A triumvirate at the testis tip: sharing the power of stem cell control

Much attention has been given to the role of the niche in controlling stem cell maintenance and differentiation. However, cells other than niche cells might direct stem cell behavior. Evidence from the Drosophila reproductive system suggests that this is the case.     

Parapatry and niche complementarity of Peruvian Desert geckos (Phyllodactylus): the ambiguous role of competition

The Sechura Desert of Peru is among the most arid, barren regions of South America. Four species of nocturnal geckos (Phyllodactylus) are parapatric in part of the desert. By comparing niche associations of these species in allopatry and parapatry, I attempt to determine whether the observed parapatric distributions and niche dimension complementarity are related to competition — as is frequently assumed. While parapatry suggests a role for competition, distributional patterns can alternatively be related to adaptations of geckos to different physical environments (sandy desert and rocky foothill) that abut in the study area. Niche complementarity might also be a result of competition, but potentially contradictory evidence suggests that niche complementarity might instead be the result of adaptations developed in allopatry and having no relationship to competition. The ambiguity of these interpretations sets limits on the significance of this kind of evidence: in the absence of attempts to falsify alternative explanations, observations of parapatry or of niche dimension complementarity do not demonstrate conclusively the impact of competition as a force structuring communities.     

Niche breadth predicts geographical range size: a general ecological pattern

The range of resources that a species uses (i.e. its niche breadth) might determine the geographical area it can occupy, but consensus on whether a niche breadth–range size relationship generally exists among species has been slow to emerge. The validity of this hypothesis is a key question in ecology in that it proposes a mechanism for commonness and rarity, and if true, may help predict species' vulnerability to extinction. We identified 64 studies that measured niche breadth and range size, and we used a meta‐analytic approach to test for the presence of a niche breadth–range size relationship. We found a significant positive relationship between range size and environmental tolerance breadth (z = 0.49), habitat breadth (z = 0.45), and diet breadth (z = 0.28). The overall positive effect persisted even when incorporating sampling effects. Despite significant variability in the strength of the relationship among studies, the general positive relationship suggests that specialist species might be disproportionately vulnerable to habitat loss and climate change due to synergistic effects of a narrow niche and small range size. An understanding of the ecological and evolutionary mechanisms that drive and cause deviations from this niche breadth–range size pattern is an important future research goal.     

Sympatric speciation: a simulation model

A model of mating and population growth dependent on competition that suggests circumstances under which sympatric speciation might occur is described. The model is similar to one in a companion paper by Rosenzweig in that a heterozygote genotype, involving a new allele, is first selected by virtue of its ability to exploit a new niche and is then eliminated through competition. The superior competitor, which eliminates the heterozygote, is the homozygote for the new allele. For this process to occur the heterozygote must be sufficiently fit to exploit and invade a new niche, but not so fit that a classical polymorphism results from heterozygous advantage. This process of speciation is most likely to occur when there are vacant niches. When and where these might occur are discussed.     

Effect of climate change in lizards of the genus Xenosaurus (Xenosauridae) based on projected changes in climatic suitability and climatic niche conservatism

Accelerated climate change represents a major threat to the health of the planet's biodiversity. Particularly, lizards of the genus Xenosaurus might be negatively affected by this phenomenon because several of its species have restricted distributions, low vagility, and preference for low temperatures. No study, however, has examined the climatic niche of the species of this genus and how their distribution might be influenced by different climate change scenarios. In this project, we used a maximum entropy approach to model the climatic niche of 10 species of the genus Xenosaurus under present and future suitable habitat, considering a climatic niche conservatism context. Therefore, we performed a similarity analysis of the climatic niche between each species of the genus Xenosaurus. Our results suggest that a substantial decrease in suitable habitat for all species will occur by 2070. Among the most affected species, X. tzacualtipantecus will not have suitable conditions according to its climatic niche requirements and X. phalaroanthereon will lose 85.75% of its current suitable area. On the other hand, we found low values of conservatism of the climatic niche among species. Given the limited capacity of dispersion and the habitat specificity of these lizards, it seems unlikely that fast changes would occur in the distribution of these species facing climate change. The low conservatism in climatic niche we found in Xenosaurus suggests that these species might have the capacity to adapt to the new environmental conditions originated by climate change.     

