Interspecific Competition Research Articles

High trophic specialization structures the epi- to bathypelagic fish community in the Bay of Biscay

The deep-pelagic ecosystem is characterized by significant environmental gradients, particularly in food resources. The absence of primary production below the epipelagic zone leads to a decrease in food resources with depth. Two opposite feeding strategies have been described for this community in response to this decline in food resources: stochasticity, with species adopting opportunistic feeding strategies with a generalist diet, and determinism, with species segregating and specializing to mitigate strong interspecific competition through niche partitioning. To test these aspects, we analyzed the isotopic niches of 16 fish species using stable isotope analysis of carbon and nitrogen carried out on muscle samples. The data were collected in canyons of the Bay of Biscay between 25 and 1335 m. Our primary objective was to identify isotopic niche segregation or overlap and determine whether species sharing similar isotopic niches show depth-based segregation by grouping them into trophic guilds and comparing their depth distribution with trawl data. We then used null model comparisons to test whether competition resulted in smaller values of isotopic niche size and overlap within each depth assemblage compared to those obtained by chance. We found that several species with similar isotopic niches were segregated based on depth. The comparison with null models showed that competition drove species to reduce niche size and specialize to avoid strong interspecific competition in the epi- to bathypelagic layers. Utilizing isotopic diversity indices weighted by biomass, our calculation showed significant divergence within the community, indicating that species with the highest biomass had extreme isotopic values. The high degree of specialization of species raises concerns about their vulnerability to various pressures, including climate change and exploitation. At the community level, this vulnerability is also a concern in maintaining the integrity of ecological processes.

Coordinated molecular and ecological adaptations underlie a highly successful parasitoid.

The success of an organism depends on the molecular and ecological adaptations that promote its beneficial fitness. Parasitoids are valuable biocontrol agents for successfully managing agricultural pests, and they have evolved diversified strategies to adapt to both the physiological condition of hosts and the competition of other parasitoids. Here, we deconstructed the parasitic strategies in a highly successful parasitoid, Trichopria drosophilae, which parasitizes a broad range of Drosophila hosts, including the globally invasive species D. suzukii. We found that T. drosophilae had developed specialized venom proteins that arrest host development to obtain more nutrients via secreting tissue inhibitors of metalloproteinases (TIMPs), as well as a unique type of cell-teratocytes-that digest host tissues for feeding by releasing trypsin proteins. In addition to the molecular adaptations that optimize nutritional uptake, this pupal parasitoid has evolved ecologically adaptive strategies including the conditional tolerance of intraspecific competition to enhance parasitic success in older hosts and the obligate avoidance of interspecific competition with larval parasitoids. Our study not only demystifies how parasitoids weaponize themselves to colonize formidable hosts but also provided empirical evidence of the intricate coordination between the molecular and ecological adaptations that drive evolutionary success.

Molecular Mechanisms of Bacterial Resistance to Antimicrobial Peptides in the Modern Era: An Updated Review.

Antimicrobial resistance (AMR) poses a serious global health concern, resulting in a significant number of deaths annually due to infections that are resistant to treatment. Amidst this crisis, antimicrobial peptides (AMPs) have emerged as promising alternatives to conventional antibiotics (ATBs). These cationic peptides, naturally produced by all kingdoms of life, play a crucial role in the innate immune system of multicellular organisms and in bacterial interspecies competition by exhibiting broad-spectrum activity against bacteria, fungi, viruses, and parasites. AMPs target bacterial pathogens through multiple mechanisms, most importantly by disrupting their membranes, leading to cell lysis. However, bacterial resistance to host AMPs has emerged due to a slow co-evolutionary process between microorganisms and their hosts. Alarmingly, the development of resistance to last-resort AMPs in the treatment of MDR infections, such as colistin, is attributed to the misuse of this peptide and the high rate of horizontal genetic transfer of the corresponding resistance genes. AMP-resistant bacteria employ diverse mechanisms, including but not limited to proteolytic degradation, extracellular trapping and inactivation, active efflux, as well as complex modifications in bacterial cell wall and membrane structures. This review comprehensively examines all constitutive and inducible molecular resistance mechanisms to AMPs supported by experimental evidence described to date in bacterial pathogens. We also explore the specificity of these mechanisms toward structurally diverse AMPs to broaden and enhance their potential in developing and applying them as therapeutics for MDR bacteria. Additionally, we provide insights into the significance of AMP resistance within the context of host-pathogen interactions.

