Niche Differences Research Articles

Theory of microbial coexistence in promoting soil–plant ecosystem health

A healthy soil plant continuum is critical for maintaining agroecosystem functions and ensuring food security, which is the basis of sustainable agricultural development. Diverse soil microorganisms form a complex assembly and play an important role in agroecosystems by regulating nutrient cycling, promoting plant growth, and alleviating biotic and abiotic stresses. Improving microbial coexistence may be an effective and practical solution for the promotion of soil–plant ecosystem health in the face of the impacts of anthropogenic activities and global climate change. Modern coexistence theory is a useful theoretical framework for studying the coexistence of species that are competing for resources. Here, we briefly introduce the basic framework of modern coexistence theory, including the theoretical definitions and mathematical calculations for niche difference and fitness difference, as well as ways to test for these differences empirically. The possible effects of several major biotic and abiotic factors, such as biological interactions, climate change, environmental stress, and fertilization, on microbial niche and fitness differences are discussed. From the perspective of stabilizing and equalizing mechanisms, the potential roles of microbe–microbe interactions and plant–microbe interactions in promoting healthy soil–microbe–plant continuum are presented. We suggest that the use of the coexistence theory framework for the design and construction of microbial communities in agricultural production can provide a solid basis for the biological improvement of agroecosystems.

Tissue engineering of mouse uterus using menstrual blood stem cells (MenSCs) and decellularized uterine scaffold

BackgroundUterine tissue engineering can provide the opportunity for curing female infertility. Natural scaffold is a good choice to recapitulate the architecture and functionality of the native tissue. In this study, we purposed the potential of uterine decellularized scaffolds as an adequate natural niche for MenSCs differentiation toward uterus-specific cell lineages.MethodsMouse’s uterus was decellularized by immersion of hypo and hypertonic salts or freeze–thaw cycle followed by immersion in Triton X-100 and SDS solutions. MenSCs were isolated from the menstrual blood of 6 healthy women. The decellularized and recellularized samples were prepared for further in vitro and in vivo analyses.ResultsHistochemical studies and Raman spectroscopy revealed uterine ECM was preserved well, and the cells were completely removed after decellularization. Scanning electron microscopy (SEM) showed that the 3D ultrastructure of the uterus remained intact. Flowcytometric examination with CD34, CD44, CD105, CD106, CD144 markers revealed stem cell characters of cells that isolated from menstrual blood. MTT assay confirmed the bioavailability of MenSCs cultured scaffolds after 7 and 10 days.ConclusionHistochemical studies, SEM images, and Raman spectra showed MenSCs seeded and growth in uterine scaffolds. Immunostaining using anti-cytokeratin (CK), anti-desmin (Des), anti-vimentin (Vim), and anti-smooth muscle actin (SMA) antibodies showed MenSCs differentiation to epithelial and smooth muscle tissues. The Raman spectroscopy revealed the extracellular matrix (ECM) of decellularized uterine scaffolds was well preserved. The decellularized uterus can be considered a promising vehicle to support cell transplantation and differentiation. MenSCs are a good choice for uterine tissue engineering. The complete decellularization from mice uterine tissue was done by combining chemical agents

Isotopic Niche of Syntopic Granivores in Commercial Orchards and Meadows.

