Population Niche Research Articles

Convergent decoupling of individual specialization and niche width during ecological release.

Trophic niche has fundamental ecological importance, but many studies consider few niche metrics and most neglect critical structuring processes. Multiple processes shape trophic niches, including inter and intra-specific competition, predation and resource diversity. These processes interact and effects vary with time and taxa. The White Sands dunefield provides an ecological gradient ideal for understanding variation in niches. We measured population niche width, trophic position and individual specialization in four lizard species across habitats over 2years. The habitats include White Sands interior, the surrounding desert scrub, and their ecotone. We used arthropod, lizard and plant stable isotopes to quantify niches. We sampled lizard competitors, predators and prey as proxies for ecological processes. We found substantial variation in niches across populations but convergence between species. Individual specialization and population niche width were surprisingly decoupled. Specialization was highest in habitats with low species diversity (White Sands) and population niche width highest at intermediate diversity (ecotone). White Sands lizards may exhibit 'ultra partitioning'; high specialization alongside low individual niche widths. Population niche width is likely constrained within White Sands by low prey diversity. High ecotonal population niche widths may be due to fewer natural enemies than desert scrub but higher resource diversity than White Sands. Trophic position and specialization were positively correlated, suggesting stronger intraspecific competition at higher trophic levels. Prey diversity, inter and intra-specific competition, and predation all interacted to shape niches. Our results highlight the need for measuring multiple components of community structure and niches, as results are likely misleading in isolation.

New year, new opossums? Comparing the diet and health related characteristics of Didelphis virginiana over four years

Abstract The Virginia opossum is an animal that plays important roles in ecosystems and is a popular model for ecological studies. However, they are short-lived (average lifespan of 1.1 years), and a question arises: can the data taken from those animals be extrapolated to other years or do their characteristics change as quickly as the members of a population? Therefore, the aim of this article is to compare several characteristics (age, weight, body condition, infestation by fleas, severity of injuries, leucocyte and erythrocyte counts, and isotopic niche) of an opossum population over four years. For this, we trapped opossums in the same location at the same time of year for four years. We found that most characteristics remained similar over the study period; however, there was a change in erythrocyte counts, and the isotopic niche changed every year. A positive correlation was found between the δ15N and body condition. This suggests that if left undisturbed, opossum populations maintain their characteristics; however, their diet changes according to food availability. Opossums that are higher in the trophic net (most likely because they consume more carrion) tend to have a higher body condition.

The role of digital marketing in enhancing the sustainability of rural retail businesses in Flagstaff, South Africa

Digital marketing has profoundly altered the marketing techniques utilised by merchants. Although a growing number of rural retail enterprises in South Africa are starting to implement these techniques, the comprehensive effect of digital marketing on their sustainability is still inadequately examined. This study seeks to investigate the impact of internet marketing on retail operations in the rural community of Flagstaff. A quantitative research methodology was utilised, distributing questionnaires to all 52 major merchants via a census technique, yielding 45 replies and an 87% response rate. The results demonstrate that merchants employ several digital marketing strategies, such as social media marketing, email marketing, and mobile marketing, to engage with customers and present sales propositions. This engagement is constrained by the minimal acceptance of digital marketing among consumers, restricted e-commerce utilisation, and inadequate digital literacy, preventing both sides from fully leveraging its advantages. The report advises businesses to persist in using digital marketing methods, including social media and email marketing, into their promotional efforts. This strategy will enable them to engage the niche population that prefers these platforms and maintain alignment with market trends, so assuring competitiveness. Furthermore, it is essential to assist rural areas in improving their digital marketing adoption to sustain retail enterprises and maintain relevance in the contemporary digital environment.