Pathogenic Bacteroides fragilis strains can emerge from gut-resident commensals.

Bacteroides fragilis is a prominent member of the human gut microbiota, playing crucial roles in maintaining gut homeostasis and host health. Although it primarily functions as a beneficial commensal, B. fragilis can become pathogenic. To determine the genetic basis of its duality, we conducted a comparative genomic analysis of 813 B. fragilis strains, representing both commensal and pathogenic origins. Our findings reveal that pathogenic strains emerge across diverse phylogenetic lineages, due in part to rapid gene exchange and the adaptability of the accessory genome. We identified 16 phylogenetic groups, differentiated by genes associated with capsule composition, interspecies competition, and host interactions. A microbial genome-wide association study identified 44 genes linked to extra-intestinal survival and pathogenicity. These findings reveal how genomic diversity within commensal species can lead to the emergence of pathogenic traits, broadening our understanding of microbial evolution in the gut.

Soil nutrient heterogeneity affects community stability through changing asynchrony in an alpine meadow on the Qinghai-Tibetan Plateau

Soil nutrients are ubiquitously heterogeneously distributed and such heterogeneity can greatly influence plant and population growth, interspecific competition and community structure and productivity. Despite these impacts, it is still unknown how soil nutrient heterogeneity affects community stability. We conducted a three-year experiment in an alpine meadow on the Qinghai-Tibetan Plateau, involving one homogeneous and six heterogeneous treatments of N, P, and K addition. The heterogeneous treatments varied in patch size, patch contrast, and number of patch types. Community stability in the homogeneous treatment tended to be the highest, likely due to high asynchrony among functional groups. However, such effects varied with patch size, patch contrast and number of patch types. Also, the effects of patch contrast and number of patch types on community stability and asynchrony among functional groups depended on patch size. The grass proportion was significantly affected by soil nutrient heterogeneity, and greater number of patch types increased the grass proportion at the small patch size, but not at the large one. Additionally, species richness, Shannon-Weiner index and Simpson index were greater in high patch contrast compared to the homogeneous treatment, but community evenness was not. These results suggest that soil nutrient heterogeneity can influence community stability by modifying functional group asynchrony and community evenness, rather than biomass proportions or other plant diversity indices. Our findings highlight the importance of incorporating soil nutrient heterogeneity in modeling the responses of alpine ecosystems to continuous nitrogen deposition and climate warming.

The Phenotypic and Molecular Identification of Phyllospheric Bacteria Possessing Antimicrobial Activity from Funtumia elastica (Preuss) Stapf.

Unlike plant phytochemicals, little has been done to explore the metabolites from phyllosphere bacterial flora, some of which enabled them to survive interspecific competition through amensalism. This study evaluated the antimicrobial activity of metabolites from Phyllospheric Bacteria (PB) isolated from Funtumia elastica (FE), against selected bacterial and fungal pathogens. Phenotypic and molecular methods were used to identify the isolated phyllo-microbiota. The PB were aseptically isolated by sonication. Their metabolites were obtained from the fresh overnight culture of the organisms. The cell-free supernatants containing the metabolites were used for antimicrobial assays against the pathogens. The DNA of the bacterial isolates were isolated using a NIMR-BIOTECH DNA extraction kit, while their 16S rRNA was amplified with the primer: 799F 5'-AACACGGATTA GATACC-3', 1193R 5'- ACGTCATCCCCACCTTCC-3', using SolisFast* Master Mix, (Solis Biodyne-Estonia). The BLAST of the sequence was done from the NCBI Gen-bank. The PB strains identified were submitted to NCBI and accession numbers were assigned to them. The phyllosphere of FE yielded 21 bacterial isolates: 7 Gram-positives and 14 Gram-negatives. The metabolites from these isolates showed varying degrees of bioactivity against Staphylococcus aureus (ATCC29213), Escherichia coli (ATCC 25922) Klebsiella pneumoniae (ATCC 35659); Trychophyton rubrum, Candida albicans and Microsporum canis. Fifteen bioactive isolates sequenced yielded four genera, Enterobacter (E. hormaechei 98.44%), Bacillus (B. cereus 100%), Pontoea (P. dispersa 99.72%), Staphylococcus (S. arlettae 99.72%). Bacteria from FE phyllosphere, produced metabolites antagonistic (cidal) to some human pathogens. This has great potential for possible drug discovery.

