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re‐introduce native snails which can control the development of filamentous algae.  相似文献   

7.
Studies on energy transformation in the freshwater snail Pila globosa   总被引:1,自引:0,他引:1  
The effects of eleven chosen feeding levels ranging from 0 to 198 mg damp dry (plant) Ceratophyllum/g live snail/day on the absorption, conversion and metabolism of the snail Pila globosa (of 1 -9 g body weight) have been studied. Absorption rates increased from 3-0 to 21-0 mg dry food/g live snail/day in snails fed 3-4-28-8 mg dry food/g live snail/day. In these snails, absorption efficiency decreased from 87.5 to 73.0%. Conversion rates increased from 0-3 mg/g/day for snails receiving 23-4 mg/g/day to 2-7 mg/g/day for those fed maximum amounts, and the efficiency (K2) also increased from 1-9% to 130%. When compared to other gastropods, Pila globosa appears to be a poor convertor. During 30 days' starvation, the test individuals lost 4.4 mg dry body substance/g/day i.e. the maintenance cost was 14-7 cal/g live snail/day. The SDA increased by four times for those feeding on maximum rations in comparison to those receiving about 5 mg/g/day, i.e. the energy cost for converting food was increased four times.  相似文献   

8.
In order to better understand the role of herbivorous snails in freshwater ecosystems, we conducted experiments investigating food preference of the snail Radix swinhoei on leaves of the submerged plant Vallisneria spiralis with and without periphyton coverage. The effects of snail grazing on the growth of V. spiralis were assessed in a no-snail control and at three snail densities (80, 160, 240 individuals m?2). Results showed that the snails chose preferentially leaves covered by periphyton. Grazing activity at low snail density (80 individuals m?2) was found to stimulate V. spiralis growth, but at higher snail density (240 individuals m?2), plant growth was apparently suppressed. An increase observed in nutrient concentrations in water column with increasing snail density may be attributed to nutrient release by snails. This study suggests that the nature of the relationship between herbivorous snails and macrophytes in freshwater ecosystems depends on the abundance of the snails. At low snail density, the relationship may be a mutualistic one, but at high density snail herbivory may impact negatively on macrophyte biomass in lakes.  相似文献   

9.
The large land snail Placostylus ambagiosus (Pulmonata: Bulimulidae) was investigated during a long-term study in northernmost New Zealand. The snails fed at night on fallen leaves from a variety of broadleaf trees and bushes. During the day, most snails in shrubland rested under plants close to their food sources at densities of up to 53 snails per m2 and mean live biomasses of 47–72 g/m2. Individual snails stayed close to their food plants for up to 12 years, seldom moving away. Resting behaviour and site fidelity in forest was not investigated in detail, but some adult snails in forest returned to their original sites after being moved up to 60 m into a fenced area built to protect them from feral domestic animals. The ovoid eggs (mean 7.0 mm long×5.6 mm wide; ranges 5.5–7.7 mm long; 5.1–6.7 mm wide) were laid in clutches averaging 43 eggs (range 1–113 eggs) in shallow cavities covered with soil. More than one snail may contribute to a clutch. Adult shell height ranged from 43 mm to 97 mm and varied with habitat quality. Where snail abundance was high adults were small. Implications of these results for conservation management are discussed.  相似文献   

10.
Metal defence against insect herbivory in hyperaccumulator plants is well documented. However, there are contradictory results regarding protection against snails. According to the joint effects hypothesis, inorganic and organic defences cooperate in plant protection. To test this hypothesis, we explored the relationships between snail (Cantareus aspersus) feeding and multiple inorganic and organic leaf components in the Cd hyperaccumulator plant Noccaea praecox. Plants grouped by rosette size growing in nutrient solution supplemented or not with 50 μM Cd were offered to the snails. After 3 days of snail feeding, the plants and snails were analysed. In addition to Cd concentrations, we analysed leaves for nutritional factors (sugar and protein), defence‐related compounds (glucosinolates, phenolics, tannins, salicylic acid and jasmonate) and essential mineral nutrients. Cadmium concentrations in the snails and in snail excrements were also analysed. Snails preferentially fed on plants grown without Cd. Medium‐sized plants exposed to Cd were the least consumed. Snail excrements from this trial weighed less and had higher Cd concentrations than those from other treatments. Cadmium increased salicylate and jasmonate production. A positive relationship between jasmonate levels and the number of attacked leaves was found. Principal component analysis revealed that leaf sugar concentration was the main factor positively affecting snails' leaf consumption, while leaf Cd had a negative but weaker influence. In conclusion, leaf sugar concentration mainly governs snails' feeding preferences. High leaf Cd concentrations do not deter herbivores from attacking leaves, but they do reduce leaf consumption. Our results clearly support the joint effects hypothesis.  相似文献   

