Alternative Stable States Research Articles

Present-day characteristics of phytoplankton, microphytobenthos and phytoepiphyton of the Kaniv Reservoir

The paper studies quantitative diversity and dominant complexes of phytoplankton, microphytobenthos and phytoepiphyton in lotic and lentic biotopes within the Kaniv Reservoir in summer seasons of 2017–2022, considers their association with some abiotic variables, assesses the trophic state, information diversity according to Shannon’s index and water quality. The cell count of planktonic algae varied within 2780–124155 thous. cells · dm–3, biomass – 0.631–11.636 mg · dm–3, benthic algae – 390–13874 thous. cells · 10 cm–2 and 0.162–2.651 mg mg · 10 cm–2, epiphytic algae – 50–680 thous. cells mg · 10 cm–2 and 0.050–1.679 mg · 10 cm–2 respectively. In lotic biotopes the phytoplankton cell count was higher than in lentic biotopes due to algal inflow from the Kyiv Reservoir and tributaries. The structural organization of phytoplankton and microphytobenthos is represented by oligodominant complexes of Cyanobacteria – Bacillariophyta and Bacillariophyta – Cyanobacteria respectively, and phytoepiphyton – by monodominant complex of Bacillariophyta. The necessity to distinguish dominant complexes according to cell count and biomass has been proven. The dominant complexes of algal communities clearly divide into three clusters (for plankton, benthos and epiphyton), and each of them – into two clusters (for lotic and lentic biotopes). The Sorensen similarity between phytoplankton and microphytobenthos was higher than between phytoplankton and phytoepiphyton, which can be explained by sedimentation of planktonic forms on the bottom under different ecological conditions. High cell count and biomass, diverse dominant complex of algal communities depend upon some abiotic variables (solar radiation, photic layer thickness, water temperature in summer, nutrient content). According to phytoplankton the trophic state of the Kaniv Reservoir is assessed as eutrophic–polytrophic, and according to contour algal communities – as oligo-mesotrophic–mesotrophic. This difference complies with the “alternative stable states” theory. That is, in summer the water reservoir is in “turbid state”, when planktonic Cyanobacteria grow intensively, screen the water surface and suppress the photosynthesis of benthic and epiphytic algal communities. The water quality of the Kaniv Reservoir is within the 1st–3rd classes (clean–satisfactory clean waters), there are no point of diffuse sources of water pollution, which mainly coincides with retrospective data.

Response of the soil microbial communities to forest ground cover manipulation in a boreal forest

In eastern Canada, boreal forests are locally experiencing a shift between two alternative stable states, productive closed-canopy feather moss (Pleurozium schreberi (Brid.) Mitt.) forests to low-productivity open lichen (Cladonia spp.) woodlands. While this shift has important consequences for ecosystem structure and productivity, little is known about the changes occurring in the diversity and composition of the soil microbial community which may be driven by this process. We evaluated the effects of 10-year moss transplantation on soil microbial communities in an open-lichen woodland. Treatments included: 1) removal of the lichen cover, 2) removal of the lichen cover followed by transplantation of a feather moss cover, 3) a control with the lichen cover kept in place (lichen control), and 4) a natural forest site with a feather moss cover (moss control). We found that changing the forest ground cover has a significant impact on the diversity, composition and function of soil microbial communities. Fungal alpha diversity was more sensitive to changes in lichen and moss cover, compared to bacterial diversity. Soil microbial community composition showed significant differences among all forest ground covers, but with greater similarities between the moss transplantation and control moss treatments. More importantly, changes of forest ground cover significantly affected the structure of microbial communities and fungal functional groups. Moss transplantation significantly increased the relative abundance of the organic nitrogen-scavenging fungal genus, Piloderma. Furthermore, moss transplantation significantly increased the overall relative abundance of ectomycorrhizal fungi and decreased the proportion of ericoid mycorrhizal fungi. Soil moisture and temperature were the main environmental variables associated to the shift in microbial community composition. Our study points out that moss transplantation in open-canopy lichen woodlands contributes to regulate and modify the composition, structure, and function of the soil microbial communities with potential implications for explaining the changes in ecosystem processes associated with these two forest ecosystems.