Environmental niche, spatial distribution and size structure of shelf-dwelling populations of the gorgonian Eunicella cavolini (Koch, 1887) in NW Mediterranean

Extensive knowledge exists about the ecology of gorgonian species dwelling in coastal areas of the Mediterranean, but less information is available regarding populations found in deep circalittoral and bathyal environments. In recent years, the use of marine imaging technology has led to the discovery of dense coral gardens below SCUBA depths. This is the case of Eunicella cavolini (Koch, 1887) populations dwelling on the continental shelf off Cap de Creus (northwestern Mediterranean), an area included in a Site of Community Importance (SCI) of the Natura 2000 Network. We characterized the environmental niche of this species using a combination of density data extracted from 60 underwater video transects (80–400 m depth) and a set of environmental factors of a geomorphologic, oceanographic and human nature. Populations of E. cavolini develop within a restricted combination of environmental conditions, predominantly in areas of the mid continental shelf (95–110 m depth) characterized by a mixture of substrates (gravels, pebbles and rocks) with intermediate yearly average bottom current velocities (0.11–0.13 m s−1) and where no records of bottom trawling activity were registered in the years prior to the surveys. The species forms dense aggregations that average 6–8 col·m−2, with local high-density peaks above 15 col·m−2. Areas suitable for the development of E. cavolini were modelled by means of a Random Forest algorithm, which predicted that an area extending over 14 ha could potentially host populations with densities over 5 col·m−2. Bottom current velocity emerged as the most important factor determining the spatial distribution of the species, followed by depth and presence of rocks. Colony height measurements indicated that populations are dominated by small-to-medium sized colonies, with average colony height positively correlated with gorgonian density. The reduced average colony height observed might respond to the strong bottom current regime characteristic of Cap de Creus, but also to the increased likelihood of larger colonies to be captured as by-catch by trammel nets, a common type of fishing gear used in the area. This study provides relevant information about the ecology of E. cavolini populations dwelling on deep circalittoral habitats, useful for policymakers when formulating specific management measures to foster the conservation of this species inside the SCI. Additionally, the data provided could assist on the restoration actions already taking place in Cap de Creus, and be used as baseline data to monitor the evolution of E. cavolini populations through time once management plans are implemented.

EPCO-44. SPATIAL TRANSCRIPTOMICS ENABLES STATISTICAL MODELING OF SEX DIFFERENCE IN GENE CO-EXPRESSION NETWORK AND IMMUNE LANDSCAPE OF GLIOBLASTOMA

Abstract Glioblastoma (GBM) is characterized by inter- and intra-tumor molecular heterogeneity and demonstrated cell plasticity. Sex differences have been observed in various aspects: a male:female GBM incidence ratio is 1.6:1; standard of care treatments (debulking, radiation, and temozolomide) benefit females more than males. 14 human GBM samples from two study sites were subject to spatial profiling on the Vizgen Merscope platform to examine whether distinct biological and therapeutic niches in GBM were evident, to understand how the tumor microenvironments (TME) contributed to the heterogeneity of GBM, and to interrogate sex difference in the immune landscape of GBM. Multiple sets of spatial probes were designed to capture the cell identities (cancer stem cells, astrocytes, oligodendrocytes, microglia, macrophages, etc.) and the spatially-resolved expression patterns of genes with different functions. Two of the 14 GBM samples were also profiled on another FISH-based spatial platform (Veranome). The data from the two platforms exhibited a linear correlation. We explored the gene-gene co-expression network, and calculated the interaction probabilities between genes which were then compared for sex difference. We found that female samples showed significantly lower (two-fold) CD4+/CD8A+ T-cell count ratios than male samples. We also observed sample-specific spatial niches of different GBM cell subtypes and immune cell populations. Our large-scale spatial transcriptomics study revealed intrinsic sex-based differences in immune response to tumor and illuminated microenvironmental influences on GBM.

