Coexistence Mechanisms Research Articles

Mechanistic approaches to investigate soil microbe‐mediated plant competition

Abstract Interactions between plants and soil microbes can influence plant population dynamics and diversity in plant communities. Traditional theoretical paradigms view the microbial community as a black box with net effects described by phenomenological models. This approach struggles to quantify the importance of plant–microbe interactions relative to other competition and coexistence mechanisms and to explain context dependence in microbe effects. We argue that a mechanistic framework focused on microbial functional groups will lead to conceptual and empirical advances, as demonstrated by extending resource ratio theory to plant–microbe interactions. We review the diverse pathways by which different microbial functional groups can influence plant resource competition. Finally, we suggest approaches to link theory with observations to measure the key parameters of our framework. Synthesis: Our review highlights recent experimental advancements for uncovering microbial mechanisms that alter plant host resource competition and coexistence. We synthesize these mechanisms into a conceptual model that provides a framework for future experiments to investigate the importance of plant–microbe interactions in structuring plant populations and communities.

Negative frequency dependent selection unites ecology and evolution.

From genes to communities, understanding how diversity is maintained remains a fundamental question in biology. One challenging to identify, yet potentially ubiquitous, mechanism for the maintenance of diversity is negative frequency dependent selection (NFDS), which occurs when entities (e.g., genotypes, life history strategies, species) experience a per capita reduction in fitness with increases in relative abundance. Because NFDS allows rare entities to increase in frequency while preventing abundant entities from excluding others, we posit that negative frequency dependent selection plays a central role in the maintenance of diversity. In this review, we relate NFDS to coexistence, identify mechanisms of NFDS (e.g., mutualism, predation, parasitism), review strategies for identifying NFDS, and distinguish NFDS from other mechanisms of coexistence (e.g., storage effects, fluctuating selection). We also emphasize that NFDS is a key place where ecology and evolution intersect. Specifically, there are many examples of frequency dependent processes in ecology, but fewer cases that link this process to selection. Similarly, there are many examples of selection in evolution, but fewer cases that link changes in trait values to negative frequency dependence. Bridging these two well-developed fields of ecology and evolution will allow for mechanistic insights into the maintenance of diversity at multiple levels.

Bioinspired spiderweb-liked protective hydrophobic layer for improving the durability of superhydrophilic/air superoleophobic coatings

Oily wastewater and oil spill have always been a common concern of environmental problems, and superwetting materials are the key to oil-water separation. However, the superwetting material is constantly blocked by oil, which is a crucial obstacle to its practical application. In this study, we proposed a novel strategy to protect the underlying superhydrophilic layer by using a hydrophobic aluminate coupling agent. And we constructed the superhydrophilic layer with cellulose and the superoleophobic surface with FS50-modified rough nanoparticles. Porous ceramics could achieve stable superhydrophilic/air superoleophobic properties through a simple soaking step (modified CM). The advanced and receding contact angles on the modified CM surface were 151.74° and 149.11° for crude oil. The modified CM could maintain the contact angle of oil above 150° at various temperatures, pH values, and abrasion. In the continuous separation process, the flux remained above 1.4 × 104 L m−2 h−1, and the separation efficiency could achieve above 99 % for soybean oil. Besides, the modified CM could also separate oil-in-water emulsion. Further, we proposed the coexistence and fabrication mechanism of superhydrophilic/air superoleophobic interface. This study provides new design ideas for developing durable oil-water separation materials.

Overlap in habitat use and activity patterns between sika deer (Cervus nippon) and Japanese serows (Capricornis crispus) in subalpine habitats: exploitative competition rather than direct interference?