Beyond individual, population, and community: Considering information, cell number, and energy flux as fundamental dimensions of life across scales

We suggest rethinking ecology as a set of continuous, interconnected dynamics and spatial networks that would represent an alternative framework to the traditional organizational levels—cell, organism, population, community, and ecosystem. We draw on unifying biological theories—information theory, cell theory, and metabolic theories—to propose a continuous space for living systems that avoids epistemological constraints imposed by a priori assumptions of discrete levels of biological organization. The discrete levels of organization that ecologists have traditionally envisioned can be viewed instead as coarse-grained, localized groupings within continuous dimensions of information (I), cell number (C), and energy flux (E). Moving from levels of organization to emergent properties of information, cells, and energy flux allows us to illustrate how diverse ecological and evolutionary phenomena—such as allometric and diversity-related scaling patterns, predator-prey dynamics, evolutionary trajectories, and alternative stable states—can be represented within the same continuum. We suggest that there may be structure within this information-cells-energetic flux (ICE) framework that unifies ecology from the beginning of life to the present and provides a useful lens through which patterns and processes in nature can be viewed.

Restoring historical grasslands in a desert national park: Resilience or unrecoverable states in an emerging climate?

Ecosystems that supported multiple biological communities during the Holocene and that form alternative stable states pose challenges for identifying appropriate and feasible target communities for ecological restoration and conservation strategies for climate adaptation. In the Chihuahuan Desert, shrubland and perennial grassland alternatively dominated for millennia. However, grassland declined beginning 100–150 years ago during concomitant change in both climate and anthropogenic land use, making it unclear whether restoring grassland is appropriate or feasible in the emerging climate. In Guadalupe Mountains National Park, Texas, USA, we characterized remnant grasslands and performed experiments including outplanting and shrub reduction to assess feasibility and techniques for restoring desert grassland. In remnant patches, grass cover was more temporally variable than shrub cover, as grass cover varied 1.5× between years. Survival of outplanted grasses, either under Larrea tridentata shrubs or in the open with or without woody material encircling outplants for protection, was high (95 %) after seven months but declined to 2 % after 19 months. Response of perennial grass cover was variable after shrub and litter removal on soil surfaces varying in stoniness. Results suggest that 1) restoration can increase native desert grasses but gains may be intermittent; 2) reducing shrubs to facilitate natural expansion of remnant grasses and propagules may be more effective than outplanting grasses; and 3) restoring native grassland by reducing shrubs appears feasible even in dry conditions projected for the emerging climate. Findings that native grasses can increase at least intermittently suggest that practitioners have multiple candidate communities for conservation management and climate change adaptation as grassland, shrubland, and mixed communities each provide unique habitat.

Fuel dynamics and rarity of fire weather reinforce coexistence of rainforest and wet sclerophyll forest

Rainforest, wet sclerophyll forest and eucalypt forest exist as Alternative Stable States moderated by fire. Eucalypt forest is flammable and subject to regular fire. Insights into the flammability of rainforest and wet sclerophyll forest are difficult to obtain because of the rarity of fire, particularly in sub-tropical and tropical environments. This study aimed to determine the relative flammability of rainforest and wet sclerophyll forest with a canopy of Lophostemon confertus in subtropical Australia. Fires in 2019, coinciding with extreme fire weather and following a long period of drought, burnt rainforest and wet sclerophyll forest in south-east Queensland. The weather record indicates these conditions recur about three to four times a century. Remapping of the vegetation overlaid with the fire-scar mapping, indicated that the 2019 fires burnt 23 % of rainforest, much of which was disturbed, but 60 % of wet sclerophyll forest suggesting greater flammability of the latter. This study revealed that above-ground biomass and litter fuel loads are more than twice as high in wet sclerophyll forest than rainforest. The litter of Lophostemon confertus, a Myrtaceae tree dominating the upper canopy, on average decomposes at less than half the rate of rainforest litter, contributing to the higher fuel loads and thus greater flammability of wet sclerophyll forest compared to rainforest. The Alternative Stable States of wet sclerophyll and rainforest are partly stabilised by the fire retardance of rainforest, the rarity of weather conditions suitable for fire in the subtropical environment and the higher fuel loads in wet sclerophyll forest that allow occasional fire. Wet sclerophyll forest requires rare fire events and the legacy of these fires over hundreds of years is evident in the multiple cohorts of ‘giant’ canopy trees.