Simple SummaryGranivorous murids, namely striped field (Apodemus agrarius), yellow-necked (Apodemus flavicollis), and harvest (Micromys minutus) mice, occur in a variety of habitats and live syntopically in agricultural areas. Agroecosystems may be quite complex isotopically with δ15N values being influenced by many internal and external fluxes. Using isotopic (δ15N and δ13C) compositions from hair samples, we analysed isotopic niches of granivores in apple and plum orchards, raspberry and currant plantations, and nearby meadows in Lithuania. As the main hypothesis, we expected differences in the isotopic niches of these species (being a proxy for their diet), minimising interspecific competition. Striped field and yellow-necked mice were trapped in every habitat. Therefore, syntopic co-occurrence of granivores depended on the presence of harvest mice in the apple orchards, raspberry plantations, and meadows that served as control habitats. All species were fully separated according to δ15N values, presuming different amounts of food of animal origin in their diet. The separation of species according to δ13C was not expressed in all habitats. The core dietary niches of these species were fully separated in the apple orchards and raspberry plantations. Intraspecific differences of the isotopic niche were not present in any of the three species: that is, resources were equally used by males and females, adults, subadults, and juveniles.In agricultural habitats, diets and trophic positions of syntopic granivorous small mammals are not known sufficiently. Agroecosystems may be quite complex isotopically and the most complex situation concerns the nitrogen-15 isotope as δ15N values are influenced by many internal and external fluxes. We analysed the isotopic niches of striped field (Apodemus agrarius), yellow-necked (Apodemus flavicollis), and harvest (Micromys minutus) mice living sympatrically and syntopically in apple and plum orchards, raspberry and currant plantations, and nearby meadows that were used as control habitats. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios from hair samples were used as a proxy for their diet. As the main hypothesis, we expected differences in the isotopic niches of these three species, minimising interspecific competition. All species were fully separated according to δ15N values, presuming different amounts of food of animal origin in their diet. The separation of species according to δ13C was not expressed in all habitats. The core dietary niches of these species were fully separated in the apple orchards and raspberry plantations. Intraspecific differences of the isotopic niche were not present in any of the three species: that is, resources were equally used by males and females, adults, subadults, and juveniles.

The roles of dispersal limitation, climatic niches and glacial history in endemism of the North American bryophyte flora.

Bryophytes (mosses, liverworts, and hornworts) tend to have very large geographic ranges, which impedes progress toward understanding the drivers of diversification and extinction. This study aimed to investigate whether North American endemics differ geographically from more widespread species and whether differences in climatic niche or traits related to dispersal and establishment differ between endemics and more widespread species. All available herbarium records of bryophytes from North America north of Mexico (106 collections) were used. Traits related to dispersal were obtained from the literature. Analyses tested whether range sizes and extents differed between endemics and nonendemics, and whether trait differences were associated with endemism. Climate data were used to determine whether differences in niche breadth are present between endemics and nonendemics, and whether suitable climate for endemics occurs outside North America. Nonendemics have range sizes twice as large as endemics and they occur farther north and have greater longitudinal extents. However, they do not have the widest niche breadths and do not differ in spore size (with few exceptions) or sexual condition. Asexual propagules are more prevalent among nonendemics. Climatic models indicate that substantial areas of climate suitable for endemics exist outside of North America. Distributions of endemics and nonendemics are consistent with an important role of glaciation in shaping the North American bryophyte flora. Endemics are not limited to the continent based on a lack of suitable climate elsewhere or by spore size or sexual condition.

Assessing climate change tolerance and the niche breadth-range size hypothesis in rare and widespread alpine plants.

Species range limits often reflect niche limits, especially for ranges constrained along elevational gradients. In this study, we used elevational transplant experiments to test niche breadth and functional trait plasticity in early life stages of narrow-range Nabalus boottii and broad-range N. trifoliolatus plants to assess their climate change vulnerability and the applicability of the niche breadth-range size hypothesis to explain their range size differences. We discovered that the earliest life stage (seed germination) was the most vulnerable and the two alpine taxa, N. boottii and N. trifoliolatus var. nanus, were unable to establish at the warm low elevation site, however non-alpine N. trifoliolatus established at all three elevations, including at the high elevation (beyond-range) site. Niche limits in seed emergence may therefore contribute to range size in these taxa. In contrast, when seedlings were planted we found substantial functional trait plasticity in later life stages (average 44% across ten traits) that was highly similar for all Nabalus taxa, suggesting that differences in plasticity do not generate niche differences or restrict range size in the focal taxa. While this substantial plasticity may help buffer populations faced by climate change, the inability of the alpine taxa to establish at lower elevation sites suggests that their populations may still decline due to decreased seed recruitment under ongoing climate change. We therefore recommend monitoring alpine Nabalus populations, particularly globally rare N. boottii.

