Regional occupancy in unicellular eukaryotes: a reflection of niche breadth,habitat availability or size‐related dispersal capacity?

1. The distribution patterns of unicellular and multicellular organisms have recently been shown to differ profoundly, with the former probably being mostly cosmopolitan, whereas the latter are mostly restricted to certain regions. However, the within‐region distribution patterns of these two organism groups may be rather similar. 2. We predicted that the degree of regional occupancy in unicellular eukaryotes would be related to niche characteristics, dispersal ability and size, as has been found previously for multicellular organisms. The niche characteristics we considered were niche position, that measures marginality in species habitat distribution, and niche breadth, that measures amplitude in species habitat distribution. Niche characteristics were determined using Outlying Mean Index (OMI) analysis. 3. We found that the regional occupancy in our model group of unicellular eukaryotes, stream diatoms, was primarily a reflection of the niche position of a species or, more generally, habitat availability. Thus, non‐marginal species (i.e. species that occupied common habitat conditions across the region) tended to be more widely distributed than marginal species (i.e. species that were restricted to a limited range of rare habitat conditions). This finding was further supported by the general linear model, with niche position, niche breadth, maximum size and attachment mode as explanatory variables: niche position was by far the most important variable accounting for variability in regional occupancy, with significant amounts of additional variation related to niche breadth and maximum size of diatoms. 4. Thus, the degree of regional occupancy among unicellular eukaryotes may be primarily governed by habitat availability, supporting former findings for multicellular organisms.     

Climate or diet? The importance of biotic interactions in determining species range size

Aim

Species geographical range sizes play a crucial role in determining species vulnerability to extinction. Although several mechanisms affect range sizes, the number of biotic interactions and species climatic tolerance are often thought to play discernible roles, defining two dimensions of the Hutchinsonian niche. Yet, the relative importance of the trophic and the climatic niche for determining species range sizes is largely unknown.

Location

Central and northern Europe.

Time period

Present.

Major taxa studied

Gall-inducing sawflies and their parasitoids.

Methods

We use data documenting the spatial distributions and biotic interactions of 96 herbivore species, and their 125 parasitoids, across Europe and analyse the relationship between species range size and the climatic and trophic dimensions of the niche. We then compare the observed relationships with null expectations based on species occupancy to understand whether the relationships observed are an inevitable consequence of species range size or if they contain information about the importance of each dimension of the niche on species range size.

Results

We find that both niche dimensions are positively correlated with species range size, with larger ranges being associated with wider climatic tolerances and larger numbers of interactions. However, diet breadth appears to more strongly limit species range size. Species with larger ranges have more interactions locally and they are also able to interact with a larger diversity of species across sites (i.e. higher β-diversity), resulting in a larger number of interactions at continental scales.

Main conclusions

We show for the first time how different aspects of species diet niches are related to their range size. Our study offers new insight into the importance of biotic interactions in determining species spatial distributions, which is critical for improving understanding and predictions of species vulnerability to extinction under the current rates of global environmental change.     

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.     

Niche breadth explains the range size of European-centred butterflies,but dispersal ability does not

Aim

The breadth of ecological niches and dispersal abilities have long been discussed as important determinants of species' range sizes. However, studies directly comparing the relative effects of both factors are rare, taxonomically biased and revealed inconsistent results.

Location

Europe.

Time Period

Cenozoic.

Major Taxa

Butterflies, Lepidoptera.

Methods

We relate climate, diet and habitat niche breadth and two indicators of dispersal ability, wingspan and a dispersal tendency index, to the global range size of 369 European-centred butterfly species. The relative effects of these five predictors and their variation across the butterfly phylogeny were assessed by means of phylogenetic generalized least squares models and phylogenetically weighted regressions respectively.

Results

Climate niche breadth was the most important single predictor, followed by habitat and diet niche breadth, while dispersal tendency and wingspan showed no relation to species' range size. All predictors together explained 59% of the variation in butterfly range size. However, the effects of each predictor varied considerably across families and genera.

Main Conclusions

Range sizes of European-centred butterflies are strongly correlated with ecological niche breadth but apparently independent of dispersal ability. The magnitude of range size–niche breadth relationships is not stationary across the phylogeny and is often negatively correlated across the different dimensions of the ecological niche. This variation limits the generalizability of range size–trait relationships across broad taxonomic groups.     