An epithelial niche in the Drosophila ovary undergoes long-range stem cell replacement

Adult epithelial stem cells are thought to reside in specific niches, where they are maintained by adhesion to stromal cells and by intercellular signals. In niches that harbor multiple adjacent stem cells, such as those maintaining Drosophila germ cells, lost stem cells are replaced by division of neighboring stem cells or reversion of transit cells. We have characterized the Drosophila follicle stem cell (FSC) niche as a model of the epithelial niche to learn whether nonneighboring cells can also generate stem cell replacements. Exactly two stroma-free FSC niches holding single FSCs are located in fixed locations on opposite edges of the Drosophila ovariole. FSC daughters regularly migrate across the width of the ovariole to the other niche before proliferating and contributing to the follicle cell monolayer. Crossmigrating FSC daughters compete with the resident FSC for niche occupancy and are the source of replacement FSCs. The ability of stem cell daughters to target a distant niche and displace its resident stem cell suggests that precancerous mutations might spread from niche to niche within stem cell-based tissues.     

Limits to the niche and range margins of alien species

We discuss the apparent paradox that while introduced populations often adapt rapidly to conditions in the new range, it is normally assumed that the species’ niche remains unchanged. Focusing on plants, we argue that studies of the niche dynamics of alien species are useful for understanding the constraints acting on species in their native ranges, and vice versa. Most hypotheses about species ecological range margins are more consistent with there being a niche shift than niche stasis in the new range. After reviewing the evidence for niche shifts in alien species, we suggest that the probability of a shift occurring depends primarily upon the ecological and genetic processes limiting the species in its native range. For example, a fundamental niche shift might occur if introduced individuals are released from maladaptive gene flow from central populations, or if genetic diversity is increased by the mixing of individuals from different sources. In addition, other factors such as species characteristics, introduction history and conditions in the new range may also influence whether a niche shift occurs. Based on these considerations, we propose conditions under which niche shifts are most likely. Such understanding is important for predicting and mitigating current and future anthropogenic impacts on species ranges.     

On the relationship between niche and distribution

Applications of Hutchinson's n -dimensional niche concept are often focused on the role of interspecific competition in shaping species distribution patterns. In this paper, I discuss a variety of factors, in addition to competition, that influence the observed relationship between species distribution and the availability of suitable habitat. In particular, I show that Hutchinson's niche concept can be modified to incorporate the influences of niche width, habitat availability and dispersal, as well as interspecific competition per se . I introduce a simulation model called NICHE that embodies many of Hutchinson's original niche concepts and use this model to predict patterns of species distribution. The model may help to clarify how dispersal, niche size and competition interact, and under what conditions species might be common in unsuitable habitat or absent from suitable habitat. A brief review of the pertinent literature suggests that species are often absent from suitable habitat and present in unsuitable habitat, in ways predicted by theory. However, most tests of niche theory are hampered by inadequate consideration of what does and does not constitute suitable habitat. More conclusive evidence for these predictions will require rigorous determination of habitat suitability under field conditions. I suggest that to do this, ecologists must measure habitat specific demography and quantify how demographic parameters vary in response to temporal and spatial variation in measurable niche dimensions.     

Of niches and distributions: range size increases with niche breadth both globally and regionally but regional estimates poorly relate to global estimates

The relationship between species’ niche breadth (i.e. the range of environmental conditions under which a species can persist) and range size (i.e. the extent of its spatial distribution) has mostly been tested within geographically restricted areas but rarely at the global extent. Here, we not only tested the relationship between range size (derived from species’ distribution data) and niche breadth (derived from species’ distribution and co‐occurrence data) of 1255 plant species at the regional extent of the European Alps, but also at the global extent and across both spatial scales for a subset of 180 species. Using correlation analyses, linear models and variation partitioning, we found that species’ realized niche breadth estimated at the regional level is a weak predictor of species’ global niche breadth and range size. Against our expectations, distribution‐derived niche breadth was a better predictor for species’ range size than the co‐occurrence‐based estimate, which should, theoretically, account for more than the climatically determined niche dimensions. Our findings highlight that studies focusing on the niche breadth vs range size relationship must explicitly consider spatial mismatches that might have confounded and diminished previously reported relationships.     

