Search Results (327)

The rapid increase in the world’s human population has largely been attributed to efforts aimed at enhancing primary productivity and enriching food resources. However, an intriguing proposition of M. Rosenzweig, known as the paradox of enrichment, challenged the notion that such enrichment schemes always lead to sustained population growth. Instead, they can disrupt the delicate equilibrium of predator–prey systems, potentially driving one or both species to extinction. In this study, we develop a comprehensive mathematical framework that unifies Rosenzweig’s six analytical models of trophic exploitation through the Richards growth model, which can be viewed as a Box–Cox transformation of one species’ abundance relative to carrying capacity. Our analysis not only elucidates the connections and similarities between each model but also presents a generalized framework that unveils the underlying relationships between the proposed functions. Using the generalized logarithm and exponential functions of nonextensive statistical mechanics, we offer a fresh perspective and highlight the importance of a cautious approach when enriching ecosystems. This unification clarifies how the parameters that govern growth dynamics and predator–prey interactions determine system stability in diverse ecological contexts. Through numerical simulations and isoclinic analysis, we demonstrate that our generalized model accurately reproduces the classic paradox of enrichment while providing new insights into the mechanisms driving population fluctuations after environmental enrichment. This mathematical synthesis advances both theoretical ecology and practical conservation efforts by enabling a more accurate assessment of enrichment risks in managed ecosystems. Full article

The eastern Baltic region is rich in hemiboreal forests, which are both commercially important and provide habitats for rare and/or endangered forest-dwelling species, which are sensitive to accelerating climatic changes. Under the intensifying climatic disturbances that are stressing forests worldwide, sanitary logging is a widely used harvesting technique for the mitigation of commercial losses. The effects of salvage logging on the biodiversity of forests remain ambiguous due to the larger scale and higher intensity of timber harvesting, which can alter the recovery of stands and succession of their vegetation. Furthermore, EU legislation is increasingly emphasizing conservation/restoration and mandating its implementation. The recovery of ecosystems, and hence the biodiversity of disturbed managed forests, can take several decades to centuries, depending on the site conditions. Long-term (~60 years, four remeasurements) changes in the composition and structure of vegetation, as an indicator of overall health and nutrient cycling, were studied in conventionally managed hemiboreal forests. Potential forest transformation (paludification) risks associated with large-scale logging were assessed in mixed coniferous stands in the Baltics, Latvia. Following logging, the stands were conventionally managed, including artificial regeneration. According to ground cover vegetation, 50 years was the period for the disturbance effects to start subsiding, as a dynamic equilibrium was reached and the canopies of regenerating trees were closing. A gradual decrease in moisture levels in the middle parts of salvage-logged areas, and later at their edges, indicated that the stands have escaped paludification, likely as the climate has been warming. Distance from the edge of the salvage-logged areas had a secondary effect on ground cover vegetation recovery after storms, alleviating concerns about the explicit negative impact of the scale of harvesting. Thus, in managed seminatural forest landscapes with a historically small to moderate scale of anthropogenic disturbance, salvage logging at a scale locally deemed as large had a transient effect in the Baltics. This indicates successful regeneration of the forest ecosystem over a timeframe shorter than the conventional rotation period, suggesting overall conservation efficiency of conventionally managed forests. Accordingly, salvage logging can be sustainable in terms of biodiversity and forest continuity in the long run under traditional management, as environmental changes accelerate. Full article

Environmental changes and anthropogenic pressures significantly influence both the tree layer and natural regeneration within forest ecosystems. Protected areas represent essential territories for the maintenance and conservation of species within forest communities. In this context, the present study aims to develop a methodological framework for the integrated application of diversity, evenness, and dominance indices in the study of forest plant communities. Analyses were conducted at both α- and β-diversity levels, providing a methodological basis for characterizing local diversity and community differentiation. Species diversity was estimated using the Shannon–Wiener (H′) and Simpson (D) indices, while evenness and dominance were assessed using the Pielou (J′) and Berger–Parker (d) indices. Differences among communities were quantified using the Bray–Curtis dissimilarity index and its components, turnover and nestedness, and structural convergence of forest communities was analyzed through the ICF. The results indicate that α-diversity, estimated by H′, ranges from low to moderate, suggesting a relatively uniform distribution of species abundance. In certain microhabitats, processes of diversification and oligodominance are observed. At the β-diversity level, the analyzed communities are characterized by high dissimilarity, mainly driven by species turnover and, to a lesser extent, by nestedness associated with species loss. The ICF highlights that these forest communities exhibit relatively high structural uniformity, characteristic of mature stands in ecological equilibrium. Full article

