Niche Differentiation

Species that exhibit geographically defined phenotypic variation traditionally have been divided into subspecies. Subspecies based on phenotypic features may not comprise monophyletic groups due to selection, gene flow, and/or convergent evolution. In many taxonomic groups the number of species once designated as widespread is dwindling rapidly, and many workers reject the concept of subspecies altogether. We tested whether currently recognized subspecies in the plainbellied watersnake Nerodia erythrogaster are concordant with relationships based on mitochondrial markers, and whether it represents a single widespread species. The range of this taxon spans multiple potential biogeographic barriers (especially the Mississippi and Apalachicola Rivers) that correspond with lineage breaks in many species, including other snakes. We sequenced three mitochondrialgenes (NADH-II, Cyt-b, Cox-I) from 156 geo-referenced specimens and developed ecological niche models using Maxent and spatially-explicit climate data to examine historical and ecological factors affecting variation in N. erythrogaster across its range. Overall, we found little support for the recognized subspecies as either independent evolutionary lineages or geographically circumscribed units and conclude that although some genetic and niche differentiation has occurred, most populations assigned to N. erythrogaster appear to represent a single, widespread species. However, additional sampling and application of nuclear markers are necessary to clarify the status of the easternmost populations.

We investigated a community of syntopically occurring horseshoe bats (Rhinolophus hipposideros, R. euryale, R. ferrumequinum) in southern Slovakia. The faecal pellets of these bat species were collected in the field and later analysed under a dissecting microscope. The three species studied are known to be very similar as far as their ecology, echolocation and preferred habitats are concerned, but they diverge significantly in their body sizes. In this study, all three species fed predominantly on moths [59–80 percentage frequency (%f); 87–95 percentage volume (%vol)], but their diet compositions differed in the size of individuals consumed. The smallest bat species (R. hipposideros) fed only on the smallest moths (%f = 59; %vol = 87), the medium-sized species (R. euryale) mainly on medium-sized moths (%f = 60; %vol = 74) and the largest one (R. ferrumequinum) especially on the largest moths (%f = 54; %vol = 89). Despite similar preferred habitat and the main prey category, the rate...

The coexistence of competing species relies on niche partitioning. Competitive exclusion is likely inevitable at high niche overlap, but such divide between competitors may be bridged if environmental circumstances displace competitor niches to enhance partitioning. Foraging-niche dimension can be influenced by environmental characteristics, and if competitors react differently to such conditions, coexistence can be facilitated. We here experimentally approach the partitioning effects of environmental conditions by evaluating the influence of water turbulence on foraging-niche responses in two competing fish species, Eurasian perch Perca fluviatilis and roach Rutilus rutilus, selecting from planktonic and benthic prey. In the absence of turbulence, both fish species showed high selectivity for benthic chironomid larvae. R. rutilus fed almost exclusively on zoobenthos, whereas P. fluviatilis complemented the benthic diet with zooplankton (mainly copepods). In turbulent water, on the ...

Many cryptic species have been discovered in various taxonomic groups based on molecular phylogenetic analyses and mating experiments. Some sympatric cryptic species share equivalent resources, which contradicts the competitive exclusion principle. Two major theories have been proposed to explain the apparent lack of competitive exclusion, i.e. niche-based coexistence and neutral model, but a conclusive explanation is lacking. Here, we report the co-occurrence of cryptic spider wasp species appearing to be ecologically equivalent. Molecular phylogenetic analyses and mating experiments revealed that three phylogenetically closely related species are found sympatrically in Japan. These species share the same resources for larval food, and two of the species have the same niche for nesting sites, indicating a lack of competitive exclusion. This evidence may suggest that ecologically equivalent species can co-occur stably if their shared resources are sufficiently abundant that they can...

Competition for resources often contributes strongly to defining an organism’s ecological niche. Biological rhythms are important adaptations to the temporal dimension of niches, but the role of other organisms in determining such temporal niches have not been much studied, and the role specifically of competition even less so. We investigate how interspecific and intraspecific competition for resources shapes an organism’s activity rhythms. For this, communities of one or two species in an environment with limited resource input were simulated. We demonstrate that when organisms are arrhythmic, one species will always be competitively excluded from the environment, but the existence of activity rhythms allows niche differentiation and indefinite coexistence of the two species. Two species which are initially active at the same phase will differentiate their phase angle of entrainment over time to avoid each other. When only one species is present in an environment, competition with...

Hidden Diversity Why are there so many species in the tropics? Niche partitioning by highly specialized plant species seems to be the main generator of high diversity. Condon et al. (p. 1240 ; see the Perspective by Godfray ) show that niche partitioning can also be generated by interactions between plant resources and parasites, resulting in hyperdiverse communities. The cryptic diversity of 14 neotropical fly pollinators and 18 of their highly specific wasp parasites induced mortality partitions between multiple narrow niches. The extreme specificity of the wasp-fly relationships was initially only revealed by molecular analysis.

