The human retinal stem niches could overlap a vascular anatomical pattern

Stem cells are undifferentiated cells which have the unique potential to self-renew and to supply, via intermediate stages of transit amplifying cells （TACs）, differentiated cells. With- in the stem cell niches not only heterologous cells, but also differentiated progeny of stem cells provide regulation to the stem cells parents. Stem cells can differentiate in various cell types during tissue maintenance or repair.

Multiple Spatial Scale Analysis of the Niche Characteristics of the Rhododendron dauricum Plant Communities in Northeast China

This study aims to verify the concept of niches at multiple spatial scales in plant communities.To this end,we analyzed the niche characteristic of Rhododendron dauricum plant communities in Northeast China at three spatial scales.At the local scale,we calculated the Importance Value(IV)of species in five communities in the north of the Da Hinggan Mountains.At the intermediate scale,we examined five communities in their entirety,calculated the niche breadth of the species,and integrated niche overlap and interspecific association to analyze interspecific relationships.Further,the generalized additive model(GAM)was used to analyze the impact of topography and soil factors on niche characteristics.At the regional scale,we analyzed the geographical distribution of dominant species of R.dauricum plant communities in Northeast China and used principal component analysis(PCA)to analyze the impact of geographical and climate factors on species distribution.The results show that at the local scale,the IV of the species in each community varies widely.At the intermediate scale,species with a wide niche breadth tend to have a high value for IV.Larix gmelinii,Betula platyphylla,R.dauricum,Ledum palustre,and Vaccinium vitis-idaea had a relatively wide niche breadth and a high niche overlap,and the interspecific associations were almost all positive.Elevation and soil nutrients were the most dominant environmental factors.At the regional scale,species with a wide niche breadth tend to have a wide range of distribution,and temperature and precipitation were the most dominant environmental factors.This study suggests that the niche characteristics at three scales are both related and different.Niche characteristics at the local scale were various and labile,and niche characteristics at the intermediate and regional scales were relatively regular.These results show some degree of consistency with previous studies from an evolutionary perspective.The action mechanisms of these communities are related to differences in the dominant environmental factors.In addition,the integration of niche overlap and interspecific association determine interspecific relationships more accurately.

Niches of dominant fish in the waters surrounding the Taishan Islands, China

An index of relative importance(IRI) was employed to screen for dominant fish in the waters surrounding the Taishan Islands, China, using data from four seasonal trawl surveys undertaken between 2012 and 2013. Niche breadth and niche overlap were measured using the Feinsinger and Morisita-Horn indices, respectively, and the characteristics and seasonal variations in the niches of dominant fish were assessed via non-metric multidimensional scaling(NMDS) and cluster analysis. A total of 80 fish species, including 16 dominant species, were recorded. Only A mblychaeturichthys hexanema was dominant in all seasons. According to niche breadth values and NMDS, the 16 dominant species were grouped into the following three types:(1) wide niche breadth species, including Cynoglossus macrolepidotus, A. hexanema, and Trypauchen vagina, among others;(2) medium niche breadth species, including Setipinna taty and Johnius belangerii; and(3) narrow niche breadth species, including A trobucca nibe and Coilia mystus. Most species with a wider niche breadth were demersal fish with a lower swimming capability and even distribution. The niche breadth of migrating fish was narrower than that of settled fish. At a given spatial scale, fish with stronger swimming capabilities had a narrower niche breadth. Niche overlap, which is associated with niche specialization, ranged from 0.000 to 0.886 and had an annual mean value of 0.314. In summer and autumn, niche overlap was relatively high within species of the Sciaenidae family and within species of the Gobiidae in autumn. Dif ferences in thermophily, feeding habits, food organism abundance/distribution and predator-prey relationships af fected the niche overlap of fish in this area. Cluster analysis revealed that species with the narrowest niche breadth and lowest niche overlap values usually displayed lower aggregation and greater distribution dif ferences compared with other species.

A niche model to predict Microcystis bloom decline in Chaohu Lake, China

Cyanobacterial blooms occur frequently in lakes due to eutrophication. Although a number of models have been proposed to forecast algal blooms, a good and applicable method is still lacking. This study explored a simple and effective mathematical-ecological model to evaluate the growth status and predict the population dynamics of Microcystis blooms. In this study, phytoplankton were collected and identified from 8 sampling sites in Chaohu Lake every month from July to October, 2010. The niche breadth and niche overlap of common species were calculated using standard equations, and the potential relative growth rates of Microcystis were calculated as a weighted-value of niche overlap. In July, the potential relative growth rate was 2.79 (a.u., arbitrary units) but then rapidly declined in the following months to -3.99 a.u. in September. A significant correlation (R=0.998, P<0.01) was found in the model between the net-increase in biomass of Microcystis in the field and the predicted values calculated by the niche model, we concluded that the niche model is suitable for forecasting the dynamics of Microcystis blooms. Redundancy analysis indicated that decreases in water temperature, dissolved oxygen and total dissolved phosphorus might be major factors underlying bloom decline. Based on the theory of community succession being caused by resource competition, the growth and decline of blooms can be predicted from a community structure. This may provide a basis for early warning and control of algal blooms.

