Coexistence Theory Research Articles

A patient with idiopathic normal pressure hydrocephalus and amyotrophic lateral sclerosis. Coincidence or a genetic link between the diseases?

Background: Idiopathic normal pressure hydrocephalus (iNPH) is usually regarded as a disease characterized by gait and balance disturbance, cognitive dysfunction, and urinary symptoms. The pathophysiology of iNPH is still unknown, but the increased number of familial cases raises the suspicion of a genetic component. The C9ORF72 expansion is known to cause frontotemporal lobar degeneration and ALS, and its prevalence is found among Finnish iNPH patients. Case Presentation: We report an interesting case of a patient with possible iNPH who also developed ALS. Conclusion: Our case raises the theory of coexistence of gene-induced etiology. Key Message: Our case also raises the question of a genetic link between iNPH and ALS.

Construction of Green Theoretical Framework of Coal Resource Capitalization

In recent years, the Chinese government has asked enterprises to follow the path of “green development”. This requirement naturally becomes the guiding ideology of coal resource capitalization theory. this paper focuses on the core contents of the green development of coal resource capitalization, and uses the software of ROSTCM6 and UCINET to construct six frameworks of the green theory of coal resource capitalization with the method of “Condensed Subgroup”: the basic theory of capitalization, the conservation theory of capitalization, the environmental protection theory of capitalization, the harmonious coexistence theory of capitalization, the mainline development theory of ecological industry of capitalization Industrial theory, benign cycle sustainable development theory of capitalization, the paper further designs the outline content of the framework.

Modern coexistence theory as a framework for invasion ecology

Modern coexistence theory as a framework for invasion ecology

Phase coexistence of active Brownian particles.

We investigate motility-induced phase separation of active Brownian particles, which are modeled as purely repulsive spheres that move due to a constant swim force with freely diffusing orientation. We develop on the basis of power functional concepts an analytical theory for nonequilibrium phase coexistence and interfacial structure. Theoretical predictions are validated against Brownian dynamics computer simulations. We show that the internal one-body force field has four nonequilibrium contributions: (i) isotropic drag and (ii) interfacial drag forces against the forward motion, (iii) a superadiabatic spherical pressure gradient, and (iv) the quiet life gradient force. The intrinsic spherical pressure is balanced by the swim pressure, which arises from the polarization of the free interface. The quiet life force opposes the adiabatic force, which is due to the inhomogeneous density distribution. The balance of quiet life and adiabatic forces determines bulk coexistence via equality of two bulk state functions, which are independent of interfacial contributions. The internal force fields are kinematic functionals which depend on density and current but are independent of external and swim forces, consistent with power functional theory. The phase transition originates from nonequilibrium repulsion, with the agile gas being more repulsive than the quiet liquid.

Titanium Distribution Ratio Model of Ladle Furnace Slags for Tire Cord Steel Production Based on the Ion–Molecule Coexistence Theory at 1853 K

High-strength tire cord steel is mainly used in radial ply tires, but the presence of brittle Ti inclusions can cause failure of the wires and jeopardize their performance in production. In order to control the titanium content during steel production, a thermodynamic model for predicting the titanium distribution ratio between CaO–SiO2–Al2O3–MgO–FeO–MnO–TiO2 slags during the ladle furnace (LF) refining process at 1853 K has been established based on the ion–molecule coexistence theory (IMCT), combined with industrial measurements, and the effect of basicity on the titanium distribution ratio was discussed. The results showed that the titanium distribution ratio predicted by the developed IMCT exhibited a dependable agreement with the measurements, and the optical basicity is suggested to reflect the correlation between basicity and the titanium distribution ratio. Furthermore, quantitative titanium distribution ratios of TiO2, CaO·TiO2, MgO·TiO2, FeO·TiO2, and MnO·TiO2 were acquired by the IMCT model, respectively. Calculation results revealed that the structural unit CaO plays a pivotal role in the slags in the de-titanium process.