Two dimensions of the ecological niche (diet and habitat) of a snake assemblage from an endemic rich area in east-central Argentina, the Sierras de Ventania mountain chain, were analyzed. Field data collection was performed in 15-week study periods between 2010 and 2014. Snakes were hand-captured using transect surveys. Field observations on diet were analyzed together with stomach content data from museum specimens. Our results supported the partitioning of the snake assemblage by both habitat use and diet into at least three functional groups: species restricted to microhabitats under rocks and with a diet composed exclusively of ants (Epictia australis); species found mostly in stream microhabitats and feeding mainly upon anurans (Erythrolamprus poecilogyrus and Lygophis elegantissimus); and species found mostly in grassland microhabitats, with specialized diets of terrestrial prey items (Philodryas patagoniensis and Bothrops alternatus). Consistent with previous work, diet was more important than habitat in explaining ecological niche partitioning of this snake assemblage. Our results showed that high overlap values of microhabitat use were compensated by low overlap values of the trophic niche dimension, thus matching the traditional complementary niches hypothesis.

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

Although widely used in ecology, comparative analyses of diversity and niche properties are still lacking for microorganisms, especially concerning niche variations. In this study, we identi ed important topoclimatic, edaphic, spatial and biotic drivers of the alpha and beta diversity of bacterial, archaeal, fungal and protist communities. Then, we calculated the niche breadth and position of each taxon along environmental gradients within all taxonomic groups, to determine how these vary within and between groups. Quantifying the niches of microbial taxa is necessary to then forecast how taxa and the communities they compose might respond to environmental changes. We found that edaphic properties were the most important drivers of both community diversity and composition for all microbial groups. Protists presented the largest niche breadths, followed by bacteria and archaea, with fungi displaying the smallest. Niche breadth generally decreased towards environmental extremes, especially along edaphic gradients, suggesting increased specialisation of microbial taxa in highly selective environments. Overall, we showed that microorganisms have well de ned niches, as do macro-organisms, likely driving part of the observed spatial patterns of community variations. Assessing niche variation more widely in microbial ecology should open new perspectives, especially to tackle global change effects on microbes.

IntroductionWhile crucial to ensuring the production of accurate and high-quality data—and to avoid erroneous conclusions—data quality control (QC) in environmental monitoring datasets is still poorly documented.MethodsWith a focus on annual inter-laboratory comparison (ILC) exercises performed in the context of the French coastal monitoring SOMLIT network, we share here a pragmatic approach to QC, which allows the calculation of systematic and random errors, measurement uncertainty, and individual performance. After an overview of the different QC actions applied to fulfill requirements for quality and competence, we report equipment, accommodation, design of the ILC exercises, and statistical methodology specially adapted to small environmental networks (<20 laboratories) and multivariate datasets. Finally, the expanded uncertainty of measurement for 20 environmental variables routinely measured by SOMLIT from discrete sampling—including Essential Ocean Variables—is provided.Re...

Background Species-specific genotypic features, local neighbourhood interactions and resource supply strongly influence the tree stature and growth rate. In mixed-species forests, diversity-mediated biomass allocation has been suggested to be a fundamental mechanism underlying the positive biodiversity-productivity relationships. Empirical evidence, however, is rare about the impact of local neighbourhood diversity on tree characteristics analysed at a very high level of detail. To address this issue we analysed these effects on the individual-tree crown architecture and tree productivity in a mature mixed forest in northern Germany. Methods Our analysis considers multiple target tree species across a local neighbourhood species richness gradient ranging from 1 to 4. We applied terrestrial laser scanning to quantify a large number of individual mature trees (N = 920) at very high accuracy. We evaluated two different neighbour inclusion approaches by analysing both a fixed radius sel...

Acanthoscelides Schilsky is a large genus of neotropical bruchid beetles, in which most species show host plant specialization. Acanthoscelides obtectus and Acanthoscelides obvelatus are two sibling species specialized on Phaseolus beans, and are therefore considered pests. Up to now, the status of these two taxa has remained unclear, the few studies conducted having failed to elucidate whether these are two differentiated species or a single morphologically variable species. In addition, A. obvelatus has not been taken into account in the great majority of studies of bean bruchids. In this morphological and genetic study, we show that A. obtectus and A. obvelatus are two ÔtrueÕ non-hybridizing species, which diverged about 22 Mya. Although the two species demonstrate only few morphological differences, we point out some diagnostic characters that enable their identification in the field. We also address a genetic method of differentiation of the two species, based on species-specific microsatellite loci. The strong morphological resemblance of these two species, despite their ancient divergence, may be the result of evolutionary stasis, which could be the consequence of stabilizing selection. Niche differentiation could enable the two species to coexist indefinitely.

1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure. 2. Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed. 3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next. 4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources. 5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches.

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.