Examining multiple niche relationships, such as habitat use and activity patterns, between sympatric species contributes to an understanding of the mechanisms of coexistence and competition. Sika deer ( Cervus nippon Temminck, 1838) and Japanese serows ( Capricornis crispus (Temminck, 1836)) often show different habitat use, and diversity in vegetation and topography seems to facilitate their coexistence. Conversely, their habitat use may overlap in areas with low-diversity habitats; however, this remains unstudied. Moreover, whether they spatiotemporally avoid each other to reduce direct interference is unclear. We examined the fine-scale patterns of habitat use and activity of deer and serows in the subalpine forests of Mount Fuji, which have low-diversity habitats, using camera trapping data over 3 years. Deer and serow habitat niches largely overlapped, especially in summer (92%–94%) and autumn (89%–91%), suggesting that low-diversity habitats facilitate overlapping habitat use. Both species selected areas frequently used by the other during spring to autumn and their temporal niches largely overlapped, especially in summer (88%) and autumn (83%), suggesting that they do not spatiotemporally avoid each other (i.e., there is no direct interference). Rapid range expansion of deer into these subalpine habitats may exclude native serows through resource exploitative competition rather than interference competition.

Competitive interactions and coexistence of sympatric flagship carnivores in Asia.

Understanding the competition and coexistence of flagship carnivores is key to creating strategies for their conservation in the face of global carnivore declines. Although studies exploring the dynamics and competition between tigers (Panthera tigris) and leopards (P. pardus) span decades, there is a lack of understanding regarding the factors that influence their coexistence mechanisms on a broad scale, as well as the drivers determining their exploitative and interference competition. We gathered a comprehensive list of research papers among which 36 papers explored the interspecific interactions between tigers and leopards and tested the influence of biotic and abiotic factors on the coexistence mechanisms along three dimensions using multiple response variables regression models; we also tested the influence of ecological drivers determining the exploitative or interference competition between tigers and leopards. Elevation and ungulate density were the most important predictors in regulating the coexistence mechanisms. Tigers and leopards exhibited more positive relations/higher overlaps as elevation increased in the spatial niche. In addition, they showed a higher dietary overlap in the prey-rich regions. We determined that interference competition between tigers and leopards was less frequently observed in habitats with dense tree cover and homogeneous vegetation structures. Meanwhile, studies with multiple metrics would promote the detection of interference competition. Our study provides new insight into the competitive interactions and coexistence mechanisms of tigers and leopards on a broad scale. Policy-makers and managers should pay more attention to the factors of elevation, prey abundance, and habitat structures for the conservation of tigers and leopards.

Human presence and infrastructure impact wildlife nocturnality differently across an assemblage of mammalian species.

Wildlife species may shift towards more nocturnal behavior in areas of higher human influence, but it is unclear how consistent this shift might be. We investigated how humans impact large mammal diel activities in a heavily recreated protected area and an adjacent university-managed forest in southwest British Columbia, Canada. We used camera trap detections of humans and wildlife, along with data on land-use infrastructure (e.g., recreation trails and restricted-access roads), in Bayesian regression models to investigate impacts of human disturbance on wildlife nocturnality. We found moderate evidence that black bears (Ursus americanus) were more nocturnal in response to human detections (mean posterior estimate = 0.35, 90% credible interval = 0.04 to 0.65), but no other clear relationships between wildlife nocturnality and human detections. However, we found evidence that coyotes (Canis latrans) (estimates = 0.81, 95% CI = 0.46 to 1.17) were more nocturnal and snowshoe hares (Lepus americanus) (estimate = -0.87, 95% CI = -1.29 to -0.46) were less nocturnal in areas of higher trail density. We also found that coyotes (estimate = -0.87, 95% CI = -1.29 to -0.46) and cougars (Puma concolor) (estimate = -1.14, 90% CI = -2.16 to -0.12) were less nocturnal in areas of greater road density. Furthermore, coyotes, black-tailed deer (Odocoileus hemionus), and snowshoe hares were moderately more nocturnal in areas near urban-wildland boundaries (estimates and 90% CIs: coyote = -0.29, -0.55 to -0.04, black-tailed deer = -0.25, -0.45 to -0.04, snowshoe hare = -0.24, -0.46 to -0.01). Our findings imply anthropogenic landscape features may influence medium to large-sized mammal diel activities more than direct human presence. While increased nocturnality may be a promising mechanism for human-wildlife coexistence, shifts in temporal activity can also have negative repercussions for wildlife, warranting further research into the causes and consequences of wildlife responses to increasingly human-dominated landscapes.

