scholarly journals Exploiting delayed transitions to sustain semiarid ecosystems after catastrophic shifts

2018 ◽  
Vol 15 (143) ◽  
pp. 20180083 ◽  
Author(s):  
Blai Vidiella ◽  
Josep Sardanyés ◽  
Ricard Solé
Keyword(s):  
Human Population ◽  
Theoretical Models ◽  
Shift Condition ◽  
Critical Rate ◽  
Semiarid Ecosystems ◽  
Intervention Method ◽  
Stochastic Fluctuations ◽  
Catastrophic Shift ◽  
Desert Areas ◽  
Catastrophic Shifts

Semiarid ecosystems (including arid, semiarid and dry-subhumid ecosystems) span more than 40% of extant habitats and contain a similar percentage of the human population. Theoretical models and palaeoclimatic data predict a grim future, with rapid shifts towards a desert state, with accelerated diversity losses and ecological collapses. These shifts are a consequence of the special nonlinearities resulting from ecological facilitation. Here, we investigate a simple model of semiarid ecosystems identifying the so-called ghost, which appears after a catastrophic transition from a vegetated to a desert state once a critical rate of soil degradation is overcome. The ghost involves a slowdown of transients towards the desert state, making the ecosystem seem stable even though vegetation extinction is inevitable. We use this model to show how to exploit the ecological ghosts to avoid collapse. Doing so involves the restoration of small fractions of desert areas with vegetation capable of maintaining a stable community once the catastrophic shift condition has been achieved. This intervention method is successfully tested under the presence of demographic stochastic fluctuations.

scholarly journals Exploiting delayed transitions to sustain semiarid ecosystems after catastrophic shifts

2017 ◽  
Author(s):  
Blai Vidiella, ◽  
Josep Sardanyés ◽  
Ricard V. Solé
Keyword(s):  
Computational Models ◽  
Warning Signal ◽  
Semiarid Ecosystems ◽  
Intervention Method ◽  
Catastrophic Shift ◽  
Future Potential ◽  
Desert Areas ◽  
Standard Models ◽  
Potential Shifts ◽  
Catastrophic Shifts

Semiarid ecosystems (including arid, semiarid and dry-subhumid ecosystems) span more than 40% of extant habitats and a similar percentage of human population. As a consequence of global warming, these habitats face future potential shifts towards the desert state characterized by an accelerated loss of diversity and stability leading to collapse. Such possibility has been raised by several mathematical and computational models, along with several early warning signal methods applied to spatial vegetation patterns. Here we show that just after a catastrophic shift has taken place an expected feature is the presence of a ghost, i.e., a delayed extinction associated to the underlying dynamical flows. As a consequence, a system might exhibit for very long times an apparent stationarity hiding in fact an inevitable collapse. Here we explore this problem showing that the ecological ghost is a generic feature of standard models of green-desert transitions including facilitation. If present, the ghost could hide warning signals, since statistical patterns are not be expected to display growing fluctuations over time. We propose and computationally test a novel intervention method based on the restoration of small fractions of desert areas with vegetation as a way to maintain the fragile ecosystem beyond the catastrophic shift caused by a saddle-node bifurcation, taking advantage of the delaying capacity of the ghost just after the bifurcation.

scholarly journals Trans-heteroclinic bifurcation: a novel type of catastrophic shift

2018 ◽  
Vol 5 (1) ◽  
pp. 171304 ◽  
Author(s):  
Josep Sardanyés ◽  
Regina Martínez ◽  
Carles Simó
Keyword(s):  
Steady State ◽  
Dynamical Systems ◽  
Fixed Points ◽  
Social Systems ◽  
Continuous Change ◽  
Heteroclinic Bifurcation ◽  
Mutation Matrix ◽  
Catastrophic Shift ◽  
Smooth Transitions ◽  
Catastrophic Shifts