Functional composition of tall-statured trees underpins aboveground biomass in tropical forests

The influences of trait diversity(i.e.,the niche complementarity effect)and functional composition(i.e.,the mass ratio effect)on aboveground biomass(AGB)is a highly debated topic in forest ecology.Therefore,further studies are needed to explore these mechanisms in unstudied forest ecosystems to enhance our understanding,and to provide guidelines for specific forest management.Here,we hypothesized that functional composition would drive AGB better than trait diversity and stem size inequality in the(sub-)tropical forests of Nepal.Using data from 101 forest plots,we tested 25 structural equation models(SEMs)to link elevation,stem DBH inequality,trait diversity(i.e.,trait richness,evenness,dispersion and divergence),functional composition[i.e.,community-weighted of maximum height mean(CWM of Hmax),specific leaf area(CWM of SLA),leaf dry matter content(CWM of LDMC),and wood density(CWM of WD)]and AGB.The best-fitted SEMs indicated that CWM of Hmax promoted AGB while overruling the impacts of trait diversity indices on AGB.However,low trait diversity indices were linked with higher AGB while overruling the effects of CWM of SLA,LDMC and WD on AGB.In addition,AGB decreased with increasing elevation,whereas stem size inequality did not influence AGB.Our results suggest that divergent species’functional strategies could shape AGB along an altitudinal gradient in tropical forests.We argue that forest management practices should include plant functional traits in the management plan for the co-benefits of biodiversity conservation and carbon sequestration that underpins human wellbeing.

Diversity analysis of soil dematiaceous hyphomycetes from the Yellow River source area:Ⅰ

Twenty-four soil samples of eight ecosystem-types around the Yellow River source area were investigated for the number and specific composition of soil dematiaceous hyphomycetes by dilution plate technique. And then the co-relationship between genus species of soil dematiaceous hyphomycetes and ecosystem-types was analyzed. The results show that the amount and species distribution of soil dematiaceous hyphomycetes had an obvious variability in different ecosystem-types, and that the dominant genus species varied in the eight ecosystem-types studied, with Cladosporium being the dominant genus in seven of the eight ecosystem-types except wetland. The index of species diversity varied in different ecosystem-types. The niche breadth analysis showed that Cladosporium had the highest niche breadth and distributed in all ecosystem-types, while the genera with a narrow niche breadth distributed only in a few ecosystem-types. The results of niche overlap index analysis indicated that Stachybotrys and Torula, Doratomyces and Scolecobasidium, Cladosporium and Chrysosporium had a higher niche overlap, whereas Arthrinium and Gliomastix, Phialophora and Doratomyces, Oidiodendron and Ulocladium had no niche overlap.

Mapping the habitat suitability of Ottelia species in Africa

Understanding the influence of environmental covariates on plant distribution is critical,especially for aquatic plant species.Climate change is likely to alter the distribution of aquatic species.However,knowledge of this change on the burden of aquatic macroorganisms is often fraught with difficulty.Ottelia,a model genus for studying the evolution of the aquatic family Hydrocharitaceae,is mainly distributed in slow-flowing creeks,rivers,or lakes throughout pantropical regions in the world.Due to recent rapid climate changes,natural Ottelia populations have declined significantly.By modeling the effects of climate change on the distribution of Ottelia species and assessing the degree of niche similarity,we sought to identify high suitability regions and help formulate conservation strategies.The models use known background points to determine how environmental covariates vary spatially and produce continental maps of the distribution of the Ottelia species in Africa.Additionally,we estimated the possible influences of the optimistic and extreme pessimistic representative concentration pathways scenarios RCP 4.5 and RCP 8.5 for the 2050s.Our results show that the distinct distribution patterns of studied Ottelia species were influenced by topography(elevation)and climate(e.g.,mean temperature of driest quarter,annual precipitation,and precipitation of the driest month).While there is a lack of accord in defining the limiting factors for the distribution of Ottelia species,it is clear that water-temperature conditions have promising effects when kept within optimal ranges.We also note that climate change will impact Ottelia by accelerating fragmentation and habitat loss.The assessment of niche overlap revealed that Ottelia cylindrica and O.verdickii had slightly more similar niches than the other Ottelia species.The present findings identify the need to enhance conservation efforts to safeguard natural Ottelia populations and provide a theoretical basis for the distribution of various Ottelia species in Africa.

