Environmental niche patterns of native and non-native fishes within an invaded African river system

To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organisation was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and non-native fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna.     

Trophic specialization influences the rate of environmental niche evolution in damselfishes (Pomacentridae)

The rate of environmental niche evolution describes the capability of species to explore the available environmental space and is known to vary among species owing to lineage-specific factors. Trophic specialization is a main force driving species evolution and is responsible for classical examples of adaptive radiations in fishes. We investigate the effect of trophic specialization on the rate of environmental niche evolution in the damselfish, Pomacentridae, which is an important family of tropical reef fishes. First, phylogenetic niche conservatism is not detected in the family using a standard test of phylogenetic signal, and we demonstrate that the environmental niches of damselfishes that differ in trophic specialization are not equivalent while they still overlap at their mean values. Second, we estimate the relative rates of niche evolution on the phylogenetic tree and show the heterogeneity among rates of environmental niche evolution of the three trophic groups. We suggest that behavioural characteristics related to trophic specialization can constrain the evolution of the environmental niche and lead to conserved niches in specialist lineages. Our results show the extent of influence of several traits on the evolution of the environmental niche and shed new light on the evolution of damselfishes, which is a key lineage in current efforts to conserve biodiversity in coral reefs.     

Assessing concurrent patterns of environmental niche and morphological evolution among species of horned lizards (Phrynosoma)

The prediction that variation in species morphology is related to environmental features has long been of interest to ecologists and evolutionary biologists. Many studies have demonstrated strong associations between morphological traits and local habitat characteristics, but few have considered the extent to which morphological traits may be associated with environmental features across broad geographic areas. Here, we use morphological, environmental and phylogenetic data compiled from Phrynosoma species to examine morphological and climatic variation across the geographic ranges of these species in an evolutionary context. We find significant phylogenetic signal in species’ environmental niches, but not in morphological traits. Furthermore, we demonstrate a significant correlation between species’ environmental niches and morphological traits when phylogenetic history is accounted for in the analysis. Our results suggest the importance of climatic variables in influencing morphological variation among species, and have implications for understanding how species distributions are constrained by environmental variation.     

Population demography influences climatic niche evolution: evidence from diploid American Hordeum species (Poaceae)

In this study, we explore the interplay of population demography with the evolution of ecological niches during or after speciation in Hordeum. While large populations maintain a high level of standing genetic diversity, gene flow and recombination buffers against fast alterations in ecological adaptation. Small populations harbour lower allele diversity but can more easily shift to new niches if they initially survive under changed conditions. Thus, large populations should be more conservative regarding niche changes in comparison to small populations. We used environmental niche modelling together with phylogenetic, phylogeographic and population genetic analyses to infer the correlation of population demography with changes in ecological niche dimensions in 12 diploid Hordeum species from the New World, forming four monophyletic groups. Our analyses found both shifts and conservatism in distinct niche dimensions within and among clades. Speciation due to vicariance resulted in three species with no pronounced climate niche differences, while species originating due to long‐distance dispersals or otherwise encountering genetic bottlenecks mostly revealed climate niche shifts. Niche convergence among clades indicates a niche‐filling pattern during the last 2 million years in South American Hordeum. We provide evidence that species, which did not encounter population reductions mainly showed ecoclimatic niche conservatism, while major niche shifts occurred in species which have undergone population bottlenecks. Our data allow the conclusion that population demography influences adaptation and niche shifts or conservatism in South American Hordeum species.     

Niches in the Anthropocene: passerine assemblages show niche expansion from natural to urban habitats

Human‐mediated habitat transformation is increasingly evident around the world. Yet, how this transformation influences species’ niche width and overlap remains unclear. On the one hand, human‐mediated habitat transformation promotes increased species similarity through trait‐based filtering, and an increased prevalence of generalist species with broad niches, resulting in functional homogenization. On the other hand, species that colonize transformed habitats could use empty niches, resulting in decreased species similarity and an expansion of assemblage‐level niche space. Here we explore these two alternatives in eight highly diverse passerine assembles in natural, rural and urban habitats in south and southwest China, a rapidly developing region of the world. Based on stable isotopes, we found that species’ niche width increased from natural to human‐made habitats, but there were no differences in niche overlap among habitats. Therefore, we found evidence for niche expansion, with generalists appearing to use empty niches created by human habitat modification, and with assemblages being comprised of complementary species. Further research is needed to determine whether increased between‐ or within‐individual niche variation is the main driver of niche expansion in transformed habitats.     

Isotopic niche is not equal to trophic niche

The work of Sheppard et al. (Ecol. Lett., 21, 2018, 1395) relies on the strong assumption that isotopic niche is equal to trophic niche. Here I raise three main concerns showing that classic hypotheses built upon trophic niche cannot be directly interpreted in isotopic space. Future studies should always keep isotopic and trophic niches distinct.     