Soil-borne fungi influence seed germination and mortality, with implications for coexistence of desert winter annual plants.

Soil-borne fungi influence coexistence of plant species in mesic environments, but much less is known about their effects on demographic processes relevant to coexistence in arid and semi-arid systems. We isolated 43 fungal strains that naturally colonize seeds of an invasive winter annual (Brassica tournefortii) in the Sonoran Desert, and evaluated the impact of 18 of them on seed germination and mortality of B. tournefortii and a co-occurring native annual (Plantago ovata) under simulated summer and winter temperatures. Fungi isolated from B. tournefortii seeds impacted germination and mortality of seeds of both plant species in vitro. Seed responses reflected host-specific effects by fungi, the degree of which differed significantly between the strains, and depended on the temperature. In the winter temperature, ten fungal strains increased or reduced seed germination, but substantial seed mortality due to fungi was not observed. Two strains increased germination of P. ovata more strongly than B. tournefortii. In the summer temperature, fungi induced both substantial seed germination and mortality, with ten strains demonstrating host-specificity. Under natural conditions, host-specific effects of fungi on seed germination may further differentiate plant species niche in germination response, with a potential of promoting coexistence. Both host-specific and non-host-specific effects of fungi on seed loss may induce polarizing effects on plant coexistence depending on the ecological context. The coexistence theory provides a clear framework to interpret these polarizing effects. Moreover, fungi pathogenic to both plant species could induce host-specific germination, which challenges the theoretical assumption of density-independent germination response. These implications from an in vitro study underscore the need to weave theoretical modeling, reductive empirical experiments, and natural observations to illuminate effects of soil-borne fungi on coexistence of annual plant species in variable desert environments.

Effects of soil microbes on plant competition: a perspective from modern coexistence theory

AbstractGrowing evidence shows that soil microbes affect plant coexistence in a variety of systems. However, since these systems vary in the impacts microbes have on plants and in the ways plants compete with each other, it is challenging to integrate results into a general predictive theory. To this end, we suggest that the concepts of niche and fitness difference from modern coexistence theory should be used to contextualize how soil microbes contribute to plant coexistence. Synthesizing a range of mechanisms under a general plant–soil microbe interaction model, we show that, depending on host specificity, both pathogens and mutualists can affect the niche difference between competing plants. However, we emphasize the need to also consider the effect of soil microbes on plant fitness differences, a role often overlooked when examining their role in plant coexistence. Additionally, since our framework predicts that soil microbes modify the importance of plant–plant competition relative to other factors for determining the outcome of competition, we suggest that experimental work should simultaneously quantify microbial effects and plant competition. Thus, we propose experimental designs that efficiently measure both processes and show how our framework can be applied to identify the underlying drivers of coexistence. Using an empirical case study, we demonstrate that the processes driving coexistence can be counterintuitive, and that our general predictive framework provides a better way to identify the true processes through which soil microbes affect coexistence.

Nutrient retention by predators undermines predator coexistence on one prey

Contemporary theory of predator coexistence through relative non-linearity in their functional responses strongly relies on the Rosenzweig and MacArthur (1963) equations in which the (autotrophic) prey exhibits logistic growth in the absence of the predators. This implies that the prey is limited by a resource such as light or space, which availability is independent of the predators. This assumption does not hold under nutrient limitation where both prey and predators bind resources such as nitrogen and phosphorus in their biomass. Furthermore, the prey’s resource uptake rate is assumed to be linear and the predator-prey system is considered to be closed. All these assumptions are unrealistic for many natural systems. Here, we show that nutrient retention in predator biomass strongly hampers the coexistence of two predators on one prey because it stabilizes the dynamics. In contrast, a non-linear resource uptake rate of the prey slightly promotes predator coexistence. Our study highlights that predator coexistence does depend not only on differences in the curvature of their functional responses but also on the type of resource constraining the growth of their prey. This has far-reaching consequences for the relative importance of fluctuation-dependent and fluctuation-independent mechanisms of species coexistence in natural systems where autotrophs experience light or nutrient limitation.