Comparing macroecological patterns across continents: evolution of climatic niche breadth in varanid lizards

Macroecological analyses often test hypotheses at the global scale, or among more closely related species in a single region (e.g. continent). Here, we test several hypotheses about climatic niche widths among relatively closely related species that occur across multiple continents, and compare patterns within and across continents to see if they differ. We focus on the lizard genus Varanus (monitor lizards), which occurs in diverse environments in Africa, Asia, and Australia. We address three main questions. 1) How do climatic niche breadths of species on a given niche axis change based on the position of species along that niche axis? (E.g. are species that occur in more extreme environments more narrowly specialized for those conditions?) 2) Are there trade‐offs in niche breadths on temperature and precipitation axes among species, or are niche widths on different axes positively related? 3) Is variation in niche breadths among species explained primarily by within‐locality seasonal variation, or by differences in climatic conditions among localities across the species range? We generate a new time‐calibrated phylogeny for Varanus and test these hypotheses within and between continents using climatic data and phylogenetic methods. Our results show that patterns on each continent often parallel each other and global patterns. However, in many other cases, the strength of relationships can change dramatically among closely related species on different continents. Overall, we found that: 1) species in warmer environments have narrower temperature niche breadths, but there is no relationship between precipitation niche breadth and niche position; 2) temperature and precipitation niche breadths tend to be positively related among species, rather than showing trade‐offs; and 3) within‐locality seasonal variation explains most variation in climatic niche breadths. Some of these results are concordant with previous studies (in amphibians and North American lizards), and might represent general macroecological patterns.     

Ecological consequences of contrasting dispersal syndromes in New World Ephedra: higher rates of niche evolution related to dispersal ability

In this study we selected the New World species of Ephedra to understand the ecological consequences of different dispersal syndromes. The twenty‐three species of Ephedra in the New World have a disjunct distribution in North and South American arid and semi‐arid habitats, exhibiting three dispersal syndromes related to dispersal by birds, wind and rodents. Using DNA sequence data we inferred phylogenetic relationships and lineage divergence times, and used these estimates to test different ecological assumptions. Using comparative methods we tested for correlations between dispersal syndromes and a set of ecological variables (niche breadth, niche evolution, distributional ranges and niche position). We found that speciation events in the New World coincided with the expansion of arid habitats in this region. We suggest that the bird dispersal syndrome is related with higher rates of climatic niche evolution for all variables used, including aridity index, mean annual temperature and mean annual precipitation. Distribution ranges were correlated with niche breadth, they were however not significantly different between dispersal syndromes. Species inhabiting the extremely arid regions on niche axes had narrower niche breadths. We conclude that species whose seeds are dispersed by birds have colonized a broader set of habitats and that those with wind and rodent dispersal syndromes might have promoted the colonization of more arid environments.     

瓦屋山2种山雀的生态位分化和共存

黑冠山雀(Parus rubidiventris)和煤山雀(P.ater)在瓦屋山同域分布,生态位相似,是潜在的竞争者。在垂直分布上,煤山雀的生态位宽度为5.237,显著高于黑冠山雀的2.792,而在水平分布和活动基质2个维度上,二者的生态位宽度值相当。尽管3个维度上2种山雀生态位重叠值均大于0.7,但是它们对3个维度上的资源利用分别存在不同的偏好和侧重。2种山雀的身体量度除了喙宽外均有极显著差异,这应该是2种山雀对环境适应的结果。这2种山雀在巢址选择上各项参数差异均不显著,表明适宜的洞巢可能是它们种间竞争的主要对象。2种山雀的种群数量可能与居留类型有关。空间生态位或食物生态位的分离及适宜的种群数量和比例是它们得以共存的几个重要因素。     

