Search Results (193)

Network approaches are commonly used to study mutualistic interactions between frugivorous birds and plants at the community level. However, most fruit–bird networks aggregate individual data and rely on species-level traits, often overlooking intraspecific variation. Here, we downscale a fruit–bird network to the individual level to evaluate intraspecific diet variation and individual specialization in the four main frugivorous passerine species of an island community. Fruit consumption was identified from fecal samples collected from mist-netted birds and individuals’ diets were modeled with a Bayesian approach. Intraspecific diet variation was quantified using the E and NODF indices, individual specialization using the Psi index, and clustering of individuals sharing fruit resources using the Cws index. We detected low intraspecific diet variation and individuals’ diets were not nested. Individual specialization was mainly related to recapture of individuals and weakly related to phenotypic traits. Clustering mainly involved heterospecific individuals whose diets matched plant fruiting phenology during the capture period. Accordingly, future community-level studies addressing the role of mutualistic interactions in biodiversity maintenance may benefit from integrating network approaches with complementary information on interindividual and interspecific competition. Full article

The evolution of herbicide resistance can increase, decrease, or have no effect on the growth rate, competitive ability, and fitness of field-selected populations. The growth response of an ACCase-resistant (R) johnsongrass [Sorghum halepense (L.) Pers.] population harboring an Ile1781Leu mutation, and a susceptible (S) population was studied in pot experiments under intraspecific and interspecific competition with corn or sunflower, using a target-neighborhood design. The R population in the intraspecific competition indicated greater fitness-related traits such as height (H), tiller number (TN), aboveground fresh weight (AFW), and rhizome fresh weight (RFW) than the S population. Aggressiveness, competitive ratio, competition intensity index, and relative competition intensity indices confirmed also the superiority of the R population. Similarly, the R population grown in interspecific competition with corn or sunflower produced greater H, TN, and AFW than the S population. In addition, both R and S populations growing in competition with corn produced more H, TN, and AFW than those growing in competition with sunflower. Furthermore, the R population in competition with corn hybrids resulted in a greater reduction in H and AFW in corn plants. These findings strongly support the evidence of fitness advantage in the R population harboring the 1781Leu mutant allele as compared to the S counterpart. Full article

The islet of Vaixell, off the west coast of Ibiza (Balearic Islands, Spain), is home to a native population of the Pityusic wall lizard, Podarcis pityusensis, with the largest body size recorded for the species. These lizards live in extreme environmental conditions on an islet with a small surface area covered by very sparse vegetation. The sex ratio is balanced, and a very high incidence of missing toes and autotomized tails is observed, indicating strong intraspecific competition involving both males and females. The body growth rate, adjusted using the Gompertz model, is intense and, apparently, juvenile lizards quickly reach relatively large body sizes. This fast body growth is probably a strategy against predation pressure from conspecifics. In P. pityusensis from Vaixell, the peak growth acceleration is prenatal and practically coincides with the moment of hatching. The diet consists mainly of aggregated prey, such as ants, with the inclusion of marine subsidies, such as halophyllous and littoral isopods, and a lower consumption of plant matter compared to other insular populations of lizards from the Balearic Islands. The lizards of Vaixell are an excellent example of the adaptive response of a lacertid lizard to the extreme conditions on the small coastal islets of the Mediterranean, with very small available areas, high population density, but a small population size, of about 50 to 100 lizards, which also reach a remarkable longevity. Full article

Negative plant–soil feedback (NPSF) drives yield decline in monocropping systems, yet how intraspecific competition modulates NPSF across planting densities remains unclear. We conducted a two-stage plant–soil feedback experiment using five crops (Triticum aestivum L., Zea mays L., Solanum lycopersicum L., Cucumis sativus L., and Panax notoginseng (Burkill) F.H. Chen) with contrasting NPSF intensities under four planting densities (30 × 30 to 8 × 8 cm). Crops with stronger NPSF (P. notoginseng) showed pronounced density-dependent biomass reductions, whereas those with moderate (S. lycopersicum, C. sativus) or low (Z. mays, T. aestivum) NPSF were largely density-insensitive. Given its sensitivity, P. notoginseng was used to explore mechanisms. High-density planting (8 × 8 cm) intensified NPSF, reducing seedling survival by 88.54% and biomass by 56.08% compared with low-density controls (30 × 30 cm). Microbiome profiling showed enrichment of pathogenic Fusarium spp. and depletion of beneficial Humicola spp. under high density. Metabolomic analysis identified linoleic acid and oleamide as key root exudates upregulated under high-density stress, which selectively stimulated Fusarium growth as preferred carbon sources. Collectively, these results reveal a density-dependent feedback in which intensified competition reshapes root exudation, promotes pathogen proliferation, and suppresses beneficial taxa, thereby amplifying NPSF. This provides mechanistic insights into microbially mediated NPSF under density stress and highlights the importance of optimizing planting density to sustain crop productivity. Full article

