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1.
S. S. S. Sarma Saúl Avelino Rivera Fabiola Elizalde Hinojosa S. Nandini 《Russian Journal of Ecology》2007,38(5):353-362
We tested separately the effect of two taxonomically related rotifers (B. patulus and B. macracanthus) on the population dynamics of another species (A. fissa) at low (0.5 ×10 6) and high food levels (1.5 × 106 cells/ml of Chlorella vulgaris) using different inoculation densities (0–100%). We also quantified the impact of A. fissa on the two brachionid species. Regardless of the presence of the competing species, an increase in the availability of food
led to increase in the abundances of the three rotifers. The population growth of B. patulus, B. macracanthus, or A. fissa was affected negatively when cultured together with another species. An increase in the initial density of any one of the
competing species became advantageous to maintain a certain population size. At a low algal food level, B. patulus was able to suppress A. fissa more strongly than B. macracanthus. On the other hand, at a high food level, B. macracanthus suppressed the population of A. fissa more strongly than B. patulus. Peak population densities for A. fissa varied from about 150 to 1000 ind./ml, depending on food density and the presence of competitors. The rate of population
increase (r) of A. fissa, B. patulus, and B. macracanthus increased with an increase in food availability but decreased with increasing initial density of the competitor. Both Brachionus spp. experienced negative growth rates in the presence of A. fissa, especially at a high initial density of the latter.
Published in Russian in Ekologiya, 2007, Vol. 38, No. 5, pp. 381–390.
The article was submitted by the authors in English. 相似文献
2.
Summary
Ips duplicatus withI. typographus co-inhabiting Norway spruce (Picea abies (L.) Karst.) would benefit from a pheromone blend distinct from that of the larger competitorI. typographus. GC-MS analysis showed thatI. duplicatus males feeding in the host produced ipsdienol (Id),cis-verbenol (cV),trans-verbenol (tV), myrtenol (Mt), andE-myrcenol (EM) and traces of 2-methyl-3-buten-2-ol (MB).I. duplicatus produced Id in approximately racemic form (48.9-54.5% (+)-(S)-isomer). The amounts of Id and EM released over a 9 day period had a maximum of 250 and 5 ng/h/male, respectively, on day 2. Exposure ofI. duplicatus males to myrcene and -pinene resulted in the production of small amounts of Id, cV, tV, Mt, andtrans-pinocarveol, but not of EM. In laboratory bioassays with walking beetles, the pheromone component Id alone was weakly attractive while EM was inactive, but in binary combination with Id strongly synergized attraction. A combination of EM and Id at a release rate equivalent to 100–200 males was more attractive in the field than 70 unmated males in a spruce log. The addition of myrcene ( a suggested pheromone precursor of Id) to Id did not enhance trap caches, while addition of EM increased catches > 10-fold. Subtracting EM from a blend of Id, EM, cV and MB drastically reduced trap catches while subtraction of cV or MB or both had no significant effect. Addition of EM over a wide concentration range to the synthetic pheromone ofI. typographus did not reduce the attraction of females of this species in the laboratory. A two-species pheromone interaction field test releasingI. typographus pheromone components (MB + cV) at 10–1000 male equivalents (ME) andI. duplicatus pheromone (Id + EM) at 0, 10–1000 ME in all possible combinations showed both positive intraspecific dose-response effects and an interspecific inhibition. Higher release rates of EM appeared to inhibitI. typographus, especially males. In a tree colonization model, the response of the two competing species to their respective pheromones show a good separation during the mass-attack with a small initial cross-attraction. It remains to be shown whether either of the two pheromone systems have in fact evolved in the present sympatry, or if they are an incidental effect of ancestry of these phylogenetically distantIps. 相似文献
3.
介绍了我国模具工业结构现状及敏捷制造的基本思想 ,论述了应用敏捷制造建立模具行业的动态联盟可缩短模具设计和制造周期 ,提高我国模具工业的竞争力。 相似文献
4.
5.
A study on root competition in alley cropping was carried out in an agroforestry system, involving Cassia siamea Lam. and maize ( Zea mays L. cv. Katumani composite B). The existence and intensity of root competition in the top soil as manifested by the distribution of the active roots of cassia and maize, in space and time, was assessed. The root length density of maize was far greater than that of cassia in the upper 10 cm, implying that cassia was not competing with maize for water and/or nutrients at that depth. However, at maize crop tasselling and grain filling stages there was a marked overlap of roots of the two plants at lower depths (20—50 cm). This varied with distance from the cassia hedge in a way that there was a tendency for highest overlap near middle maize rows. This partly explained observed yield differences. Therefore cassia may not be a suitable choice for alley cropping with maize under semi-arid conditions on non-sloping land, unless most of its active roots can be properly managed to absorb resources below the feeding rhizosphere of the active maize roots. 相似文献
6.