The unbridled pursuit of statistical rationality has precipitated a crisis of value rationality in e-commerce ecosystems, leading to algorithmic involution—a dilemma characterized by destructive hyper-competition. To reconcile this theoretical paradox and explore effective governance pathways, this paper constructs a tripartite evolutionary game model involving e-commerce platforms, government regulators, and consumers. Simulation results indicate that high-intensity government deterrence constitutes the necessary stability foundation of hard constraints, while consumer activism acts as the decisive accelerator of the soft environment contingent on high synergistic gains and low information screening costs. Furthermore, a platform’s pivot toward “algorithm for good” is not driven by altruism, but by the rational calibration between short-term extractive gains and long-term benevolent returns. Sensitivity analysis confirms that reducing the ratio of these two factors is the effective lever to speed up system convergence. Finally, effective governance requires restructuring this payoff matrix by establishing dynamic penalty mechanisms and transparent low-cost feedback channels to render ethical algorithmic behavior a dominant strategy in terms of economic rationality. This research aims to guide the e-commerce ecosystem from a zero-sum game of involution toward a sustainable equilibrium of multi-party value co-creation. Full article

Coastal wetlands are among the most ecologically valuable yet vulnerable ecosystems, particularly in regions experiencing rapid urban expansion. This study provides a four-decade assessment of land use and land cover (LULC) dynamics and their implications for ecosystem service value (ESV) in the Beidagang Wetland Nature Reserve (BWNR), located adjacent to the fast-developing Tianjin region in China. Using an integrated geospatial framework, combining multi-temporal remote sensing, supervised classification, and a modified benefit-transfer valuation approach, we analyzed LULC transitions and the associated variations in ecosystem service values (ESVs) across three critical phases: (i) a period of minimal anthropogenic pressure and climate influence (1984–1999); (ii) a phase of increased human activities (2000–2013); and (iii) an active ecological restoration period (2014–2023). Findings across the three phases show that the LULC changes are not in equilibrium, as indicated by the decrease in vegetation (−46.43%) and bare ground (−31.34%), while the water areas (+547.50%) and built-up areas (+14.40%) increased remarkably. This indicates an intensive human-induced environmental transformation; although some ecosystem service functions degraded, the total ecosystem service value (ESV) of BWNR continued to increase due to water area expansion. The variations in ecosystem service value (ESV) in response to LULC changes resulting from anthropogenic activities and climate change were estimated, and the results show that the total ESV of BWNR was approximately CNY 10,631.1 million in 1984, CNY 15,078.7 million in 2000, CNY 17,768.3 million in 2013, and CNY 19,365.4 million in 2023. Findings from this study will contribute to the theoretical understanding of coastal wetland vulnerability and provide empirical evidence for the coordinated management of wetland ecological conservation and economic development in the context of rapid urbanization in Tianjin’s coastal areas. Full article

Soil moisture regulation is critical for vegetation restoration in arid ecosystems. Polymeric hydrogels, notably polyacrylic acid (PAA) and polyacrylamide (PAM), are widely employed as water-retaining agents to enhance soil water availability. However, the coupling between their distinct chemical structures and key performance metrics, particularly cycling stability and water retention kinetics in desert substrates, remains unclear. In this work, we present an integrated experimental–computational study to establish a “molecular structure–interfacial behavior–macroscopic property” framework for PAA and PAM. The results show that PAA exhibits a higher equilibrium water absorption (WAC ~242 g/g) and more stable water uptake capacity under cycling, whereas PAM displays much higher zero-shear viscosity and pronounced shear thinning with a yield plateau (~30 Pa). DFT and MD simulations trace these macroscopic disparities to their distinct electronic structures and hydration dynamics. Specifically, PAA’s strong electrostatic interactions and extended chain conformations promote a more rigid and ordered hydration shell, whereas PAM adopts a compact structure with greater chain mobility, resulting in a less ordered hydration layer. Collectively, these findings provide a structure-property framework for the scientifically grounded selection of water-retaining agents. The integrated experimental–computational methodology presented herein establishes a predictive framework for the rational design of functional materials in arid land restoration. Full article