Among‐river pattern in relative abundance of two salmonid fishes reflects temperature‐dependent competition

Abstract Temperature is a key driver in determining species distribution and abundance across climatic and geographical gradients. This occurs through direct physiological effects of temperature on performance, but may also result from temperature effects on species interactions. In the current study we experimentally test for temperature‐dependent competition between juvenile anadromous Atlantic salmon and brown trout and evaluate the role of temperature in shaping the relative abundance of these species across 88 Norwegian rivers. When the two species were reared in allopatry their somatic growth rates were similar across a range of temperatures (4–16°C). When reared in sympatry, the growth of salmon was greatly reduced at the coldest temperature relative to when reared in allopatry, whereas this was not the case for trout. The effect of interspecific competition on growth was more similar for the two species at warmer temperatures. Thus, interspecific competition effects were strongly asymmetric only at the lowest temperature, with trout outcompeting salmon. The results from the experiment were reflected in qualitative patterns of relative abundance of salmon and trout in natural populations, which shifted from being trout dominated in rivers with low summer temperatures to being salmon dominated in warmer rivers. These results provide an empirical example of how temperature effects on the relative abundance of species can only be understood in light of information about temperature‐dependent species interactions.

Invasive vegetation encroachment modulates dual threats faced by island-endemic scaly crickets

The mechanisms by which non-native species impact island-endemic populations are varied and often convoluted. For effective invertebrate conservation where capacity is limited, it is vital to understand both direct and indirect species interactions. Those interactions define specific threats and therefore highlight possible solutions. We quantified several of the non-native species threats faced by an endemic scaly cricket, Discophallus ascension (family: Mogoplistidae), found on Ascension Island’s naturally barren coastlines. We hypothesized that encroaching non-native Mexican thorn Prosopis juliflora (1) directly reduced microclimate suitability, (2) indirectly increased resource competition with non-native species, and (3) indirectly increased non-native predation. Our aim was to assess how rapidly spreading Mexican thorn might reduce endemic cricket populations. Lab trials first confirmed the temperature and diet preferences of D. ascension. Mexican thorn significantly increased ground-level temperature but not above the estimated optimum for D. ascension within key habitat. Observed interspecific resource competition was significantly greater in habitat degraded by Mexican thorn and was driven by non-native ants, house crickets Gryllodes sigillatus and cockroaches Periplaneta americana. Recorded cricket predation was almost entirely by non-native rats Rattus rattus in barren habitat but primarily by ants in Mexican thorn habitat. Threats to D. ascension were therefore modulated by invasive vegetation, but driven by non-native insects and rats at all sites. We conclude that removal of vegetation alone is likely to reduce resource competition but not predation. Managing multiple invasive species is likely necessary for successful species conservation.

