• Development and Reproduction
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• v.27 no.4
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• pp.221-226
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• 2023

A stem cell niche provides an environment that governs stem cell maintenance and division. Thus, the development of a proper niche is of prime importance to stem cell behaviors. Mechanisms of niche development are beginning to be revealed in the Drosophila male gonad. Niche cells are initially dispersed throughout the gonad, then assemble at its apical tip through the anterior migration of posteriorly located niche cells. The molecular mechanisms of this migration and assembly are still poorly understood. Here we show evidence suggesting that Lin28, an RNA-binding protein and regulator of let7 genesis, might be an intrinsic factor for the anterior migration of niche cells. We found that a dispersed, ectopic niche, a phenotype observed with anterior migration defects, occurs in lin28 mutant gonads. This phenotype is rescued by expression of lin28 in the niche cells. These findings suggest that Lin28 might be required for the anterior migration of niche cells.

• Journal of Korean Elementary Science Education
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• v.34 no.1
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• pp.72-85
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• 2015

Conception in learner's cognitive structure has a niche as species in ecosystems. The purpose of this study is to analyze the change of niche overlap of photosynthesis concept through instruction. The photosynthesis concepts were selected from literature review. Selected concepts were in 4 areas: Location of photosynthesis, reactants, products, and environmental factors. The subjects consisted 304 elementary students. The respondent marked the relevance between the presented concepts and each area on a scale of 1~30 points. The analysis of niche overlap in concepts was performed by changing in niche overlap graph, niche space size, and overlap index before and after instruction. The results are as follows. First, on the whole understanding level and relevance of the scientific concepts was increased through instruction as a result of learning. Second, elementary school students cognitive concepts in the form of chunking concepts through classification process. Based on the results, this study has the following suggestion. Students' conceptual ecologies and niche analyzed by this study will be used as material for development of instruction strategy.

• Journal of Ecology and Environment
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• v.44 no.3
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• pp.162-177
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• 2020

Background: Ecologists have achieved much progress in the study of mechanisms that maintain species coexistence and diversity. In this paper, we reviewed a wide range of past research related to these topics, focusing on five theoretical bodies: (1) coexistence by niche differentiation, (2) coexistence without niche differentiation, (3) coexistence along environmental stress gradients, (4) coexistence under non-equilibrium versus equilibrium conditions, and (5) modern perspectives. Results: From the review, we identified that there are few models that can be generally and confidently applicable to different ecological systems. This problem arises mainly because most theories have not been substantiated by enough empirical research based on field data to test various coexistence hypotheses at different spatial scales. We also found that little is still known about the mechanisms of species coexistence under harsh environmental conditions. This is because most previous models treat disturbance as a key factor shaping community structure, but they do not explicitly deal with stressful systems with non-lethal conditions. We evaluated the mainstream ideas of niche differentiation and stochasticity for the coexistence of plant species across salt marsh creeks in southwestern Denmark. The results showed that diversity indices, such as Shannon-Wiener diversity, richness, and evenness, decreased with increasing surface elevation and increased with increasing niche overlap and niche breadth. The two niche parameters linearly decreased with increasing elevation. These findings imply a substantial influence of an equalizing mechanism that reduces differences in relative fitness among species in the highly stressful environments of the marsh. We propose that species evenness increases under very harsh conditions if the associated stress is not lethal. Finally, we present a conceptual model of patterns related to the level of environmental stress and niche characteristics along a microhabitat gradient (i.e., surface elevation). Conclusions: The ecology of stressful systems with non-lethal conditions will be increasingly important as ongoing global-scale climate change extends the period of chronic stresses that are not necessarily fatal to inhabiting plants. We recommend that more ecologists continue this line of research.

• Journal of Ecology and Environment
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• v.35 no.3
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• pp.227-234
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• 2012

Quercus aliena and Q. serrata are both occur as natural vegetation alongside natural freshwater bodies of the southern Korea Peninsula. Q. serrata dominates over Q. aliena as secondary forest vegetation in the present day. In order to explain these natural distributional traits of the oak species, we conducted some experiments with oak seedlings which treated with major important environmental resources, including light, moisture and nutrients, under controlled conditions. We then measured the ecological niche breadths and overlap from 15 eco-morphological characteristics. The ecological niche breadth of Q. aliena and Q. serrata were higher in terms of the nutrient factor applied, but was lower terms of light. The niche breadth of Q. serrata was wider than that of Q. aliena in light and moisture exposure. On the other hand, the niche breadth of Q. aliena was similar with that of Q. serrata in terms of the nutrient factor applied. These results imply that Q. serrata has a broader ecological distribution in over a wider variety of light and moisture environments than that of Q. alien. Ecological niche overlap between two oak species was the widest in terms of the light treatment factor applied, and narrowest in terms of moisture. This response pattern was also verified by cluster and principle component analysis. These results suggest competitive interactions between Q. serrata and Q. aliena seedlings may be higher for light resources than moisture or nutrient resources, and that Q. serrata is more shade tolerant than Q. aliena.

• Management & Information Systems Review
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• v.18
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• pp.115-132
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• 2006

The main findings of this study are summarized as follows; 1) For medium-small size Family Restaurant(FR) in the FR market, nowadays, survival is the key issue. If the medium-small size FR is to survive and continue to grow under this competitive environment, it must pursued the efficiency of management with niche marketing strategy. 2) This study is to describe the niche marketing strategy for medium-small size FR. Strategic niche marketing must be based on the target market, market positioning and strategic marketing mix. 3) Medium-small size FR needs to develop the marketing mix factors for the niche marketing strategy. It needs to make customers understand what the FR differs from current and potential competitors. Essentially the medium-small size FR must take a competitive advantage. Hence it will appeal to a substantial number of the segments customers. 4) In using niche marketing strategy, a medium-small size FR must establish the objectives, select the tools, develop the decisions on product differentiation, market segmentation and positioning under various strategic niche marketing factors 5) By carrying out the niche marketing strategy on the target market, customer's desire can be further fulfilled. When management efficiency is improved, we can better cope with changing environment.