Habitat destruction is a major driver of biodiversity decline, yet how it reshapes multispecies coexistence by altering interaction structure remains unclear. We adopt a spatially explicit metacommunity model framework under a homogeneity assumption and introduce a tunable parameter controlling intransitive competition. Within this framework, we represent the system using a generalized Lotka–Volterra model to examine how coexistence mechanisms respond to habitat destruction. Our findings demonstrate that (1) coexistence is not driven by a single mechanism: under transitive competition, it highly relies on niche differentiation, whereas in intransitive structures, coexistence can be maintained even with low niche differentiation. (2) Habitat destruction compresses the feasible coexistence space, but regions dominated by different mechanisms respond asymmetrically, with niche-difference-driven coexistence shrinking and intransitive-dominated coexistence expanding under certain conditions. (3) The difference stems from habitat destruction, altering the relative proportions of intraspecific and interspecific competition, driving the community beyond the coexistence threshold. This reduces the probability of coexistence and reshapes the relative importance of several coexistence mechanisms. This finding provides a new theoretical perspective for biodiversity in fragmented landscapes. Full article

Fatal intraspecific aggression in brown bears (Ursus arctos) remains poorly documented, yet elucidating its dynamics is critical in order to understand species’ physiology, informing management strategies, and advancing wildlife forensic science applications, which are useful in cases where a natural or illegal cause of death needs to be discerned. In this study, we reported four confirmed cases of lethal aggression (two yearlings and two adults) in the Italian Alps. Comprehensive autopsies were performed to characterize lesion patterns and infer the aggressor identity. Claw-induced lacerations, bite marks and the aspect of hemorrhages suggested the attack sequence. Aggressor identity was investigated by using forensic odontology through inter-canine distance (I-CD) and genetic analysis of peri-lesional saliva. I-CD allowed us to plausibly hypothesize the aggressor’s species and, in the cases where it was possible, to classify the sex and/or age group of the aggressors. While genetic analysis allowed the identification of the four brown bear victims, it did not provide informative results on the aggressors. The cause and manner of death were coded according to international criteria (International Classification of Diseases 11th Revision [ICD-11], WHO). Adult fatalities, supported by gastric content analysis, reflect trophic competition regardless of the mating context and highlight the role of anthropogenic food sources in conflict emergence. These findings underscore the value of integrated approaches in wildlife investigations and provide new insights into ecophysiological factors driving lethal intraspecific aggression. Full article

(1) The bird colouration is the result of adaptation to environmental conditions, predator–prey relationships, and sexual selection (intraspecific competition and signalling of quality). Only a few studies have explicitly explored the plumage colouration of birds at the level of species communities. (2) Methods: We combined data with bird plumage colours and their spatial distribution at a large spatial scale in Italy, exploring the relationship between community colours and different types of habitats and landscape heterogeneity. (3) Results: Overall, we found that the more representative colours of avian communities were grey, white, black, and brown. The percentage of black colour in the community was smaller in close habitats (e.g., forests). A high percentage of brown was observed in forests and shrublands, whereas a high percentage of white was found in wetlands, water bodies, and urban areas. The percentage of yellow was relatively low overall, but it was slightly higher in deciduous forests. Land use richness increased the percentage of brown, green, rufous, and yellow, while negatively affecting other pigments (black and grey = melanins, purple = structural, and red = carotenes). The community colour inequality decreased when the species and land use richness increased, while it increased when the weighted edge density of surrounding landscapes increased. Finally, we found that bird communities that are made up of closely related species show a wider variety of colours (e.g., lower colour inequality). This supports the idea that closely related species that live together develop different features to improve species recognition. (4) Conclusions: We found that the colours of bird communities are related to the type of environment. Full article