Balance between community assembly processes mediates species coexistence in agricultural soil microbiomes across eastern China.

Revealing the linkages between community assembly and species coexistence, which is crucial for the understanding of ecosystem diversity and functioning, is a fundamental but rarely investigated subject in microbial ecology. Here we examined archaeal, bacterial, and fungal community assembly in adjacent pairs of maize (water-unsaturated) and rice (water-saturated) fields across different habitats and regions throughout Eastern China. The high-throughput sequencing dataset was analyzed by variation partitioning, null model, and neutral community model analyses. We demonstrated that microbial community assembly was governed more by species sorting than by dispersal limitation in maize fields, and to a lesser extent in rice fields. The relative importance of species sorting in maize soils was greater at low latitudes than at high latitudes, while rice soils exhibited an opposite trend. Microbial co-occurrence associations tended to be higher when communities were primarily driven by dispersal limitation relative to species sorting. There were greater community dissimilarities between maize and rice soils in low-latitude regions, which was consistent with the higher proportion of negative edges in the correlation networks. The results indicate that a balance between species sorting and dispersal limitation mediates species coexistence in soil microbiomes. This study enhances our understanding of contemporary coexistence theory in microbial ecosystems.

The evolution of coexistence theory

The evolution of coexistence theory

Stable coexistence of equivalent nutrient competitors through niche differentiation in the light spectrum.

Niche‐based theories and the neutral theory of biodiversity differ in their predictions of how the species composition of natural communities will respond to changes in nutrient availability. This is an issue of major environmental relevance, as many ecosystems have experienced changes in nitrogen (N) and phosphorus (P) due to anthropogenic manipulation of nutrient loading. To understand how changes in N and P limitation may impact community structure, we conducted laboratory competition experiments using a multispecies phytoplankton community sampled from the North Sea. Results showed that picocyanobacteria (Cyanobium sp.) won the competition under N limitation, while picocyanobacteria and nonmotile nanophytoplankton (Nannochloropsis sp.) coexisted at equal abundances under P limitation. Additional experiments using isolated monocultures confirmed that Cyanobium sp. depleted N to lower levels than Nannochloropsis sp., but that both species had nearly identical P requirements, suggesting a potential for neutral coexistence under P‐limited conditions. Pairwise competition experiments with the two isolates seemed to support the consistency of these results, but P limitation resulted in stable species coexistence irrespective of the initial conditions rather than the random drift of species abundances predicted by neutral theory. Comparison of the light absorption spectra indicates that coexistence of the two species was stabilized through differential use of the underwater light spectrum. Our results provide an interesting experimental example of modern coexistence theory, where species were equal competitors in one niche dimension but their competitive traits differed in other niche dimensions, thus enabling stable species coexistence on a single limiting nutrient through niche differentiation in the light spectrum.

On the Consequences of the Interdependence of Stabilizing and Equalizing Mechanisms.

We present an overlooked but important property of modern coexistence theory (MCT), along with two key new results and their consequences. The overlooked property is that stabilizing mechanisms (increasing species' niche differences) and equalizing mechanisms (reducing species' fitness differences) have two distinct sets of meanings within MCT: one in a two-species context and another in a general multispecies context. We demonstrate that the two-species framework is not a special case of the multispecies one, and therefore these two parallel frameworks must be studied independently. Our first result is that, using the two-species framework and mechanistic consumer-resource models, stabilizing and equalizing mechanisms exhibit complex interdependence, such that changing one will simultaneously change the other. Furthermore, the nature and direction of this simultaneous change sensitively depend on model parameters. The second result states that while MCT is often seen as bridging niche and neutral modes of coexistence by building a niche-neutrality continuum, the interdependence between stabilizing and equalizing mechanisms acts to break this continuum under almost any biologically relevant circumstance. We conclude that the complex entanglement of stabilizing and equalizing terms makes their impact on coexistence difficult to understand, but by seeing them as aggregated effects (rather than underlying causes) of coexistence, we may increase our understanding of ecological dynamics.