Stabilising role of seed banks and the maintenance of bacterial diversity

AbstractCoexisting species often exhibit negative frequency dependence due to mechanisms that promote population growth and persistence when rare. These stabilising mechanisms can maintain diversity through interspecific niche differences, but also through life‐history strategies like dormancy that buffer populations in fluctuating environments. However, there are few tests demonstrating how seed banks contribute to long‐term community dynamics and the maintenance of diversity. Using a multi‐year, high‐frequency time series of bacterial community data from a north temperate lake, we documented patterns consistent with stabilising coexistence. Bacterial taxa exhibited differential responses to seasonal environmental conditions, while seed bank dynamics helped maintain diversity over less‐favourable winter periods. Strong negative frequency dependence in rare, but metabolically active, taxa suggested a role for biotic interactions in promoting coexistence. Together, our results provide field‐based evidence that niche differences and seed banks contribute to recurring community dynamics and the long‐term maintenance of diversity in nature.

Ecological niches of an introduced species Typha laxmannii and native Typha species in Austria

We studied fruit morphology, germination and growth of juvenile plants and clonal ramets of the non-native species Typha laxmannii and the two common native species Typha angustifolia and Typha latifolia in Lower Austria by means of morphological measurements, germination tests in an environmental test chamber and garden experiments with different water and nutrient levels. The ecological niche of T. laxmannii was close to the niches of the native species T. latifolia and T. angustifolia. All species were light-dependent and quick germinating under suitable conditions. Fruit morphology of T. laxmannii was very similar to that of T. angustifolia, but viability and germination of T. laxmannii were comparable to that of T. latifolia. All three species were profiting from higher water and nutrient levels in the experiments. Only minor advantages or disadvantages of T. laxmannii compared to the native species were detected, hence a direct replacement of them is not expectable. Additional factors like the availability of diaspores in the study area of the Tullnerfeld and Danube valley could be more crucial for the present distribution of T. laxmannii than differences in ecological niches of species themselves.

Does co‐occurrence drive vertical niche partitioning in parapatric tamarins (Saguinus spp.)?

AbstractStable species coexistence is a result of a balance between niche and fitness differences. One of the most common competitive patterns that arise from interactions between closely related species is character displacement, which may lead to divergence of certain traits and niche partitioning in areas where species co‐occur. In this study, we used data on 35 groups of two parapatric tamarins (Saguinus midas and S. bicolor) to test for asymmetries in group size and competitively driven divergence in forest strata use, under the influence of resource availability fluctuation across the year. We hypothesised that S. midas is competitively superior to S. bicolor, and this would result from differences in fitness‐related traits (group size). If so, species patterns of vertical habitat across the year should shift in sympatry relative to allopatry. We found that species had similar group sizes, suggesting they have similar competitive abilities. Further, both pied and red‐handed tamarins used lower heights whenever in larger groups, which may be related to a diet shift in response to increases in intragroup competition. In addition, we refuted our prediction of vertical niche partitioning in sympatry. Instead, S. midas moved upwards into the canopy with increasing rainfall over the year (a proxy for resource availability) both in sympatry and allopatry, whereas S. bicolor was unresponsive to both rainfall and geographic contact with S. midas groups. Therefore, the difference in vertical habitat use between these species over part of the year is probably more related to the degree of resource seasonality experienced by each species within their ranges, than to competition.

Cartilage tissue engineering by co-transplantation of chondrocyte extracellular vesicles and mesenchymal stem cells, entrapped in chitosan–hyaluronic acid hydrogel

Mesenchymal stem cells (MSCs) on injectable hydrogels are mostly used to regenerate articular cartilage, which would have a variety of outcomes. Chondrocyte extracellular vesicles (EVs) have attracted many attentions for their chondrogenic differentiation capacity; however, the roles of EVs in both chondrogenic differentiation of MSCs and cartilage regeneration are poorly understood yet. In the current study, to investigate the differentiation effects of human articular chondrocyte EVs on adipose-derived MSCs, they were cultured in injectable chitosan–hyaluronic acid (CS–HA) hydrogel and then treated with chondrocyte EVs for 21 days. The continuous treatment of EVs performed on MSCs increased chondrogenic genes’ expressions of SOX9 and COL2A1 and induced expression of Col II protein. In addition, glycosaminoglycans secretion was detected in the EV-treated MSCs after about 14 days. The therapeutic efficiency of this hydrogel and EVs was studied in a rabbit osteochondral defect model. MRI results revealed that the cartilage regeneration capacity of EV-treated MSCs with CS–HA hydrogel was greater than the untreated MSCs or the EV-treated MSCs without hydrogel. Moreover, histological results showed hyaline-like cartilage in the CS–HA/MSC and CS–HA/EV/MSC groups in the cartilage defect sites. These findings suggested that the chondrocyte-EVs and CS–HA hydrogel could provide the preferable niche for chondrogenic differentiation of MSCs and cartilage regeneration in osteoarthritis cartilage injuries.