Outbreaks of Ips hauseri, a major bark beetle pest in Central Asian Picea schrenkiana forests, have intensified under climate warming and prolonged droughts. However, the reproductive behavior and gallery construction strategies of this species remain poorly understood, limiting our ability to predict its population dynamics. Here, we dissected 219 galleries from infested spruce trees in Hami, Xinjiang, during an outbreak period (2024–2025). We identified 11 distinct gallery morphologies, with harem size (number of females per male) ranging from one to seven. Gallery length was positively correlated with egg production. Reproductive output peaked at a harem size of five, beyond which both gallery dimensions and fecundity declined. Host tree diameter at breast height (DBH) significantly influenced gallery complexity, with larger trees supporting more maternal galleries. Upward-oriented galleries were longer and contained more eggs than downward ones. Intraspecific competition, mediated by gallery adjacency and spatial orientation, strongly affected offspring development. Our results demonstrate that I. hauseri exhibits flexible gallery architecture and reproductive adjustments in response to resource availability and competition—a behavioral plasticity that likely contributes to its outbreak potential. Monitoring gallery morphology and harem size could enhance early detection and population forecasting for this increasingly damaging forest pest. Full article

Mixed forests provide several ecosystem service benefits, and they also often show higher productivity than pure forests. In mixed forests, several interactions among tree species occur, with size-symmetric and size-asymmetric competition being particularly important. We studied diameter growth of European beech in pure stands and in mixtures with oak, maple, pine, spruce, fir, and spruce and fir combined on extremely diverse beech sites in Slovenia, using forest inventory sample plots (n = 26,793, 500 m² each). For each mixture, we developed models of 10-year individual tree diameter increment (id) using natural splines and incorporating tree, competition, stand, site, and climate variables that were mainly gathered in regular forest inventories. Competition was represented using simple indices: stand basal area (BA) for size-symmetric competition, basal area of overtopping trees (BAL) for size-asymmetric competition, and reduced competition due to harvesting (CUT). The models revealed differences among mixtures and a strong influence of competition. Id was among the lowest in pure stands and substantially higher in mixtures, indicating strong intraspecific competition. Overall, size-symmetric competition was more influential, but size-asymmetric competition appeared important in some mixtures. We recommend growing beech in mixtures with other species and applying a forest management approach that accounts for competition symmetry, which proved crucial in each mixture. Full article

Although sympatric carnivores typically exhibit dietary differentiation to reduce interspecific competition, contemporary isotopic comparisons of European mustelids remain scarce. In this study, we present the first modern stable isotope analysis of hair to evaluate the dietary niches and trophic relationships of pine martens (Martes martes), stone martens (Martes foina), and European polecats (Mustela putorius) in Lithuania and Latvia. The stable carbon and nitrogen isotope values differed among the species. M. martes showed lower δ¹⁵N values and more depleted δ¹³C signatures than the two more synanthropic species. Isotopic niche analyses revealed that M. martes occupied the broadest niche, while M. foina and M. putorius exhibited narrower niches with substantial overlap. Habitat influenced trophic position: individuals from settlements showed higher δ¹⁵N values than those from forests or wetlands. In contrast, sex- and age-related differences were weak or absent. These results demonstrate that despite partial spatial coexistence, sympatric mustelids differ primarily in isotopic niche structure rather than mean isotope values and that human-modified environments promote trophic convergence among generalist mesocarnivores. However, the small sample sizes for M. foina and M. putorius mean that estimates of isotopic niche width and overlap should be regarded as preliminary, and observed sex- and age-related patterns likely reflect limited statistical power rather than the absence of intraspecific dietary variation. Full article

Invasive plant species persist under environmental conditions due to phenotypic plasticity, which allows them to cope with conditions such as herbivory, competition, and resource availability. However, plant responses to individual and combined stressors are variable. In addition, fluctuating asymmetry (FA) has been proposed as an indicator of plant stress, although its reliability remains debated, and few studies have evaluated its responses under interacting stressors. We evaluated, in two greenhouse experiments, the isolated and combined effects of herbivory and shading; and belowground intraspecific competition and fertilization on performance, trait plasticity, and leaf FA in seedlings of the invasive plant Tithonia diversifolia. Shading reduced shoot biomass, but promoted plastic adjustments in architectural, photosynthetic, and leaf structural traits that enhance light capture, and also increased FA. Herbivory interaction with shade induced high leaf mass per area of plants. In contrast, high herbivory and intraspecific competition consistently reduced plant performance across multiple traits. Fertilization enhanced overall performance and mitigated the negative effects of herbivory and competition. Overall, our results emphasize the need to consider interacting environmental factors when assessing invasive plant performance and plasticity. Furthermore, FA showed inconsistent responses across treatments, suggesting its limited reliability as a biomarker of isolated and combined environmental stress. Full article