A model of niche overlap and interaction in ecological systems

Ecological niches are the result of ecosystem element (compartment) interaction under the influence of environmental factors. The competence model is devised to map this interaction. It includes the assumption of an overall physiological state of a compartment depending only on intensive environmental factors, expressions for the adaptedness and competence of the compartment in interaction. Consequently, niches are environmental factor domains of superior competence. The situation of niches (niche structure) and competence maxima are extensively studied in the fundamental case of two interacting compartments and in the special case of n concentric compartments. The impact of one immigrating compartment is discussed. All detailed investigations made involve only one intensive environmental factor and the special assumption of similar physiological state functions of all compartments.     

不同倍性猕猴桃的适生区预测及生态位分化

多倍体与2倍体植物之间的生态位分化是多倍体植物成功建立的重要条件。2倍体、4倍体和6倍体猕猴桃分布在不同的地区,目前尚不明确不同倍性猕猴桃之间是否发生了明显的生态位分化,也不明确影响不同倍性猕猴桃生态位的主要环境因子。本研究通过文献查阅和野外调查收集不同倍性猕猴桃的自然分布点,利用最大熵模型预测不同倍性猕猴桃在当前气候条件下的潜在适生区及影响其分布的主导气候因子,并通过生态位一致性检验评估不同倍性猕猴桃间的生态位差异。结果表明: 不同倍性猕猴桃的潜在适生区存在明显差异,2倍体猕猴桃的高适生区集中在海拔较低的湖南丘陵;4倍体猕猴桃的高适生区大部分与2倍体重叠,但有部分向贵州北部、重庆东部区域偏移;6倍体猕猴桃的高适生区则集中分布在贵州大部、湖南西北部、湖北西南部和陕西南部。6倍体猕猴桃明显向高海拔、高纬度地区偏移,并且有更广的高适生区面积。生态位一致性检验证明,2倍体与4倍体猕猴桃有重叠的生态位,而2倍体与6倍体、4倍体与6倍体猕猴桃之间均发生了明显的生态位分化。最冷月最低温(Bio6)和最干月降雨量(Bio14)是影响不同倍性猕猴桃生态位分化的主要环境因素。多倍体猕猴桃在较低的Bio6和Bio14下能保持较高的存在概率,表明多倍体猕猴桃能占据低温、干旱的极端生态位。     

Towards a trait-based quantification of species niche

Aims Although the niche concept is of prime importance in ecology, the quantification of plant species' niches remains difficult. Here we propose that plant functional traits, as determinants of species performance, may be useful tools for quantifying species niche parameters over environmental gradients.Important findings Under this framework, the mean trait values of a species determine its niche position along gradients, and intraspecific trait variability determines its niche breadth. This trait-based approach can provide an operational assessment of niche for a potentially large number of species, making it possible to understand and predict species niche shifts under environmental changes. We further advocate a promising method that recently appeared in the literature, which partitions trait diversity into among- and within-community components as a way to quantify the species niche in units of traits instead of environmental parameters. This approach allows the switch of the focus from ecological niches to trait niches, facilitating the examination of species coexistence along undefined environmental gradients. Altogether, the trait-based approach provides a promising toolkit for quantifying the species ecological niche and for understanding the evolution of species niche and traits.     

应用生态位模型研究外来入侵物种生态位漂移

由于基础生态位和实际生态位的改变,外来入侵物种在入侵地成功定殖、扩散后常会发生生态位漂移,而物种生态位漂移往往很难直接证明。生态位模型在假设入侵物种的生态位需求保守的前提下,以物种在其原产地的生态位需求为基础,预测其在入侵地的潜在分布,通过比较预测分布与实际分布的差异可以从一定程度上得到外来入侵物种的生态位是否发生漂移的间接证据。以我国入侵杂草胜红蓟在原产地的生态位需求为基础,应用生态位模型预测其在其他地区的潜在分布。研究结果表明,生态位模型可以很好地预测胜红蓟在亚太平洋地区和非洲地区的分布,但在我国,其预测分布与实际分布存在较大差别。胜红蓟在我国预测分布主要为云南、海南、台湾部分地区,而胜红蓟入侵我国后现已广泛分布于长江以南地区,其实际分布比预测分布广泛得多,由此推测胜红蓟在入侵我国后其生态位已经产生了漂移。     

长苞铁杉群落优势种群高度生态位研究

基于天宝岩国家级自然保护区内长苞铁杉群落的调查数据 ,以不同高度作为一维资源位状态 ,以个体多度为生态位计测的资源状态指标 ,对群落中的 1 2个优势树种进行了生态位的计测和分析。结果表明 ,长苞铁杉具有较大的生态位宽度值 ,具有一定的稳定性 ;各优势树种 ,均表现出一定程度的对环境适应的相似性和生态位重叠。长苞铁杉与阳性树种柳杉、耐荫树种中偏阳性树种木荷之间的生态位相似性和生态位重叠值比与耐荫性树种深山含笑、细叶青冈之间的都要大。这些分析结果为珍稀濒危植物长苞铁杉的保护提供了科学依据     