TMET-40. UPREGULATION OF URIDINE SALVAGE IN MESENCHYMAL GLIOBLASTOMA STEM-LIKE CELLS

Abstract Glioblastoma is a heterogenous tumor comprised of multiple molecular subtypes of cancer cells and cancer stem-like cells. Of particular importance are the cancer stem-like cell niche population as they are believed to be more resistant to existing therapies and re-seed the tumor following initial response to standard-of-care treatment. To better understand glioblastoma stem-like cells we completed an untargeted proteomic analysisof 35 patient derived glioblastoma stem cell lines. This system driven analysis revealed an increase in several important proteins, in the mesenchymal subtype, involved in the uridine salvage pathway. A subset of these proteins, including ecto-5’-nucleotidase (NT5E/CD73), uridine phosphorylase (UPP1), phosphoglucomutase-2-like-1 (PGM2L1), nicotinamide phosphoribosyltransferase (NAMPT), and nicotinamide N-methyltransferase (NNMT), suggest an augmented pathway for utilization of UMP and uridine as a fuel source and to replenish NAD+. Uridine and UMP are present in human serum and are enriched in the tumor microenvironment providing a sustainable resource to resupply the tumor. The upregulation of this pathway was validated in established cell lines and orthogonal patient-derived xenograft cell lines not included in the proteomics study. Further work is underway to selectively inhibit or exploit this pathway with small molecule inhibitors.

TMET-35. UPREGULATION OF THE URIDINE SALVAGE PATHWAY IN MESENCHYMAL GLIOBLASTOMA STEM-LIKE CELLS

Abstract Glioblastoma is a heterogenous tumor comprised of multiple molecular subtypes of cancer cells and cancer stem-like cells. Of particular importance are the cancer stem-like cell niche population as they are believed to be more resistant to existing therapies and re-seed the tumor following initial response to standard-of-care treatment. To better understand glioblastoma stem-like cells we completed an untargeted proteomic analysis of 35 patient derived glioblastoma stem cell lines. This revealed an increase in several important proteins involved in the uridine salvage pathway, in the mesenchymal subtype. A subset of these proteins, including ecto-5’-nucleotidase (NT5E/CD73), uridine phosphorylase (UPP1), phosphoglucomutase-2-like-1 (PGM2L1), nicotinamide phosphoribosyltransferase (NAMPT), and nicotinamide N-methyltransferase (NNMT), suggest an augmented pathway for utilization of UMP and uridine as a fuel source and to replenish NAD+. Uridine and UMP are present in human serum and are enriched in the tumor microenvironment, providing a sustainable resource to resupply the tumor. The upregulation of this pathway was validated in established cell lines and orthogonal patient-derived xenograft cell lines not included in the proteomics study. Further work is underway to selectively inhibit or exploit this pathway with small molecule inhibitors.

Working memory training in students with dyslexia: Additional effects to reading and spelling remediation not likely

BackgroundPoor decoding and spelling (literacy) skills have been associated with weak working memory. Aims. The aim of this study was to elucidate the contribution of working memory to literacy progress in students with dyslexia. It has been suggested that working memory can be enhanced by training, which in turn may have a positive effect on reading and spelling abilities (e.g., Peijnenborg et al., 2023). Methods and ProceduresParticipants consisted of a specific group of children with dyslexia and weak working memory skills (n = 62). The effect of Cogmed training on decoding and spelling progress during remediation was investigated using a randomized controlled trial with three research groups (experimental: Cogmed training; active control: fixed computerized training; passive control group). Outcomes and resultsFindings revealed that the Cogmed training enhanced working memory to a rather small extent and that no effects of the Cogmed training on literacy progress occurred over and above the reading and spelling remediation program. Conclusions and implicationsMost likely, Cogmed training does not contribute to literacy development in children with dyslexia. The null results are important information for teachers of this specific group of students, albeit inevitably small samples in intervention studies applied to niche populations increase the risk of type-II errors. Therefore, replication studies are needed.