Ben C. Scheele David A. Hunter Laura A. Brannelly Lee F. Skerratt Don A. Driscoll 《Conservation biology》2017,31(3):592-600
Emerging wildlife pathogens are an increasing threat to biodiversity. One of the most serious wildlife diseases is chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd), which has been documented in over 500 amphibian species. Amphibians vary greatly in their susceptibility to Bd; some species tolerate infection, whereas others experience rapid mortality. Reservoir hosts—species that carry infection while maintaining high abundance but are rarely killed by disease—can increase extinction risk in highly susceptible, sympatric species. However, whether reservoir hosts amplify Bd in declining amphibian species has not been examined. We investigated the role of reservoir hosts in the decline of the threatened northern corroboree frog (Pseudophryne pengilleyi) in an amphibian community in southeastern Australia. In the laboratory, we characterized the response of a potential reservoir host, the (nondeclining) common eastern froglet (Crinia signifera), to Bd infection. In the field, we conducted frog abundance surveys and Bd sampling for both P. pengilleyi and C. signifera. We built multinomial logistic regression models to test whether Crinia signifera and environmental factors were associated with P. pengilleyi decline. C. signifera was a reservoir host for Bd. In the laboratory, many individuals maintained intense infections (>1000 zoospore equivalents) over 12 weeks without mortality, and 79% of individuals sampled in the wild also carried infections. The presence of C. signifera at a site was strongly associated with increased Bd prevalence in sympatric P. pengilleyi. Consistent with disease amplification by a reservoir host, P. pengilleyi declined at sites with high C. signifera abundance. Our results suggest that when reservoir hosts are present, population declines of susceptible species may continue long after the initial emergence of Bd, highlighting an urgent need to assess extinction risk in remnant populations of other declined amphibian species. 相似文献
7.
The competition between submersed plants has been recognized as an important factor influencing the structure of plant communities
in shallow lakes. The ability of different species to take up and store nutrients from the surrounding ambience varies, and hence plant
community structure might be expected to affect the cycling of nutrients in lake ecosystems. In this study, the uptake of phosphorus
by Hydrilla verticillata and Vallisneria natans was studied and compared in monoculture and competitive mixed-culture plantings.
Results showed that for both studied species the phosphorus concentrations of different tissues and of whole plants was unaffected by
competition. However, the quantity of phosphorus accumulated by whole plants of H. verticillata was significantly higher in mixture
culture than in monoculture, while that of V. natans was lower in the mixed culture. The results indicated that H. verticillata has a
competitive advantage over V. natans, when the two species are grown in competition, and is able to accumulate a greater quantity of
phosphorus. 相似文献
8.
In the meerkat (Suricata suricatta), a cooperative mongoose, pups follow potential feeders while the group is foraging and emit incessant calls when soliciting
food from them. In contrast to a ’stationary’ brood of chicks, in which nestlings are fed at a fixed location, meerkat pups
are ’mobile’ and become spread out. The question arises whether meerkat pups that experience different constraints to those
facing chicks have evolved similar begging strategies. This paper describes the vocalisations that meerkat pups emit in the
context of begging and investigates the influence of these calls on food allocation by older group members and on the behaviour
of littermates. Meerkat pups use two types of calls when soliciting food from a potential feeder. The most common is a ’repeat’
call, which pups emit continuously when following an older forager over several hours a day. In addition, when a potential
feeder finds a prey item, the pups next to it emit a bout of calls with increased calling rate, amplitude and fundamental
frequency, termed ’high-pitched’ calls. Observations, together with playback experiments, showed that more prey was allocated
to pups that called longer and more intensely. The pup closest to a feeder was almost always fed. The probability of emitting
high-pitched calls did not depend on the time since a pup had received food, and the change from repeat to high-pitched calls
occurred suddenly. The main function of the high-pitched call, therefore, does not appear to be to signal a pup’s hunger state.
More likely, the two calls, in the context of begging, may be an adaptation to energetic constraints in a mobile feeding system.
Pups, which are dispersed during foraging, may emit repeat calls over long periods to prevent potential feeders from eating
all the prey themselves. At the moment a potential feeder finds prey, pups may give the more intense high-pitched calls to
direct feeders to bring the food item to them and not to a littermate. Therefore, unlike the stationary feeding system where
chicks emit one type of begging call when the feeder approaches the nest, meerkats, with a mobile feeding system, have evolved
two discrete types of vocalisations in the context of begging.
Received: 22 November 1999 / Revised: 1 July 2000 / Accepted: 17 July 2000 相似文献
9.
各级政府贯彻落实绿色发展的理念,实现经济增长与环境保护的共赢,才能真正实现"绿水青山就是金山银山"。在经济"新常态"背景下,防治环境污染是个复杂而系统性的工程,需要进行经济追因与综合治理,其中,制定实施有效的环境政策工具尤为关键。本文把微观经济学中的双寡头产量竞争模型作为基准模型拓展用于环境经济分析,并把环境税、环境规制、排污权交易这三类主要环境工具对企业生产决策的影响纳入基准模型,旨在对比研究不完全竞争行业中环境工具的有效性问题。结果表明:主要基于市场机制的环境经济政策比行政色彩浓厚的环境规制更有效率。提高环境税率或排污权价格均能显著削减行业污染物排放量,如果环境税率恰好等于排污权价格,则环境税与排污权交易这两类环境工具的效力相等。这对进一步建立和完善我国尚处于探索或初始实施阶段的环境工具,促进石化、电力、钢铁等不完全竞争行业的主要污染物减排,具有一定参考价值和借鉴意义。 相似文献
10.
当前我国环保产业普遍存在着企业规模较小、缺乏核心技术、中低端供给过剩、优质供给不足等现象,环保产业的供给侧水平明显无法满足日益提高的环境治理需求。以全国最大的环保产业基地宜兴市为例,分析上述问题特质及产生原因,总结政府及企业改革创新中的经验和不足,提出环保产业供给侧改革的参考对策与建议。 相似文献