Identifying important habitats for waterbird conservation at a Greek Regional Nature Park

Background:Small coastal wetlands are vital sites for wintering waterbirds.Identifying important habitats is critical for managing waterbirds effectively.The Vourkari inlet is a small coastal wetland located near the capital Athens,within the most urbanized and industrialized area of Greece.We aimed at identifying the most important habitats for waterbirds at the Vourkari inlet during winter.Methods:Data about habitat use and availability were collected for 14 waterbird species and for seven habitat classes.Habitat selection(Manly’s selection ratio),overlap indices(Pianka’s niche overlap index)and null models were calculated.Results:All the studied waterbird species selected available habitats nonrandomly.Shallow waters(0–2 m),were used by 13 waterbirds and selected by five waterbirds.Pools and channels were used and selected by 10 species.Mud was used by nine species and selected by six species.Mud with rocky substrate was used by nine species and selected by eight species.Medium(2–4 m)and deep(4–6 m)open water habitats were used by seven species and selected by four species.Halophytic vegetation was used by six species and selected by two species.Several habitats were selected by nationally important populations:mudflat habitats(i.e.,mud,mud with rocky substrate and pools and channels)by Common Redshanks(Tringa totanus),halophytic vegetation by Little Egrets(Egretta garzetta),shallow waters by Common Shelducks(Tadorna tadorna)and medium and deep waters by Sandwich Terns(Thalasseus sandvicencis),whilst shallow waters and mudflat habitats were preferred by a possibly internationally important population of Mediterranean Gulls(Ichthyaetus melanocephalus).Although overlap in habitat use between species was generally low,null models indicated habitat sharing and a lack of competition.Conclusions:Waterbirds coexisted in the absence of competition for habitats at Vourkari,where they mostly used and preferred shallow water and mudflats.Small coastal wetlands are numerous,both in Greece and worldwide,therefore our findings would be useful as a basis for comparisons,both temporal at the inlet and spatial with other sites,that would help assess the importance of habitats and improve management strategies to benefit waterbirds,especially in areas with similar Mediterranean-type habitats and climate.

The coexistence of seven sympatric fulvettas in Ailao Mountains,Ejia Town,Yunnan Province

The coexistence of ecologically similar species sharing sympatric areas is a central issue of community ecology. Niche differentiation is required at least in one dimension to avoid competitive exclusion. From 2012-2014, by adopting the methods of mist-nets and point counts to evaluate spatial niche partitioning and morphological differentiations, we explored the coexistence mechanisms of seven sympatric fulvettas in Ailao Mountains, Ejia town, Yunnan Province, China. The microhabitats of these seven fulvettas were significantly different in elevation, roost site height and vegetation coverage, indicating a spatial niche segregation in different levels. Approximately, 90.30% of the samples were correctly classified by linear discriminant analysis（LDA） with correct rates at 91.20%-100%, except the White-browed fulvetta（Alcippe vinipectus）（65.4%） and the Streak-throated fulvetta（A. cinereiceps）（74.6%）. The seven fulvettas were classified into four guilds based on their specific morphological characters, suggesting that the species in each guild use their unique feeding ways to realize resource partitioning in the overlapped areas. These finding indicate that through multi-dimensional spatial niche segregation and divergence in resource utilizing, the interspecific competition among these seven fulvettas is minimized, whereas, coexistence is promoted.

The effects of prey depletion on dietary niches of sympatric apex predators in Southeast Asia

Resource depletion exerts opposing pressures on co-occurring consumers to expand diets while limiting overlap with competitors.Using foraging theory as a framework,we tested the effects of prey availability on diet spe-cialization and overlap among competing Asian predators:dhole,leopard,and tiger.We used scat analysis from a prey-poor site,combined with a quantitative synthesis of 40 other diet studies,to determine biomass of different prey types consumed by each predator.We then assessed diet composition in relation to prey density,and compared diet breadth and overlap between prey-poor and prey-rich sites.In prey rich areas,all three predators specialized on energetically profitable medium and large ungulates(>30 kg),resulting in narrow,overlapping niches.Each predator shifted toward less profitable small-bodied prey(≤30 kg)as preferred ungulates declined,whereas con-sumption of preferred ungulates was unrelated to small prey abundance,as predicted by foraging theory.Diet breadths doubled under prey depletion(except leopard),but overlap declined as diets diverged via species-specific traits that facilitated capture of different types of alternative prey.Asia’s apex predators adapt similarly to depletion of mutually preferred ungulates by switching to more numerous but less profitable small prey.Yet they can also partition a depleted prey base through intrinsic niche differences,thereby avoiding competitive exclusion.Our find-ings illuminate the stabilizing properties of adaptive foraging and niche differences in ecological communities,and provide insights into the behavior and resilience of Asia’s endangered apex predators in response to prey depletion in the heavily poached forests of this region.

Stable isotope evidence for trophic niche partitioning in a South African savanna rodent community

Species＇ partitioning of resources remains one of the most integral components for understanding community assem- bly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning be- cause these proxies represent the individual＇s diet and trophic niche, respectively. Using free-ranging rodents in a southern Afri- can savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, spe- cies with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel ana- lytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices