Interspecific Niche Overlap Research Articles

Human habitat modification, not apex scavenger decline, drives isotopic niche variation in a carnivore community.

Top carnivores can influence the structure of ecological communities, primarily through competition and predation; however, communities are also influenced by bottom-up forces such as anthropogenic habitat disturbance. Top carnivore declines will likely alter competitive dynamics within and amongst sympatric carnivore species. Increasing intraspecific competition is generally predicted to drive niche expansion and/or individual specialisation, while interspecific competition tends to constrain niches. Using stable isotope analysis of whiskers, we studied the effects of Tasmanian devil Sarcophilus harrisii declines upon the population- and individual-level isotopic niches of Tasmanian devils and sympatric spotted-tailed quolls Dasyurus maculatus subsp. maculatus. We investigated whether time since the onset of devil decline (a proxy for severity of decline) and landscape characteristics affected the isotopic niche breadth and overlap of devil and quoll populations. We quantified individual isotopic niche breadth for a subset of Tasmanian devils and spotted-tailed quolls and assessed whether between-site population niche variation was driven by individual-level specialisation. Tasmanian devils and spotted-tailed quolls demonstrated smaller population-level isotopic niche breadths with increasing human-modified habitat, while time since the onset of devil decline had no effect on population-level niche breadth or interspecific niche overlap. Individual isotopic niche breadths of Tasmanian devils and spotted-tailed quolls were narrower in human-modified landscapes, likely driving population isotopic niche contraction, however, the degree of individuals' specialisation relative to one another remained constant. Our results suggest that across varied landscapes, mammalian carnivore niches can be more sensitive to the bottom-up forces of anthropogenic habitat disturbance than to the top-down effects of top carnivore decline.

Interspecific niche overlap and climatic associations of native Quercus species in the Zagros forests of Iran

In the arid regions surrounding southwestern Asia, oak trees play an important role in the environment by conserving water and preserving soil and supporting wildlife. There are concerns for the health and continued productivity of these forests, and there is a widespread oak decline. In this study, ecological niche modeling (ENM) and multivariate principal component analysis (PCA) were used to determine the environmental variations among Quercus brantii, Q. infectoria, and Q. libani in the Zagros forests of western Iran. Based on the area under the curve (AUC > 0.9) and the true skill statistic (TSS > 0.8), three algorithms, including random forest (RF), maximum entropy (MaxEnt), and maximum picking neural net (MAXnet), were used in an ensemble approach to explore the most important environmental variables within the projected suitable habitat of each species. Environmental variables related to climate, including annual precipitation (bio12) and annual mean temperature (bio1), were among the most important drivers of habitat suitability for oak species. The results illustrated that suitable areas for Q. infectoria and Q. libani often occur in the northern parts of the Zagros, which are humid and cooler than the southern areas. The results suggested that Q. brantii has a higher tolerance for harsh conditions in Zagros and therefore inhabits almost all areas of Zagros, including the southern parts. The climatic overlap between pairs of species was found to be significant based on equivalency and similarity tests, suggesting that the environmental conditions of the two species compared are more similar than would be expected by chance. The gap analysis for the three oak species revealed that only a few protected areas currently exist within their suitable habitats, with most of the highly suitable habitats located on non-protected lands, particularly for Q. libani and Q. infectoria. In addition, deforestation is known to sometimes occur within the boundaries of protected areas. Improving the level of protection by upgrading the current protected areas to national parks can help with conservation.

Grassland degradation induces high dietary niche overlap between two common livestock: cattle and sheep

AbstractIntroductionDiet selection of grazing livestock is one of the critical factors affecting the diversity and composition of plant communities in grasslands, with consequent impacts for ecosystem functioning. Co‐grazing of multiple livestock species could create additive or complementary effects on plant communities due to diet overlap or differentiation among livestock species. However, there is only limited knowledge about diet overlap and differentiation of co‐occurring livestock species and whether or how these diet characteristics change with grassland degradation.Materials and MethodsWe experimentally test the diets of two commonly co‐occurring livestock species (cattle and sheep) and the dietary niche partitioning/overlap between them in non‐degraded, moderately and severely degraded grasslands.ResultsCattle exhibited broader diet than sheep, and diet overlap between species was lower in non‐degraded grasslands. As grassland degradation increased the availability of annual plants, interspecific niche overlap between cattle and sheep gradually increased, and cattle suffered a resulting dietary niche compression. Sheep maintained a relatively narrow and constant dietary breadth.ConclusionThe increasing dietary niche overlap between livestock species with increasing extent of grassland degradation indicated increased additive effects of cattle and sheep co‐grazing on plant community, and thus stronger effects on plant community composition and diversity.

Trait based niche differentiation in tetrakas (Bernieridae) endemic to Madagascar: A multi-isotope approach

Introduction Tropical rainforest species interact with each other and their environment over a wide range of spatiotemporal scales. However, our understanding of resource partitioning and the mechanisms of avian species coexistence is largely restricted to subjective visual observations or acoustic monitoring. Therefore, the relative magnitudes of interspecific and intraspecific differences in resource use have remained difficult to quantify, particularly regarding different diets and habitat use. The eastern rainforest belt of Madagascar is inhabited by several species of insectivorous tetrakas belonging to an endemic bird family of Madagascar (Bernieridae). These species occupy similar habitats in the forest understory and are morphologically similar but because of likely differences (e.g., in foraging behaviors) we expect their foraging niches to be segregated allowing coexistence. Methods We examined the niche differentiation of four of these species: the Grey-crowned Tetraka ( Xanthomixis cinereiceps ), Long-billed Tetraka ( Bernieria madagascariensis ), Spectacled Tetraka ( Xanthomixis zosterops ), and White-throated Oxylabes ( Oxylabes madagascariensis ) in the Maromizaha rainforest in eastern Madagascar combining morphometry with stable carbon, nitrogen, and sulfur isotope ratios (δ 13 C, δ 15 N, and δ 34 S) from feathers. Results We show considerable variation in isotopic niche positions, niche breadth and interspecific niche overlap. In two species, the Long-billed Tetraka and Spectacled Tetraka, we found an indication of sex-specific niche space, with males exhibiting a larger isotopic niche-area relative to females. Morphological traits of five species (including the Wedge-tailed Tetraka, Hartertula flavoviridis ) coupled with stable isotope data provided explanations of patterns of niche overlap and isotopic position. Discussion The observed isotopic niche differences may be explained by differences in resource acquisition strategies that might be associated with specific morphological traits and spatial distribution. This may play an important role in niche differentiation among coexisting and phylogenetically closely related species.

Influence of grazing on the activity pattern and temporal niche of two dominant rodent species in Alxa desert

Grazing by large herbivores can potentially affect interspecific interactions between small herbivores by reducing the ecological fitness of animals. Desert rodents are important components in desert ecosystems and indicators of environmental change. Grazing reduces food resources, but rodents can decrease interspecific niche overlap by adaptive behavior. However, the key factors driving rodent behavioral activities and coexistence in the Alxa desert remains unstudied. We monitored population density and behavioral activities of Midday gerbil (Meriones meridianus) and northern three-toed jerboa (Dipus sagitta) in a grazing exclusion experiment in Alxa desert, Inner Mongolia, China, in 2017. We assessed the relationship between environmental factors (such as plant height, density, coverage, rainfall and temperature) and the behavioral activities of two coexisting rodent species. The results showed that: (1) In summer, grazing significantly reduced the activity time of gerbil and jerboa compared to that in grazing exclusion areas (gerbil: F = 5.98, p < 0.05, η2 = 0.22; jerboa: F = 8.57, p < 0.01, η2 = 0.28). Grazing reduced the temporal niche overlap with an obvious shifting of activity peaks between two species. (2) Grazing exclusion enhanced the temporal niche overlap between the two rodent species due to greater food availability which relieved inter-specific competition in each season. (3) Grazing strengthened the sensitivity of rodents to environmental changes in all seasons. These results indicated that grazing affected competition between the rodent species by altering vegetation conditions, which in turn affected the temporal niche and activity patterns of rodents.

喀斯特石漠化锑矿区植物群落主要物种生态位特征及其种间联结

PDF HTML阅读 XML下载 导出引用 引用提醒 喀斯特石漠化锑矿区植物群落主要物种生态位特征及其种间联结 DOI: 10.5846/stxb202203300794 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划场地污染土壤成因与治理技术专项项目（2020YFC1807704） Niche characteristics and interspecific association of main plant species in antimony mining sites of karst rocky desertification area, Guizhou, China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:锑矿的开采等活动剥离了喀斯特石漠化区的地上植被，导致该区群落物种组成与结构被破坏、生态系统受损或功能丧失。为了解锑矿开采后生态破坏区优势物种亮叶桦（Betula luminifera）群落特征及演替状态，并为复层植被重建的物种选择提供理论依据。基于贵州晴隆大厂镇锑矿生态破坏区调查数据，分析了该区优势物种的Levins生态位宽度和Pianka生态位重叠度，并运用卡方检验（χ2）、Ochiai指数（OI）和Pearson相关性计算了群落优势物种种间联结性。结果表明：（1）石漠化锑矿生态破坏区物种组成远低于未破坏区（30科53属68种），仅为14科18属22种，乔木层物种仅为亮叶桦，灌木层物种重要值由高到低依次为密蒙花（Buddleja officinalis）、茅莓（Rubus parvifolius）和水麻（Boehmeria penduliflora）等，草本层物种重要值由高到低依次为芒（Miscanthus sinensis）、头花蓼（Polygonum capitatum）、破坏草（Ageratina adenophora）、艾草（Artemisia argyi）和鬼针草（Bidens pilosa）等。（2）锑矿生态破坏区灌草层和未破坏区乔灌草层的物种重要值与生态位宽度呈极显著正相关，但不同物种的生态位宽度不同，这是物种生物学属性不同所致；锑矿生态破坏区除水麻与插田泡（Rubus coreanus）的生态位重叠值为1外，其他物种间的生态位重叠程度较低。（3）石漠化锑矿生态破坏区灌木层总体呈显著负联结，种对间负联结数占比较高（5对）；草本层总体联结性不显著，但种对间负联结数有15对，其中艾草与芒、艾草与白三叶（Trifolium repens）、芒与破坏草种对间联结程度较高，表明植被群落处于演替前期，极不稳定且易受破坏。未破坏区乔木层和灌木层总体联结性不显著，草本层总体为显著正联结，表明未破坏区植被群落相对稳定。（4）石漠化锑矿生态破坏区植被恢复应选择生态习性相近、重叠程度较小、种间为正联结的物种，例如乔本层的亮叶桦和山苍子（Litsea cubeba）等，灌木层的密蒙花和茅莓等，草本层的艾草、蕨（Pteridium aquilinum）、芒和马唐（Digitaria sanguinalis）等，以达到乔灌草配置具有高稳定性植物群落的效果。锑矿生态破坏区物种组成较少，植物群落结构不稳定，处于演替早期；未来喀斯特石漠化锑矿生态破坏区植物群落仍需要很长一段时间演替才能达到未破坏区植物群落状态，适宜的乡土植物和合理的配置模式有助于加快植被恢复进程。 Abstract:The plant community was damaged or stripped by antimony (Sb) mining activities in the karst rocky desertification of Guizhou, China, which destroyed the species composition and structure of the community, damaged the function of this ecosystem. This study aims to well understand the actual vegetation, community characteristics and succession stage of the community with dominant species Betula luminifera in the Sb mining area, and provide the theoretical basis for revegetation and ecological rehabilitation. After the field investigation dataset of the ecological damaged area by Sb mining and control areas, the Levins's and Pianka's method were applied to evaluate the niche width of species, the interspecific niche overlap, and the interspecific associations were assessed by the chi-square test (χ2), Ochiai index (OI) and Pearson correlation. The results show that (1) there is only 14 families, 18 genera and 22 species in the ecological damaged area by Sb mining, which is lower than that of the undamaged area of control, with 30 families, 53 genera and 68 species. The only tree species is Betula luminifera, the shrubs layer species with top three importance values (IV) are Buddleja officinalis, Rubus parvifolius, Boehmeria penduliflora, and the herb layer with top five IV are Miscanthus sinensis, Polygonum capitatum, Ageratina Adenophora, Artemisia argyi and Bidens Pilosa in the ecological damaged area by Sb mining. (2) There are significantly positive between IV and niche width of species in the shrub-herb layer of Sb mining area and the layer of control area, while the niche width of different species shows inconsistence, which may be ascribed to the specific biological properties of the different species. Except for the niche overlap between Rubus coreanus and B. penduliflora is 1 in the Sb mining area, the niche overlap of others interspecies are low. (3) The main species of shrub layer in Sb mining area of karst rocky desertification has a significantly negative association, and the species pairs of negative associations are relatively high (5 pairs). The main species of herb layer of Sb mining area has no significant association, while high association values are observed between A. argyi and M. sinensis, A. argyi and Trifolium repens, T. repens and Ageratina Adenophora. It suggested the community at the early succession with extremely unstable stage. In the control area, the main species of tree and shrub layer show no significant associations, the main species of herb layer indicates the significantly positive association, indicating that the community is at relatively stable stage. (4) The results suggest that ideal plant candidates are the species with similar ecological habits, low niche overlap, and positive interspecific association for the purpose of Sb mining area revegetation, such as B. luminifera, Litsea cubeba, B. officinalis, R. parvifolius, A. argyi, Pteridium aquilinum, M. sinensis and Digitaria sanguinalis. It will help to construct the plant community with high stability of multiple stratified of trees, shrubs and herbs. Taken together, the plant community in Sb mining area characterized with low species composition, and unstable plant community, and an early stage of succession. It will take a long time for rebuilding the stable plant community in the Sb mining area, and the suitable native plant application and vegetation arrangement during the ecological rehabilitation help to facilitate the revegetation and sucession. 参考文献 相似文献 引证文献

Comparative trophic ecology of nearshore juvenile salmonids in Lake Ontario

The trophic ecology of juvenile salmonids in nearshore Lake Ontario is not well understood. We used stomach content and stable isotope diet and niche metrics, as well as condition metrics to understand the trophic ecology of juvenile Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), and lake trout (Salvelinus namaycush). Salmonids had comparable length-weight slopes and stomach mass, and allometric patterns existed between fork-length and both relative stomach content mass and energy density for all species. Interspecific differences existed with respect to diet, and the magnitude of difference generally increased with increasing body size. Small sized salmonid (fork length < 100 mm) diets mainly consisted of Diptera (% volume = 66 – 100; prey isotope %: 11.7 – 78.4), while large sized salmonids (fork length 200 – 300 mm) consumed fish (% volume = 20–100; prey isotope % = 21.5 – 42.7). Salmonids exhibited high interspecific niche overlap, with lake trout (SEAB = 22.9 ‰2) and brown trout (18.6 ‰2) having the largest isotopic niche size, and Atlantic salmon having the smallest (2.7 ‰2). Our study addressed a knowledge gap in trophic ecology between mostly stream-dwelling juvenile and open lake adult salmonid life stages, revealing differences in diet but comparable condition metrics which suggests different strategies to optimise performance in the nearshore environment.

Niche overlap in rodents increases with competition but not ecological opportunity: A role of inter-individual difference.

Niche variation at population level mediates niche packing (i.e. patterns of species' spread within the niche space) and species coexistence at community level. Competition and ecological opportunity (resource diversity) are two of the main mechanisms underlying niche variation. Dense niche packing could occur through increased niche partitioning or increased niche overlap. In this study, we used stable carbon and nitrogen isotope data of 635 individual rodents from four species across nine sites in the montane region of a subtropical island to test the effects of competition and ecological opportunity on population isotope niche size, inter-individual niche difference within population and interspecific niche overlap within community. We used the Bayesian Standard Ellipse Area (SEAB, the ellipse area enclosed by carbon and nitrogen isotope values of organisms on a bi-plot) to estimate population niche size and interspecific niche overlap. Inter-individual niche difference within population was quantified as isotopic divergence and isotopic uniqueness. We used rodent abundance (the number of unique individuals captured) to measure competition and plant isotope niche size (plant SEAB) to measure ecological opportunity. The rodents experienced competition as evidenced by a negative relationship between population change rate and conspecific abundance. Rodent population niche size increased with ecological opportunity but not competition. The inter-individual niche difference (isotopic uniqueness) increased with competition (interspecific competition only) but not ecological opportunity. At community level, interspecific niche overlap (herbivore-omnivore pair only) increased with competition (the combined abundance of the pair) but not ecological opportunity. This study demonstrated that isotope niche variation of the rodents could be hierarchically influenced by ecological opportunity and competition, with the former setting the limit of population niche size across communities and the latter shaping inter-individual niche difference and interspecific niche overlap within communities. Under strong intraspecific competition and limited ecological opportunity for niche expansion, individuals may choose to increase their isotopic uniqueness from conspecifics at the cost of overlapping with heterospecifics of different trophic roles within the community niche space as overall competition increases. Denser niche packing of these rodent communities might be achieved through increased niche overlap.

Artificial illumination influences niche segregation in bats

Artificial light at night (ALAN) is a pervasive form of pollution largely affecting wildlife, from individual behaviour to community structure and dynamics. As nocturnal mammals, bats are often adversely affected by ALAN, yet some “light-opportunistic” species exploit it by hunting insects swarming near lights. Here we used two potentially competing pipistrelle species as models, Kuhl’s (Pipistrellus kuhlii) and common (Pipistrellus pipistrellus) pipistrelles, both known to forage in artificially illuminated areas. We set our study in a mountainous area of central Italy, where only recently did the two species become syntopic. We applied spatial modelling and radiotracking to contrast potential vs. actual environmental preferences by the two pipistrelles. Species distribution models and niche analysis showed a large interspecific niche overlap, including a preference for illuminated areas, presenting a potential competition scenario. Pipistrellus pipistrellus association with ALAN, however, was weakened by adding P. kuhlii as a biotic variable to the model. Radiotracking showed that the two species segregated habitats at a small spatial scale and that P. kuhlii used artificially illuminated sites much more frequently than P. pipistrellus, despite both species potentially being streetlamp foragers. We demonstrate that ALAN influences niche segregation between two potentially competing species, confirming its pervasive effects on species and community dynamics, and provide an example of how light pollution and species’ habitat preferences may weave a tapestry of complex ecological interactions.

Resource partitioning among sympatric elasmobranchs in the central-western Mediterranean continental shelf

Knowledge of the mechanisms that allow coexistence among sympatric species is fundamental to understand ecosystem functioning. Resource partitioning among seven elasmobranchs inhabiting the Sardinian continental shelf (40°07′N, 9°00′E): Dasyatis pastinaca; Raja asterias; R. brachyura; R. clavata; R. miraletus; R. polystigma and Scyliorhinus canicula, was investigated through stomach content analysis. Data from 1680 samples collected between 2005 and 2014, in 26–200 m depth, were analysed with respect to population, sex, season (winter and summer) and size groups. Species living in shallower waters (characterized by a narrower bathymetric range) had the most specialized diets. All species appeared to be mesopredators, feeding mainly on Crustacea, Actinopterygii, Mollusca and Polychaeta. Despite shared common morphological features, from the high ecological diversity of prey items, we hypothesized the presence of different predatory behavior among the species studied: some species were able to feed on endobenthic and/or epibenthic organisms, while others had made limited movements in the water column. Non-parametric Multi-Dimensional Scaling analysis highlighted the presence of five predator groups, confirming strong resource partitioning, as also demonstrated by low levels of interspecific niche overlap. The observed variations in feeding habits could be ascribed only to size and not to sex or season. Generally, diet changed from small Crustacean prey, to larger prey, like Actinopterygii and Mollusca. Some species became more generalist during development, others restricted their prey range. Shifts in feeding habits affected species’ roles in the food web, with different species occupying different functional trophic groups over the course of their life cycles.

Spatial variation in the feeding strategies of Mediterranean fish: flatfish and mullet in the Gulf of Gaeta (Italy)

Marine coastal areas are highly productive due to the presence of various inputs of organic matter, including terrestrial material, which fuels food webs. However, the ecological mechanisms underlying the productivity of benthic and demersal fish species in estuarine areas are poorly understood. By means of C and N stable isotope analysis and Bayesian mixing models, we investigated the trophic niches of three common fish species: Citharus linguatula, Pegusa lascaris (flatfish) and Liza ramada (mullet) in the Gulf of Gaeta (Italy). Fish were collected from the north-western area and the south-eastern area of the Gulf of Gaeta, the latter affected by organic inputs from the Garigliano River. The results highlighted the riverine terrestrial origin of the organic matter at the base of the food web in the south-eastern area and marine autochthonous input in the north-western area. All fish species increased their trophic specialisation in proximity to the river mouth. L. ramada specialised on seston of terrestrial origin, reducing its niche overlap with C. linguatula and P. lascaris. Away from the river mouth, all species were characterised by longer individuals, increased intraspecific diet variability and higher interspecific similarity in resource use. Organic input from the river represented a complementary trophic niche axis that enabled lower interspecific niche overlap in the south-eastern area, where fish populations were found at higher densities. In conclusion, this study provided information about the effects of the flow of material from the basal compartment up to abundant fish species in areas enriched by organic matter of varying origin.

Competition and resource breadth shape niche variation and overlap in multiple trophic dimensions.

Competition plays a central role in the maintenance of biodiversity. A backbone of classic niche theory is that local coexistence of competitors is favoured by the contraction or divergence of species' niches. However, this effect should depend on the diversity of resources available in the local environment, particularly when resources vary in multiple ecological dimensions. Here, we investigated how available resource breadth (i.e. prey diversity) and competition together shape multidimensional niche variation (between and within individuals) and interspecific niche overlap in 42 populations of congeneric tropical frog species. We modelled realized niches in two key trophic dimensions (prey size and carbon stable isotopes) and sampled available food resources to quantify two-dimensional resource breadth. We found a 14-fold variation in multidimensional population niche width across populations, most of which was accounted for by within-individual diet variation. This striking variation was predicted by an interaction whereby individual niche breadth increased with resource breadth and decreased with the number of congeneric competitors. These ecological gradients also interact to influence the degree of niche overlap between species, which surprisingly decreased with population total niche width, providing novel insights on how similar species can coexist in local communities. Together, our results emphasize that patterns of exploitation of resources in multiple dimensions are driven by both competitive interactions and extrinsic factors such as local resource breadth.

Trophic ecology of large herbivores in a reassembling African ecosystem

Abstract Megafauna assemblages have declined or disappeared throughout much of the world, and many efforts are underway to restore them. Understanding the trophic ecology of such reassembling systems is necessary for predicting recovery dynamics, guiding management, and testing general theory. Yet, there are few studies of recovering large‐mammal communities, and fewer still that have characterized food‐web structure with high taxonomic resolution. In Gorongosa National Park, large herbivores have rebounded from near‐extirpation following the Mozambican Civil War (1977–1992). However, contemporary community structure differs radically from the prewar baseline: medium‐sized ungulates now outnumber larger bodied species, and several apex carnivores remain locally extinct. We used DNA metabarcoding to quantify diet composition of Gorongosa’s 14 most abundant large‐mammal populations. We tested five hypotheses: (i) the most abundant populations exhibit greatest individual‐level dietary variability; (ii) these populations also have the greatest total niche width (dietary diversity); (iii) interspecific niche overlap is high, with the diets of less‐abundant species nested within those of more‐abundant species; (iv) partitioning of forage species is stronger in more structurally heterogeneous habitats; and (v) selectivity for plant taxa converges within guilds and digestive types, but diverges across them. Abundant (and narrow‐mouthed) populations exhibited higher among‐individual dietary variation, but not necessarily the greatest dietary diversity. Interspecific dietary overlap was high, especially among grazers and in structurally homogenous habitat, whereas niche separation was more pronounced among browsers and in heterogeneous habitat. Patterns of selectivity were similar for ruminants—grazers and browsers alike—but differed between ruminants and non‐ruminants. Synthesis. The structure of this recovering food web was consistent with several hypotheses predicated on competition, habitat complexity, and herbivore traits, but it differed from patterns observed in more intact assemblages. We propose that intraspecific competition in the fastest‐recovering populations has promoted individual variation and a more nested food web, wherein rare species use subsets of foods eaten by abundant species, and that this scenario is reinforced by weak predation pressure. Future work should test these conjectures and analyse how the taxonomic dietary niche axis studied here interacts with other mechanisms of diet partitioning to affect community reassembly following wildlife declines.

Difference of trophic niche between Sebastiscus marmoratus and Larimichthys polyactis in marine ranching of Ma'an Archipelago, China.

Marine ranching is an effective way to protect and restore coastal fishery resources. In order to assess the impacts of marine ranching construction on the trophic niches and interspecific competition of Sebastiscus marmoratus and Larimichthys polyactis, we analyzed the relationship between the changes of intraspecies trophic niche and the interspecific competition, based on the carbon and nitrogen stable isotope data of these two species collected from 2013 to 2016. The results showed that the intraspecies trophic niches of both species increased significantly in marine ranching area from 2013 to 2016. The total area of the convex polygon (TA) niche increased from 1.89 to 12.43 for S. marmoratus, and increased from 0.34 and 8.86 for L. polyactis, with the interspecific niche overlap area of these two species increasing from 0.13 to 7.69. The standard elliptic trophic niche increased from 1.11 to 4.94 for S. marmoratus, and from 0.14 to 4.06 for L. polyactis, with the interspecific niche overlap area increasing from 0 to 0.26. Values of the δ13C and δ15N of both species showed a tendency of decreasing with time, with significant changes of δ13C, but non-signi-ficant for δ15N. Dietary overlap between those two species increased from 68.9% to 90.6%.

Isotopic niche variation from the Holocene to today reveals minimal partitioning and individualistic dynamics among four sympatric desert mice

Species interact with each other and their environment over a range of temporal scales, yet our understanding of resource partitioning and the mechanisms of species coexistence is largely restricted to modern time-scales of years to decades. Furthermore, the relative magnitudes of inter- vs. intraspecific variation in resource use are rarely considered, despite the potential for the latter to influence a species' ability to cope with changing environmental conditions. Modern desert rodent communities are thought to be strongly structured by competitive interactions, with niche partitioning of food resources hypothesized to explain the coexistence of multiple sympatric granivores. Yet the stability of niche dynamics over extended temporal scales within desert rodent communities is unknown. I examined the isotopic niche dynamics of four common sympatric desert mice (three granivores: Chaetodipus formosus, Perognathus longimembris and Reithrodontomys megalotis, and one omnivore: Peromyscus maniculatus) in the Smoke Creek Desert of northwestern Nevada using 13 C and 15 N isotopes obtained from "Modern" (2008-2013 CE), "Historical" (1989-2005 CE) and Holocene fossil specimens spanning the last c. 7,500years. I found significant variation in niche position, niche breadth and interspecific niche overlap of these species through time. The niche breadth dynamics of the cricetids (P.maniculatus and R.megalotis) were positively correlated with one another, while the niche breadth dynamics of the heteromyid C.formosus were negatively correlated with those of all other species. Body size, dietary functional group, palaeoenvironmental trends and time-averaging provided little explanatory power. Importantly, Modern and Historical patterns of resource use and partitioning differed from Holocene baselines in terms of decreased niche overlap and in the absolute and relative position of each species' niche in at least one isotopic axis. These observations suggest that each species' resource use changed individualistically over the Holocene, hence niche dynamics are poorly explained by the hypothesis of temporally stable species interactions at millennial time-scales. Furthermore, changes to the resource base over the last century (likely due to the spread of invasive cheatgrass) may be increasing resource partitioning in the Modern, pushing species past their baseline ranges of resource use variation.