Going green: Framing effects in a dynamic coordination game

We study decision-making in a (novel) dynamic coordination game that simulates ‘social tipping’. The game involves groups of three subjects who initially find themselves in a stable state with positive network externalities. Over seven rounds, they have the opportunity to transition to an alternative stable state with higher payoff, based on the other network. The transition is slow, costly and requires coordination to minimize costs.In the experiment, the game is repeated five times, which enables groups to learn to coordinate. We compare a neutral language treatment with a ‘green framing’ treatment, in which meaningful context is added to the instructions. Our findings reveal that green framing significantly increases the number of successful transitions, but also reduces the group's ability to coordinate in subsequent games. Consequently, while green framing results in twice as many transitions, these are also more costly such that payoffs do not differ between treatments.In the context of environmental policy, the experiment suggests general support for ‘going green’, but it also points to green framing causing proponents and opponents to stick to their strategies reducing potential gains from coordination between proponents and opponents of environmentally friendly actions.

Mean exit times as global measure of resilience of tropical forest systems under climatic disturbances-Analytical and numerical results.

Both remotely sensed distribution of tree cover and models suggest three alternative stable vegetation states in the tropics: forest, savanna, and treeless states. Environmental fluctuation could cause critical transitions from the forest to the savanna state and quantifying the resilience of a given vegetation state is, therefore, crucial. While previous work has focused mostly on local stability concepts, we investigate here the mean exit time from a given basin of attraction, with partially absorbing and reflecting boundaries, as a global resilience measure. We provide detailed investigations using an established model for tropical tree cover with multistable precipitation regimes. We find that higher precipitation or weaker noise increases the mean exit time of the forest state and, thus, its resilience. Upon investigating the transition times from the forest state to other tree cover states, we find that in the bistable precipitation regime, the size of environmental fluctuations has a greater impact on the transition probabilities from the forest state compared to precipitation.

Emergent structure and dynamics of tropical forest-grassland landscapes

Previous work indicates that tropical forest can exist as an alternative stable state to savanna. Therefore, perturbation by climate change or human impact may lead to crossing of a tipping point beyond which there is rapid forest dieback that is not easily reversed. A hypothesized mechanism for such bistability is feedback between fire and vegetation, where fire spreads as a contagion process on grass patches. Theoretical models have largely implemented this mechanism implicitly, by assuming a threshold dependence of fire spread on flammable vegetation. Here, we show how the nonlinear dynamics and bistability emerge spontaneously, without assuming equations or thresholds for fire spread. We find that the forest geometry causes the nonlinearity that induces bistability. We demonstrate this in three steps. First, we model forest and fire as interacting contagion processes on grass patches, showing that spatial structure emerges due to two counteracting effects on the forest perimeter: forest expansion by dispersal and forest erosion by fires originating in adjacent grassland. Then, we derive a landscape-scale balance equation in which these two effects link forest geometry and dynamics: Forest expands proportionally to its perimeter, while it shrinks proportionally to its perimeter weighted by adjacent grassland area. Finally, we show that these perimeter quantities introduce nonlinearity in our balance equation and lead to bistability. Relying on the link between structure and dynamics, we propose a forest resilience indicator that could be used for targeted conservation or restoration.

Ecosystem-based fishery management that accounts for trade-offs between fishing and enhancement stocking: A case study of Juehua Island in the Bohai Sea