Seasonal variation in dietary patterns and trophic niche overlap among three sympatric medium-sized carnivores in a cool-temperate zone

To understand and sustain carnivore communities and ecosystems, it is important to determine the mechanisms of coexistence and potential competitive interactions among carnivores. This study examined how carnivores coexist and how climatic environmental shifts affect the potential competitive interactions among medium-sized carnivores. The seasonal trophic niche overlap of red foxes, Japanese martens, and raccoon dogs in the cool-temperate zone in Japan was evaluated, where there are distinct seasonal changes, especially from heavy snowfall. Faecal analysis of red foxes (n = 107), Japanese martens (n = 125), and raccoon dogs (n = 100) from 2019 to 2021 showed that carnivores share the main food items and their annual dietary overlap is relatively high despite the co-occurrence of carnivores. These results have indicated that the carnivores have potentially strong competitive interactions, and various competition avoidance mechanisms besides niche partitioning may facilitate the coexistence of carnivores in Japan. The study also found that the degree of trophic niche overlap varied by season, indicating that shifts in environmental conditions, particularly food abundance and snowfall, may affect potential competitive interactions among carnivore guilds.

Nitrogen Adsorption on Cu(001): Mechanisms of Stress Relief and Coexistence of Two Domains

Nitrogen Adsorption on Cu(001): Mechanisms of Stress Relief and Coexistence of Two Domains

Mechanistic Models of Trophic Interactions: Opportunities for Species Richness and Challenges for Modern Coexistence Theory.

AbstractMany potential mechanisms promote species coexistence, but we know little about their relative importance. To compare multiple mechanisms, we modeled a two-trophic planktonic food web based on mechanistic species interactions and empirically measured species traits. We simulated thousands of possible communities under realistic and altered interaction strengths to assess the relative importance of three potential drivers of phytoplankton and zooplankton species richness: resource-mediated coexistence mechanisms, predator-prey interactions, and trait trade-offs. Next, we computed niche and fitness differences of competing zooplankton to obtain a deeper understanding of how these mechanisms determine species richness. We found that predator-prey interactions were the most important driver of phytoplankton and zooplankton species richness and that large zooplankton fitness differences were associated with low species richness, but zooplankton niche differences were not associated with species richness. However, for many communities we could not apply modern coexistence theory to compute niche and fitness differences of zooplankton because of conceptual issues with the invasion growth rates arising from trophic interactions. We therefore need to expand modern coexistence theory to fully investigate multitrophic-level communities.

Local adaptation, phenotypic plasticity, and species coexistence

Understanding the mechanisms of species coexistence has always been a fundamental topic in ecology. Classical theory predicts that interspecific competition may select for traits that stabilize niche differences, although recent work shows that this is not strictly necessary. Here, we ask whether adaptive phenotypic plasticity could allow species coexistence (i.e., some stability at an equilibrium point) without ecological differentiation in habitat use. We used individual-based stochastic simulations defining a landscape composed of spatially uncorrelated or autocorrelated environmental patches, where two species with the same competitive strategies, not able to coexist without some form of phenotypic plasticity, expanded their ranges in the absence of a competition—colonization trade-off (a well-studied mechanism for species diversity). Each patch is characterized by a random environmental value that determines the optimal phenotype of its occupants. In such a scenario, only local adaptation and gene flow (migration) may interact to promote genetic variation and coexistence in the metapopulation. Results show that a competitively inferior species with adaptive phenotypic plasticity can coexist in a same patch with a competitively superior, non-plastic species, provided the migration rates and variances of the patches' environmental values are sufficiently large.

Do plant-soil feedbacks promote coexistence in a sagebrush steppe?

Recent studies have shown the potential for negative plant-soil feedbacks (PSFs) to promote stable coexistence, but have not quantified the stabilizing effect relative to other coexistence mechanisms. We conducted a field experiment to test the role of PSFs in stabilizing coexistence among four dominant sagebrush steppe species that appear to coexist stably, based on previous work with observational data and models. We then integrated the effects of PSF treatments on focal species across germination, survival, and first-year growth. To contribute to stable coexistence, soil microbes should have host-specific effects that result in negative feedbacks. Over two replicated growing seasons, our experiments consistently showed that soil microbes have negative effects on plant growth, but these effects were rarely host-specific. The uncommon host-specific effects were mostly positive at the germination stage, and negative for growth. Integrated effects of PSF across early life-stage vital rates showed that PSF-mediated self-limitation occasionally had large effects on projected plant biomass, but occurred inconsistently between years. Our results suggest that while microbially-mediated PSF may not be a common mechanism of coexistence in this community, it may still affect the relative abundance of dominant plant species via changes in host fitness. Our work also serves as a blueprint for future investigations that aim to identify underlying processes and test alternative mechanisms to explain important patterns in community ecology.