Ecologists have long sought general explanations for the co-occurrence of ecologically similar taxa. Niche theory explains co-occurrence via functional differences among taxa that reduce competition and promote resource partitioning. Alternatively, the unified neutral theory of biodiversity and biogeography suggests that co-occurrence can be attributed to stochastic processes, and thus, presupposes that ecologically similar species that occur in sympatry are functionally analogous. We test these alternative hypotheses in multiple dimensions using the most diverse crustacean-sea anemone symbiosis from coral reefs in the Tropical Western Atlantic. δ13C and δ15N stable isotope analyses of six crustacean symbionts that co-occur around the host anemoneBartholomea annulataexhibit highly differentiated isotopic niche space spanning three trophic levels. As multiple crustacean species within the symbiosis have been documented as cleaners that remove parasites from reef fishes, we extended o...

Despite the many studies using trait-based approaches to assess the impact of environmental gradients in forest trait composition, the relative roles of (i) intraspecific variation in community assembly and (ii) microclimatic or fine scale abiotic variation in shaping local trait diversity remain poorly understood. To advance their understanding we tested several assumptions and predictions of trait driver theory (TDT). We quantified the shape of trait distributions related to tree carbon, nutrient economics and stem hydraulics across a small-scale but steep gradient of soil water availability. We utilized a unique and steep environmental gradient in the coastal Brazilian Atlantic forest (restinga) communities that spans a very short distance (207 +/-60 meters). We collected leaf and wood samples of tree species across 42 patches (or plots) of restinga forest. Furthermore, to detect if species directionally shift in niche space, we analyzed species composition in multidimensional hy...

Ecological niche models (ENMs) are widely used tools for predicting species geographic distribution as a function of environmental variables. The inclusion of biotic factors in the predictor suite can significantly increase the predictive power of such models, leading to a model closer to the realized niche for the species under investigation. In this study, we provide evidence of niche overlap between gray woolly monkeys (Lagothrix cana) and black-faced black spider monkeys (Ateles chamek) based on locality and ecological data covering their complete geographic range in the Amazon forests of Brazil, Peru and Bolivia. We also estimate the potential distribution of L. cana using environmental predictors, and the distribution of A. chamek as a biotic factor. Finally, we quantified current and future habitat loss and areas under legal protection. We found that only 39% of the L. cana area of occupancy is under legal protection and that the species could potentially lose up to 58% of habitat in the next 30 years. We also show that the use of a closely-related species that has a more robust dataset can improve ENMs of poorly studied, rare and/or cryptic species. The framework developed here can be applied to a wide range of sympatric species if they share similar ecological requirements. Since our focal species are the most frugivorous primates in our study region and especially vulnerable to habitat loss, the identification of highly suitable areas for both taxa can help to protect other forest-dwelling species, reducing the rate of overall biodiversity loss.

The trophic niche of a species is one of the fundamental traits of species biology. The ideal trophic niche of a species is realized in the absence of interspecific competition, targeting the most profitable and easy-to-handle food resources. However, when a competitor is present, species adopt different strategies to reduce competition and promote coexistence. In this study, we assessed the potential mechanisms that allow the coexistence of two generalist salamanders: the Italian cave salamander (Speleomantes italicus) and the fire salamander (Salamandra salamandra). We surveyed, in April 2021, a forested area of Emilia-Romagna (Italy) during rainy nights. Analyzing the stomach contents of the captured individuals, we obtained information on the trophic niche of these two sympatric populations. Comparing our results with those of previous studies, we found that the two species did not modify their trophic niche, but that alternative mechanisms allowed their coexistence. Specificall...

We examined physical condition, niche dimensions, and survival of New England cottontails (Sylvilagus transitionalis) that occupied 21 habitat patches of different sizes during winter. Rabbits on small patches (_<2.5 ha) were predominantly males, and both sexes had lower body mass than individuals on large patches (>5.0 ha). Niche indices (fi, where fi ranges from 0 to I, and values approaching t indicate generalized resource use) of habitat use revealed that rabbits on small patches used a greater variety of microhabitats (based on understory stem density: fis = 0.81, and proximity to cover: fie =0.79) than rabbits occupying large patches (fis = 0.65, rio = 0.66). Rabbits on small patches also consumed low quality forage more often and fed at sites farther from escape cover than rabbits on large patches. There were no significant correlations between rabbit densities and niche dimensions. Niche expansion was not a result of competitive release or relaxation of predator pressure. Rabbits on small patches apparently modified their niche dimensions in response to resource limitations. This response included occupying sites with limited understory cover that apparently resulted in rabbits on small patches having a lower survival rate (0.35) than rabbits on large patches (0.69) during a 10-week monitoring period. Skewed sex ratios and low survival rates among rabbits on small patches suggest that these habitats act as sinks to dispersing, juveniles from large (source) patches. As a result, local populations of New England cottontails may become vulnerable to extinction if large patches of habitat are not maintained.