The interplay of resource availability and parent foraging strategies on juvenile sparrow individual specialization

Temporal variation in resource availability, amplified by global change, may have strong impacts on species breeding at temperate and high latitudes that cue their reproduction to exploit seasonal resource pulses. This study examines how resource availability and parental care influence niche partitioning between and within age classes in the rufous‐collared sparrow, which provides extensive parental care. We hypothesized juveniles would exhibit narrower niches focused on high‐quality resources compared to adults, regardless of resource availability. We used stable isotope analysis to quantify individual and population niches in juveniles and adults across the breeding season in two cohorts experiencing contrasting resource landscapes. Contrary to our initial hypothesis, juveniles exhibited greater among‐individual diet variation and smaller total niche widths (i.e. higher levels of individual specialization, IS) during periods of high food availability in comparison to periods of food scarcity. Interestingly, total niche width and IS of adults remained stable across seasons despite a shift in trophic level, highlighting their potential role in providing a consistent diet for their young. These findings reveal a dynamic interplay between resource availability, parental care, and IS, with important implications for understanding population resilience under variable resource scenarios. The study also suggests that adult sparrows modify their provisioning strategies based on resources, potentially buffering offspring from environmental fluctuations. Understanding age‐specific responses to resource variation is crucial for predicting species responses to ecological conditions, particularly in regions like central Chile where seasonal resource limitation is expected to become more variable in response to climate change.

Characteristics of patients who are initiated on long-acting buprenorphine (Buvidal®) in France: A retrospective cross-sectional study

The long-acting buprenorphine Buvidal® is a recent type of opioid agonist treatment (OAT) used for opioid use disorder (OUD). It was initially suggested to preferentially use Buvidal® for specific OUD populations, including people in prison, or patients in recovery and on sublingual buprenorphine. We conducted a national study to examine whether the profile of patients treated with Buvidal® in France matched these initial recommendations. A retrospective cross-sectional study was conducted in 13 national addiction centers (outside prison), using the individual medical records of patients initiated on Buvidal®. Baseline characteristics were collected and described, including sociodemographic features, comorbid medical conditions, concurrent substance use and prescription drug misuse, and OAT features before Buvidal® initiation, respectively. In total 101 patients (72.3% males, mean age 43.9±11.3years) were identified, which corresponded to one sixth of all patients treated with Buvidal® in France at the time of the study. Of them, 36 (36.4%) of them were professionally active, 35 (35.4%) were durably inactive, and the rest in an intermediary situation. Furthermore, 90 (90.0%) patients had at least one medical comorbidity (all types), and 83 (83.0%) at least one psychiatric comorbidity. Most frequent non-psychiatric comorbidities were chronic pain (n=20, 20.0%) and chronic viral infection (n=16, 17.8%). Current use of psychoactive substances included cocaine and crack (n=43, 42.6%), heroin (n=19, 18.8%), but also misuse of prescription drugs (n=20, 20%), mainly opioid analgesics. Moreover, 99 (98.0%) patients had an OAT before Buvidal® initiation, including 7 (8.1%) patients on methadone. The profile of patients initiated on Buvidal® in France was extremely similar to that of patients treated for OUD in France, either in terms of social or clinical features. While initial recommendations essentially underlined the interest of Buvidal® for some niche populations, the on-the-ground practice reveals a more widespread use, including for unrecovered patients, or patients treated with methadone.

Niche of woody plant populations in Picea purpurea community in the upper Taohe River