• The Journal of the Korea Contents Association
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• v.15 no.10
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• pp.116-126
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• 2015

The purpose of this study is to analyze the change of programming strategies of chinese broadcasting as competitions intensify in the niche dimension. Specifically, the niche breadth which indicates the diversity of program genre and way of program production, the niche overlap which indicates the degree of competition among the channels, are investigated. The results show, as the competition has intensified, three chinese television pursued different programming strategies; CCTV1 maintained programming strategy without big change, while Hunan and Gangso pursued change of programming strategy. However the change of programming strategies of Hunan and Gangso showed different direction; Hunan has tended narrows niche breadth of program genre and the way of progrm production, while Gangso broadens niche breadth. In overall, Chinese broadcastings have found the way of co-exist pursuing different programming strategy. And the programming strategy of Gangso satellite broadcasting which broadens niche breadth has showed better performance in rating and advertising revenue.

• Journal of Information Technology Applications and Management
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• v.13 no.3
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• pp.129-143
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• 2006

Diversity of available communication media has increased as the use of Internet and mobile technology increased rapidly. The traditional media tend to transform their roles and functionality. This change brings about the expansion of the span of media to be selected by users. In this study, we examined the characteristics of emerging communication media use based on Niche Theory. Online communication media in this study include Internet messenger, mobile phone, and e-mail. We also analyzed the relationship between the nature of task and the selection of communication media, that is, the effects of communication contexts(formal vs. informal, notification vs. request, superior vs. inferior) where by the communication partners are involved. The result of this study, mobile phone had the highest niche competitive superiority in all communication contexts, and internet messenger and e-mail made difference according to communication contexts. Also, we can notify internet messenger and e-mail have a mutual substitutive relationship by analysis of niche overlap.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.2
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• pp.274-282
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• 2011

This paper overviews the concept of the strategic niche management, which emphasises the social aspects of new technologies and calls for relevant government policies for socio-technical transition. Hydrogen energy technologies remain in the niche level, thus the SNM perspective is appropriate to be applied. The reason why, and the way how to see hydrogen as a socio-technical niche are discussed, followed by an analytic argument on hydrogen policies and their SNM characteristics. Final part of the paper deals the design of the socio-technical experiment. It is expected that this paper would contribute to not only policy development but also improving understandings on the socio-technical nature of hydrogen energy of hydrogen community.

• Korean Journal of Ecology and Environment
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• v.46 no.3
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• pp.429-439
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• 2013

This study was conducted to determine the changes of the ecological niche breadth and niche overlap of Quercus acutissima and Quercus variabilis under elevated $CO_2$ concentrations and under elevated temperature conditions. We investigated the growth responses by environmental factor, $CO_2$ concentration, air temperature, light, soil moisture and nutrients. Rising $CO_2$ concentration was treated with 1.6 times than control (ambient) and increased temperature with $2.2^{\circ}C$ above the control (ambient) in the glass greenhouse. Ecological niche breadth and niche overlap was calculated the two oak species (Q. acutissima and Q. variabilis), which were cultivated with light, soil moisture and nutrient gradients at four levels. As a result, the ecological niche breadth of Quercus acutissima was determined to be increased under the warming treatment, but decreased under soil moisture and nutrient environments. The ecological niche breadth of Quercus variabilis was increased under light, soil moisture and nutrients of the warming treatment than control. Ecological niche overlap between Quercus acutissima-Quercus variabilis was increased under light of the warming treatment than control, but decreased under soil moisture and nutrient environments. These results means that two oak species are more severe competition in light environments than soil moisture and nutrient environments. According to analyses of the Cluster and PCA, the two oak species were more sensitive react under light environment than to elevated $CO_2$ concentration or elevated temperature.

• Korean Journal of Environmental Biology
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• v.27 no.2
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• pp.191-197
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• 2009

In order to characterize the ecological traits of Q. mongolica, we treated the seedlings of this species with three environmental factors, light, moisture and nutrient gradients from March to October 2007, and measured morphological and ecological 17 characters. Lastly calculated ecological niche breadth and niche overlap between Q. mongolica-Q. acutissima and Q. mongolica-Q. variabilis, and analysed them with a special reference to ecological distribution pattern and their competition relationship in Korea. The ecological niche breadth of Q. mongolica showed the lowest in nutrient treatment, but the highest in soil moisture treatment. The ecological niche value under light was intermediate. On comparison of the ecological niche breadth of three oak species, Q. mongolica showed the highest in light environment, which might be a reason for the dominant distribution in the forest plant community, Korea. The ecological niche overlap of Q. mongolica-Q. acutissima and Q. mongolica-Q. varabilis was the widest in moisture treatment, but the narrowest in nutrient treatment and the intermediate in light one. These results means that these three oak species be most competitive in moisture environment than light or nutrient one, and that there are least differentiated among oak species for soil moisture condition. Cluster and PCA ordination showed that Q. mongolica and Q. acutissima were more closely arranged than Q. mongolica and Q. variabilis. From these results, it can be explained that Q. mongolica have more similar ecological niche with Q. acutissima than with Q. variabilis, consequently competition between Q. mongolica and Q. acutissima is intensive than Q. mongolica and Q. variabilis for environment condition, especially in soil moisture.