11.
本文采用连续施用和轮换施用农药方式对福建烟区烟蚜进行抗药性及其体内酶变化的测定,研究结果表明,在连续施用3次、5次、7次和9次后,施用灭多威后的烟蚜抗性分别增长了1.397倍、2.608倍、4.891倍和7.598倍;施用吡虫啉则分别增长了1.717倍、2.114倍、2.861倍和4.169倍;施用高效氯氟氰菊酯则分别...  相似文献   

12.
Biomphalaria glabrata infected with Schistosoma mansoni and maintained on an artificial diet of Spirulina alga displayed reduced growth during the 5 wk following patency. Food consumption per unit snail weight was unaffected. Infected snails also failed to lay eggs. No difference in percentage of assimilation was observed between control and infected individuals, but infected snails had significantly decreased gross conversion efficiencies. The effects of infection on nutrition of B. glabrata were similar to those observed in nutrient-deprived snails fed diets containing low Spirulina levels. Nutrient deprivation, however, did not alter conversion efficiency.  相似文献   

13.
Summary Freshwater snails and anuran tadpoles have been suggested to have their highest population densities in ponds of intermediate size where abiotic disturbance (e.g. desiccation) is low and large predators absent. Both snails and tadpoles feed on periphytic algae and, thus, there should be a large potential for competitive interactions to occur between these two distantly related taxa. In a field experiment we examined the relative strength of competition between two closely related snail species, Lymnaea stagnalis and L. peregra, and between L. stagnalis and tadpoles of the common frog, Rana temporaria. Snail growth and egg production and tadpole size at and time to metamorphosis were determined. Effects on the common food source, periphyton, were monitored with the aid of artificial substrates. Periphyton dry weight was dramatically reduced in the presence of snails and/or tadpoles. There were no competitive effects on growth or egg production of the two snail species when they were coexisting. Mortality of L. peregra was high (95%) after reproduction, but independent of treatment. Growth of L. stagnalis was reduced only at the highest tadpole densities, whereas egg production was reduced both by intraspecific competition and by competition with tadpoles. Differences in egg production were retained after tadpole metamorphosis. Tadpole larval period increased, weight of metamorphosing frogs decreased and growth rate was reduced as a function of increasing tadpole density. However, contrary to expectation, snails had a positive effect on tadpole larval period, weight and growth rate. Further, in experimental containers without snails there was a dense growth of the filamentous green alga Cladophora sp. We suggest that the facilitative effects of snails on tadpoles are due to an indirect mutualistic mechanism, involving competition between food sources of different quality (microalgae and Cladophora sp.) and tadpoles being competitively dominant over snails for the preferred food source (microalgae). In the presence of tadpoles snails will be forced to feed on low-quality Cladophora, increasing nutrient turnover rates, which results in enhanced productivity of microalgae, increasing tadpole food resources. Thus, tadpoles have a negative effect on snails through resource depression, while snails facilitate tadpole growth through an indirect enhancement of food availability.  相似文献   

14.
纤维素酶高效降解纤维素生产单糖,在纺织、造纸、食品、饲料等行业有重要应用价值.近年来,动物源的纤维素酶展现出优良的降解能力,其应用受到广泛关注.软体动物福寿螺是入侵我国华南地区的恶性外来物种,已经对水稻生产和湿地生物多样性造成了严重危害.福寿螺对多种植物的强消化能力与其体内的内生纤维素酶有密切关系.本文聚焦于福寿螺组织...  相似文献   