Climatic‐niche evolution with key morphological innovations across clades within Scutiger boulengeri (Anura: Megophryidae)

The studies of climatic‐niche shifts over evolutionary time accompanied by key morphological innovations have attracted the interest of many researchers recently. We applied ecological niche models (ENMs), ordination method (environment principal component analyses; PCA‐env), combined phylogenetic comparative methods (PCMs), and phylogenetic generalized least squares (PGLS) regression methods to analyze the realized niche dynamics and correspondingly key morphological innovations across clades within Scutiger boulengeri throughout their distributions in Qinghai–Tibet Plateau (QTP) margins of China. Our results show there are six clades in S. boulengeri and obvious niche divergences caused by niche expansion in three clades. Moreover, in our system, niche expansion is more popular than niche unfilling into novel environmental conditions. Annual mean temperature, annual precipitation, and precipitation of driest month may contribute to such a shift. In addition, we identified several key climatic factors and morphological traits that tend to be associated with niche expansion in S. boulengeri clades correspondingly. We found phenotypic plasticity [i.e., length of lower arm and hand (LAHL), hind‐limb length (HLL), and foot length (FL)] and evolutionary changes [i.e., snout–vent length (SVL)] may together contribute to niche expansion toward adapting novel niche, which provides us a potential pattern of how a colonizing toad might seed a novel habitat to begin the process of speciation and finally adaptive radiation. For these reasons, persistent phylogeographic divisions and accompanying divergences in niche occupancy and morphological adaption suggest that for future studies, distinct genetic structure and morphological changes corresponding to each genetic clade should be included in modeling niche evolution dynamics, but not just constructed at the species level.     

Geographic variability of ecological niches of plant species: are competition and stress relevant?

A species’ niche position may differ strongly between geographic regions, for instance due to the effect of competitors or ecophysiological stress. However, it is unclear whether such strong geographic niche variation is the rule or the exception. We compared the niche positions of plant species between central England and eastern central Europe (as available from the literature), using phylogenetically independent contrasts. We found that most species occupied similar niche positions in both regions. More importantly, we found that niche variation was not higher in species susceptible to competitive displacement. Nor was niche variation higher in species that reach the edge of their range and thus suffer ecophysiological stress. We suggest that although these species might be easily displaced in their position along a niche axis, they may only be displaced over a short distance. Overall, ecological mechanisms that cause niche variation at the local scale may be much less relevant at the geographic scale.     

Sexual Dimorphism of Head Size in Phrynocephalus przewalskii: Testing the Food Niche Divergence Hypothesis

Sexual size dimorphism （SSD） is a general phenomenon in lizards, and can evolve through sexual selection or natural selection. But natural selection, which was thought to operate mainly through reducing the competition be- tween the two sexes （niche divergence hypothesis）, gave rise to a lot of controversy. We tested the niche divergence hypothesis in the toad-headed lizard Phrynocephalus przewalskii by comparing diet composition and prey sizes between males and females. The species was found to be sexual dimorphic, with males having relatively larger snout-vent length, head width, head length, and tail length, while females have relatively larger abdomen length. Based on analysis of 93 studied stomachs, a total of 1359 prey items were identified. The most common prey items were formicid, lygaeid and tenebrionid. The two sexes did not differ in the relative proportions of prey size categories they consumed and the dietary overlap based on prey species was high （O = 0.989）. In addition, the meal size, the volume or any maximal dimension of the largest prey item in the stomach was not explained by the sexes. According to our results, food niche divergence might not play an important role in the SSD evolution ofP. przewalskii.     