The implementation of marine ecosystem management requires modeling that accounts for the trade-off between exploitation in fisheries and protection activities (e.g., enhancement and release, artificial reefs). Researchers are increasingly interested in the trends of fishery resources under these joint driving forces due to the negative impacts of resource exploitation and the positive impacts of marine protection. Using the sea around Juehua Island in China’s Bohai Sea as a case study, we developed a marine ecosystem model based on the Ecopath with Ecosim software to analyze the trends in fishery resources driven both by fishing and stock enhancement. When the fishing effort exceeded 42 % of the 2019 value, the biomass of top predator Platycephalus indicus decreased by 50 %, indicating a regime shift. When the fishing effort increased to 340 % of the 2019 level, the ecosystem shifts to an alternative stable state occurs, indicating destabilization of the marine ecosystem. The impact of fishing effort on the marine ecosystem was not well compensated by release of a single target species. We also designed an orthogonal experiment with three factors (the key species Fenneropenaeus chinensis, Paralichthys olivaceus, and Charybdis japonica) and four restocking release levels to determine both the optimal release rate for each species individually and the optimal combination of different species. If the 2019 fishing effort is maintained, the release of 125 × 106 juvenile F. chinensis, 400 × 103 juvenile P. olivaceus, and 15 × 106 juvenile C. japonica would be an optimal solution to improve the marine biomass, trophic level, and biodiversity. Our results provide insights into ecosystem-based management strategies for implementing a policy to limit fishing in the study area and for scientifically determining the restocking release rates.

Using the Alternative Stable States Framework to understand the persistence of secondary shrubland within a Mexican oak forest with livestock and agricultural legacies

Many forests exist in human-modified mosaic landscapes subject to logging, agriculture, and livestock grazing. These disturbances can reduce ecosystem resilience and ultimately result in crossing thresholds, leading to the transition of the ecosystem into new stable states with different plant communities. The interaction between these disturbances and forest succession is still poorly understood, despite the growing need to manage these human-modified landscapes for biodiversity and productivity. We studied abrupt changes in vegetation composition in a Central Mexican oak forest and explored how these changes could indicate the coexistence of various alternative stable states caused by agricultural and livestock legacies. We established 36 strip transects covering 9000 m2 in patches with various land use legacies where we sampled vegetation, soil characteristics, and human disturbance. We assessed future and past tendencies in vegetation spatial patterns by evaluating seedling composition and analyzed time series of NDVI signals recorded by LANDSAT images (1972–2019). We utilized NMDS, PERMANOVA, and ANOVA analyses to assess if stable states can be distinguished based on historical and current variations in vegetation composition and structure in patches with different management legacies. We then assess potential factors that may contribute to differences in plant community composition by fitting edaphic, topographic, and anthropogenic disturbance variables to the ordination analyses.We identified three distinct plant communities: oak forest (dominated by late-successional Oak species), secondary shrubland (dominated by Vachellia-Dodonaea association), and a transitional forest-shrub community (a mixture of the first two communities). Time-series analyses and seedling composition provide evidence of long-term community segregation. Variation partition analysis demonstrated that anthropogenic disturbance (particularly livestock browsing), had a greater impact on species composition differentiation than environmental variables.A state-and-transition model is proposed, where cattle browsing and agricultural legacies trigger the transition from oak forests to a stable secondary shrubland community. Three potential self-reinforcing and interacting feedbacks are suggested: (i) micro-environmental filtering, (ii) plant-trait mediated assembly process, and (iii) cascading effects on tree recruitment caused by cattle browsing. The proposed state-and-transition model explains forest successional dynamics in systems with multiple anthropogenic disturbances and provides a conceptual framework for understanding and guiding successional trajectories.

Geochemical dynamics of phosphorus and metals in sediments of a shallow coastal lake (Xuño Lake, Galicia-NW Iberian Peninsula)

The shallow lakes are important freshwater ecosystems, since they support much of biodiversity and ecosystem services of life on land. Shallow lakes are highly dynamic ecological entities that can exist in several alternative stable states through regime shift caused by a natural or human disturbance that exceeds ecological thresholds for biological communities composition and structure equilibria. The sediment as a reservoir has a key role in the limnological regulation of wetlands linked to the fluxes of nutrients and elements in the biogeochemical interplay with the water and macrophytes. For this reason, the role of sediment in the limnology of the shallow coastal lake of Xuño (NW Iberian Peninsula) was explored by seasonally monitoring the chemical composition of water and sediments, also according to macrophyte species. The shallow depth determines the high availability of light in the bottom and a well-mixed water column maintain the surface of the water–sediment interface oxygenated. The oxic conditions of the bottom implies a top-down regulation of the water column in the Xuño shallow lake that limits the diffusion of phosphorus and trace metals (Fe, Mn, Cu, and Co) to the water, buffering eutrophication or contamination levels by immobilization in the sediments. In fact, the concentration of Hg in the lake water in spring, and also its bioavailability, are high due to its release from the sediment in suboxic conditions. The cover of helophyte species Phragmites Australis and Schoenoplectus Lacustris showed differences in the assimilation of organic monoester and diester phosphorus forms in the sediment. However, the water of the Xuño Lake shows an eutrophic status by the nutrient input associated with the birds populations as indicated by microbiological data.