莱州湾鱼类群落优势种生态位

根据2011年5月、8月、10月和12月莱州湾底拖网调查资料,对该海域鱼类群落优势种的生态位进行了研究。结果表明,全年调查共捕获鱼类49种,各季节优势种种类数分别为春季3种,夏季5种,秋季3种,冬季4种。夏、冬季优势种的丛生指数较低,春、秋季较高;冬、春季优势种的平均拥挤度较低,夏、秋季较高。基于欧氏距离的优势种丰度聚类结果同优势度排序结果吻合。主成分分析(PCA)表明,青鳞小沙丁鱼(Sardinella zunasi)和赤鼻棱鳀(Thryssa kammalensis)分别是影响第一轴和第二轴的主要种类。绯鱼衔(Callionymus beniteguri)、鲬(Platycephalus indicus)、髭缟虾虎鱼(Tridentiger barbatus)和短吻红舌鳎(Cynoglossus joyneri)是时空二维生态位宽度最高的种类(2)。时空生态位显著重叠(0.6)的种类有7组,其中银姑鱼(Pennahia argentata)和皮氏叫姑鱼(Johnius belengerii)重叠值最高(0.798)。δ~(13)C值变幅(CR)最大的种类为斑鱼祭(Konosirus punctatus),δ~(15)N值变幅(NR)最大的种类为青鳞小沙丁鱼;青鳞小沙丁鱼和鱼祭生态位总面积超过20,皮氏叫姑鱼生态位总面积最小(1.38)且与其他优势种营养生态位重叠较高。等级聚类、排序、PCA和优势种排序结果较一致,而与时空生态位宽度分析结果差异较大,表明莱州湾鱼类群落结构受洄游鱼类的影响较大。时空生态位宽度较高的种类主要为集群特征不明显的周年定居种(绯鱼衔、鲬、短吻红舌鳎等底层鱼类),而季节洄游种(青鳞小沙丁鱼、鱼祭、赤鼻棱鳀等中上层鱼类)因时间生态位宽度较低导致时空生态位宽度较低。时空生态位和营养生态位分析表明,生态位重叠导致的资源利用性竞争并不是导致莱州湾鱼类群落结构现状的决定性因素,而更多可能是人为干扰形成的。     

Morphological and niche divergence of pinyon pines

The environmental variables that define a species ecological niche should be associated with the evolutionary patterns present in the adaptations that resulted from living in these conditions. Thus, when comparing across species, we can expect to find an association between phylogenetically independent phenotypic characters and ecological niche evolution. Few studies have evaluated how organismal phenotypes might mirror patterns of niche evolution if these phenotypes reflect adaptations. Doing so could contribute on the understanding of the origin and maintenance of phenotypic diversity observed in nature. Here, we show the pattern of niche evolution of the pinyon pine lineage (Pinus subsection Cembroides); then, we suggest morphological adaptations possibly related to niche divergence, and finally, we test for correlation between ecological niche and morphology. We demonstrate that niche divergence is the general pattern within the clade and that it is positively correlated with adaptation.     

Ecological niche models of invasive seaweeds

Ecological niche models (ENMs) are commonly used to calculate habitat suitability from species’ occurrence and macroecological data. In invasive species biology, ENMs can be applied to anticipate whether invasive species are likely to establish in an area, to identify critical routes and arrival points, to build risk maps and to predict the extent of potential spread following an introduction. Most studies using ENMs focus on terrestrial organisms and applications in the marine realm are still relatively rare. Here, we review some common methods to build ENMs and their application in seaweed invasion biology. We summarize methods and concepts involved in the development of niche models, show examples of how they have been applied in studies on algae and discuss the application of ENMs in invasive algae research and to predict effects of climate change on seaweed distributions.     

Evidence that niche specialization explains species-energy relationships in lake fish communities

1. Interspecific niche differences have long been identified as a major explanation for the occurrence of species-rich communities. However, much fieldwork studying variation in local species richness has focused upon physical habitat attributes or regional factors, such as the size of the regional species pool. 2. We applied indices of functional diversity and niche overlap to data on the species niche to examine the importance of interspecific niche differentiation for species richness in French lake fish communities. We combined this information with environmental data to test generalizations of the physiological tolerance and niche specialization hypotheses for species-energy relationships. 3. We found evidence for a largely non-saturating relationship (relative to random expectation) between species richness and functional evenness (evenness of spacing between species in niche space), while functional richness (volume of niche space occupied) peaked at moderate levels of species richness and niche overlap showed an initial decrease followed by saturation. This suggests that increased niche specialization may have allowed species to coexist in the most species-rich communities. 4. We tested for evidence that increased temperature, local habitat area, local habitat diversity and immigration affected species richness via increased niche specialization. Temperature explained by far the largest amount of variation in species richness, functional diversity and niche overlap. These results, combined with the largely non-saturating species richness-functional evenness relationship, suggest that increased temperature may have permitted increased species richness by allowing increased niche specialization. 5. These results emphasize the importance of niche differences for species coexistence in species-rich communities, and indicate that the conservation of functional diversity may be vital for the maintenance of species diversity in biological communities. Our approach may be applied readily to many types of community, and at any scale, thus providing a flexible means of testing niche-based hypotheses for species richness gradients.