The niche of plant populations is affected by the environment, species characteristics and anthropogenic disturbance. Picea purpurea, as a major constructive species in the northeastern Qinghai-Tibetan Plateau, had been severely damaged. Although the national project for the protection of natural forests has promoted the recovery of its community, its structure, survival status, development trend, and the factors affecting it are still unclear. We selected P. purpurea communities in Zecha, Dayugou and Yeliguan forest zones at different altitudes and disturbance levels. We analyzed niche characteristics of the woody plants and the relationship between niche and altitude, and disturbance. P. purpurea has absolute advantages as a constructive species, and its population dominance and niche width in the tree layer show a decreasing trend with decreasing altitude, there is niche overlap between all species pairs. In the shrub layer, the dominant species are mostly Caprifoliaceae and Rosaceae besides P. purpurea seedlings, the proportion of species pairs with niche overlap is YLG>ZC>DYG, and all appeared niche divergence and convergence species pairs. In addition, P. purpurea seedlings had niche overlap with most woody species, and this overlap index was the highest. The mean values of the niche overlap index between species in the tree and shrub layers were all YLG>DYG>ZC. The niche overlap index between species in the tree layer was greater than that in the shrub layer in the same forest zones, indicating that the tree layer is more stable than the shrub layer, providing evidence that niche overlap maintains community stability. Regression analyses showed that minimum temperature was the main factor affecting dominance, niche, niche overlap and shrub layer species richness of the P. purpurea population. Disturbance did not significantly affect dominance and niche of P. purpurea seedling populations, but promoted niche differentiation of shrub layer species. We conclude that the P. purpurea community is mainly influenced by altitude and anthropogenic disturbance. Altitude-induced climatic variation fundamentally determines the distinct community composition and population niche. Anthropogenic disturbance has altered habitat heterogeneity and enriched community structure. Furthermore, the P. purpurea populations show a trend towards expansion. Understanding the structure and niche characteristics of P. purpurea communities on different environmental gradients enriches our ideas for implementing vegetation restoration and sustainable forest management in subalpine zones in the context of climate change, and is conducive to improving the conservation capacity of this population or community type.

Suicidal Ideation and Behaviors Among LGBTQ+ Adolescents and Young Adults Who Have Experienced Sexual Violence: A Scoping Review of the Literature.

The relationship between sexual violence (SV) experiences and suicidal ideation (SI) is known. However, when applied to lesbian, gay, bisexual, transgender, queer, and more (LGBTQ+) populations, the impact that experiences with SV have on the severity and magnitude of SI continues to be explored. A scoping review of the literature was conducted to summarize the current literature related to SI experienced by LGBTQ+ adolescents and young adults (AYAs) who have experienced SV. Studies were found by searching electronic databases. To be included in the review, the study must have (a) been written in the English language, (b) been conducted in the United States, (c) presented empirical data, (d) been exclusively focused on LGBTQ+ AYAs, (e) focused on experiences with SV or have analyses separate from other types of violence, and (f) investigated suicidality as an outcome. All relevant studies published to date were included. Forty-one articles were retrieved for full-text review, of which five were determined to meet eligibility. LGBTQ+ AYAs were significantly associated with increased rates of SI compared with their cisgender heterosexual peers. LGBTQ+ AYAs were also associated with higher rates of SV victimization, ranging from intimate partner violence to previous child sexual abuse. Higher rates of depression were also associated with the population studied in each included article. The relationship between SV and SI in this population is not well studied, as highlighted through this completed review. Targeting this knowledge gap through future research can lead to intervention development for this population niche.

Hidden invasiveness of non-native Schlegel's Japanese gecko (Reptilia: Squamata: Gekkonidae) and three-way competition among natives and non-natives in Japan.

In this study, we investigated the invasiveness of Gekko japonicus, a prevalent gecko species in Japan and an ancient non-native species, focusing on its competition with both the undescribed endemic Gekko species (referred to as Nishiyamori in Japanese) and G. hokouensis. These species are co-distributed with G. japonicus, leading us to hypothesize that G. japonicus was invasive upon its initial introduction. We employed niche analysis and population genetics through ddRAD-seq to assess the historical invasiveness of G. japonicus by comparing regions with and without interspecies competition. Our niche analysis across the Goto Islands, Hiradojima Island (colonized by G. japonicus) and the Koshikishima Islands (not colonized by G. japonicus) indicated that endemic Gekko sp. alter their microhabitat usage in response to invasions by other gecko species, despite having similar suitable habitats and microhabitat preferences. Population genetic analysis revealed significant population declines in Gekko sp. within areas of introduced competition, in contrast to stable populations in areas without such competition. These findings suggest a tripartite competitive relationship among the gecko species, with G. japonicus and G. hokouensis invasions restricting the distribution of the endemic Gekko sp. Consequently, G. japonicus may have historically acted as an invasive species. Acknowledging the historical dynamics of current biodiversity is crucial for addressing complex ecological issues and making informed conservation decisions.

