Adult Human Neurogenesis: Early Studies Clarify Recent Controversies and Go Further

Evidence on adult mammalian neurogenesis and scarce studies with human brains led to the idea that adult human neurogenesis occurs in the subgranular zone (SGZ) of the dentate gyrus and in the subventricular zone (SVZ). However, findings published from 2018 rekindled controversies on adult human SGZ neurogenesis. We systematically reviewed studies published during the first decade of characterization of adult human neurogenesis (1994–2004) – when the two-neurogenic-niche concept in humans was consolidated – and compared with further studies. The synthesis of both periods is that adult human neurogenesis occurs in an intensity ranging from practically zero to a level comparable to adult mammalian neurogenesis in general, which is the prevailing conclusion. Nonetheless, Bernier and colleagues showed in 2000 intriguing indications of adult human neurogenesis in a broad area including the limbic system. Likewise, we later showed evidence that limbic and hypothalamic structures surrounding the circumventricular organs form a continuous zone expressing neurogenesis markers encompassing the SGZ and SVZ. The conclusion is that publications from 2018 on adult human neurogenesis did not bring novel findings on location of neurogenic niches. Rather, we expect that the search of neurogenesis beyond the canonical adult mammalian neurogenic niches will confirm our indications that adult human neurogenesis is orchestrated in a broad brain area. We predict that this approach may, for example, clarify that human hippocampal neurogenesis occurs mostly in the CA1-subiculum zone and that the previously identified human rostral migratory stream arising from the SVZ is indeed the column of the fornix expressing neurogenesis markers.

Conceptualizing Core Aspects on Circular Economy in Cities

Currently, there are many different interpretations in the literature of what a circular economy is and how it functions. As cities are still facing challenges to become fully sustainable, the need for a comprehensive analysis of how the circular economy can be implemented in urban areas is increasing. This article aims at outlining circular cities by their key characteristics and to further explore and provide a framework for fostering circularity at the city level. In order to achieve this goal, we performed a systematic review and analyzed key papers published in the field of circular economy to determine how circular economy practices form circular cities. We discovered that cities play a focal role in facilitating the transition towards circularity through the closing of the loops, recirculation, technical innovation, policy elaboration and citizens’ support. However, city policymakers are still uncertain about how a circular city looks like and what its purpose is, as views are ranging from a strategic ambition to a niche concept of a smart city. Such uncertainty brings challenges, especially in the transition phase that many cities are in at the moment. This further implies that circular economy applied at the urban level still needs effort and innovation to successfully pass the transition phase from the linear economy. Therefore, lastly, we developed a framework model that can be adapted in other cities to facilitate their transition to circular cities.

TOURISTS’ MOTIVATIONS FOR VISITING DARK TOURISM SITES. CASE OF ROMANIA

Nowadays, tourism plays an essential role in economic growth and development in many countries. Tourists have different travelling motivations and behavioural manifestations, helping tour operators decide suitable for them. Developing a dark tourism niche concept is a necessary step for correct use of it in theory and practice. Dark tourism is an important concept studied in the past twenty years in worldwide literature. This empirical paper aimed to determine the tourists’ motivations for travelling to Romania’s dark tourism destinations and establishing them. A quantitative research method was applied based on a survey using a non-probabilistic technique based on convenience sampling. Secondary, it was studied the relationship between motivational determinants and tourists’ attitude-behaviour in visiting dark tourism sites (Theory of Planned Behaviour, TPB). The survey conducted online was primarily made of 40 items evaluated on the Likert scale. It has been used a sample based on 475 Romanian respondents: 72.3% who had already visited a dark tourism destination in Romania, and 27.8% who stated they planned to visit one. The theoretical framework has analysed five constructs as motivational determinants in the relationships with behavioural construct attitude (TPB). The results show support for two of five research hypotheses (H1 and H4). Dark experience (H1) and Unique learning experience (H4) have a significant and positive effect on Attitude. We did not find any significant effect of Engaging entertainment, Casual interest, and Emotional recreation on Attitude. Hence, H2, H3 and H5 are not supported. Based on these results, the government can develop tourism economic and marketing policy to develop dark tourism as important post-communist niche tourism. The practitioners can develop and promote tourism packages and products by applying the correct use of dark tourism sense. The present scientific paper’s originality is given by the lack of literature review studies based on empirical research on this topic. Limits of the research and future research directions are also pointed out in the conclusion part.

The environmental niche of soil bacterial, archaeal, fungal and protist communities differ along edaphic and topoclimatic gradients in the Alps

BackgroundThe niche concept describes the range of conditions supporting the establishment and persistence of species in the environment. Although widely used in ecology, it has not been often applied to microbes, for which comparative niche analyses are still lacking. Yet, quantifying the niche of microbial taxa is necessary to forecast how taxa and the communities they compose might respond to environmental changes. In this study, we identified important topoclimatic, edaphic, spatial and biotic drivers of the alpha and beta diversity of bacterial, archaeal, fungal and protist communities. Then, we established a method to calculate the niche breadth and position of each taxon along environmental gradients to determine whether microorganisms have distinct environmental niches. ResultsFor all microbial groups, edaphic properties were identified as the most important drivers of both community diversity and composition. Protists presented the largest niche breadths, followed by bacteria and archaea, with fungi displaying the smallest. Niche breadth generally decreased towards environmental extremes, especially along edaphic gradients, suggesting increased specialisation of all microbial taxa in highly selective environments. ConclusionIn this study, we showed that microorganisms have well defined niches, as do macro-organisms, and that these likely drive part of the observed spatial patterns of community variations, but with notable differences among taxonomic groups. Applying the niche concept more widely to microbial ecology should open many novel perspectives, especially to tackle global change challenges.