15.
1. Biological invasions have become a serious threat to ecosystems worldwide. Various factors can contribute to the success of biological invasion. We examined how different macrophyte food affected feeding and life‐history traits of the invasive herbivorous snail Pomacea canaliculata, and whether differences in snail life‐history traits could explain its successful infestation of agricultural and non‐agricultural wetlands in Asia. 2. We tested five cultivated and five wild semi‐aquatic macrophytes. Snail daily feeding rate varied substantially with plant species, ranging from 1.3% to 22% of its body mass. Snails fed with four (Amaranthus gangeticus, Apium graveolens dulce, Ipomoea aquatica and Nasturtium officinale) of the five cultivated macrophyte species exhibited high survivorship, fast growth and high fecundity. Snails fed with Colocasia esculenta, however, grew poorly, did not reproduce and eventually died. 3. Of the five wild species (Eichhornia crassipes, Ludwigia adscendens, Murdannia nudiflora, Myriophyllum aquaticum and Polygonum hydropiper), M. nudiflora supported a high snail survival, but snails had slower growth and lower fecundity than those reared on the four palatable cultivated species. Snails fed with L. adscendens grew substantially slower than those fed with M. nudiflora, and produced only a small clutch of eggs. Snails fed with E. crassipes, M. aquaticum and P. hydropiper had very low survivorship, grew very little and did not reproduce. 4. We determined six plant properties and their correlation with the feeding, growth and reproduction of the apple snails. Cultivated macrophytes in general had a higher nutritional value and lower physical and chemical defences. Phenolic content was negatively correlated with snail feeding rate, while plant nitrogen and phosphorus contents were positively correlated with snail egg production and growth, respectively. 5. These results indicate that, due to their higher nutritional value and lower chemical and physical defences, cultivated macrophytes are in general desirable for the apple snail which may partly explain its successful invasion into wet agricultural areas in Asia. This snail may also selectively graze poorly defended wild macrophytes in non‐agricultural wetlands, leading to changes in floral diversity and wetland functioning. Management of this and other apple snails with similar life‐history traits should thus focus on the prevention of their further spread.  相似文献   

16.
The effects of herbivore size and hunger level were tested on lotic periphyton community structure and ash-free dry mass (AFDM). My hypotheses were 1) that small herbivores would remove more periphyton per unit biomass than large herbivores of the same species because of energetic demands and 2) that within the same size class, starved herbivores would remove more periphyton than nonstarved herbivores. The herbivore used was the prosobranch snail Elimia clavaeformis Lea. Seven treatments were employed: 1) no snails (control); 2) small “starved” snails; 3) large “starved” snails; 4) small and large “starved” snails; 5) small fed snails; 6) large fed snails; and 7) small and large fed snails. Although snails removed significant amounts of periphyton AFDM relative to controls, neither snail size nor degree of starvation had a significant effect on loss of total AFDM. Small snails removed significantly more erect forms of Stigeoclonium tenue (C. A. Ag.) Kütz. than large snails, but snail size had no other significant effect. Starved snails removed significantly more Cocconeis placentula Ehr. than fed snails, suggesting that after the more susceptible growth forms (e.g. erect Stigeoclonium) were removed, Cocconeis cells became more vulnerable to grazing by hungry snails. When small and large snails were combined in chambers, large snails gained weight over time, whereas small snails lost weight. These results suggest that intraspecific competition may occur within populations of Elimia.  相似文献   

17.
This study investigated the feasibility of using an invasive snail, Pomacea canaliculata, as a food source and water purifier for the commercial breeding of the loach Misgurnus anguillicaudatus. The predatory potential of M. anguillicaudatus (3.5–5.5?g) against hatchling snails was evaluated in aquaria and simulated paddy fields. Some hatchling snails left the water to avoid being preyed upon by the loaches, and approximately 10 hatchlings died per day in the presence of five loaches in aquaria, whereas a weaker snail control effect was observed in the simulated paddy fields. The growth of rice seedlings (Oryza sativa) was not reduced by the presence of hatchling snails alone, but the shoot biomass of seedlings coexisting with snails was promoted after introducing the loaches. Additionally, the presence of P. canaliculata adults improved the aquatic environment in the short term for loach breeding by decreasing the turbidity of the water. Importantly, M. anguillicaudatus (12–18?g) mortality decreased and its weight increased in the presence of adult snails.  相似文献   