There is now strong evidence that foraging niche specialisation plays a critical role in the very early stages of resource driven speciation. Here we test critical elements of models defining this process using a known polymorphic population of Arctic charr from subarctic Norway. We test the long-term stability of niche specialisation amongst foraging predators and discuss the possibility that contrasting foraging specialists are exposed to differing selection regimes. Inter-individual foraging niche stability was measured by combining two time-integrated ecological tracers of the foraging niche (each individual's d 13 C and d 15 N stable isotope (SI) signatures and their food borne parasite fauna) with a short-term measure of foraging niche use (stomach contents composition). Three dietary subgroups of predators were identified, including zooplankton, gammarid and benthivore specialists foragers. Zooplanktivorous specialists had muscle low in d 13 C, a high abundance of parasites transmitted from pelagic copepods, a smaller head, longer snout and a more slender body-form than gammaridivorous specialist individuals which had muscle more enriched in d 13 C and high abundance of parasites transmitted from benthic Gammarus. Benthivorous individuals were intermediate between the other two foraging groups according to muscle SI-signals (d 13 C) and loadings of parasites transmitted from Electronic supplementary material The online version of this article (

Marked germline clones homozygous for Egfr CO (shown) or Egfr ts induced in adults using MARCM with 37 ЊC heat-shock for one hour 29 . Full genotype: UAS-mCD8-GFP,hs-FLP/ Y;FRT G13 ,top co /FRT G13 ,tubP-GAL80;tubP-GAL4/+. Flies aged at 25 ЊC for 6 days scored for germline phenotypes and GFP expression by phase-contrast and fluorescence microscopy. 50 Egfr CO testes (n = 182) and 36 Egfr ts testes (n = 93) had GFP-germline cells: none showed germline overproliferation. Egfr mutant GFP-cyst progenitor clones were not detected (n = 275), compared with 35 in controls (n = 60).

It is often hypothesized that two species competing for the same resource cannot stably coexist unless they partition their resources in space and time. More recently stable isotope analyses have complemented traditional, observation-based niche research by conceptualizing many of the characteristics of communities, for example, trophic niche width and the partitioning of resources. Here we quantify resource partitioning of sympatric small mammal species in an African ecosystem by analysing stable isotope ratios of hair collected from a South African forest-grassland vegetation mosaic, and combine this with known spatial and temporal behavioural data to interpret community competition and resource partitioning.We observe niche separation to different degrees across the entire community, with different species displaying either unique isotopic dietary preferences, or partitioning resources in space and/or time. d 13 C values were more enriched in species that inhabited afromontane grassland compared with those that inhabited afromontane forest, a reflection of the dominant vegetation in each habitat. Contrary to expectations, arboreal rodents occupied higher trophic positions than terrestrial rodents and approaching d 15 N values similar to insectivorous shrews, suggesting that arboreal rodents feed on items such as arthropods enriched in 15 N. While grassland species display phenotypic plasticity in terms of dietary preferences, small mammals that occurred in forests display narrow niche preferences, suggesting these species may be particularly sensitive to habitat modifications. Our results illustrate that the use of stable isotopes can be used in conjunction with spatial and temporal behavioural knowledge to elucidate resource partitioning in small African mammal communities.

Ecological studies investigating niche breadth and overlap often have limited spatial and temporal scale, preventing generalizations across varying environments and communities. For example, it is not clear whether species having restricted diets maintain such patterns relative to closely related species and across their geographic range of co-occurrence. We used stable isotope analysis of hair and fur samples collected from four regions of sympatry for Canada lynx (Lynx canadensis) and bobcat (Lynx rufus) spanning southern Canada and the northern United States, to test the prediction that the more generalist species (bobcat) exhibits a wider dietary niche than the more specialist species (Canada lynx) and that this pattern is consistent across different regions. We further predicted that Canada lynx diet would consistently exhibit greater overlap with that of bobcat compared to overlap of bobcat diet with Canada lynx. We found that Canada lynx had a narrower dietary niche than bobcat, with a high probability of overlap (85-95%) with bobcat, whereas the bobcat dietary niche had up to a 50% probability of overlap with Canada lynx. These patterns of dietary niche breadth and overlap were consistent across geographic regions despite some regional variation in diet breadth and position, for both species. Such consistent patterns could reflect a lack of plasticity in species dietary niches. Given the increasingly recognized importance of understanding dietary niche breadth and overlap across large spatial scales, further research is needed to investigate the mechanisms by which broad-scale patterns are maintained across species and systems.

No endemic Madagascar animal with body mass &gt;10 kg survived a relatively recent wave of extinction on the island. From morphological and isotopic analyses of skeletal ‘subfossil’ remains we can reconstruct some of the biology and behavioral ecology of giant lemurs (primates; up to ~160 kg), elephant birds (up to ~860 kg), and other extraordinary Malagasy megafauna that survived well into the past millennium. Yet much about the evolutionary biology of these now extinct species remains unknown, along with persistent phylogenetic uncertainty in some cases. Thankfully, despite the challenges of DNA preservation in tropical and sub-tropical environments, technical advances have enabled the recovery of ancient DNA from some Malagasy subfossil specimens. Here we present a nuclear genome sequence (~2X coverage) for one of the largest extinct lemurs, the koala lemur Megaladapis edwardsi (~85kg). To support the testing of key phylogenetic and evolutionary hypotheses we also generated new h...