Niche Characteristics of Alternanthera philoxeroide-Invaded Plant Communities in Heterogeneous Habitats and Their Latitudinal Trends

Plant invasions are closely related to environmental filtering and biointeractions; however, the variations in invasive plant niches along latitudinal gradients in heterogeneous habitats remain unclear. In this study, we conducted a two-year survey in China spanning 21° N–37° N to explore the niche characteristics of plant species within communities invaded by the amphibious alien weed Alternanthera philoxeroides in both terrestrial and aquatic habitats as well as their latitudinal trends. We found that A. philoxeroides had the greatest niche breadth in the studied communities. The species pairs with the highest niche similarity were A. philoxeroides–Digitaria sanguinalis in terrestrial communities and Cyperus rotundus–Kyllinga brevifolia in aquatic communities. The niche similarity between A. philoxeroides and its accompanying species in terrestrial habitats was significantly higher than that in aquatic habitats (t = 5.954; p < 0.001). The niche breadth of A. philoxeroides had no obvious latitudinal trend, while the niche breadth of its accompanying species in the terrestrial community significantly decreased with increasing latitude (F7, 57 = 4.364, p = 0.001). In the terrestrial communities, the niche similarity between A. philoxeroides and its accompanying species significantly decreased with increasing latitude (F7, 57 = 3.671, p = 0.003), while the niche overlap significantly increased with increasing latitude (F7, 57 = 8.916, p < 0.001). However, the aquatic species’ niche characteristics had no obvious latitudinal trends. These findings indicated that habitat heterogeneity significantly affected the species’ niche characteristics in A. philoxeroides-invaded communities. Environmental filtering at low latitudes allowed the invasive and accompanying species to evolve similar niches, while the cold climate at high latitudes increased the niche overlap between the invader and accompanying species. Our findings are crucial for predicting the dynamics of invasive plant communities under global change and for understanding the mechanisms of species coexistence.

Integrated acoustic-optic-mechanics (AOM) multi-physics field characterization methods for a crack: Tension vs. shear

Rock macrofracturing often involves the tension-shear coexistence mechanism on the microscopic scale. This paper addresses the occurrence of tension and shear mechanisms in rock macrofracturing process based on the self-developed integrated acoustic-optic-mechanics (AOM) multi-physics field monitoring technique. With this advanced technique, three-point bending (3-p-b) tests with conventional loading and unconventional loading, as a control of the conditions that produce the different mechanisms, are first carried out on sandstone to establish AOM criteria for crack nature classifications. By using the AF-RA-based Kernel density median criterion and the optical angular bisector criterion, a coupled analysis of acoustical-optical data for the distinction of tension- vs shear-induced cracks in two different flaw configurations under uniaxial compression has been available. Results show that the crack initiation mode in tension-type rock bridge tests is dominated by the tension mechanism, while the ultimate failure pattern is shear-dominated. Comparably, failure of shear-type rock bridge is faithfully dominated by the shear mechanism. The paper, therefore, makes two contributions—a better understanding of rock fracturing process and providing a method of establishing the simple and intuitive criteria to justify the crack natures.

Interactions between fitness components across the life cycle constrain competitor coexistence.