Alternative stable microbiome state triggered by the introduction of functional microbes in oil reservoirs drives sustainable microbial enhanced oil recovery

Microbial enhanced oil recovery (MEOR) is a promising substitute for other enhanced oil recovery methods in terms of sustainable development. However, the response mechanism of the microbial community to the introduction of functional microbes remains unclear, which limits MEOR strategic planning to achieve a long-term effect. In this study, we reveal the existence of alternative stable states in an oil reservoir for the first time and examine the correlation between the microbiota status and the oil production increment. There existed a basal state A and alternative state B in the reservoir microbial community, and this resulted in a differential microbial oil displacement effect. The oil production increased by up to 50% in basal state A, because Halomonas dominated most niches and restrained other functional microbes. The introduction of biosurfactant-producing bacteria triggered the microbiota status to shift to the alternative state B associated with higher oil recovery. In state B, the high microbial diversity and positive interaction among Dietzia, Bacillus and other species significantly activated the effectiveness of the microbial oil displacing function. Due to the hysteresis of the microbial community, it required frequent and intensive introduction of functional microbes to improve the microbiota in the reservoir and sustainably promote oil recovery. Overall, this study provides new insights into the response mechanism of the microbial community to the introduction of functional microbes in an oil reservoir. This study also provides guidance for effective management of a MEOR strategy to achieve sustainably enhanced oil production.

Impact of selective grazing on the dynamics of a diffusive plankton model with component Allee effect and additional food

In order to explore the pattern formation of non-toxic phytoplankton, toxin-producing phytoplankton, and zooplankton, a spatiotemporal plankton model is formulated by incorporating the component Allee effect, additional food, and selective grazing. For the non-spatial scenario, the qualitative analyses and numerical simulations show that the system admits rich dynamics such as Hopf bifurcation and alternative stable states. For the spatial model, the stability analyses demonstrate that the moderate component Allee effect and adequate additional food promote stable coexistence. Furthermore, our findings illustrate that selective grazing facilitates toxin-producing phytoplankton biomass. Low grazing selectivity decreases zooplankton biomass. Moderate grazing selectivity contributes to coexistence. Excessive grazing selectivity promotes the rapid reproduction of toxin-producing phytoplankton and leads to spatiotemporal chaos. In addition, the variations in the component Allee effect, additional food, and grazing selectivity give rise to the transitions of spatial patterns, which shed valuable insights into controlling plankton distribution.

River connectivity determines microbial assembly processes and leads to alternative stable states in river networks

River network is a common form of lotic ecosystems. Variances in river connection modes would form networks with significantly different structures, and further affect aquatic organisms. Microbial communities are vital organisms of river networks, they participate in numerous biogeochemical processes. Identifying associations between microbial community and structural features of river networks are essential for maintaining environmental quality. Thus, dendritic (DRN) and trellised river networks (TRN) were studied by combining molecular biological tools, ecological theory and hydrodynamic calculation. Results illustrated that river connectivity, a vital structural feature exhibiting mass transport ability of river network, increased relative importance of homogeneous selection processes in microbial assembly, which would further shape community with alternative stable states. Between the two researched river networks, DRN possessed higher connectivity, which made homogeneous selection as the driving force in community assembly. The microbial communities in DRN were consisted of species occupying similar ecological niche, and exhibited two alternative stable states, which can decrease influences of environmental disturbance on community composition. On the contrary, lower connectivity of TRN decreased proportions of homogeneous selection in community assembly, which further led to species occupying varied ecological niche. The microbial community exhibited only one stable state, and environmental disturbance would cause loss of ecological niche and significantly alter community composition. This study could provide useful information for the optimization of river connection engineering.