The climatic niche is a central concept for understanding species distribution, with current and past climate interpreted as strong drivers of present and historical-geographical ranges. Our aim is to understand whether Atlantic Forest snakes follow the general geographical pattern of increasing species climatic niche breadths with increasing latitude. We also tested if there is a tradeoff between temperature and precipitation niche breadths of species in order to understand if species with larger breadths of one niche dimension have stronger dispersal constraints by the other due to narrower niche breadths. Niche breadths were calculated by the subtraction of maximal and minimal values of temperature and precipitation across species ranges. We implemented Phylogenetic Generalized Least Squares to measure the relationship between temperature and precipitation niche breadths and latitude. We also tested phylogenetic signals by Lambda statistics to analyze the degree of phylogenetic n...

In this paper we studied the diet in four allopatric populations of alpine salamanders in the Dinarides (Salamandra atra prenjensis). Food consumption was assessed by stomach flushing while food availability by pitfall traps and netting. We aimed to: (i) assess the realized dietary niche, (ii) investigate prey preferences, (ii) explore individual specialization, clustering and nestedness. All populations have an equally wide dietary span that is among the largest reported for terrestrial salamanders. On the other hand, the amount of ingested prey is rather low compared to other salamander species; the quantity of consumed prey did not differ among populations but younger individuals fed more than adults. Food composition somewhat differed among populations but not among sex/age classes. In all four populations, the bulk of diet consisted of beetles, spiders, snails and millipedes; except for beetles, such prey was also preffered together with centipedes and isopods. For most of the ...

Constrained multivariate analysis is a common tool for linking ecological communities to environment. The follow-up is the development of the double-constrained correspondence analysis (dc-CA), integrating traits as species-related predictors. Further, methods have been proposed to integrate information on phylogenetic relationships and space variability. We expand this framework, proposing a dc-CA-based algorithm for decomposing variation in community structure and testing the simple and conditional effects of four sets of predictors: environment characteristics and space configuration as predictors related to sites, while traits and niche (dis)similarities as species-related predictors. In our approach, ecological niches differ from traits in that the latter are distinguished by and characterize the individual level, while niches are measured on the species level, and when compared, they are characteristics of communities and should be used as separate predictors. The novelties of...

Coexistence between closely related species can lead to intense competition for resources. Stable isotope analysis (SIA) is a reliable tool to estimate the extent of species competition. We employed SIA to evaluate niche partitioning among two syntopic species of Galápagos land iguanas: Conolophus subcristatus and C. marthae. Samples were collected on Wolf Volcano, Isabela Island, where C. marthae is endemic and syntopic with C. subcristatus. We determined δ 13 C and δ 15 N ratios and described the isotopic niche of each species using corrected standard ellipse area (SEA c ). We tested for differentiation between the isotopic niches, while controlling for sex, body size, spatial location of samples and mean annual primary productivity at capture points, using bivariate linear models. Despite the extensive overlap of the isotopic niches, we found species and sex to be a significant, interacting predictor of a sample's location in the δ 13 C, δ 15 N space, indicating the existence of niche partitioning mechanisms acting between species and sexes. We also found that body size and productivity at the capture points, compounded with yet undetermined spatial effects, explain ca. 75% of the differences observed between species and sexes, providing evidence for differential microhabitat and food-items usage. Our study provides essential baselines for evaluating conservation actions for C. marthae, such as the potential translocation to a sanctuary area free of competition from C. subcristatus. Competition is a critical determinant of population dynamics and community structure 1-3 . Closely related species that diverged in allopatry may retain their common ancestral niche and be expected to competitively exclude each other when they come into secondary contact 4 . Under these circumstances and given appropriate conditions 5 , natural selection acting on one or both species may favor traits that reduce niche-overlap and, therefore, competition 6 . This mechanism has been often called into question to explain patterns of coexistence between syntopic (sensu Rivas 7 ) closely related species competing for limited resources . On the other hand, neutral models of community evolution ("community drift") 13-15 may also explain niche divergence and, ultimately, coexistence between sister species. These neutral mechanisms may be expected to be particularly important where community structures are strongly limited by incomplete dispersal, as is typically the case for communities of terrestrial vertebrates living in oceanic islands . Such communities are shaped by complex patterns of extinction and recolonization 17 , and species that happen to coexist on one island may have well spent large portions of their evolutionary past confined into different islands, experiencing different biotic and abiotic conditions and, hence, selective pressures . Beyond its fundamental importance as a key concept of animal ecology, a better understanding of competitive dynamics between co-occurring, closely related species can contribute important insights to the conservation of interacting endangered species. One such case involves two species of Galápagos land iguanas: Conolophus

Coexistence between closely related species can lead to intense competition for resources. Stable isotope analysis (SIA) is a reliable tool to estimate the extent of species competition. We employed SIA to evaluate niche partitioning among two syntopic species of Galápagos land iguanas: Conolophus subcristatus and C. marthae. Samples were collected on Wolf Volcano, Isabela Island, where C. marthae is endemic and syntopic with C. subcristatus. We determined δ13C and δ15N ratios and described the isotopic niche of each species using corrected standard ellipse area (SEAc). We tested for differentiation between the isotopic niches, while controlling for sex, body size, spatial location of samples and mean annual primary productivity at capture points, using bivariate linear models. Despite the extensive overlap of the isotopic niches, we found species and sex to be a significant, interacting predictor of a sample’s location in the δ13C, δ15N space, indicating the existence of niche part...