Critical assessment of mixing thermodynamic functions of Fe–Al binary melts based on atom–molecule coexistence theory

In order to further verify the accuracy and feasibility of the calculated mass action concentrations $$N_{i}$$ of Al and Fe by the developed atom and molecule coexistence theory (AMCT) model, i.e., AMCT–$$N_{i}$$ model, for representing activities $$a_{{{\text{R, }}i}}^{{}}$$ of Al and Fe in Fe–Al binary melts reported in the first part of the serial studies, the molar mixing thermodynamic functions of Fe–Al binary melts over a temperature range from 1823 to 1973 K have been calculated based on $$N_{i}$$ of Al and Fe as well as the effect of temperature on activity coefficients $$\gamma_{i}^{{}}$$ of Al and Fe as $${{\partial \ln \gamma_{i} } \mathord{\left/ {\vphantom {{\partial \ln \gamma_{i} } {\partial T}}} \right. \kern-0pt} {\partial T}} = {{\partial \ln \left( {{{N_{i} } \mathord{\left/ {\vphantom {{N_{i} } {x_{i} }}} \right. \kern-0pt} {x_{i} }}} \right)} \mathord{\left/ {\vphantom {{\partial \ln \left( {{{N_{i} } \mathord{\left/ {\vphantom {{N_{i} } {x_{i} }}} \right. \kern-0pt} {x_{i} }}} \right)} {\partial T}}} \right. \kern-0pt} {\partial T}}$$ by the developed AMCT–$$N_{i}$$ model, where T is absolute temperature and xi is the mole fraction of element i or compound i in metallic melts. The reported molar mixing thermodynamic functions of Fe–Al binary melts as well as the reported excess molar mixing thermodynamic functions of Fe–Al binary melts relative to ideal solution as a basis from the available literatures have been critically assessed and applied as criteria to verify the developed AMCT–$$N_{i}$$ model. The effect of changing temperature on $$\gamma_{i}^{{}}$$ of Al and Fe, i.e., activity coefficient gradients $${{\partial \ln \gamma_{\text{Al}}^{{}} } \mathord{\left/ {\vphantom {{\partial \ln \gamma_{\text{Al}}^{{}} } {\partial T}}} \right. \kern-0pt} {\partial T}}$$ and $${{\partial \ln \gamma_{\text{Fe}}^{{}} } \mathord{\left/ {\vphantom {{\partial \ln \gamma_{\text{Fe}}^{{}} } {\partial T}}} \right. \kern-0pt} {\partial T}}$$, which are two indispensable parameters to calculate the molar mixing thermodynamic functions of Fe–Al binary melts, can be accurately obtained by the developed AMCT–$$N_{i}$$ model and expressed by the cubic polynomial functions. Not only the partial molar mixing thermodynamic functions of Al and Fe in Fe–Al binary melts but also the integral molar mixing thermodynamic functions of Fe–Al binary melts can be accurately calculated by the developed AMCT–$$N_{i}$$ model. Furthermore, the excess partial and integral molar mixing thermodynamic functions of Fe–Al binary melts relative to ideal solution as a basis can also be precisely calculated by the developed AMCT–$$N_{i}$$ model.

Neighborhood effects explain increasing asynchronous seedling survival in a subtropical forest