Elevational range size of the breeding bird assemblages and its relationships with richness in the Eastern Himalayas

Species range size reflects the underlying niche of species and directly affects the spatial pattern of species richness. However, the exploration of community mean range size has received relatively limited attention compared to the emphasis on species richness patterns. Additionally, few studies have tested how the rescue effect (the proximity of the distribution limits of potentially interacting species) relates to species richness. In this study, we used a two-year dataset of breeding birds along an elevational gradient in the Lebu Valley, Eastern Himalayas of China, aiming to explore (a) the association between the mean elevational range size of bird community and elevation, using three different ways to calculate the mean elevational range size (Stevens' method, midpoint method and specimen method), (b) examine the influence of drivers (including temperature seasonality, precipitation seasonality, net primary productivity, habitat diversity, geometric constraint, and interspecific competition) on the mean elevational range size pattern, and (c) investigate the effect of rescue effect on species richness pattern. Our results showed that the pattern of mean elevational range size and its underlying drivers vary significantly depending on the assessment method used. Using Stevens' method, which were calculated based on species occurrences, we observed a low-plateau pattern in mean elevational range size. In contrast, the midpoint and specimen methods, which calculate based on the species' distributing midpoint and abundance center, respectively, revealed a mid-peak pattern. Besides, our study supports several ecological hypotheses, including the ambient energy hypothesis, mid-domain hypothesis, and interspecific competition hypothesis. Furthermore, we found that geometric constraints and interspecific competition were the most influential predictors of mean elevational range size patterns, irrespective of the calculation method. Additionally, a significantly positive correlation was observed between the overlap of range margins and species richness, suggesting a contribution of the rescue effect to species richness patterns. The significance of the correlation is associated with the definition of species range size boundaries. Remarkably, this correlation becomes significant only when species range margins reach their 43 % threshold; beyond the 78 % range margin, the increase in correlation strength becomes minimal. Moreover, the rescue effect from low-elevation species was significantly more pronounced than that from high-elevation species, resulting in a species richness hump skewed towards lower elevations. Our findings contribute to validating the applicability and limitations of hypotheses related to species distribution, enhancing both theoretical and empirical aspects of research. This provides deeper insights for a more comprehensive and profound understanding of the local dynamics and interactions within the ecosystem.

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.

Sexual dimorphisms in body proportions of Masai giraffes and the evolution of the giraffe’s neck

Giraffes exhibit a large sexual dimorphism in body size. Whether sexual dimorphisms also exist in body proportions of the axial and appendicular skeleton has been debated, particularly regarding the giraffe’s iconic long neck. We examined the anatomical proportions of the neck, forelegs, hindlegs, and body trunk of the Masai giraffe (G. tippelskirchi) in captive and wild populations. We found that female Masai giraffes have proportionally longer necks relative to their forelegs than males in contradiction to the original necks-for-sex hypothesis that proposed that the evolution of the giraffe’s long neck was driven by male-male competition. However, male neck width and apparent mass are proportionally larger than females’, supporting a modification of the necks-for-sex hypothesis. Moreover, male foreleg length is proportionally longer whereas female trunk length is proportionally longer. These sexual dimorphisms were found in both captive and wild Masai giraffes. We speculate that the initial evolution of the giraffe’s long neck and legs was driven by interspecific competition and the maternal nutritional demands of gestation and lactation through natural selection to gain a competitive advantage in browsing, and then later the neck mass was further increased as a consequence of male-male competition and sexual selection. Differences in the proportions of major body components define sex phenotypes, but several giraffes display opposite-sex phenotypes with a significantly higher level of discordancy seen in captive males. We speculate that body proportion sexual dimorphisms are maintained in the wild by natural and/or sexual selection, but in captivity selection is relaxed resulting in a higher occurrence of discordances in sexual phenotypes.