Invader abundance and contraction of niche breadth during replacement of a native gammarid amphipod

The introduction of non‐native species to new locations is a growing global phenomenon with major negative effects on native species and biodiversity. Such introductions potentially bring competitors into contact leading to partial or total species replacements. This creates an opportunity to study novel species interactions as they occur, with the potential to address the strength of inter‐ and intraspecific interactions, most notably competition. Such potential has often not been realized, however, due to the difficulties inherent in detecting rapid and spatially expansive species interactions under natural field conditions. The invasive amphipod crustacean Gammarus pulex has replaced a native species, Gammarus duebeni celticus, in river and lake systems across Europe. This replacement process is at least partially driven by differential parasitism, cannibalism, and intraguild predation, but the role of interspecific competition has yet to be resolved. Here, we examine how abundance of an invasive species may affect spatial niche breadth of a native congeneric species. We base our analyses of niche breadth on ordination and factor analysis of biological community and physical parameters, respectively, constituting a summative, multidimensional approach to niche breadth along environmental gradients. Results derived from biological and environmental niche criteria were consistent, although interspecific effects were stronger using the biological niche approach. We show that the niche breadth of the native species is constrained as abundance of the invader increases, but the converse effect does not occur. We conclude that the interaction between invasive G. pulex and native G. d. celticus under natural conditions is consistent with strong interspecific competition whereby a native, weaker competitor is replaced by a superior invasive competitor. This study indicates a strong role of interspecific competition, alongside other known interactions such as differential intraguild predation, in rapid and expansive species replacements following biological invasions.     

Truncation of thermal tolerance niches among Australian plants

Aim

Despite recognition that realized distributions inherently underestimate species' physiological tolerances, we are yet to identify the extent of these differences within diverse taxonomic groups. The degree to which species could tolerate environmental conditions outside their observed distributions may have a significant impact on the perceived extinction risk in ecological models. More information on this potential error is required to improve our confidence in management strategies.

Location

Australia.

Time Period

1983–2012.

Major Taxa Studied

Plants.

Methods

To quantify the scale and spatial patterns of this disparity, we estimated the existing tolerance to thermal extremes of 7,124 Australian plants, more than one‐third of the native continental flora, using data from cultivated records at 128 botanical gardens and nurseries. Hierarchical Bayesian beta regression was used to assess whether factors such as realized niches, traits or phylogeny could predict the incidence or magnitude of niche truncation (underestimation of thermal tolerances), while controlling for sources of collection bias.

Results

Approximately half of the cultivated species analysed could tolerate temperature extremes beyond those experienced in their native range. Niche truncation was predictable from the breadth and extremes of their realized niches and by traits such as plant growth form. Phylogenetic relationships with niche truncation were weak and appeared more suited to predicting thermal tolerances directly.

Main conclusions

This study highlights a widespread disparity between realized and potential thermal limits that may have significant implications for species' capacity to persist in situ with a changing climate. Identifying whether thermal niche truncation is the result of biotic interactions, dispersal constraints or other environmental factors could provide significant insight into community assembly at macroecological scales. Estimating niche truncation may help to explain why certain ecological communities are more resilient to change and may potentially improve the reliability of model projections under climate change.     

A global analysis of the determinants of alien geographical range size in birds

Aim Determining the causes of range size variation in the distributions of alien species is important for understanding the spread of invasive species. Factors influencing alien range size have been explored for some species at a regional level, but to date there has been no global analysis of an entire class. Here, we present such an analysis for birds, testing for the effects of introduction event, location and species‐level variables on alien range sizes. Location Global. Methods We used a novel dataset on the global distributions of alien bird species to test for relationships between alien range size and colonization pressure, residence time, extent of the global climatic niche, native range size, body mass and specialization, using a statistical approach based on phylogenetic generalized least squares models. We performed this analysis globally, and for separate biogeographical realms. Results Approximately half of the variation in alien bird range size is explained by colonization pressure in univariate analysis. We identified consistent effects of higher colonization pressure at global and realm levels, as well as support for effects of native range size and residence time. We found less support for effects of body mass, specialization or extent of the global climatic niche on alien range size. Main conclusions Alien bird range sizes are generally small relative to their native range sizes, and many are continuing to expand. Nevertheless, current variation is predictable, most strongly by the event‐level factor of colonization pressure. Whether a species is widespread is a better predictor of alien range size than whether a species could be widespread (estimated by global climatic niche extent), while we also find effects of residence time on alien range size. These relationships may help to identify those alien species that are more likely to spread and hence have greater environmental and economic impacts where they have been introduced.     