Urban forests are highly valued for the multiple benefits they provide to city dwellers. The strategic provision of ecosystem services by these forests is threatened by climate change, warming conditions being responsible for heat waves and chronic droughts that inflict stress and mortality on trees. A three-year study (2011–2013) conducted at Parco Nord Milano (PNM) (Milano, Italy) assessed the impact of thinning interventions on the dynamics of fungal pathogens in declining forest plots. Symptomatic trees of the genera Alnus, Acer, Fraxinus, Platanus, Quercus and Ulmus, exhibited in thinned subplot pronounced decline/dieback, exhibiting symptoms like microphyllia, leaf yellowing, leaf shedding, sunken cankers, shoot wilting and branch dieback. Comparative analyses between the thinned and unthinned subplots revealed a significantly higher incidence of pathogens in the thinned one. Five species of Botryosphaeriaceae, namely Botryosphaeria dothidea, Diplodia corticola, Diplodia seriata, Dothiorella omnivora and Neofusicoccum parvum, were consistently isolated from tissues of declining hosts. There is evidence that thinning altered plot-level microclimate conditions and microbial equilibrium, favoring the proliferation of latent, pathogenic Botryosphaeriaceae. In fact, during the study period, the presence of N. parvum increased tenfold and that of B. dothidea fivefold in thinned subplot. Conversely, in unthinned subplot, the same pathogenic taxa maintained stable proportions. These results demonstrate that thinning altered ecological balances increasing tree susceptibility to harmful, cosmopolitan botryosphaeriaceous fungi. Our findings challenge assumptions about thinning as a universally beneficial practice, emphasizing the need for silvicultural strategies that take into account host and pathogen ecology and the microclimatic resilience of forest stands. This study emphasizes the importance of adaptive management in urban forestry to mitigate the unintended ecological consequences of climate change. Full article

In this paper, we investigate the asymptotic behavior of solutions to a diffusive forest kinematic model, which describes the interactions among young trees, old trees, and airborne seeds. Our study focuses on the stability of the positive equilibrium, the occurrence of Hopf bifurcation yielding spatially homogeneous periodic solutions, and the subsequent Turing instability induced by diffusion in these periodic states. The analysis highlights that the juvenile tree mortality rate, represented by a quadratic function of mature tree density, plays a central dynamical role. Specifically, the parameter corresponding to the mature tree density at which juvenile mortality is minimized serves as a key Hopf bifurcation parameter. This indicates that the system’s transition to periodic solutions and later to diffusion-driven pattern formation can be effectively regulated through this parameter. From an ecological perspective, these results suggest that forest management strategies capable of indirectly influencing factors related to this critical parameter could help control the emergence of spatial patterns, such as forest patches. Furthermore, the functional form of the mortality rate offers a useful foundation for future studies examining how different assumptions regarding tree interaction morphology may influence ecosystem patterning. Full article

Dryland coastal–mountain systems stand at the frontline of climate change, where steep topographic gradients amplify the balance between resilience and collapse. Mount Elba—Egypt’s hyper-arid coastal–mountain reserve—embodies this fragile equilibrium, preserving a seventy-year climatic record across a landscape poised between sea and desert. Here, we present the first multi-decadal, spatio-temporal assessment (1950–2021) integrating the Standardized Precipitation–Evapotranspiration Index (SPEI-6) with satellite-derived vegetation responses (NDVI) along a ten-grid coastal–highland transect. Results reveal a pervasive drying trajectory of −0.42 SPEI units per decade, with vegetation–climate coherence (r ≈ 0.3, p < 0.05) intensifying inland, where orographic uplift magnifies hydroclimatic stress. The southern highlands emerge as an “internal drought belt,” while maritime humidity grants the coast partial refuge. These trends are not mere numerical abstractions; they trace the slow desiccation of ecosystems that once anchored biodiversity and pastoral livelihoods. A post-1990 regime shift marks the breakdown of wet-season recovery and the rise in persistent droughts, modulated by ENSO teleconnections—the first quantitative attribution of Pacific climate signals to Egypt’s coastal mountains. By coupling climatic diagnostics with ecological response, this study reframes drought as a living ecological process rather than a statistical anomaly, positioning Mount Elba as a sentinel landscape for resilience and adaptation in northeast Africa’s rapidly warming drylands. Full article