Biotic interactions play a critical role in mediating community responses to temporal environmental variation, but the importance of these effects relative to the direct effects of environmental change remains poorly understood, particularly in diverse forest communities. Here we combine a neighborhood modeling approach with insights from coexistence theory to assess the effects of temporal variation in species interactions and environmental conditions (e.g., precipitation, temperature, and understory light availability) on seedling survival over nine census years in a subtropical forest. We find significant temporal shifts in the magnitude of neighborhood effects on both community-wide and species-level seedling survival (statistically significant random effects of neighborhood × year and neighborhood × species × year interactions). These results are consistent with the idea that environmental change will play a fundamental role on forest regeneration dynamics by altering biotic interactions at the neighborhood scale. Moreover, differences among species in response to neighbors over time contribute to a pattern of temporal decoupling of seedling survival between species, which can help to promote diversity in certain contexts. In separate analyses of multiple regression on distance matrices (MRM), altered interactions with neighbors are much stronger predictors of asynchronousseedling survival among species than the pure effects of climate and plant functional traits, explaining twice as much variation (43.9% vs. 22.2%). In sum, these results reveal that divergent species responses to interannual environmental variability detected are driven primarily by indirect effects mediated by changing biotic environments. This highlights the importance of including indirect effects from local biotic (neighborhood) interactions in forecasts of forest community responses to global change.

Determination of the thermodynamic properties of Ni-Ti, Ni-Al, and Ti-Al, and nickel-rich Ni-Al-Ti melts based on the atom and molecule coexistence theory

The thermodynamic properties of the full composition range of liquid Ni-Ti, Ni-Al, and Ti-Al alloys were determined using the atom and molecule coexistence theory (AMCT), which is an established thermodynamic model that was used to calculate the mass action concentration (activity) of the structural units in the abovementioned three alloy systems. The temperature dependence of the activity coefficients γiθ of Ti and Al dissolved in molten nickel to form dilute solutions (0 ≤ xi ≤ 0.01) relative to pure liquid were estimated from the calculated activity coefficients of Ti and Al at different temperatures. The standard Gibbs free energy changes ΔsolGm,iθ of dissolving Ti and Al in nickel and the enthalpies of mixing ΔmixHm, i of liquid Ni-Ti, Ni-Al, and Ti-Al were also obtained. The results indicated that the determined thermodynamic properties, such as the ΔsolGm,iθ, and ΔmixHm, i of the liquid binary alloys reasonably agreed with the experimental data previously reported in the literatures. Thermodynamic properties were predicted for three important subsystems, which included the Ni-Ti, Ni-Al, and Ti-Al alloys, and therefore, the activity ai and ΔmixHm, Ni‐Al‐Ti of the nickel-rich liquid Ni-Al-Ti ternary alloys were also obtained at 1873 K. Furthermore, the values calculated using the classical geometric models, including the Toop, Kohler, and Muggianu models, were compared with those determined by the GSM in this study.

Generation Mechanism of MgO and Al2O3 Inclusions in 51CrV4 Spring Steel Based on the Ion–Molecule Coexistence Theory

The presence of MgO·Al2O3 inclusions in 51CrV4 spring steel is detrimental to the alloy’s castability and fatigue properties. To effectively suppress these inclusions during production, accretions were collected from the immersion nozzle, and the MgO·Al2O3 inclusions in the steel billet were investigated. The generation mechanism of the inclusions was evaluated based on the ion–molecule coexistence theory, and the mass action–concentration model of CaO–SiO2–Al2O3–MgO–FeO–MnO slag was developed. Industrial experiments showed that nozzle clogging was primarily caused by MgAl2O4 spinel inclusions, and the MgO·Al2O3 spinel inclusions in the steel billet were investigated by non-aqueous electrolysis. The model calculation results indicate that the Mg content increased with an increasing basicity, CaO/Al2O3 ratio, and Al content during the ladle furnace (LF) process. In contrast, the Mg content decreased with increasing CO pressure under Ruhstahl-Hausen vacuum degassing process (RH) conditions.