Coexistence between closely related species can lead to intense competition for resources. Stable isotope ratio analysis (SIRA) is a reliable tool to estimate the extent of species competition. We performed SIRA to assess niche partitioning among two syntopic species of Galápagos land iguanas: Conolophus subcristatus and the critically endangered C. marthae. We collected samples from 60 C. marthae and 58 C. subcristatus within an area of about 2 km2 on Wolf Volcano, Isabela Island, where C. marthae is endemic. We determined δ13C and δ15N ratios and described the isotopic niche of each species using corrected standard ellipse area (SEAc). We tested for differentiation between the isotopic niches, while controlling for sex, using bivariate linear models. Despite the extensive overlap of the isotopic niches, our results indicate the existence of niche partitioning mechanisms acting between species and sexes. Evaluating the effect of ecological variables, we found that body size and pro...

Ecological theory predicts that species coexisting locally may either be functionally more dissimilar than expected by chance due to niche differentiation ('trait divergence'), or rather be functionally similar given that species bearing traits associated with low competitive ability are likely to be excluded ('trait convergence'). How the importance of trait divergence and convergence varies with productivity and depending on different plant traits still remains controversial. However assessing the effect of site productivity on meadow species assembly can help defining proper management practice for these ecosystems. We sought evidences for trait convergence and divergence across a productivity gradient over 21 wet meadows in Železné hory Mts. (Czech Republic), considering 13 plant traits. In each meadow, we recorded species composition in four 1 m 2 plots divided into 100 subplots, and different environmental parameters and site characteristics linked to productivity (standing biomass, soil water table and soil nutrients content). Species spatial aggregation within plots (calculated by the V-score metric on the 100 subplots per plot averaged across all plots in each meadow) was correlated with trait dissimilarity between species in a rather limited number of cases. Significant divergence was observed when traits were considered in combination or when using phylogeny as a proxy of functional similarity. Moreover, plot level patterns of trait divergence and convergence depended on local environmental characteristics. Specifically, for several of the traits studied (e.g. lifespan, combined traits) there was evidence that functional divergence of species decreased with increasing productivity. Overall from these results at fine scale we cannot rule out neutrality, but, where significant, patterns suggest stronger effects of niche differentiation between coexisting species (trait divergence) rather than convergence of functionally similar species. Nevertheless our results also support the view that increased productivity, coupled with intense competition for resources (mainly for light), can lead to the coexistence of more functionally similar species. This is relevant because biodiversity enhancement is generally achieved by maintaining low productivity in these meadows. In general our study gives insights on how species coexistence is related to life history traits and environmental variation, which is also relevant for the conservation and management of species-rich meadows.

Modern North American carnivorous mammal assemblages consist of species from a single clade: the Carnivora. Carnivorans once coexisted with members of other meat-eating clades, including the creodonts (Hyaenodontida and Oxyaenida). Creodonts, however, went extinct in North America during the late Eocene and early Oligocene, potentially due to niche overlap and resource competition with contemporary carnivorans. In this study, we employ a community ecology approach to understand whether the dietary niches of coexisting creodonts and carnivorans overlapped during the late Eocene (Chadronian North American Land Mammal Age), a time when creodonts were dwindling and carnivorans were diversifying. We quantify niche overlap based on inferences of diet from carnassial tooth shape estimated using Orientation Patch Count, Dirichlet’s Normal Surface Energy, and linear dental measurements as well as from body mass for all species in the Calf Creek Local Fauna of Cypress Hills, Saskatchewan (Tre...

The Qinghai–Tibetan Plateau (QTP) has the highest elevations of all biodiversity hotspots. Difficulties involved in fieldwork at high elevations cause challenges in researching mechanisms facilitating species coexistence. Herein, we investigated Snow Partridge (Lerwa lerwa) and Tibetan Snowcock (Tetraogallus tibetanus), the only two endemic Galliformes on the QTP, to understand species coexistence patterns and determine how they live in sympatry for the first time. We assembled occurrence data, estimated habitat suitability differences and the underlying factors between two species at different scales using ecological niche models. Niche overlap tests were used to investigate whether niche differences between these species allow for their coexistence. We found that elevation was the most important factor determining habitat suitability for both species. At the meso‐scale, two species have similar ecological niches with their suitable habitats lying predominantly along ridge crests. ...