Short-term responses of the soil microbiome and its environment indicate an uncertain future of restored peatland forests

Restoring peatland ecosystems involves significant uncertainty due to complex ecological and socio-economic feedbacks as well as alternative stable ecological states. The primary aim of this study was to investigate to what extent the natural functioning of drainage-affected peat soils can be restored, and to examine role of soil microbiota in this recovery process. To address these questions, a large-scale before-after-control-impact (BACI) experiment was conducted in drained peatland forests in Estonia. The restoration treatments included ditch closure and partial tree cutting to raise the water table and restore stand structure. Soil samples and environmental data were collected before and 3–4 years after the treatments; the samples were subjected to metabarcoding to assess fungal and bacterial communities and analysed for their chemical properties. The study revealed some indicators of a shift toward the reference state (natural mixotrophic bog-forests): the spatial heterogeneity in soil fungi and bacteria increased, as well as the relative abundance of saprotrophic fungi; while nitrogen content in the soil decreased significantly. However, a general stability of other physico-chemical properties (including pH remaining elevated by ca. one unit) and annual fluctuations in the microbiome suggested that soil recovery will remain incomplete and patchy for decades. The main implication is the necessity to manage hydrologically restored peatland forests while explicitly considering an uncertain future and diverse outcomes. This includes their continuous monitoring and the adoption of a precautionary approach to prevent further damage both to these ecosystems and to surrounding intact peatlands.

Transient properties of grazing ecosystem driven by Lévy noise and Gaussian noise

This paper explores how Lévy noise and Gaussian noise affect the ecological grazing system by using the fourth-order Runge–Kutta method to simulate dynamic system and the Janicki-Weron algorithm to produce Lévy noise. Two deterministic quantities, the mean first passage time (MFPT) and the probability density function (PDF) of the first passage time (FPT), are utilized to explore the transient properties of grazing ecosystem. Our research results show that: (i) The transitions between two alternative stable states can be induced by the Gaussian noise intensity, Lévy noise intensity, Lévy stability index and Lévy skewness parameter. (ii) A higher Lévy noise intensity and a larger Lévy stability index or Lévy skewness parameter make the MFPT from desert state to sustainable vegetated state shorter; a higher Gaussian noise intensity makes it longer, which indicates that increased Lévy noise intensity can mitigate ecosystem degradation; increased Gaussian noise intensity will lead to desertification of vegetation. (iii) For larger Lévy noise intensity, the MFPT from sustainable vegetated state to desert state as a function of Gaussian noise intensity exhibits one maximum value when it transformation from the sustainable vegetated state to the desert state, the noise enhanced stability (NES) phenomena of grazing ecosystems are observed.

Dam-induced flow alternations drive the regime shift towards a cyanobacteria-dominated microbiota state in the Yangtze River

While satisfying the demands of social and economic development, dams act as physical barriers affecting both abiotic and biotic factors in large rivers. These altered factors can interact with each other and gradually reshape the local ecosystem state. The reshaped state may spread downstream and affect ecosystem states on a large scale. However, the spread extent and characteristics of ecosystem states along large rivers remain understudied. To address this problem, alternative microbiota states and their responses to environmental conditions in the Yangtze River were investigated, considering the preponderance of alternative stable states theory in explaining the response of ecosystem states as well as the role of benthic microorganisms in indicating ecosystem states. In this study, flow discharge was identified as the main hydrological factor that clustered benthic microbiota into two types, and these two microbiota types were bistable and characterized by differential enrichment of the Cyanobacteria phylum. Potential analysis demonstrated that reducing flow discharge beneath a threshold (i.e., flow discharge < 12,900 m3/s) could shift benthic microbiotas to a state where benthic cyanobacteria would become the dominant species (the Microbiota State B). In the bistable region (i.e., 12,900 < flow discharge < 28,000 m3/s), both the ecological resilience and the contribution of deterministic process were found weak by relative potential depth calculations and neutral community modeling, suggesting that this region is susceptible to the microbiota state of its upstream and thus deserves more scientific attention to prevent the unfavorable state from spreading downstream. In addition, high denitrification potential at sites of the Microbiota State B was likely responsible for the low N:P ratio, further benefiting the dominance of N-fixing cyanobacteria. This study empirically showed the response of alternative microbiota states to flow gradients, and explored the distribution and characteristics of the microbiota states along the mainstream of the Yangtze River, therefore providing insights into environmental flow design and reservoir regulation of large rivers.