生态位概念及其在昆虫生态学中的应用

生态位理论已成为现代生态学的重要内容。在生态位概念百年演变史中,“空间生态位”、“功能生态位”与“多维超体积生态位”最具代表性。生态位宽度和生态位重叠是描述物种内和物种间生态位关系最重要的2个指标。本文系统总结了生态位概念的演变历史及其主要测度公式在昆虫生态学中的应用概况;并就如何利用生态位理论,开展害虫综合治理提出了几点看法;最后就生态位理论在昆虫生态学中存在的问题及应用前景进行了分析和展望。合理利用生态位理论,将为切实制定有害生物综合治理策略和探讨外来入侵物种种群形成机理等方面提供理论指导。     

Alpha richness and niche breadth of a widespread group of aquatic insects in Nearctic and Neotropical streams

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Tolerance niche expansion and potential distribution prediction during Asian openbill bird range expansion

It is prevalent to use ecological niche models in the analysis of species expansion and niche changes. However, it is difficult to estimate the niche when alien species fail to establish in exotic areas. Here, we applied the tolerance niche concept, which means that niche of species can live and grow but preclude a species from establishing self‐sustaining populations, in such fail‐to‐establish events. Taking the rapidly expanded bird, Asian openbill (Anastomus oscitans), as a model species, we investigated niche dynamics and its potential effects on the population by Niche A and ecospat, predicted potential distribution by biomod2. Results showed that niche expansion has occurred in two non‐native populations caused by the tolerance of colder and wetter environments, and potential distribution mainly concentrated on equatorial islands. Our study suggested that the expanded niche belongs to tolerance niche concept according to the populations'' dynamics and GPS tracking evidence. It is essential to consider source populations when we analyze the alien species. We recommended more consideration to the application of tolerance niche in alien species research, and there is still a need for standard measurement frameworks for analyzing the tolerance niche.     

Contrasting climate niches among co‐occurring subdominant forbs of the sagebrush steppe

Aim

Abiotic conditions are key components that determine the distribution of species. However, co‐occurring species can respond differently to the same factors, and determining which climate components are most predictive of geographic distributions is important for understanding community response to climate change. Here, we estimate and compare climate niches of ten subdominant, herbaceous forb species common in sagebrush steppe systems, asking how niches differ among co‐occurring species and whether more closely related species exhibit higher niche overlap.

Location

Western United States.

Methods

We used herbarium records and ecological niche modelling to estimate area of occupancy, niche breadth and overlap, and describe characteristics of suitable climate. We compared mean values and variability in summer precipitation and minimum temperatures at occurrence locations among species, plant families, and growth forms, and related estimated phylogenetic distances to niche overlap.

Results

Species varied in the size and spatial distribution of suitable climate and in niche breadth. Species also differed in the variables contributing to their suitable climate and in mean values, spatial variation and interannual variation in highly predictive climate variables. Only two of ten species shared comparable climate niches. We found family‐level differences associated with variation in summer precipitation and minimum temperatures, as well as in mean minimum temperatures. Growth forms differed in their association with variability in summer precipitation and minimum temperatures. We found no relationship between phylogenetic distance and niche overlap among our species.

Main conclusions

We identified contrasting climate niches for ten Great Basin understorey forbs, including differences in both mean values and climate variability. These estimates can guide species selection for restoration by identifying species with a high tolerance for climate variability and large climatic niches. They can also help conservationists to understand which species may be least tolerant of climate variability, and potentially most vulnerable to climate change.

     

Flow intermittency decreases nestedness and specialisation of diatom communities in Mediterranean rivers

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Positive relationship between regional distribution and local abundance in stream insects: a consequence of niche breadth or niche position?

A positive relationship between regional distribution and local abundance of species is almost ubiquitous macroecological pattern, yet the mechanisms behind this pattern remain poorly understood. I tested for the relationship between regional distribution and local abundance of stream insect species in a boreal drainage system, with a specific aim to examine if this relationship follows the mechanistic basis of either the niche-based (niche breadth and niche position) or metapopulation models. There was a positive relationship between regional distribution and local abundance of stream insects, and there also were significant relationships between distribution/abundance and niche breadth or niche position. These results thus suggest that widely distributed species tend to be, on average, locally more abundant, have wider niches and lower marginality of niche position with regard to environmental factors than species that have more restricted distributions. However, although significant, there was much unexplained variability around these relationships, suggesting that other mechanisms (e.g. metapopulation dynamics) besides differences in species' niches are likely to affect the distribution and abundance of stream insects, at least within a drainage system. The results thus showed that 1) although niche position was more consistently related to the positive distribution-abundance relationship, ecologists should not abandon niche breadth as a potential mechanism behind this relationship, and 2) that several mechanisms are likely to act in concert in determining the relationship between distribution and abundance of species.     