Evolutionary dynamics of ecological niche in three Rhinogobio fishes from the upper Yangtze River inferred from morphological traits

In the past decades, it has been debated whether ecological niche should be conserved among closely related species (phylogenetic niche conservatism, PNC) or largely divergent (traditional ecological niche theory and ecological speciation) and whether niche specialist and generalist might remain in equilibrium or niche generalist could not appear. In this study, we employed morphological traits to describe ecological niche and test whether different niche dimensions exhibit disparate evolutionary patterns. We conducted our analysis on three Rhinogobio fish species (R. typus, R. cylindricus, and R. ventralis) from the upper Yangtze River, China. Among the 32 measured morphological traits except body length, PCA extracted the first four principal components with their loading scores >1.000. To find the PNC among species, Mantel tests were conducted with the Euclidean distances calculated from the four principal components (representing different niche dimensions) against the pairwise distances calculated from mitochondrial cytochrome b sequence variations. The results showed that the second and the third niche dimension, both related to swimming ability and behavior, exhibited phylogenetic conservatism. Further comparison on niche breadth among these three species revealed that the fourth dimension of R. typus showed the greatest width, indicating that this dimension exhibited niche generalism. In conclusion, our results suggested that different niche dimensions could show different evolutionary dynamic patterns: they may exhibit PNC or not, and some dimensions may evolve generalism.     

Evolution of niche width and adaptive diversification

Theoretical models suggest that resource competition can lead to the adaptive splitting of consumer populations into diverging lineages, that is, to adaptive diversification. In general, diversification is likely if consumers use only a narrow range of resources and thus have a small niche width. Here we use analytical and numerical methods to study the consequences for diversification if the niche width itself evolves. We found that the evolutionary outcome depends on the inherent costs or benefits of widening the niche. If widening the niche did not have costs in terms of overall resource uptake, then the consumer evolved a niche that was wide enough for disruptive selection on the niche position to vanish; adaptive diversification was no longer observed. However, if widening the niche was costly, then the niche widths remained relatively narrow, allowing for adaptive diversification in niche position. Adaptive diversification and speciation resulting from competition for a broadly distributed resource is thus likely if the niche width is fixed and relatively narrow or free to evolve but subject to costs. These results refine the conditions for adaptive diversification due to competition and formulate them in a way that might be more amenable for experimental investigations.     

Saying it with genes,species and habitats: biodiversity education and the role of zoos

This paper considers the role of zoological gardens as vehicles for teaching about biodiversity and conservation. The general importance of conservation and biodiversity education is outlined in the context of Agenda 21 and the Global Biodiversity Strategy, and the unique niche of zoo education for meeting these challenges is defined. This includes the exhibition of real live animals, accessibility. immediacy, popularity, egalitarianism and the unique combination of strengths and resources offered by zoo education departments. Effective zoo education for biodiversity conservation depends on answering certain criticisms (including behavioural distortion, ecological context and people/animal relationships); working within the available resource framework; and careful strategic planning that considers appropriate messages, target audiences and communication methods. Future zoo education trends might include developing the unique niche; teaching about zoos' role in interactive management; and the contribution of zoo networks to education.     

Inhibition of the integrin signal constitutes a mouse iPS cell niche

Stem cells are regulated by their surrounding microenvironments, called niche, such as cell–cell interaction and extracellular matrix. Classically, feeder cells as a niche have been used in the culture of iPS cells from both the mouse and the human. However, the regulation mechanism of stem cells by feeder cells as a niche still have been partially unclear. In this study, we used three murine iPS cell lines, iPS‐MEF‐Ng‐20D‐17, iPS‐MEF‐Ng‐178B‐5 and iPS‐MEF‐Fb/Ng‐440A‐3, which were generated by different reprogramming methods. In general, these cell lines commonly need the feeder cells as a niche to culture. Recently, the effect of substrate stiffness is known in stem cell study. First, we focused on the mechanical properties of feeder cells, and then we speculated that feeder‐less culture might be made possible by using molecules in place of the mechanical properties of the niche. Finally, we found that the combination of disintegrin (echistatin) and 2i (GSK3 inhibitor and MEK inhibitor) is a sufficient condition for three murine iPS culture. This novel method of mimicking the murine iPS cell niche may be useful to understand signaling pathways to maintain the pluripotency of stem cells.