Anticipating critical transitions in psychological systems using early warning signals: Theoretical and practical considerations.

Many real-world systems can exhibit tipping points and multiple stable states, creating the potential for sudden and difficult to reverse transitions into a less desirable regime. The theory of dynamical systems points to the existence of generic early warning signals that may precede these so-called critical transitions. Recently, psychologists have begun to conceptualize mental disorders such as depression as an alternative stable state, and suggested that early warning signals based on the phenomenon of critical slowing down might be useful for predicting transitions into depression and other psychiatric disorders. Harnessing the potential of early warning signals requires us to understand their limitations as well as the factors influencing their performance in practice. In this article, we (a) review limitations of early warning signals based on critical slowing down to better understand when they can and cannot occur, and (b) study the conditions under which early warning signals may anticipate critical transitions in online-monitoring settings by simulating from a bistable dynamical system, varying crucial features such as sampling frequency, noise intensity, and speed of approaching the tipping point. We find that, in sharp contrast to their reputation of being generic or model-agnostic, whether early warning signals occur or not strongly depends on the specifics of the system. We also find that they are very sensitive to noise, potentially limiting their utility in practical applications. We discuss the implications of our findings and provide suggestions and recommendations for future research. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The Potential for Alternative Stable States in Food Webs Depends on Feedback Mechanism and Trait Diversity.

AbstractAlternative stable ecosystem states are possible under the same environmental conditions in models of two or three interacting species and an array of feedback loops. However, multispecies food webs might weaken the feedbacks loops that can create alternative stable states. To test how this potential depends on food web properties, we develop a many-species model where consumer Allee effects emerge from consumer-resource interactions. We evaluate the interactive effects of food web connectance, interspecific trait diversity, and two classes of feedbacks: specialized feedbacks, where consumption of individual resources declines at high resource abundance (e.g., from schooling or reaching size refugia), and aggregate feedbacks, where overall resource abundance reduces consumer recruitment (e.g., from resources enhancing competition or mortality experienced by recruits). We find that aggregate feedbacks maintain, and specialized feedbacks reduce, the potential for alternative states. Interspecific trait diversity decreases the prevalence of alternative stable states more for specialized than for aggregate feedbacks. Increasing food web connectance increases the potential for alternative stable states for aggregated feedbacks but decreases it for specialized feedbacks, where losing vulnerable consumers can cascade into food web collapses. Altogether, multispecies food webs can limit the set of processes that create alternative stable states and impede consumer recovery from disturbance.

The Drape: a new way to characterize ecosystem states, dynamics, and tipping points from process-based models

There are many ways to study ecosystem dynamics, all having several issues. Main limitations of differential equation systems are the necessarily small number of interactions between few variables used, and parameter values to be set before the system dynamics can be studied. Main drawbacks of large-scale snapshot observation datasets to build a stability landscape are assuming that the most represented conditions are the most stable states, and using the computed landscape to directly study the system’s dynamics. To remedy these aforementioned shortcomings and study complex systems based on the processes that characterize them without having to limit the number of variables, neither set parameter values, nor to use observations serving both model buildup and system’s dynamics analysis, we propose a geometric model as an additional and novel aid to study ecosystem dynamics. The Drape is a generic multi-dimensional analysis, derived from process-based model datasets that include disturbances. We illustrate the methodology to apply our concept on a continental-scale system and by using a mechanistic vegetation model to obtain values of state variables. The model integrates long-term dynamics in ecosystem components beyond the theoretical stability and potential landscape representations currently published. Our approach also differs from others that use resolution of differential equation systems. We used Africa as example, representing it as a grid of 9395 pixels. We simulated each pixel to build the ecosystem domain and then to transform it into the Drape – the mean response surface. Then, we applied a textural analysis to this surface to discriminate stable states (flat regions) from unstable states (gradient or crest regions), which likely represent tipping points. Projecting observed data onto the Drape surface allows testing ecological hypotheses, such as illustrated here with the savanna-forest alternative stable states, that are still today debated topics, mainly due to methods and data used. The Drape provides new insights on all ecosystem types and states, identifying likely tipping points (represented as narrow ridges versus stable states across flat regions), and allowing projection and analysis of multiple ecosystem types whose state variables are based on the same three variables.