Numerous mechanisms can promote competitor coexistence. Yet, these mechanisms are often considered in isolation from one another. Consequently, whether multiple mechanisms shaping coexistence combine to promote or constrain species coexistence remains an open question. Here, we aim to understand how multiple mechanisms interact within and between life stages to determine frequency-dependent population growth, which has a key role stabilizing local competitor coexistence. We conducted field experiments in three lakes manipulating relative frequencies of two Enallagma damselfly species to evaluate demographic contributions of three mechanisms affecting different fitness components across the life cycle: the effect of resource competition on individual growth rate, predation shaping mortality rates, and mating harassment determining fecundity. We then used a demographic model that incorporates carry-over effects between life stages to decompose the relative effect of each fitness component generating frequency-dependent population growth. This decomposition showed that fitness components combined to increase population growth rates for one species when rare, but they combined to decrease population growth rates for the other species when rare, leading to predicted exclusion in most lakes. Because interactions between fitness components within and between life stages vary among populations, these results show that local coexistence is population specific. Moreover, we show that multiple mechanisms do not necessarily increase competitor coexistence, as they can also combine to yield exclusion. Identifying coexistence mechanisms in other systems will require greater focus on determining contributions of different fitness components across the life cycle shaping competitor coexistence in a way that captures the potential for population-level variation.

Coexistence in spatiotemporally fluctuating environments

Ecologists have put forward many explanations for coexistence, but these are only partial explanations; nature is complex, so it is reasonable to assume that in any given ecological community, multiple mechanisms of coexistence are operating at the same time. Here, we present a methodology for quantifying the relative importance of different explanations for coexistence, based on an extension of the Modern Coexistence Theory. Current versions of Modern Coexistence Theory only allow for the analysis of communities that are affected by spatial or temporal environmental variation, but not both. We show how to analyze communities with spatiotemporal fluctuations, how to parse the importance of spatial variation and temporal variation, and how to measure everything with either mathematical expressions or simulation experiments. Our extension of Modern Coexistence Theory shows that many more species can coexist than originally thought. More importantly, it allows empiricists to use realistic models and more data to better infer the mechanisms of coexistence in real communities.

Invasion Consequences in Communities Maintained by Niche and Intransitive Coexistence Mechanisms

Understanding invasion mechanisms or identifying their potential outcomes has been a longstanding objective of invasion. Many recent empirical and theoretical works tend to frame a perspective of invasion biology within the field of coexistence theory. With increasing emphasis on indirect competitions, more researches hold that niche departure, intransitive loop structure or the integration of these two would be the potential mechanisms to promote native coexistence. But how invasion dynamics rely on these key properties of native competitive network is seldom investigated. Here, we introduce one alien species to a three-species competition system. By setting the structure of coexistence coefficient matrix, we consider three native coexistence mechanisms. After analyzing the equilibrium consequences of alien species invasion under these three mechanisms, we have found that (1) in the native communities supported by strong niche differentiation, alien species can certainly establish their population but would not pose great destruction to native species. (2) Invasion exclusion would happen in the community maintained by intransitive competition loop. However, whether alien species coexist with or exclude resident populations depends on both intraspecific and interspecific competition of invader. (3) The community assembled by the combination of these two mechanisms are most resistant to invasion, and where invasion consequences are more diverse. (4) Finally, the species long-term steady state and short-term respond always keep consistent. We have explicitly situated invasion process within the recent coexistence framework. Our results would broaden the understanding of invasion mechanisms and provide insights into the combination of invasion and coexistence theory.

Non-Alcoholic Fatty Liver Disease or Type 2 Diabetes Mellitus-The Chicken or the Egg Dilemma.

In clinical practice, we often deal with patients who suffer from non-alcoholic fatty liver disease (NAFLD) concurrent with type 2 diabetes mellitus (T2DM). The etiopathogenesis of NAFLD is mainly connected with insulin resistance (IR) and obesity. Similarly, the latter patients are in the process of developing T2DM. However, the mechanisms of NAFLD and T2DM coexistence have not been fully elucidated. Considering that both diseases and their complications are of epidemic proportions and significantly affect the length and quality of life, we aimed to answer which of these diseases appears first and thereby highlight the need for their diagnosis and treatment. To address this question, we present and discuss the epidemiological data, diagnoses, complications and pathomechanisms of these two coexisting metabolic diseases. This question is difficult to answer due to the lack of a uniform procedure for NAFLD diagnosis and the asymptomatic nature of both diseases, especially at their beginning stages. To conclude, most researchers suggest that NAFLD appears as the first disease and starts the sequence of circumstances leading ultimately to the development of T2DM. However, there are also data suggesting that T2DM develops before NAFLD. Despite the fact that we cannot definitively answer this question, it is very important to bring the attention of clinicians and researchers to the coexistence of NAFLD and T2DM in order to prevent their consequences.