Global and local bifurcations are extremely important since they govern the transitions between different qualitative regimes in dynamical systems. These transitions or tipping points, which are ubiquitous in nature, can be smooth or catastrophic. Smooth transitions involve a continuous change in the steady state of the system until the bifurcation value is crossed, giving place to a second-order phase transition. Catastrophic transitions involve a discontinuity of the steady state at the bifurcation value, giving place to first-order phase transitions. Examples of catastrophic shifts can be found in ecosystems, climate, economic or social systems. Here we report a new type of global bifurcation responsible for a catastrophic shift. This bifurcation, identified in a family of quasi-species equations and named as trans-heteroclinic bifurcation , involves an exchange of stability between two distant and heteroclinically connected fixed points. Since the two fixed points interchange the stability without colliding, a catastrophic shift takes place. We provide an exhaustive description of this new bifurcation, also detailing the structure of the replication–mutation matrix of the quasi-species equation giving place to this bifurcation. A perturbation analysis is provided around the bifurcation value. At this value the heteroclinic connection is replaced by a line of fixed points in the quasi-species model. But it is shown that, if the replication–mutation matrix satisfies suitable conditions, then, under a small perturbation, the exchange of heteroclinic connections is preserved, except on a tiny range around the bifurcation value whose size is of the order of magnitude of the perturbation. The results presented here can help to understand better novel mechanisms behind catastrophic shifts and contribute to a finer identification of such transitions in theoretical models in evolutionary biology and other dynamical systems.

Dietary Change and Human Population at Indian Creek, Antigua

1985 ◽  
Vol 50 (3) ◽  
pp. 518-536 ◽  
Author(s):  
Alick R. Jones
Keyword(s):  
Human Population ◽  
Theoretical Models ◽  
Dietary Change ◽  
Bivalve Mollusks ◽  
Resource Exploitation ◽  
Faunal Remains ◽  
Single Model ◽  
Animal Food ◽  
Indian Creek ◽  
Food Consumed

The midden at Indian Creek, Antigua, is very probably a nearly complete record of the animal food consumed by the inhabitants over about 1,100 years of occupation. During that time the resource exploitation pattern changed in a number of major and minor ways. The most obvious change, when crab gave way to bivalve mollusks as an important dietary element, has been examined in some detail and the possible causes for the change discussed. Although the data presented here could be used for a variety of theoretical models it seems likely that no single model is sufficient to explain all the changes. The faunal remains obtained from the excavation have been used to calculate the amount of protein represented and this in turn used to calculate the approximate mean human population over the period of occupation. The figure obtained is between 21-53 depending upon the criteria adopted. The possible sources of error in the calculations are identified and discussed.

scholarly journals Synthetic soil crusts against green-desert transitions: a spatial model

2019 ◽  
Author(s):  
Blai Vidiella ◽  
Josep Sardanyés ◽  
Ricard V. Solé
Keyword(s):  
Spatial Model ◽  
Soil Degradation ◽  
Mean Field ◽  
Nonlinear Effects ◽  
Mean Field Model ◽  
Dispersal Capacity ◽  
Semiarid Ecosystems ◽  
Current Trends ◽  
Degradation Rates ◽  
Catastrophic Shifts

Semiarid ecosystems are threatened by global warming due to longer dehydration times and increasing soil degradation. Mounting evidences indicate that, given the current trends, drylands are likely to expand and possibly experience catastrophic shifts from vegetated to desert states. Here we explore a recent suggestion based on the concept of ecosystem terraformation, where a synthetic organism is used to counterbalance some of the nonlinear effects causing the presence of such tipping points. Using an explicit spatial model incorporating facilitation and considering a simplification of states found in semiarid ecosystems i.e., vegetation, fertile and desert soil, we investigate how engineered microorganisms can shape the fate of these ecosystems. Specifically, two different, but complementary, terraformation strategies are proposed: Cooperation-based: C-terraformation; and Dispersion-based: D-terraformation. The first strategy involves the use of soil synthetic microorganisms to introduce cooperative loops (facilitation) with the vegetation. The second one involves the introduction of engineered microorganisms improving their dispersal capacity, thus facilitating the transition from desert to fertile soil. We show that small modifications enhancing cooperative loops can effectively change the location of the critical transition found at increasing soil degradation rates, also identifying a stronger protection against soil degradation by using the D-terraformation strategy. The same results are found in a mean field model providing insights into the transitions and dynamics tied to these terraformation strategies. The potential consequences and extensions of these models are discussed.