Mixed stands enhance climate resilience and ecosystem service provision through functional diversity, but their productivity depends on intra- and interspecific competition, forest structure, stand density, and site conditions. In this study, we analyzed the effects of competition and aridity on the growth of European beech (Fagus sylvatica L.) in mixed and pure stands, using data from 38 plots of the Italian National Forest Inventory (NFI, 2015). To understand the variables influencing European beech growth, tree-level basal area increment models were applied, incorporating different competition structures (intraspecific, interspecific, size-symmetric, and size-asymmetric) and aridity index (De Martonne). Results showed that size-asymmetric intraspecific competition negatively affected European beech growth, highlighting low self-tolerance, especially in pure stands where growth was lower than in mixed stands. In mixed stands, European beech growth was shaped by size-dependent competition and the relative dominance of coexisting species, benefiting from size-asymmetric and hindered by size-symmetric interactions. Additionally, European beech growth was shaped by aridity and stand structure (Gini coefficient and density), with drought sensitivity mitigated in mixed stands and enhanced growth in structurally diverse, low-density stands. This study highlights how species interactions, aridity, and stand structure jointly shape tree growth, underscoring their importance for climate-adaptive forest management. Full article

Plant interactions and their responses to stress environments are important ecological processes for ecosystem stability and biodiversity formation, but how plant intraspecific relationships respond to environmental stresses remains to be studied in depth. In this study, annual Populus euphratica seedlings were planted in singles or doubles, and two stress treatments were set up: two drought levels (0.7 and 0.4 L) and two salinity levels (200 and 400 mmol L⁻¹). P. euphratica seedlings’ total and part biomass, root/shoot ratio, net photosynthetic rate, stomatal conductance, nonstructural carbohydrate concentration, and proline content were measured. Relative interaction indices were calculated to clarify their intraspecific relationships. The results of the study showed that compared to the single-planted P. euphratica, the double-planted P. euphratica was more significantly inhibited by drought and salt stress, the total biomass decreased, photosynthesis declined, proline content increased, and non-structural carbohydrates changed, which reflected a competitive intraspecific relationship. Secondly, as drought and salt stress intensified, the relative interaction index indicated that the intraspecific relationship of P. euphratica seedlings gradually shifted from neutrality to competition, which indicated that the intraspecific competitive relationship of P. euphratica seedlings was exacerbated by environmental stresses. These findings highlight the need to account for stress-mediated competition in P. euphratica seedlings during ecological restoration in arid environments. Full article

New postcranial material of Panthera gombaszoegensis, a large pantherine felid, is analyzed from the English site of Corton (early Middle Pleistocene, possibly 0.7–0.6 mya) and the Polish site of Rogóżka Cave (0.45–0.35 mya). Both records are attributable to Panthera gombaszoegensis gombaszoegensis. This robust chronosubspecies is characteristic of the late Early and Middle Pleistocene, ca. last 1.5 mya. Both findings contribute valuable data on the knowledge of the species. The most likely factors that contributed to the extinction of P. gombaszoegensis were intraspecific competition with African newcomers, such as P. s. fossilis and C. crocuta, combined with climatic fluctuations and shifts in prey availability. Full article

Variable Rate Seeding (VRS) in soybean (Glycine max [L.] Merr.) cultivation is a critical strategy for managing soil spatial variability, which often constrains yield. However, conventional practices that increase plant density in low-yield zones to compensate for poor fertility may unintentionally intensify intraspecific competition for already limited resources. This study addresses the need for a mechanistically sound basis for VRS prescriptions that moves beyond this counterproductive assumption. Field experiments were conducted in the Cerrado region of Brazil to evaluate different soybean population densities within management zones (MZs) delineated according to Liebig’s Law of the Minimum. This approach identified soil potassium (K) as the most growth-limiting nutrient and was used to define MZs representing distinct yield potentials. Three seeding densities were tested, Low (200,000 seeds ha⁻¹), Medium (240,000 seeds ha⁻¹), and High (280,000 seeds ha⁻¹), with particular emphasis on comparing the medium and high populations in potassium-limited zones. Results revealed that, contrary to the conventional strategy, increasing the soybean population from medium to high in low-fertility (low-K) MZs significantly decreased grain yield. This yield reduction was attributed to intensified intraspecific competition, which promoted excessive vegetative growth (increased plant height) at the expense of root development and photosynthetic efficiency. Notably, maintaining a moderate population (240,000 seeds ha⁻¹) in these low-fertility zones produced yields statistically equivalent to those in higher-fertility areas. These findings demonstrate that applying Liebig’s Law of the Minimum to identify the most limiting factor provides a robust, mechanistically sound foundation for developing VRS prescriptions. For nutrient-limited zones, the optimal and most resilient strategy is not to increase sowing density but to maintain a moderate population that balances yield potential with resource availability. Future research should investigate the phenotypic plasticity of different cultivars under this VRS strategy and assess its economic viability at a commercial scale. Full article