Trophic niche segregation among native whitefish and invasive vendace in a north Norwegian lake system

AbstractIntroductions and invasions of non‐native species alter nutrient cycling and trophic dynamics resulting in significant ecological disturbance. Stable isotope data were used to test for evidence of invader‐induced trophic niche differences in a north Norwegian lake system differentially dominated by native European whitefish (Coregonus lavaretus) morphotypes and invasive vendace (Coregonus albula). Aspects of both realised trophic niche position and trophic niche width were affected by the invader, with the effects varying by whitefish morphotype. Densely rakered pelagic whitefish demonstrated a relatively lower reliance on pelagic resources in the presence of the invader and the isotopic niche size was relatively larger in conjunction with the broadening of the prey base. Within the benthic‐dwelling sparsely rakered whitefish morphotype, the trophic impacts of invading vendace were size‐dependent, with larger individuals experiencing niche compression. Smaller sparsely rakered whitefish increased, contrary to our hypothesis, reliance on pelagic‐based energy in the face of invasion. Our findings demonstrate that the trophic ecology of invaded systems can differ in multiple and subtle ways that have consequences for community‐ and ecosystem‐level energy flows, which if persisting over time are likely to have implications for the recruitment, growth and reproductive rate of the native fishes.

Climatic niche differences among Zootoca vivipara clades with different parity modes: implications for the evolution and maintenance of viviparity

Parity mode (oviparity/viviparity) importantly affects the ecology, morphology, physiology, biogeography and evolution of organisms. The main hypotheses explaining the evolution and maintenance of viviparity are based on bioclimatic predictions and also state that the benefits of viviparity arise during the reproductive period. We identify the main climatic variables discriminating between viviparous and oviparous Eurasian common lizard (Zootoca vivipara) occurrence records during the reproductive period and over the entire year.Analyses based on the climates during the reproductive period show that viviparous clades inhabit sites with less variable temperature and precipitation. On the contrary, analyses based on the annual climates show that viviparous clades inhabit sites with more variable temperatures.Results from models using climates during reproduction are in line with the “selfish-mother hypothesis”, which can explain the success of viviparity, the maintenance of the two reproductive modes, and why viviparous individuals cannot colonize sites inhabited by oviparous ones (and vice versa). They suggest that during the reproductive period viviparity has an adaptive advantage over oviparity in less risky habitats thanks to the selfish behaviour of the mothers. Moreover, the results from both analyses stress that hypotheses about the evolution and maintenance of viviparity need to be tested during the reproductive period.

Abundance-Occupancy Relationships Along Taxonomic Ranks Reveal a Consistency of Niche Differentiation in Marine Bacterioplankton With Distinct Lifestyles.

Abundance-occupancy relationships (AORs) are an important determinant of biotic community dynamics and habitat suitability. However, little is known about their role in complex bacterial communities, either within a phylogenetic framework or as a function of niche breadth. Based on data obtained in a field study in the St. Lawrence Estuary, we used 16S rRNA gene sequencing to examine the vertical patterns, strength, and character of AORs for particle-attached and free-living bacterial assemblages. Free-living communities were phylogenetically more diverse than particle-attached communities. The dominant taxa were consistent in terms of their presence/absence but population abundances differed in surface water vs. the cold intermediate layer. Significant, positive AORs characterized all of the surveyed communities across all taxonomic ranks of bacteria, thus demonstrating an ecologically conserved trend for both free-living and particle-attached bacteria. The strength of the AORs was low at the species level but higher at and above the genus level. These results demonstrate that an assessment of the distributions and population densities of finely resolved taxa does not necessarily improve determinations of apparent niche differences in marine bacterioplankton communities at regional scales compared with the information inferred from a broad taxonomic classification.