Feeding Strategies and Trophic Niche Divergence of Three Groups of Dosidicus gigas off Peru: Based on Stable Carbon and Nitrogen Isotopes and Morphology of Feeding Apparatuses

Dosidicus gigas (D. gigas) is a pelagic cephalopod of ecological and economic importance widely distributed in the eastern Pacific Ocean. Generally, small-, medium-, and large-sized groups of the squids have been respectively identified on the basis of the mantle length (ML) of adults. Intraspecific feeding variability maximizes the utilization of available food resources by D. gigas. However, the coexistence mechanism of three groups has not been fully understood yet. In our study, based on the analyses of beak morphology and stable carbon and nitrogen isotopes, the feeding strategies and coexistence patterns of large-, medium-, and small-sized groups of D. gigas were investigated. D. gigas had a wide range of 13C/12C (δ13C) and 15N/14N (δ15N) values in muscle tissue, variable feeding behaviors, and wide food sources. The δ13C or δ15N values showed no significant difference between the small- and medium-sized groups, which shared the same habitats and fed on preys with the similar trophic level. Compared to small- and medium-sized groups, the large-sized group had a smaller range of habitats and consumed more nearshore foods. Both isotopes and feeding apparatus morphology indicated a high degree of niche overlap between the small- and medium-sized groups, whereas the large-sized group differed significantly from other groups. In addition, the niche width of the female was larger than that of the male in all three groups. We inferred that the sex differences in body length and reproductive behavior led to the difference in niche width. The isotopic niche overlap between female and male samples was the most significant in large-sized group and the least significant in the small-sized group, indicating that different feeding strategies were adopted by the three groups. These findings proved that the three groups of D. gigas off Peruvian waters adopted a feeding strategy with inter- and intra-group regulation. This feeding strategy maximizes the use of food and habitat resources and ensures that different size groups can coexist in the same waters.

Effects of Stage Structure on Coexistence: Mixed Benefits.

The properties of competition models where all individuals are identical are relatively well-understood; however, juveniles and adults can experience or generate competition differently. We study here less well-known structured competition models in discrete time that allow multiple life history parameters to depend on adult or juvenile population densities. A numerical study with Ricker density-dependence suggested that when competition coefficients acting on juvenile survival and fertility reflect opposite competitive hierarchies, stage structure could foster coexistence. We revisit and expand those results. First, through a Beverton-Holt two-species juvenile-adult model, we confirm that these findings do not depend on the specifics of density-dependence or life cycles, and obtain analytical expressions explaining how this coexistence emerging from stage structure can occur. Second, we show using a community-level sensitivity analysis that such emergent coexistence is robust to perturbations of parameter values. Finally, we ask whether these results extend from two to many species, using simulations. We show that they do not, as coexistence emerging from stage structure is only seen for very similar life-history parameters. Such emergent coexistence is therefore not likely to be a key mechanism of coexistence in very diverse ecosystems, although it may contribute to explaining coexistence of certain pairs of intensely competing species.

Trophic niche overlap among Neotropical carnivores in a silvicultural landscape

Abstract To enable long-term coexistence, species need to differentiate at least one of the three main dimensions of the ecological niche (temporal, spatial, or trophic dimension). Here, we investigated whether mammalian predators (Chrysocyon brachyurus, Cerdocyon thous, Lycalopex vetulus, and Puma concolor) follow the prediction of trophic niche partitioning, which is expected when partitioning of food resources represents an important mechanism for coexistence. We predicted low niche overlap in general and low between P. concolor and the other species. We analyzed 207 fecal samples collected at a landscape composed of forest remnants immersed in Eucalyptus plantations. Food items (animals and plants) were identified using exoskeletons, feathers, scales, teeth, hair, and seeds. We calculated the frequency and percentage of occurrence of food items, niche breadth, and niche overlap between pairs of species. Prey size was similar among all predators, consuming mainly small-sized prey (<1 kg). However, niche breadth was larger for smaller carnivores compared to larger ones. No species pair showed significantly lower niche overlap than expected by chance. Our study provided detailed information on trophic resource use of sympatric carnivores, showing that trophic niche partitioning seems not to be crucial for the coexistence of carnivores in the study area.