Plant spatial configurations and their influences on phenological traits of cereal and legume crops under maize‐based intercropping systems

AbstractIntroductionIntercropping systems have a great potential for crop diversification thus increasing smallholder systems' resilience to climate change while improving soil health. However, optimal benefits associated with intercropping systems are rarely realised because of the interspecific competition for growth resources among the intercropped species.MethodologySix trials were established in the high and low rainfall agroecological zones of Babati district in Tanzania to assess how promising cropping systems with different plant spatial configurations would influence the phenological development of intercropped maize, bean and pigeonpea. Cropping systems under study included a sole maize system rotated with a pigeonpea‐bean intercrop dubbed Doubled‐up legume (DUL), maize‐pigeonpea system both with and without de‐topping, an innovation comprising double maize rows alternated with pigeonpea and beans (Mbili‐Mbili), maize‐pigeonpea system with two maize seeds sown within a 50 cm intra‐row space, a vertical‐architecture Meru H513‐pigeonpea system and a farmer practice.ResultsBranch formation was significantly higher in DUL than in maize‐based systems (p ≤ 0.05). Seasonal weather had upto 30% influence on pigeonpea flowering, with DUL having highest (p ≤ 0.05) flower production. The rate of pigeonpea branch and flower production in Mbili‐Mbili was stable across seasons relative to other maize‐pigeonpea systems. Doubled‐up legume and farmer practice had pigeonpea litter yield of between 1 and 2 t ha−1 which was at least 0.5 t ha−1 higher than in maize‐based systems (p ≤ 0.05). During the period preceding early maize reproductive stages, Mbili‐Mbili increased light interception by 30% and 63% compared to maize‐based systems and DUL, respectively. Maize toppings had higher (94%) P content than stover biomass that remained until harvest.ConclusionOverall, maize‐legume systems had higher intercropping efficacy than sole maize system, both in interception use efficiency, soil mulch cover, among other soil health benefits. Mbili‐Mbili and DUL also had increased phenological benefits on intercropped legumes however, the latter was prone to seasonal weather variability.

Extreme specificity in obligate mutualism-A role for competition?

Obligate mutualisms, reciprocally obligate beneficial interactions, are some of the most important mutualisms on the planet, providing the basis for the evolution of the eukaryotic cell, the formation and persistence of terrestrial ecosystems and the establishment and expansion of coral reefs. In addition, these mutualisms can also lead to the diversification of interacting partner species. Accompanying this diversification is a general pattern of a high degree of specificity among interacting partner species. A survey of obligate mutualisms demonstrates that greater than half of these systems have only one or two mutualist species on each side of the interaction. This is in stark contrast to facultative mutualisms that can have dozens of interacting mutualist species. We posit that the high degree of specificity in obligate mutualisms is driven by competition within obligate mutualist guilds that limits species richness. Competition may be particularly potent in these mutualisms because mutualistic partners are totally dependent on each other's fitness gains, which may fuel interspecific competition. Theory and the limited number of empirical studies testing for the role of competition in determining specificity suggest that competition may be an important force that fuels the high degree of specificity. Further empirical research is needed to dissect the relative roles of trait complementarity, mutualism regulation, and competition among mutualist guild members in determining mutualism specificity at local scales.

Adult poison dart frogs avoid potential heterospecific competitors using their sense of smell

AbstractOlfaction is the oldest sense in the animal kingdom. It is used during a multitude of behaviours, such as the encounter of food, the detection of predators, the recognition of habitat‐related cues or the communication with conspecifics. While the use of olfaction and chemical communication has been studied widely in some animals, it is barely known in others. Anurans (frogs and toads), for example, are well known to use acoustic and visual senses, but their chemical sense is still largely understudied. Studies concerning the chemical sense in anurans have been mostly based on the use of semiochemicals in juvenile stages, while the information on adult anurans remains limited. In this study, we analysed the behavioural response of the Neotropical poison frog Ranitomeya sirensis (Sira poison frog, Dendrobatidae) when presented with the odours of prey, novel/prey‐luring fruit, habitat, conspecific faeces and heterospecifics. For this, we offered each of the odours by placing them into one of two testing tubes fixed in an arena, with the other tube left empty as a control. We then measured the time the frogs spent in the vicinity of the odour versus the control tube and calculated a response index. While the frogs did not show a significant avoidance or attraction towards most of the tested odours, they showed a strong response towards the heterospecific odour, which was significantly avoided. This is the first evidence of a poison dart frog responding towards the odours of adult heterospecific frogs. We consider potential reasons for this strong negative reaction, such as the interspecific competition avoidance hypothesis, and discuss our results in the context of other animal species being deterred or attracted by heterospecific chemical cues.