18.
Livestock grazing is a common management practise in semi-natural grasslands in Central Europe. Different types of livestock (horses, cattle, sheep) and grazing intensity are known to affect the richness and composition of plant species. However, knowledge of grazing-dependent effects on invertebrates is limited. We examined the influence of horse, cattle and sheep grazing on the richness, abundance and composition of land snail species in 21 calcareous nutrient-poor grassland areas in the northwestern Jura Mountains, Switzerland. Grazing by different livestock species did not affect the species richness, abundance and species composition of land snails. Furthermore, the number of open-land species and the ratio of large- to small-sized snail species or individuals did not differ among the three pasture types. However, independent of livestock species, grazing intensity negatively influenced the snail fauna. Snail species richness, abundance and number of Red list species decreased with increasing grazing intensity. Grazing intensity also affected the occurrence of individual snail species (Truncatellina cylindrica, Cecilioides acicula, Candidula unifasciata and Trichia plebeia). To preserve the snail fauna in nutrient-poor grasslands, pastures can be stocked with horses, cattle or sheep. However, both maximum stocking rate (number of livestock units per hectare) and grazing duration (number of grazing days per year) must be carefully defined for the proper management of the pastures.  相似文献   

19.
Summary An experimental investigation under field conditions of enclosures containing freshwater pulmonate snails, the macrophyteCeratophyllum demersum and epiphytes, produced evidence of beneficial interactions.Ceratophyllum growth, measured in terms of stem length, numbers of leaf-nodes and growing tips and leaf survival was significantly enhanced in the presence of snails. This effect was attributed to the increased availability of plant nutrients of snail origin, such as phosphates and ammonia, as well as to the snails' action as “cleaning symbionts” in reducing the density of bacterial and algal epiphyton potentially deleterious to macrophytes. Principal component analysis revealed both seasonal and treatment effects of snail grazing on algal epiphyton. Small adnate algal species (e.g.Cocconeis placentula) survived grazing and benefited from the removal of larger, competitor, species. Snail densities increased in all treatments, despite high (86%) juvenile mortality. It is concluded that freshwater pulmonate snails are strong interactors in lentic habitats, enhancing the growth ofCeratophyllum and producing characterisic epiphyte communities. This benefits not only the snails, but also the plants and epiphytes that are associated with them. Thus the interactions between these component parts of the community can be considered as mutualistic.  相似文献   

20.
Wild edible plants form an important constituent of traditional diets in the Himalaya. In the Sikkim Himalaya a total of 190 species have been screened as edible species out of which nearly 47 species come to the market. The present paper deals with nutritive values of 27 most commonly consumed wild edible plants in the Sikkim Himalaya. Of 27 plant species that were analyzed for their nutritive values, 22 were edible for their fruits and five for leaves/shoots. Among different plant parts, generally higher nutrient concentration was recorded for leaves, followed by new shoots and fruits. For different species the crude fiber content ranged between 2.15–39.90%, and the total soluble salts between 4.66–21.00%, and the vitamin C content from 6–286 mg/100 g. The fat content was determined high in the fruits ofCastanopsis hystrix, Machilus edulis, andCinnamomum species, while the protein content was highest inHippophae rhamnoides, Cucumis melo, andEleagnus latifolia. The total carbohydrate content ranged from 32–88% in the fruits of various wild edibles, the reducing sugar from 1.25–12.42%, total sugar from 2.10–25.09%, the lignin content varied from 9.05–39.51%, the hemicellulose between 25.63–55.71% and cellulose content varied from 9.57–33.19% in different species. Among the various macronutrients estimated in the plant samples of different wild edible species, nitrogen was present in highest quantity, followed by potassium, calcium, magnesium, phosphorus, and sodium. Micronutrients, such as iron, zinc, magnesium, and copper contents were analyzed in different plant parts of various wild edible species. The iron content was higher in leaves and new shoots. The nutritive values of certain wild edible species determined in this study are comparable with various commercial fruits. It is suggested that a few wild edible species need to be grown for commercial cultivation and adopted in the traditional agroforestry systems, which will lead to reduced pressure on them in natural forest stands as well as producing economic benefits for poor farmers.  相似文献   

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