Non-overlapping climatic niches and biogeographic barriers explain disjunct distributions of continental Urania moths

Larvae of Urania moths feed exclusively on Omphalea plants, which are widely distributed in the Neotropics. However, the distributions of the two Urania species in this region are disjunct. This distributional pattern could derive from the presence of the Andes, but it could also be related to differences in ecological niches, the presence of negative interactions, or the absence of conditions that can only be observed at a habitat level. We tested whether differences in the ecological niches of continental Urania moths play a role in their disjunct distribution. Using species records and climatic variables, we characterized the ecological niches of Urania moths and their host plants and analyzed the overlap of the moths' niches. Using ecoregions as a proxy of habitat-level environmental conditions, we explored the role of host plant availability on the moth distributions. Suitable conditions for the species were widespread, with a lack of suitability mostly restricted to the Andean highlands. The two moth distributions were closely related to that of their host plants. There was medium-high overlap of niche models when available conditions were considered; however, niche overlap was not found to be statistically significant. Our results corroborate the barrier effect of the Andes on the dispersal of these moths, but they also show that niche differences contribute to the disjunct distributions of U. fulgens and U. leilus. Furthermore, other non-climatic factors appear to play a crucial role in the disjunction of the species ranges in areas where overlapping suitable conditions are continuous. Our findings support speciation in Urania moths as allopatric and indicate that their disjunct distributions can be attributed to multiple factors. Other studies exploring the causes of similar distributional patterns should consider that a single factor may not be enough to explain such patterns.

Niche adaptation promoted the evolutionary diversification of tiny ocean predators

Unicellular eukaryotic predators play a crucial role in the functioning of the ocean ecosystem by recycling nutrients and energy that are channeled to upper trophic levels. Traditionally, these evolutionarily diverse organisms have been combined into a single functional group (heterotrophic flagellates), overlooking their organismal differences. Here, we investigated four evolutionarily related species belonging to one cosmopolitan group of uncultured marine picoeukaryotic predators: marine stramenopiles (MAST)-4 (species A, B, C, and E). Co-occurrence and distribution analyses in the global surface ocean indicated contrasting patterns in MAST-4A and C, suggesting adaptation to different temperatures. We then investigated whether these spatial distribution patterns were mirrored by MAST-4 genomic content using single-cell genomics. Analyses of 69 single cells recovered 66 to 83% of the MAST-4A/B/C/E genomes, which displayed substantial interspecies divergence. MAST-4 genomes were similar in terms of broad gene functional categories, but they differed in enzymes of ecological relevance, such as glycoside hydrolases (GHs), which are part of the food degradation machinery in MAST-4. Interestingly, MAST-4 species featuring a similar GH composition (A and C) coexcluded each other in the surface global ocean, while species with a different set of GHs (B and C) appeared to be able to coexist, suggesting further niche diversification associated with prey digestion. We propose that differential niche adaptation to temperature and prey type has promoted adaptive evolutionary diversification in MAST-4. We show that minute ocean predators from the same phylogenetic group may have different biogeography and genomic content, which needs to be accounted for to better comprehend marine food webs.

From competition to facilitation and mutualism: a general theory of the niche

AbstractNiche Theory is a central framework in ecology based on the recognition that most interactions between organisms are indirect, mediated by the biotic and abiotic dynamical environment these organisms live in. Despite its potential generality, the theory still mostly focuses on how resource–consumer dynamics mediate competition in ecological communities. However, it is being increasingly recognized that positive interactions between organisms also play an important role in driving the structure and functioning of ecological communities, from plants to microbes. In this paper, we present a unified theory of the niche that applies to both positive and negative interactions between organisms, mediated by one or two environmental factors. We show that classical concepts such as niche differences and fundamental and realized niches can naturally be expanded to facilitative and mutualistic interactions. In addition, we introduce and formalize new general niche concepts that appear exclusively in the presence of positive interactions: (1) the Allee niche, a region of environmental conditions for which a species can persist but not invade from low densities and (2) niche facilitation, when the presence of a species expands the set of environmental conditions under which a second species can invade and/or persist. To show the broad applicability of this theory, we illustrate these concepts using a diverse set of theoretical examples, from bacteria feeding on an inhibiting substrate, to nitrogen‐fixing plants and the indirect mutualism between a plant and a carnivore species. In sum, our work shows how Niche Theory provides a natural framework for positive interactions in ecology, bringing a unified perspective and new conceptual tools to study ecological systems where these positive interactions occur.