Some studies have suggested that non-native species invasions may threaten local diversity by creating homogenized environments. However, many studies have been based on limited or anecdotal data, and/or have failed to consider the influence of habitat modification together with possible influences of non-native species on native ones. Hemidactylus mabouia (Squamata, Gekkonidae) likely invaded natural environments in Brazil hundreds of years ago. Yet, little is known about whether it affects native lizard fauna. We tested whether H. mabouia negatively influences native lizard species richness and abundance on a regional scale and locally through niche overlap. We analyzed species abundance and richness of nine lizard assemblages, in five of which H. mabouia occurred. We evaluated niche overlap of species in a lizard assemblage with high H. mabouia abundance through null models. Niche axes included spatial use, temporal activity and diet. Although species abundance did not differ among sites with and without the invasive species, the presence of H. mabouia seems constrained to the richer assemblages sampled. We observed significantly higher niche overlap in spatial (ɸ obs = 0.63; ɸ exp = 0.37; P obs ≥ P exp = 0.0002) and trophic axes (ɸ obs = 0.46; ɸ exp = 0.17; P obs ≥ P exp < 0.001), but not in activity. When we considered all axes (three-dimensional niche), there was no overlapping among the lizard species. Our findings did not support the hypothesis that this non-native species negatively influences other sympatric lizard species.

The high diversity of soil bacteria is attributed to the spatial complexity of soil systems, where habitat heterogeneity promotes niche partitioning among bacterial taxa. This premise remains challenging to test, however, as it requires quantifying the traits of closely-related soil bacteria and relating these traits to bacterial abundances and geographic distributions. Here, we sought to investigate whether the widespread soil taxon Curtobacterium consists of multiple coexisting ecotypes with differential geographic distributions. We isolated Curtobacterium strains from six sites along a climate gradient and assayed four functional traits that may contribute to niche partitioning in leaf litter, the top layer of soil. Our results revealed that cultured isolates separated into fine-scale genetic clusters that reflected distinct suites of phenotypic traits, denoting the existence of multiple ecotypes. We then quantified the distribution of Curtobacterium by analyzing metagenomic data...

Investigating the ontogeny of niche differentiation enables to determine at which life-stages sexual segregation arises, providing insights into the main factors driving resource partitioning. We investigated the ontogeny of foraging ecology in Antarctic fur seals (Arctocephalus gazella), a highly dimorphic species with contrasting breeding strategies between sexes. Sequential δ 13 C and δ 15 N values of whiskers provided a longitudinal proxy of the foraging niche throughout the whole life of seals, from weaning, when size dimorphism is minimal to the age of 5. Females exhibited an early-life ontogenetic shift, from a total segregation during their first year at-sea, to a similar isotopic niche as breeding females as early as age 2. In contrast, males showed a progressive change in isotopic niche throughout their development such that 5-year-old males did not share the same niche as territorial bulls. Interestingly, males and females segregated straight after weaning with males appearing to feed in more southerly habitats than females. This spatial segregation was of similar amplitude as observed in breeding adults and was maintained throughout development. Such early-life niche differentiation is an unusual pattern and indicates size dimorphism and breeding constraints do not directly drive sexual segregation contrary to what has been assumed in otariid seals.

Mutualistic interactions among free-living species generally involve weak links and highly asymmetric dependence among partners, yet our understanding of factors beyond their emergence is still limited. Using individual-based interactions of a super-generalist fleshy-fruited plant with its frugivore assemblage we estimate the Resource Provisioning Effectiveness (RPE) and Seed Dispersal Effectiveness (SDE) to assess the balance in the exchange of resources. Plants were highly dependent on a few super-generalist frugivore species, while these interacted with most individual plants, resulting in strong asymmetries in mutual dependence. Both RPE and SDE were mainly driven by interaction frequency. Despite highly asymmetric dependencies, the strong reliance on quantity largely determined high reciprocity in rewards between partners (i.e., higher energy provided, more seedlings recruited), not obscured by minor variations in the quality of animal or plant service. We anticipate reciprocit...

The diadem snake Spalerosophis diadema (Schlegel, 1837) is found in most arid and semi-arid regions of Iran. However,little is known about ecology and lifestyle of this species in the area.  In the present study, we used MaxEnt software to predict suitable habitats and determine the factors influencing its distribution pattern. Four variables have the most importance in the distribution of S. diadema : 1. Average temperature of the coldest quarter of the year (Bio11) 2. Precipitation of the warmest quarter of the year (Bio 18) 3. Precipitation of the wettest month (Bio 13) 4. Slope. Considering  the distribution areas of S. diadema and its closely relates species, S. microlepis , and effective factors on their distribution in Iran, it can be concluded that geographical separation and the type of habitat have the most important roles in their speciation.

Kalakad Mundanthurai Tiger Reserve (KMTR), which is the home for many endemic, rare and endangered species of plants and animals, is one of the priority hotspot for conservation. Insect pests, being the most destructive agents affecting forest and shade trees are by far the most numerous animal life inhabiting the forest. As the primary predators of nocturnal insects, bats play a significant role in all forested ecosystems. The insect eating bats allocate considerable time and effort with different flight strategies to forage the available insect prey. Among the insectivorous bats of the forest ecosystem, the species of Rhinolophus genus help to control insect pest populations throughout its geographic range. The studies on faecal pellet analysis has proved their control over the lepidopteran, coleopteran, dipteran, hymenopteran, homopteran, orthopteran, hemipteran trichopteran and neuropteran group of insect pests that infects the forest trees of KMTR. The valuable pest controlling service provided by the study species needs special protection through conservation measures.