入侵植物藿香蓟与常见伴生杂草的生态位特征

基于传统生态位理论的生物入侵机制假说认为外来种和土著种生态位的差异是决定入侵成功与否和危害程度的关键。藿香蓟(Ageratum conyzoides L.)是一种在我国南方快速蔓延的恶性入侵种。为了了解藿香蓟与其他杂草在群落中的生态关系,探究造成藿香蓟成功入侵的可能机制及危害,在浙西南的丽水市开展了杂草群落调查,计算了藿香蓟和16种常见本地杂草的生态位宽度、生态位重叠和种间相关系数,并对主要物种进行典范对应分析(CCA)排序。结果表明(1)藿香蓟与常见本地杂草间的生态位重叠度显著高于本地杂草间的生态位重叠度,这与藿香蓟具有最大的生态位宽度有关;(2)藿香蓟与常见本地杂草的Pianka生态位重叠指数介于0.04-0.296之间,重叠度处于中下水平;(3)常见本地杂草对于藿香蓟的n-维超体积生态位重叠值显著高于藿香蓟对于常见本地杂草的n-维超体积生态位重叠值;(4)藿香蓟在CCA排序图上处于较中心的位置,说明其具有较高的中生性;不仅如此,外来杂草和本地杂草在排序图上充分混杂,说明外来种相对于本地种并无明显特化;(5)群落中大多数常见杂草间未出现显著种间负相关,仅7个种对显著正相关,大多数种对不相关。总的来说,丽水农村的杂草群落稳定较差,资源相对充足,种间生态位重叠较低,本地植物对于藿香蓟的竞争阻抗较小,加上藿香蓟本身较大的生态位宽度,导致了藿香蓟在本地区广泛而严重的入侵。     

From introduction to equilibrium: reconstructing the invasive pathways of the Argentine ant in a Mediterranean region

Determining the geographical range of invasive species is an important component of formulating effective management strategies. In the absence of detailed distributional data, species distribution models can provide estimates of an invasion range and increase our understanding of the ecological processes acting at various spatial scales. We used two complementary approaches to evaluate the influence of historical and environmental factors in shaping the distribution of the Argentine ant ( Linepithema humile ), a widespread, highly invasive species native to South America. Occurrence data were combined with environmental data at incremental spatial scales (extent and resolution) to predict the suitable range of the ant invasion using ecological niche models. In addition, we also used a spread model that simulated the jump dispersal of the species to identify the most plausible scenarios of arrival of L. humile in the NE Iberian Peninsula at local scales. Based on the results of both modelling practices, we suggest that L. humile might have reached its maximum geographic range at regional scales in the NE Iberian Peninsula. However, the species does not appear in equilibrium with the environment at small spatial scales, and further expansions are expected along coastal and inland localities of the Costa Brava. Long-distance jumps are ultimately responsible for the spread of the Argentine ant in the area. Overall, our study shows the utility of combining niche based models with spread models to understand the dynamics of species' invasions.     

Evaluating niche changes during invasion with seasonal models in Capsella bursa-pastoris

Premise

Researchers often use ecological niche models to predict where species might establish and persist under future or novel climate conditions. However, these predictive methods assume species have stable niches across time and space. Furthermore, ignoring the time of occurrence data can obscure important information about species reproduction and ultimately fitness. Here, we assess compare ecological niche models generated from full-year averages to seasonal models.

Methods

In this study, we generate full-year and monthly ecological niche models for Capsella bursa-pastoris in Europe and North America to see if we can detect changes in the seasonal niche of the species after long-distance dispersal.

Results

We find full-year ecological niche models have low transferability across continents and there are continental differences in the climate conditions that influence the distribution of C. bursa-pastoris. Monthly models have greater predictive accuracy than full-year models in cooler seasons, but no monthly models can predict North American summer occurrences very well.

Conclusions

The relative predictive ability of European monthly models compared to North American monthly models suggests a change in the seasonal timing between the native range to the non-native range. These results highlight the utility of ecological niche models at finer temporal scales in predicting species distributions and unmasking subtle patterns of evolution.     