Genetic diversity and geographic distribution of parasitic flies of the Philornis torquans complex in Argentina.

Philornis Meinert 1890 (Diptera: Muscidae) is a genus of flies that parasitize birds in the Neotropical region. The characteristics of the host-parasite interactions and its consequences may depend on the Philornis species involved, and thus precise identification of these parasites is crucial for the interpretation of ecological and epidemiological studies. However, morphological identification of Argentine Philornis species is elusive while molecular evidence points towards the existence of a complex of cryptic species or lineages undergoing a speciation process, which were named the 'Philornis torquans complex'. Herein the authors extended the current knowledge on the systematics and biogeography of parasitic Philornis flies from Argentina, analysing samples collected in several ecoregions, including the Atlantic Forest, Iberá Wetlands, Open Fields and Grasslands, Espinal, Pampa, Dry Chaco, Humid Chaco, Delta and Paraná River Islands, Monte of Plains and Plateaus. The results of the present study strengthen the evidence on previously described Philornis genotypes using four genetic markers (ITS2, COI, ND6, 12S rRNA). The authors report new patterns of occurrence and describe the presence of a novel genotype of subcutaneous Philornis. In addition, the present study unveils ecological niche differences among genotypes of the Philornis torquans complex in southern South America.

Driving forces of cultivated land evolution in agro-pastoral areas on the Qinghai-Tibet Plateau based on ecological niche theory

Scattered cultivated lands in the agro-pastoral areas on the Qinghai-Tibet Plateau (QTP) cause pressure on the structure, function and evolvement of landscape and affect regional ecological sustainability. Based on niche theory, this study is the first to apply the niche breadth, niche entropy and niche overlap model to explore how the cultivated land expansion and development forms affect ecological roles from ecosystem interaction aspects from 1990 to 2015 at regional scales on the QTP. The results showed that: (1) Grassland was overall dominant in most counties, while the interface between the cultivated land and grassland showed great spatial variability and the main land use conversion occurred between them. From 1990 to 2015, the transfer percentage of grassland into cultivated land was 0.27%. (2) Results of cultivated land niche breadth and entropy indicated that at provincial scale, the occupancy rates of cultivated lands in Tibet and Xinjiang were lower than Sichuan, Gansu and Qinghai. (3) Cultivated land niche overlap exhibited by network graph revealed that Gansu, Sichuan and Qinghai had a high niche overlap over 0.994 at provincial scale. At city scale, the maximum overlap was Haibei-Guoluo and Lanzhou-Wuwei (0.999) while the minimum was Bayingol-Kizilsu Kirghiz (0.243), indicating that the development forms and competition of cultivated land between each two regions were quite different. (4) The driving forces derived by niche difference of different ecosystems showed that cultivated land niche was affected the evolution of grassland niche, and the social benefit was the leading benefit of cultivated land change. Overall, this study can assist local government in building the cultivated land management system. Moreover, the results of this study contribute to understand the characteristics and driving forces of the cultivated land evolution on the QTP, thus providing valuable decision reference for ecological protection, land use structure regulation and policy formulation.

Two species? - Limits of the species concepts in the pygmy grasshoppers of the Tetrix bipunctata complex (Orthoptera, Tetrigidae).