Although mining activities are economically essential, they have led to significant environmental contamination, particularly in northern Chile. The discharge of untreated tailings has impacted coastal and soil ecosystems. This analysis investigates the biosorption and desorption of copper using the dried biomass of Lessonia berteroana, a brown alga, focusing on its reuse over multiple cycles. Biosorption experiments were conducted using synthetic copper sulfate solutions and real leachates (PLS) obtained from historically contaminated soils, obtaining maximum uptakes of 66.1 and 41.1 mg/g, respectively. In addition, four isotherm models—Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R)—were applied to describe equilibrium behavior. In synthetic systems, the Langmuir model described the data better. In the real matrix, the D–R model showed superior performance, indicating a more heterogeneous mechanism and a lower adsorption capacity. Desorption experiments, fundamental to evaluating the recyclability capacity of biosorbents, used HCl, HNO₃, H₂SO₄, and C₆H₈O₇ as desorbing agents. These experiments showed high initial efficiency (>95%) for all desorbents, and regeneration remained consistent over five cycles. In real PLS systems, nitric and citric acids maintained high desorption efficiencies with minimal degradation of biosorbent capacity. This study highlights the potential of L. berteroana as a sustainable biosorbent for copper recovery in both controlled and real-world applications, supporting its integration into circular economy strategies for mine-impacted environments. Full article

Pb²⁺ and Cd²⁺ represent common heavy metal contaminants in aquatic environments, posing significant risks to ecosystem stability and human health. To develop efficient adsorbents for removing Cd²⁺ and Pb²⁺ while achieving resource utilization of industrial by-products (red mud and distiller’s grains), this study synthesized a novel composite biochar—red mud–Lactobacillus plantarum composite biochar (RM)—by immobilizing red mud and Lactobacillus plantarum onto biochar derived from distiller’s grains. The structural and chemical properties of RM were characterized using SEM-EDS, XRD, and FTIR. Batch adsorption experiments were conducted to evaluate the effects of various experimental factors on Cd²⁺ and Pb²⁺ adsorption. The adsorption process was further elucidated through kinetic and isothermal models, revealing that it follows the pseudo-second-order kinetic model. Equilibrium data were best described by the Langmuir model for Cd²⁺ and the Freundlich model for Pb²⁺. The maximum adsorption capacities reached 12.13 mg/g for Cd²⁺ and 130.10 mg/g for Pb²⁺. The primary mechanisms involved in Cd²⁺ and Pb²⁺ adsorption by RM include surface complexation, cation–π interactions, ion exchange, and coprecipitation. These findings demonstrate that RM represents a promising and effective adsorbent for the remediation of heavy metal-contaminated water. Full article

This study examines the relationship between national open educational resource (OER) policies and Sustainable Development Goal 4 (SDG4) outcomes across 187 countries between 2015 and 2024, with particular attention to the moderating role of artificial intelligence (AI) readiness. Despite widespread optimism about digital technologies as catalysts for universal education, systematic evidence linking formal OER policy frameworks to measurable improvements in educational access and completion remains limited. The analysis employs fixed effects and difference-in-differences estimation strategies using an unbalanced panel dataset comprising 435 country-year observations. The research investigates how OER policies associate with primary completion rates and out-of-school rates while testing whether these relationships depend on countries’ technological and institutional capacity for advanced technology deployment. The findings reveal that AI readiness demonstrates consistent positive associations with educational outcomes, with a ten-point increase in the readiness index corresponding to approximately 0.46 percentage point improvements in primary completion rates and 0.31 percentage point reductions in out-of-school rates across fixed effects specifications. The difference-in-differences analysis indicates that OER-adopting countries experienced completion rate increases averaging 0.52 percentage points relative to non-adopting countries in the post-2020 period, though this estimate remains statistically imprecise (p equals 0.440), preventing definitive causal conclusions. Interaction effects between policies and readiness yield consistently positive coefficients across specifications, but these associations similarly fail to achieve conventional significance thresholds given sample size constraints and limited within-country variation. While the directional patterns align with theoretical expectations that policy effectiveness depends on digital capacity, the evidence should be characterized as suggestive rather than conclusive. These findings represent preliminary assessment of policies in early implementation stages. Most frameworks were adopted between 2019 and 2022, providing observation windows of two to five years before data collection ended in 2024. This timeline proves insufficient for educational system transformations to fully materialize in aggregate indicators, as primary education cycles span six to eight years and implementation processes operate gradually through sequential stages of content development, teacher training, and institutional adaptation. The analysis captures policy impacts during formation rather than at equilibrium, establishing baseline patterns that require extended longitudinal observation for definitive evaluation. High-income countries demonstrate interaction coefficients between policies and readiness that approach marginal statistical significance (p less than 0.10), while low-income subsamples show coefficients near zero with wide confidence intervals. These patterns suggest that OER frameworks function as complementary interventions whose effectiveness depends critically on enabling infrastructure including digital connectivity, governance quality, technical workforce capacity, and innovation ecosystems. The results carry important implications for how countries sequence educational technology reforms and how international development organizations design technical assistance programs. The evidence cautions against uniform policy recommendations across diverse contexts, indicating that countries at different stages of digital development require fundamentally different strategies that coordinate policy adoption with foundational capacity building. However, the modest short-term effects and statistical imprecision observed here should not be interpreted as evidence of policy ineffectiveness, but rather as confirmation that immediate transformation is unlikely given implementation complexities and temporal constraints. The study contributes systematic cross-national evidence on aggregate policy associations while highlighting the conditional nature of educational technology effectiveness and establishing the need for continued longitudinal research as policies mature beyond the early implementation phase captured in this analysis. Full article