张掖国家湿地公园优势鸟类种群生态位研究

鸟类时空格局影响下鸟类种群生态位的变化是认识鸟类环境适应机制的理论基础。在张掖国家湿地公园保育区,采用样带法研究了冬春季节5种优势鸟类种群生态位宽度和生态位重叠的时间异质性。结果表明:随着月份的更替,5种优势鸟类种群的生态位宽度呈现出先增大后减小的变化趋势,赤麻鸭(Tadornaferruginea)、绿头鸭(Anasplatyrhynchos)、麻雀(Passer montanus)、白骨顶鸡(Fulicaatra)的最高值出现在1月分别为1.601、1.415、1.627、1.771,大白鹭(Ardea alba)的最高值出现在3月为0.556;不同月份间鸟类优势种群生态位重叠存在差异,3月、11月生态位的重叠值最大,1月份最小;优势鸟类种群的生态位宽度和重叠在时间尺度上表现出"此消彼长"的关系。湿地公园时间尺度上的鸟类生态位宽度和重叠的差异与湿地食物资源及隐蔽条件、鸟类群体迁徙规律、鸟类种间的竞争密切相关,反应了湿地鸟类适应生境变化的可塑性机制。     

Habitat niche breadth predicts invasiveness in solitary ascidians

A major focus of invasion biology is understanding the traits associated with introduction success. Most studies assess these traits in the invaded region, while only few compare nonindigenous species to the pool of potential invaders in their native region. We focused on the niche breadth hypothesis, commonly evoked but seldom tested, which states that generalist species are more likely to become introduced as they are capable of thriving under a wide set of conditions. Based on the massive introduction of tropical species into the Mediterranean via the Suez Canal (Lessepsian migration), we defined ascidians in the Red Sea as the pool of potential invaders. We constructed unique settlement plates, each representing six different niches, to assess ascidian niche breadth, and deployed them in similar habitats in the native and invaded regions. For each species found on plates, we evaluated its abundance, relative abundance across successional stages, and niche breadth, and then compared (1) species in the Red Sea known to have been introduced into the Mediterranean (Lessepsian species) and those not known from the Mediterranean (non‐Lessepsian); and (2) nonindigenous and indigenous species in the Mediterranean. Lessepsian species identified on plates in the Red Sea demonstrated wider niche breadth than non‐Lessepsian species, supporting the niche breadth hypothesis within the native region. No differences were found between Lessepsian and non‐Lessepsian species in species abundance and successional stages. In the Mediterranean, nonindigenous species numerically dominated the settlement plates. This precluded robust comparisons of niche breadth between nonindigenous and indigenous species in the invaded region. In conclusion, using Red Sea ascidians as the pool of potential invaders, we found clear evidence supporting the niche breadth hypothesis in the native region. We suggest that such patterns may often be obscured when conducting trait‐based studies in the invaded regions alone. Our findings indicate that quantifying the niche breadth of species in their native regions will improve estimates of invasiveness potential.     

舟山长白海域主要游泳动物生态位及其分化研究

基于2016年10月（秋季）和2017年4月（春季）舟山长白海域的渔业资源调查数据,运用生态位宽度、生态位重叠及冗余分析等方法,研究了主要游泳动物的生态位,种间生态关系及生态位分化。结果显示：春、秋季主要游泳动物分别11种与8种,两季生态位宽度值差异均较大,其中春季广生态位种、中生态位种均为3种,而秋季均为2种,窄生态位种分别为5种与4种。相对重要性指数（IRI）与生态位宽度值（B_i）之间呈显著正相关。生态位重叠程度不均衡,秋季主要游泳动物的生态位重叠程度较高,O_ik > 0.6的种对数占总种对数的42.86%;春季的重叠程度较低,仅占总种对数的21.82%。RDA分析得出温度、盐度为影响主要游泳动物分布的直接因素,而溶解氧、悬浮物和pH等则为重要因素,主要游泳动物在这些资源维上存在生态分化现象。综上,分布在毗邻杭州湾口且位于著名的岱衢洋的主要游泳动物种类总体营养级较低却生态宽度值较大,大黄鱼（Larimichthys crocea）、黄姑鱼（Nibea albiflora）等一些传统的高营养级、典型特色经济种类却沦为生态位宽度极小的一般种或少有种,群落种类显著减少,资源量下降,群落结构与功能退化,稳定性下降。因此,加强游泳动物资源修复、保护与管理十分迫切且具有重要意义。