MacArthur (1970) and mechanistic coexistence theory

MacArthur (1970) and mechanistic coexistence theory

Identifying niche and fitness dissimilarities in invaded marine macroalgal canopies within the context of contemporary coexistence theory

Contemporary coexistence theory provides a framework for predicting invasiveness and impact of Invasive Non-Native Species (INNS) by incorporating differences in niche and fitness between INNS and co-occurring native species. The widespread invasive kelp Undaria pinnatifida is considered a high-risk INNS, although a robust evidence base regarding its invasiveness and impact is lacking in many regions. Invaded macroalgal canopies at nine coastal sites in the southwest UK were studied over three years to discern whether Undaria is coexisting or competing with native canopy-forming species across different habitat types. Spatial, temporal and depth-related trends in species distributions and abundance were recorded within intertidal and subtidal rocky reef as well as on marina pontoons. A primary succession experiment also examined competitive interactions between species. In rocky reef habitats, Undaria had lower fitness compared to long-lived native perennials, but was able to coexist due to niche dissimilarity between species. In contrast, Undaria was likely to be competing with short-lived native annuals on rocky reef due to large niche overlap and similar fitness. In marina habitats, Undaria dominated over all other canopy formers due to low niche diversification and higher fitness. Generalisations on INNS impact cannot be made across habitats or species, without considering many abiotic factors and biotic interactions.

When rarity has costs: coexistence under positive frequency-dependence and environmental stochasticity.

Stable coexistence relies on negative frequency-dependence, in which rarer species invading a patch benefit from a lack of conspecific competition experienced by residents. In nature, however, rarity can have costs, resulting in positive frequency-dependence (PFD) particularly when species are rare. Many processes can cause positive frequency-dependence, including a lack of mates, mutualist interactions, and reproductive interference from heterospecifics. When species become rare in the community, positive frequency-dependence creates vulnerability to extinction, if frequencies drop below certain thresholds. For example, environmental fluctuations can drive species to low frequencies where they are then vulnerable to PFD. Here, we analyze deterministic and stochastic mathematical models of two species interacting through both PFD and resource competition in a Chessonian framework. Reproductive success of individuals in these models is reduced by a product of two terms: the reduction in fecundity due to PFD, and the reduction in fecundity due to competition. Consistent with classical coexistence theory, the effect of competition on individual reproductive success exhibits negative frequency-dependence when individuals experience greater intraspecific competition than interspecific competition, i.e., niche overlap is less than one. In the absence of environmental fluctuations, our analysis reveals that (1) a synergistic effect of PFD and niche overlap that hastens exclusion, (2) trade-offs between susceptibility to PFD and maximal fecundity can mediate coexistence, and (3) coexistence, when it occurs, requires that neither species is initially rare. Analysis of the stochastic model highlights that environmental fluctuations, unless perfectly correlated, coupled with PFD ultimately drive one species extinct. Over any given time frame, this extinction risk decreases with the correlation of the demographic responses of the two species to the environmental fluctuations, and increases with the temporal autocorrelation of these fluctuations. For species with overlapping generations, these trends in extinction risk persist despite the strength of the storage effect decreasing with correlated demographic responses and increasing with temporal autocorrelations. These results highlight how the presence of PFD may alter the outcomes predicted by modern coexistence mechanisms.

The role of seasonal timing and phenological shifts for species coexistence.

Shifts in the phenologies of coexistence species are altering the temporal structure of natural communities worldwide. However, predicting how these changes affect the structure and long-term dynamics of natural communities is challenging because phenology and coexistence theory have largely proceeded independently. Here, I propose a conceptual framework that incorporates seasonal timing of species interactions into a well-studied competition model to examine how changes in phenologies influence long-term dynamics of natural communities. Using this framework I demonstrate that persistence and coexistence conditions strongly depend on the difference in species' mean phenologies and how this difference varies across years. Consequently, shifts in mean and interannual variation in relative phenologies of species can fundamentally alter the outcome of interactions and the potential for persistence and coexistence of competing species. These effects can be predicted by how per-capita effects scale with differences in species' phenologies. I outline how this approach can be parameterized with empirical systems and discuss how it fits within the context of current coexistence theory. Overall, this synthesis reveals that phenology of species interactions can play a crucial yet currently understudied role in driving coexistence and biodiversity patterns in natural systems and determine how species will respond to future climate change.