Microfluidic Ecology Unravels the Genetic and Ecological Drivers of T4r Bacteriophage Resistance in E. coli: Insights into Biofilm-Mediated Evolution.

We use a microfluidic ecology which generates non-uniform phage concentration gradients and micro-ecological niches to reveal the importance of time, spatial population structure and collective population dynamics in the de novo evolution of T4r bacteriophage resistant motile E. coli. An insensitive bacterial population against T4r phage occurs within 20 hours in small interconnected population niches created by a gradient of phage virions, driven by evolution in transient biofilm patches. Sequencing of the resistant bacteria reveals mutations at the receptor site of bacteriophage T4r as expected but also in genes associated with biofilm formation and surface adhesion, supporting the hypothesis that evolution within transient biofilms drives de novo phage resistance.

The spatiotemporal context of individual specialization in resource use and environmental associations.

1. Individual niche specialization is widespread in natural populations and has key implications for higher levels of biological organization. This phenomenon, however, has been primarily quantified in resource niche axes, overlooking individual variation in environmental associations (i.e. abiotic conditions organisms experience). 2. Here, we explore what we can learn from a multidimensional perspective of individual niche specialization that integrates resource use and environmental associations into a common framework. 3. By combining predictions from theory and simple simulations, we illustrate how (i) multidimensional intraspecific niche variation and (ii) the spatiotemporal context of interactions between conspecifics scale up to shape emergent patterns of the population niche. 4. Contemplating individual specialization as a multidimensional, unifying concept across biotic and abiotic niche axes is a fundamental step towards bringing this concept closer to the n-dimensional niche envisioned by Hutchinson.

Traversing the Great Lakes: Post‐glacial colonization by a widespread terrestrial salamander

AbstractAimsGlacial retreat at the end of the Pleistocene epoch opened vast expanses of emergent habitat in the northern hemisphere that were colonized by opportunistic taxa. However, species that undergo post‐glacial expansion may have originated from one or several glacial refugia. We inferred the post‐glacial expansion history of the Eastern Red‐backed Salamander (Plethodon cinereus), a fully terrestrial species with a vast distribution despite severe dispersal limitations. Previous studies indicated populations south of the glacial boundary at the eastern and western limits of the distribution were closely related, suggesting either multiple refugia or an extraordinary post‐glacial expansion event.LocationEastern North America.Taxon Plethodon cinereus (Green, 1818), Caudata: Plethodontidae.MethodsWe collected ddRAD‐seq data from 106 individuals throughout the distribution of P. cinereus. We estimated phylogeographic structure, including finer‐scale structure among the post‐glacial populations. To test the origins and routes of colonization, we used ecological niche modelling, population trees and analyses of directional range expansion.ResultsAnalyses supported our hypothesis of a southeastern glacial refugium, with northward expansion along the Eastern Seaboard prior to westward invasion into the Great Lakes region, including southwestern expansion into unglaciated areas at the western end of the distribution. However, a distinct subgroup in the northwestern portion of the range raises the possibility of a second refugium near the ice‐free Driftless Area.Main ConclusionsBased on our results, we hypothesize a southeastern refugium from which most of today's northern populations undertook extensive post‐glacial colonization. Our results indicate a geographically non‐linear colonization history for P. cinereus.

Ecological Niche Studies on Hylurgus ligniperda and Its Co-Host Stem-Boring Insects