The healthy evolution of an entrepreneurial ecosystem relies on the symbiotic relationships among its diverse internal actors. This study addresses a gap in entrepreneurial ecosystem research, which has predominantly focused on two-agent models, by constructing a tripartite symbiotic evolution model that incorporates entrepreneurial ventures, incubation chains, and customers. Based on the Logistic and Lotka-Volterra models, the research identifies the system’s equilibrium points and their stability conditions. Simulations reveal evolutionary paths from parasitism and commensalism to mutualism. A comparative case study of SenseTime (Shanghai, China) and Lanma Technology (Shanghai, China) validates these findings. The comparison shows that an influx of multiple agents, coupled with the core venture’s ability to strengthen key symbiotic coefficients, drives the ecosystem towards a dynamic multi-agent symbiosis in the post-optimization phase. Conversely, the failure to establish these robust reciprocal value flows leads to ecosystem fragility. The results indicate that: (1) Multi-agent entrepreneurial ecosystems are complex systems where symbiotic units form adaptive relationships for value creation, adhering to market laws. (2) The system’s equilibrium depends on symbiotic coefficients, leading to four modes—independent coexistence, parasitism, commensalism, and mutualism—with mutualism being the optimal state. (3) The contrasting cases further demonstrate that the evolution towards mutualism is not automatic but hinges on the core venture’s strategic agency in constructing and strengthening synergistic pathways with forward and backward linkages. This study provides a theoretical model for understanding the evolutionary mechanisms of entrepreneurial ecosystems and offers practical insights for optimizing ecosystem governance. Full article

This study investigates the adsorption and migration of sulfadiazine (SDZ) in soda saline–alkali soils under Cu/Zn co-pollution using equilibrium adsorption and soil column experiments. Freundlich and Langmuir isothermal models, combined with Hydrus-1D two-site modeling, revealed concentration-dependent interactions. Low Cu (10–100 mg kg⁻¹) and Zn (10–100 mg kg⁻¹) enhanced SDZ adsorption via charge regulation and complexation, while high concentrations (300 mg kg⁻¹) suppressed adsorption through competitive adsorption and hydroxide precipitation. Synergistic Cu-Zn coexistence further reduced adsorption to 3.035 mg kg⁻¹. Freundlich modeling (R² = 0.922–0.995) outperformed Langmuir, confirming adsorption site heterogeneity. Column experiments showed Cu (300 mg kg⁻¹) and Zn (300 mg kg⁻¹) accelerated SDZ migration (peaks 0.93–0.94), delaying breakthrough versus Br⁻. Hydrus-1D simulations (R² ≥ 0.915, RMSE < 0.1) effectively quantified nonlinear dynamics between instantaneous adsorption sites (f = 0.101–0.554) and metal concentrations. Results demonstrate heavy metals critically regulate antibiotic fate via concentration-dependent mechanisms in saline–alkali ecosystems. Full article

In this paper, we consider a generalist predator–prey model with nonlinear harvesting, which has at most eight non-negative equilibria. We prove that the double positive equilibrium is a cusp of codimension up to 3; therefore, the system exhibits a cusp-type degenerate Bogdanov–Takens bifurcation of the same codimension. The elementary antisaddle equilibrium can act as a weak focus of the order of no more than two, giving rise to a degenerate Hopf bifurcation of codimension up to two. These high-codimension bifurcations identify organizing centers in parameter space, indicating regions where the ecosystem is highly sensitive and prone to abrupt regime shifts. Our results indicate that the generalist predator can induce a richer bifurcation phenomenon and more complex dynamics and can drive the system to certain desired stable states. Full article