Microhabitat use within a contact zone of parapatric land salamanders in the Swiss Alps

Studies investigating the contact zones in parapatric species can provide valuable insights into the mechanisms that cause range borders. Such studies can also provide a better understanding of the mechanisms which allow coexistence within contact zones. In land salamanders, parapatric range limits among species are often determined by abiotic factors and interspecific competition. The ranges of the parapatricSalamandra salamandraandS. atranarrowly overlap in the European Alps. Climatic gradients that determine their parapatric range margins suggest dissimilar species-habitat-relationships. However, habitat use for these species has not yet been studied in the contact zone where the parapatric ranges overlap and where the species locally co-occur in syntopy. To better understand their parapatric range limits and local syntopy, we compared the species’ microhabitat use in a contact zone in Switzerland and quantified the degree of interspecific niche overlap in relation to resource availability. We observed that most studied microhabitat variables were neither selected nor avoided by the two species, suggesting random use of the habitat for the variables that we studied. Interspecific niche overlap was generally large, but did not differ from that expected by chance. Unlike previous studies that analyzed patterns of co-occurrence of these species at larger spatial scales, we observed no niche differentiation within the contact zone. Both species likely select the same areas that are suitable and available for salamanders while they similarly avoid generally unsuitable habitat. This indicates that niche differentiation can vary depending on the spatial scale where it is investigated.

Resource partitioning among five sympatric species of freshwater turtles from the wet–dry tropics of northern Australia

Context Resource partitioning of diet and microhabitat was examined for five sympatric species of freshwater turtles in the Daly River in the northern end of Northern Territory (Top End) in Australia. The Daly River supports a high diversity of freshwater turtles, making it the ideal place to study a freshwater turtle community. Aims To determine the dry-season diet and microhabitat use of Carettochelys insculpta, Elseya dentata, Chelodina oblonga, Emydura victoriae and Emydura subglobosa worrelli and examine intraspecific and interspecific niche overlap and ontogenetic dietary shift. Methods Gut contents were collected by stomach flushing, and microhabitat use was determined by recording where each turtle was first seen before capture. Diet and microhabitat use were compared using an index of relative importance. Niche overlap was measured with Horn’s overlap index. Key results Carettochelys insculpta is an opportunistic omnivore that feeds mostly on ribbonweed (Vallisneria spiralis) and aquatic snails. Elseya dentata is herbivorous, feeding primarily on aquatic algae. The diets of C. insculpta and E. dentata overlapped moderately, but the overall niche overlap was low because they occupied different microhabitats within the river. Chelodina oblonga fed very little, and may use the Daly River as a dry-season refuge. Emydura victoriae is molluscivorous, consuming more molluscs as it grows. This ontogenetic dietary shift was associated with megacephaly (extreme broadly expanded head that is too large to fit into the carapace) and expanded triturating surfaces. This specialisation allows adult E. victoriae to feed exclusively on molluscs and so their diet overlapped little with other species. Emydura subglobosa worrelli was omnivorous, consuming mostly freshwater sponge and apparently preferring more lentic water. Conclusions The freshwater turtles of the wet–dry tropics are usually reported as being heavily reliant on the seeds, fruits and leaves of riparian vegetation; however, the present study showed that the dry-season diet in perennial rivers is primarily of aquatic origin. Implications The study suggested that populations of C. insculpta, E. dentata and E. victoriae could be threatened by broad-scale development in northern Australia if there were substantive impacts on aquatic macrophytes and molluscs in the Daly River system.