Today, integrative taxonomy is often considered the gold standard when it comes to species recognition and delimitation. Using the Tetrix bipunctata complex, we here present a case where even integrative taxonomy may reach its limits. The Tetrix bipunctata complex consists of two morphs, bipunctata and kraussi, which are easily distinguished by a single character, the length of the hind wing. Both morphs are widely distributed in Europe and reported to occur over a large area in sympatry, where they occasionally may live also in syntopy. The pattern has led to disparate classifications, as on the one extreme, the morphs were treated merely as forms or subspecies of a single species, on the other, as separate species. For this paper, we re-visited the morphology by using multivariate ratio analysis (MRA) of 17 distance measurements, checked the distributional data based on verified specimens and examined micro-habitat use. We were able to confirm that hind wing length is, indeed, the only morphological difference between bipunctata and kraussi. We were also able to exclude a mere allometric scaling. The morphs are, furthermore, largely sympatrically distributed, with syntopy occurring regularly. However, a microhabitat niche difference can be observed. Ecological measurements in a shared habitat confirm that kraussi prefers a drier and hotter microhabitat, which possibly also explains the generally lower altitudinal distribution. Based on these results, we can exclude classification as subspecies, but the taxonomic classification as species remains unclear. Even with different approaches to classify the Tetrix bipunctata complex, this case is, therefore, not settled. We recommend continuing to record kraussi and bipunctata separately.

Trophic niches of native and nonnative fishes along a river-reservoir continuum

Instream barriers can constrain dispersal of nonnative fishes, creating opportunities to test their impact on native communities above and below these barriers. Deposition of sediments in a river inflow to Lake Powell, USA resulted in creation of a large waterfall prohibiting upstream movement of fishes from the reservoir allowing us to evaluate the trophic niche of fishes above and below this barrier. We expected niche overlap among native and nonnative species would increase in local assemblages downstream of the barrier where nonnative fish diversity and abundance were higher. Fishes upstream of the barrier had more distinct isotopic niches and species exhibited a wider range in δ15N relative to downstream. In the reservoir, species were more constrained in δ15N and differed more in δ13C, representing a shorter, wider food web. Differences in energetic pathways and resource availability among habitats likely contributed to differences in isotopic niches. Endangered Razorback Sucker (Xyrauchen texanus) aggregate at some reservoir inflows in the Colorado River basin, and this is where we found the highest niche overlap among species. Whether isotopic niche overlap among adult native and nonnative species has negative consequences is unclear, because data on resource availability and use are lacking; however, these observations do indicate the potential for competition. Still, the impacts of diet overlap among trophic generalists, such as Razorback Sucker, are likely low, particularly in habitats with diverse and abundant food bases such as river-reservoir inflows.

Dispersal syndromes are poorly associated with climatic niche differences in the Azorean seed plants

AbstractAimEnvironmental niche tracking is linked to the species ability to disperse. While well investigated on large spatial scales, dispersal constraints also influence small‐scale processes and may explain the difference between the potential and the realized niche of species at small scales. Here we test whether niche size and niche fill differ systematically according to dispersal syndrome within isolated oceanic islands. We expect that species with higher dispersal abilities (anemochorous or endozoochorous) will have a higher niche fill, despite their environmental niche size.LocationAzores archipelago.TaxonNative seed plants.MethodsWe combined a georeferenced database of the species distribution within the archipelago (Azorean Biodiversity Portal/GBIF) with an expert‐based dispersal syndrome categorization and a high‐resolution climatic grid (CIELO model). Using four climatic variables (Annual Mean Temperature, Mean Diurnal Range, Annual Precipitation, Precipitation Seasonality), we calculated a four‐dimensional hypervolume to estimate the niche size of each species. Niche fill was quantified as the suitable climatic space of the island that was occupied by the focal species.ResultsWe found a significant relationship between dispersal syndromes and niche size, and also between dispersal syndromes and niche fill. Such relationships presented no phylogenetic signal. Endozoochorous species display higher niche fill compared to epizoochorous and hydrochorous species, and larger niches than anemochorous and epizoochorous. Differences among the remaining groups are not significant for either niche size or for niche fill.Main conclusionsThe ability of a species to track its niche at small scales is not tightly related to its dispersal syndrome, although endozoochorous species track their niche more efficiently than the rest of groups. Despite being intuitively appealing, dispersal syndrome classifications might not be the most appropriate tools for understanding dispersal processes at small scales.