Species from the viewpoint of biocoenology

Some questions of the use of the “species” concept in biocoenology and hydrobiology are considered. The existence of certain difficulties and ambiguities in the use of this concept is shown. It is proposed to clarify the goals and objectives of identifying the species structure of biocoenoses. The examples show that ecomorphs and coeno-ecomorphs are not less important elements of a biocenotic system and require thorough research. The question of the possibility and feasibility of definitions "to species level" of all members of the community is considered. The ecological niche concept is associated with species, although there is also the guild concept that unites species according to the principle of convergent similarity of trophic, topical, or other preferences. Various systems of bioindication have become widespread, which are based on the principle of compliance of a particular species population to certain conditions. First of all, we are talking about disturbed conditions, including various impacts by pollution. It was shown that not only species, but also more easily identifiable higher taxa could be used as bioindicators of certain conditions.

Defining the niche for niche construction: evolutionary and ecological niches

Niche construction theory (NCT) aims to transform and unite evolutionary biology and ecology. Much of the debate about NCT has focused on construction. Less attention has been accorded to the niche: what is it, exactly, that organisms are constructing? In this paper I compare and contrast the definition of the niche used in NCT with ecological niche definitions. NCT’s concept of the evolutionary niche is defined as the sum of selection pressures affecting a population. So defined, the evolutionary niche is narrower than the ecological niche. Moreover, when contrasted with a more restricted ecological niche concept, it has a slightly different extension. I point out three kinds of cases in which the evolutionary niche does not coincide with realized ecological niches: extreme habitat degradation, commensalism, and non-limiting or super-abundant resources. These conceptual differences affect the role of NCT in unifying ecology and evolutionary biology.

Predicting Bird Distributions Under Global Change

Global change creates an urgent need to predict spatial responses of biota to support the conservation of sufficient habitat to maintain biodiversity. We present species distribution model theory and a synthesis of avian literature on approaches to collecting occurrence data, selecting explanatory variables and analytical processes currently in use to predict future distributions. We find that interpreting the validity of current predictive distributions is hindered by variation in spatio-temporal resolution of data sets that force hypothesis testing under the Grinnellian niche concept. Broadly, the capacity of species to shift their geographic ranges under land use and climate change is expected to be limited by both large scale (i.e., the physiological or fundamental niche) and small scale (i.e., the realized or tolerance niche) factors. We highlight the strengths and weaknesses of widely used explanatory variables and analytical approaches tailored to macrohabitat characteristics and the Grinnellian niche concept. This synthesis addresses if and how current approaches align with theory and makes recommendations for future directions to improve the accuracy of predictive distribution modelling.

Microhabitat segregation of two coexisting tadpole species on Emei Mountain

Understanding mechanisms determining the coexistence between different species is one of the key issues in community ecology and biodiversity conservation. Microhabitat segregation is a way for species to coexist, which reflects the specific habitat selection of coexisting species in a finer spatial scale. Despite quantitative studies have been conducted to investigate the microhabitat segregation of coexisting species, this type of studies was not often performed on tadpoles. In this study, we assessed the habitat selection of two coexisting tadpoles (Quasipaa boulengeri and Leptobrachium boringii) in a stream on Emei Mountain, China. Our results demonstrated that L. boringii and Q. boulengeri tadpoles occupied different microhabitats. Specifically, Q. boulengeri tadpoles preferred deep, narrow, and weak acid stream segments with slow current velocity and low value of conductivity, while L. boringii tadpoles tended to occur in a wide, shallow water bodies with relatively higher pH, conductivity, and current velocity. Overall, our study supported the Hutchinson’s niche concept, showing that at least one dimension of niche differentiation (i.e., microhabitat) occurred between coexisting tadpole species.

Niche-Driven Socio-Environmental Linkages and Regional Sustainable Development

The changes in niche roles and functions caused by competition for survival resources have implications in various domains, with natural science and social science standing out. Currently, expanding the ecological niche concept and its practical interpretation in the fields of social ecology, geography and sustainable science is becoming a crucial challenge. This paper is based on niche theory to observe niche evolution and resulting socio-ecological effects of 1186 towns in 19 prefecture cities in Yangtze River delta. The results indicate that: Towns around the Taihu Lake displayed obvious spatial agglomeration, which was leading the development of the entire region. The town niche shows obvious characteristics of north-south differences and hierarchy distribution. The niche coordination degree of Jiangsu Province was higher than that of Zhejiang Province. The higher the subsystem coordination degree, the better the town development. Towns with poor ecological conditions are often subject to competition, while towns with better ecological conditions often benefit from cooperative development. The niche separation and collaboration could enhance niche competition of towns and cities in the region. The proposed framework can facilitate interdisciplinary exchanges among geography, sociology, landscape ecology and regional planning and provide insights for understanding regional co-opetition relationship and regional sustainable development.