The role of climate for the range limits of parapatric European land salamanders

Abrupt range limits of parapatric species may serve as a model system to understand the factors that determine species’ range borders. Theory suggests that parapatric range limits can be caused by abiotic conditions along environmental gradients, biotic interactions or a combination of both. Geographic ranges of the parapatric salamanders,Salamandra salamandraandS. atra, meet in small contact zones in the European Alps and to date, the cause of parapatry and the restricted range ofS. atraremain elusive. We combine multivariate approaches and climatic data analysis to explore niche differentiation among the two salamanders with respect to the available climatic environment at their contact zones. Our purpose is to evaluate whether climatic conditions explain the species’ sharp range limits or if biotic interactions may play a role for range delimitation. Analyses were carried out in three contact zones in Switzerland to assess possible geographic variation. Our results indicate that both species occur at localities with different climatic conditions as well as the presence of a strong climatic gradient across the species’ range limits. Although the species’ climatic niches differ moderately (with a wider niche breadth forS. atra), interspecific niche overlap is found. Comparisons among the contact zones confirm geographic variation in the species’ climatic niches as well as in the conditions within the geographically available space. Our results suggest that the change in climatic conditions along the recognized gradient represents a determining factor for species’ range limits within contact zones. However, our analyses of geographic variation in climatic conditions reveal that both salamander species can occur in a much wider range of conditions than observed within contact zones. This finding and the interspecific climatic niche overlap within each contact zone provides indirect evidence that biotic interactions (likely competition) between the two species may also determine their range limits.

High‐throughput sequencing offers insight into mechanisms of resource partitioning in cryptic bat species

Sympatric cryptic species, characterized by low morphological differentiation, pose a challenge to understanding the role of interspecific competition in structuring ecological communities. We used traditional (morphological) and novel molecular methods of diet analysis to study the diet of two cryptic bat species that are sympatric in southern England (Plecotus austriacus and P. auritus) (Fig. 1). Using Roche FLX 454 (Roche, Basel, CH) high-throughput sequencing (HTS) and uniquely tagged generic arthropod primers, we identified 142 prey Molecular Operational Taxonomic Units (MOTUs) in the diet of the cryptic bats, 60% of which were assigned to a likely species or genus. The findings from the molecular study supported the results of microscopic analyses in showing that the diets of both species were dominated by lepidopterans. However, HTS provided a sufficiently high resolution of prey identification to determine fine-scale differences in resource use. Although both bat species appeared to have a generalist diet, eared-moths from the family Noctuidae were the main prey consumed. Interspecific niche overlap was greater than expected by chance (Ojk = 0.72, P < 0.001) due to overlap in the consumption of the more common prey species. Yet, habitat associations of nongeneralist prey species found in the diets corresponded to those of their respective bat predator (grasslands for P. austriacus, and woodland for P. auritus). Overlap in common dietary resource use combined with differential specialist prey habitat associations suggests that habitat partitioning is the primary mechanism of coexistence. The performance of HTS is discussed in relation to previous methods of molecular and morphological diet analysis. By enabling species-level identification of dietary components, the application of DNA sequencing to diet analysis allows a more comprehensive comparison of the diet of sympatric cryptic species, and therefore can be an important tool for determining fine-scale mechanisms of coexistence.

Resource‐based habitat definition, niche overlap and conservation of two sympatric glacial relict butterflies

The precise knowledge of ecological resources and conditions required by species threatened by rapidly changing environmental conditions is of prime importance for conservation biology. Transferability of this knowledge between species with similar ecological requirements is often assumed, but rarely tested. This is especially the case for glacial relict populations confined to climate‐habitat traps from where they cannot move to rejoin areas with suitable environmental conditions. Using two glacial relict butterflies as model organisms, we first quantitatively define larval and adult resource‐based habitat use of each species. Secondly, we test the transferability of ecological profiles (both habitat and ecological niche) between these two species that share both the same biotope and the same host plant. Our results show that both species have markedly different ecological requirements relating to differences in life history and behavioural traits (i.e. egg‐laying strategies and mate‐locating behaviour). Although the two species share many ecological features, they use different functional habitats within our study site. The high degree of interspecific niche overlap should indicate a high interspecific competition. However, we argue that their co‐existence can be explained by the non‐limiting abundance of some resources (e.g. host plants), by the partial separation in time of adult flight periods and by the territorial behaviour of one of the species. We discuss the following general messages: (1) functional habitat of a (threatened) species should be defined in a spatial context corresponding to individual station keeping, and (2) quick diagnosis based on similar ecological requirements may be misleading for the design of reliable conservation and restoration strategies. Detailed mechanistic and quantitative ecological understanding of resource‐use and environmental tolerances across an organism's life cycle is essential for effective conservation in changing environments, like for glacial relict species.