Closely related bird species can coexist in areas of range overlap due to differentiation of their ecological niches. If coexisting species have similar habitat requirements, separation of food niches presumably plays a crucial role. Theoretically, two possible food niche separation scenarios are possible: (1) use of different food resources or (2) temporal differences in feeding activity. We examined these mechanisms by investigating the feeding habits of two short-billed sunbirds (Cinnyris reichenowi and C. bouvieri) coexisting locally in the Bamenda Highlands, NW Cameroon. Daily feeding activity in both species showed a similar pattern, with two peaks (0800-0900 hours and 1500-1600 hours, respectively) and a prominent decrease in activity between 1100 and 1400 hours. However, the studied species clearly differed in their exploitation of plant resources. C. bouvieri mostly visited Lobelia columnaris, while C. reichenowi regularly visited three plant species, namely, Hypericum revolutum, Hypoestes aristata and Impatiens sakerana, with the most time spent at the second species. Such resource partitioning was probably caused by interspecific aggressive behaviour, since C. bouvieri actively repelled C. reichenowi from Lobelia columnaris plants, forcing C. reichenowi to feed on other plant species.

In order to differentiate between mechanisms of species coexistence, we examined the relative importance of local biotic neighbourhood, abiotic habitat factors and species differences as factors influencing the survival of 2330 spatially mapped tropical tree seedlings of 15 species of Myristicaceae in two separate analyses in which individuals were identified first to species and then to genus. Using likelihood methods, we selected the most parsimonious candidate models as predictors of 3 year seedling survival in both sets of analyses. We found evidence for differential effects of abiotic niche and neighbourhood processes on individual survival between analyses at the genus and species levels. Niche partitioning (defined as an interaction of taxonomic identity and abiotic neighbourhood) was significant in analyses at the genus level, but did not differentiate among species in models of individual seedling survival. By contrast, conspecific and congeneric seedling and adult density were retained in the minimum adequate models of seedling survival at species and genus levels, respectively. We conclude that abiotic niche effects express differences in seedling survival among genera but not among species, and that, within genera, community and/or local variation in adult and seedling abundance drives variation in seedling survival. These data suggest that different mechanisms of coexistence among tropical tree taxa may function at different taxonomic or phylogenetic scales. This perspective helps to reconcile perceived differences of importance in the various non-mutually exclusive mechanisms of species coexistence in hyper-diverse tropical forests.

Aims and scope: The Western Indian Ocean Journal of Marine Science provides an avenue for the wide dissemination of high quality research generated in the Western Indian Ocean (WIO) region, in particular on the sustainable use of coastal and marine resources. This is central to the goal of supporting and promoting sustainable coastal development in the region, as well as contributing to the global base of marine science. The journal publishes original research articles dealing with all aspects of marine science and coastal management. Topics include, but are not limited to: theoretical studies, oceanography, marine biology and ecology, fisheries, recovery and restoration processes, legal and institutional frameworks, and interactions/relationships between humans and the coastal and marine environment. In addition, Western Indian Ocean Journal of Marine Science features state-of-the-art review articles and short communications. The journal will, from time to time, consist of special issues on major events or important thematic issues.

Dolphins are mobile apex marine predators. Over the past three decades, warm-water adapted dolphin species (short-beaked common and striped) have expanded their ranges northward and become increasingly abundant in British waters. Meanwhile, cold-water adapted dolphins (white-beaked and Atlantic white-sided) abundance trends are decreasing, with evidence of the distribution of white-beaked dolphins shifting from southern to northern British waters. These trends are particularly evident in Scottish waters and ocean warming may be a contributing factor. This mobility increases the likelihood of interspecific dietary overlap for prey among dolphin species previously separated by latitude and thermal gradients. Foraging success is critical to both individual animal health and overall population resilience. However, the degree of dietary overlap and plasticity among these species in the Northeast Atlantic is unknown. Here, we characterise recent (2015-2021) interspecific isotopic niche an...

The change of natural environments into agricultural areas is generally accompanied by the control of invertebrate populations, which can alter prey availability for amphibians. The way frogs deal with such changes will determine their survival or extinction from these agricultural landscapes. We compared changes in the diet of the semiaquatic frog Pseudis minuta between populations from natural and agricultural environments in the Pampa biome, southern Brazil. We evaluated 34 individuals from agricultural environments and 42 from natural environments, located 1 km from each other, and we also analysed prey availability. In agricultural environments, the diet was composed mostly of beetles, one of the less frequently consumed prey groups in natural environments. This suggests that individuals of P. minuta are forced into a narrower trophic niche in agricultural areas, with the availability of food types likely a consequence of the anthropic changes.