Elevated nitrogen and co-evolution history with competitors shape the invasion process of Galinsoga quadriradiata

Abstract Invasive plants usually experience population differentiation as they expand from their initial invasive range to the edge. Moreover, invasive plants usually encounter competitors which shared different co-evolutionary histories with them. These factors may lead to varying responses of invasive plant populations to elevated nitrogen deposition during expansion. However, this issue has received limited attention in prior research. To address these challenges, we conducted a greenhouse experiment to investigate how population differentiation of Galinsoga quadriradiata interacts with the presence of various competitors in response to increased nitrogen deposition. Competitor types (new or old that shared short or long co-evolutionary history with the invader, respectively) were set to compete with the invasive central and edge populations under different nitrogen addition treatments. Individuals from the central population of G. quadriradiata, originating from the initial invasion range, showed greater total mass, reproduction and interspecific competitiveness compared with the edge population. Nitrogen addition improved growth and reproductive performance in both populations, and the central population had a stronger response compared with the edge population. The performance of G. quadriradiata was inhibited more effectively by old competitors than new competitors. Our results indicate that population differentiation occurs in terms of growth and competitiveness during the range expansion of G. quadriradiata, with the central population exhibiting superior performance. Co-evolutionary history with competitors is considered unfavorable for invasive plants in this study. Our results highlight the combined effects of population differentiation in invasive species and their co-evolution history with competitors in the context of global change factors.

Multidimensional primate niche space sheds light on interspecific competition in primate evolution

Characterising how the totality of primate diversity is distributed across the order, and how it evolved, is challenging because diversity in individual traits often show opposing phylogenetic patterns. A species’ combination of traits can be conceptualised as its ‘niche’. Here, we describe and analyse seven-dimensional niche space, comprising 11 traits, for 191 primate species. Multifaceted diversity is distributed unequally among taxonomic groups. Cercopithecoidea and Hominidae occupy the largest areas of niche space, and are the most diverse families; platyrrhine families occupy small areas, and this space overlaps with strepsirrhines. The evolution of species’ locations in niche space is regulated by selection for adaptive optima in trait combinations. Given that niche similarity results in interspecific competition, we quantify two measures of species’ niche locations relative to others. We find that omnivores, frugivores, and species tolerating higher temperatures experience stronger interspecific competition. Hominidae occupation of niche space suggests competitive exclusion from niches by Cercopithecoidea over evolutionary time; but living great apes experience the lowest levels of interspecific competition. Callitrichids experience the highest levels of interspecific competition. Our results provide a standardised measure of primate niches that sheds light on the partitioning and evolution of primate diversity, and how this is driven by interspecific competition.

Intraguild processes drive space-use patterns in a large-bodied marine predator community.

Interspecific interactions, including predator-prey, intraguild predation (IGP) and competition, may drive distribution and habitat use of predator communities. However, elucidating the relative importance of these interactions in shaping predator distributions is challenging, especially in marine communities comprising highly mobile species. We used individual-based models (IBMs) to predict the habitat distributions of apex predators, intraguild (IG) prey and prey. We then used passive acoustic telemetry to test these predictions in a subtropical marine predator community consisting of eight elasmobranch (i.e. shark and ray) species in Bimini, The Bahamas. IBMs predicted that prey and IG prey will preferentially select habitats based on safety over resources (food), with stronger selection for safe habitat by smaller prey. Elasmobranch space-use patterns matched these predictions. Species with predator-prey and asymmetrical IGP (between apex and small mesopredators) interactions showed the clearest spatial separation, followed by asymmetrical IGP among apex and large mesopredators. Competitors showed greater spatial overlap although with finer-scale differences in microhabitat use. Our study suggests space-use patterns in elasmobranchs are at least partially driven by interspecific interactions, with stronger spatial separation occurring where interactions include predator-prey relationships or IGP.