Hylurgus ligniperda (Fabricius), a significant quarantine pest, has recently invaded China, marking a new spread outside its known global distribution. This study aims to clarify the invasion and colonization mechanisms of H. ligniperda in Shandong Province, a primary colonization site. This study employed sampling surveys and analysis of damaged wood, discovering that the wood-boring insects sharing the same host as H. ligniperda mainly include Cryphalus sp., Arhopalus rusticus, and Shirahoshizo sp. Through ecological niche theory, the study analyzed the ecological niche relationships between H. ligniperda and these three wood-boring insects, from the perspectives of temporal and spatial resource utilization. The results reveal that these insects could cause damage to P. thunbergii trees at different health levels, with H. ligniperda being the most destructive. The ecological niches of insect populations varied significantly by tree vigor and height. Cryphalus sp. occupied the entire trunk, whereas A. rusticus and Shirahoshizo sp. were concentrated in the lower-middle trunk and the root section up to a depth of 1 m. Notably, H. ligniperda primarily targeted tree roots. Due to the differences in spatial distribution, there was no intense competition between H. ligniperda and other wood-boring insects. With a decline in the health of the host tree, Cryphalus sp. ascended the trunk, whereas H. ligniperda spread deeper into the roots and A. rusticus moved towards the base of the trunk and the top of the roots. Shirahoshizo sp. showed a less defined distribution pattern. Therefore, H. ligniperda was more dominant during the later stage of damage. The position occupied by each insect on the trunk was relatively stable, and the ecological niche overlap value with H. ligniperda was low in terms of temporal resources. Therefore, H. ligniperda and other stem-boring pests exhibit coexisting populations mainly through the allocation and utilization of spatial resources, eventually promoting the successful colonization of H. ligniperda.

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.

Comparative analysis of the diversity of trinucleotide repeats in bacterial genomes.

The human gut is the most favorable niche for microbial populations, and few studies have explored the possibilities of horizontal gene transfer between host and pathogen. Trinucleotide repeat (TNR) expansion in humans can cause more than 40 neurodegenerative diseases. Further, TNRs are a type of microsatellite that resides on coding regions can contribute to the synthesis of homopolymeric amino acids. Hence, the present study aims to estimate the occurrence and diversity of TNRs in bacterial genomes available in the NCBI Genome database. Genome-wide analyses revealed that several bacterial genomes contain different types of uninterrupted TNRs. It was found that TNRs are abundant in the genomes of Alcaligenes faecalis, Mycoplasma gallisepticum, Mycoplasma genitalium, Sorangium cellulosum, and Thermus thermophilus. Interestingly, the genome of Bacillus thuringiensis strain YBT-1518 contained 169 uninterrupted ATT repeats. The genome of Leclercia adecarboxylata had 46 uninterrupted CAG repeats, which potentially translate into polyglutamine. In some instances, the TNRs were present in genes that potentially encode essential functions. Similar occurrences in human genes are known to cause genetic disorders. Further analysis of the occurrence of TNRs in bacterial genomes is likely to provide a better understanding of mismatch repair, genetic disorders, host-pathogen interaction, and homopolymeric amino acids.

Resource diversity mitigates the effects of intraspecific competition in co-occurring cryptic nematode species

Intraspecific competition and resource diversity are considered major drivers of niche differentiation, which are expected to promote population niche expansion by driving individuals to feed on alternative resources and/or by enhancing individual diet specialization. Nevertheless, experimental studies on the interaction effects of both factors on animal behavior and population dynamics remain scant. Here, we investigate how resource diversity alters the impact of intraspecific competition on resource preference and fitness of three co-occurring cryptic species of the marine nematode complex Litoditis marina (Pm I, Pm III and Pm IV). For each cryptic species, two competition regimes (‘low nematode density’ and ‘high nematode density’) were established in microcosms with varying resource diversity (E. coli, low-, medium- and high-diversity food). Our results show differences in resource preference and population fitness depending on intraspecific competition and resource diversity, but the response also varied considerably between cryptic species. Pm III did not exhibit resource preference under low intraspecific competition, but preferred the two most diverse food sources under high intraspecific competition. Pm IV also showed preference for medium-diversity food under high competition, whereas no resource preference was observed in Pm I regardless of competition regimes and resource diversity. Nevertheless, all cryptic species exhibited enhanced adult population growth on a more diverse food source under stronger intraspecific competition. These results indicate that resource diversity can alleviate intraspecific competition and affect niche diversification, which may impact diversity maintenance in ecological communities.