Assessing climatic response and drought resilience in growth of Pinus tabulaeformis Carr. and Tsuga chinensis Pritz. on the southern slope of the Qinling Mountains

Climate anomalies have significant impacts on forest productivity and tree mortality worldwide, leading to ecological disturbances. Understanding the climate-growth relationship and species-specific responses to climate and drought events are crucial for developing effective conservation strategies for tree growth. However, studies on such issues are scarce in the Qinling Mountains (QLM), a significant geo-ecological boundary for climate, vegetation distribution, and river systems in China. This study focuses on the southern slope of the QLM, where we developed tree-ring-width chronologies for Pinus tabulaeformis Carr. and Tsuga chinensis Pritz. in the same habitat, and analyzed their response to climate and two extreme drought events. Both species were found to have a positive correlation with temperature, but their responses to precipitation and scPDSI differed. Specifically, P. tabulaeformis showed a negative correlation with precipitation and scPDSI, while T. chinensis exhibited a positive correlation with precipitation. These differences in response may be attributed to species-specific preferences and interspecific competition between the two coniferous species. Results of the 31-year sliding correlation analysis and K-S test analysis, which aimed to explore the dynamic relationship between chronologies and their most limiting climate factors, demonstrated that both P. tabulaeformis and T. chinensis have experienced a qualitative change in their response patterns to certain climatic factors. Under the backdrop of warming climate, the response of P. tabulaeformis to the maximum temperatures from June to September of the previous year has diminished to a non-response; the response to precipitation from July to September of the previous year, although still significantly negatively correlated, has seen a decrease in significance. In contrast, T. chinensis has exhibited an increasing sensitivity to precipitation from September of the previous year to June of the current year. Study on resistance (Rt), recovery (Rc), and resilience (Rs) of tree growth to drought events revealed that P. tabuliformis and T. chinensis did not exhibit a negative response to the transient drought event in 1933 AD. However, when faced with the prolonged and severe drought event in 1941–1944 AD, both species experienced a decline in growth. It was observed that T. chinensis displayed weaker drought tolerance compared to P. tabuliformis and was more susceptible to the negative impacts of drought conditions. These findings suggest that forest management in the context of climate change should be species-specific, and more effort is needed for species with weaker drought resistance in the QLM, such as T. chinensis.

Recent expansion of the Atlantic cownose ray (Rhinoptera bonasus) into Bermudian waters

Cownose rays (Family Rhinopteridae) are highly migratory pelagic rays that are generally restricted to continental shelves. Despite 100's of years of natural history records, cownose rays have never been reported in Bermuda, an atoll-like coral reef ecosystem that is separated from the continental mainland United States by ~1,000 km. Here we compile evidence that the Atlantic cownose ray (Rhinoptera bonasus) has recently established in Bermuda, supported by both morphological and genetic data. Potential ecological and inter-specific competition concerns are presented as well as probable physical mechanisms that facilitated this recent and presumed range expansion.

Mosquito Egg Raft Distribution Is Affected by Semiochemicals: Indication of Interspecific Competition.

Numerous species of animals alter their behavior in response to increasing competition. To do so, they must possess the ability to detect the presence and density of interspecific competitors. We studied the role of semiochemicals released by increasing densities of larval Culiseta longiareolata Macquart on female oviposition habitat selection in two field experiments. Similarly to C. longiareolata larvae, subordinate Culex laticinctus Edwards are periphyton grazers who dwell in rain-filled pools in the Mediterranean region. We show that C. laticinctus females oviposited significantly less in mesocosm pools that were treated with crowding signals originating from C. longiareolata larvae. In the second experiment, we placed a similar number of larvae directly inside the 50 L mesocosms. These low-density mesocosms did not affect C. laticinctus oviposition but were attractive to conspecific oviposition. These results increase our understanding of the female ability to detect species-specific signals, indicating increased larval competition.