Multiple Stable States and Catastrophic Shifts in Ecosystems

Ecology ◽  
2019 ◽  
Author(s):  
Sonia Kéfi
Keyword(s):  
Alternative Stable States ◽  
Direct Consequence ◽  
Theoretical Models ◽  
Economic Consequences ◽  
Design Management ◽  
Stable States ◽  
Natural Systems ◽  
Restoration Strategies ◽  
Multiple Stable States ◽  
Catastrophic Shifts

The idea that ecosystems may have multiple alternative stable states dates back to the late 1960s–early 1970s, when ecologists realized that this type of behavior could arise in simple mathematical models. A direct consequence is that such ecosystems can suddenly switch (or “tip”) between their alternative stable states rather than gradually responding to changes. In other terms, in these ecosystems, a small environmental perturbation can cause large, discontinuous, and irreversible changes, referred to as catastrophic shifts. This idea has attracted increasing interest in the literature over the years, and has become even more relevant in the current context of global change. Examples of catastrophic shifts in ecosystems include the eutrophication of shallow lakes, the desertification of drylands, and the degradation of coral reefs. Theoretical models have investigated the conditions under which alternative stable states and catastrophic shifts occur. A well-recognized cause of alternative stable states is the presence of strong positive—or self-reinforcing—feedback processes that maintain each of the stable ecosystem states. Understanding the mechanisms underlying the emergence of alternative stable states can help design management as well as restoration strategies for ecosystems. Because catastrophic shifts can have dramatic ecological and economic consequences, approaches have been proposed to detect possible alternative stable states in natural systems, and indicators of approaching ecosystem transitions have been identified (so-called early warning signals of critical slowing down).

Discontinuities in Regional Development

1986 ◽  
Vol 4 (1) ◽  
pp. 71-84 ◽  
Author(s):  
M S Gertler
Keyword(s):  
Regional Development ◽  
Capital Flows ◽  
Catastrophe Theory ◽  
Capital Mobility ◽  
Investment Decisions ◽  
Scale Economies ◽  
Division Of Labour ◽  
Alternative Conception ◽  
Catastrophic Shift ◽  
Catastrophic Shifts

Historically, geographers have been keen to adopt bodies of theory from other disciplines in a somewhat uncritical manner. This practice has surfaced again in the recent attempts to apply notions from catastrophe theory to the study of regional development. This paper is an examination of one such application to the modeling of interregional capital flows and critically evaluates it from a number of perspectives. On empirical grounds, there is little evidence that ‘catastrophic’ shifts in the geography of US manufacturing capital have indeed occurred. The presumption of a catastrophic shift is shown to be based on poor empirical indicators of capital mobility or on an incomplete understanding of the process of interregional investment decisions. The paper offers an alternative conception of this process in which the Kaldorian principles of scale economies, specialization, and division of labour are shown to be in continuing operation, albeit now in a spatially discontinuous manner.

scholarly journals Synthetic soil crusts against green-desert transitions: a spatial model

2020 ◽  
Vol 7 (8) ◽  
pp. 200161
Author(s):  
Blai Vidiella ◽  
Josep Sardanyés ◽  
Ricard V. Solé
Keyword(s):  
Spatial Model ◽  
Soil Degradation ◽  
Mean Field ◽  
Nonlinear Effects ◽  
Mean Field Model ◽  
Dispersal Capacity ◽  
Semiarid Ecosystems ◽  
Current Trends ◽  
Degradation Rates ◽  
Catastrophic Shifts

Semiarid ecosystems are threatened by global warming due to longer dehydration times and increasing soil degradation. Mounting evidence indicates that, given the current trends, drylands are likely to expand and possibly experience catastrophic shifts from vegetated to desert states. Here, we explore a recent suggestion based on the concept of ecosystem terraformation, where a synthetic organism is used to counterbalance some of the nonlinear effects causing the presence of such tipping points. Using an explicit spatial model incorporating facilitation and considering a simplification of states found in semiarid ecosystems including vegetation, fertile and desert soil, we investigate how engineered microorganisms can shape the fate of these ecosystems. Specifically, two different, but complementary, terraformation strategies are proposed: Cooperation -based: C -terraformation; and Dispersion -based: D -terraformation. The first strategy involves the use of soil synthetic microorganisms to introduce cooperative loops (facilitation) with the vegetation. The second one involves the introduction of engineered microorganisms improving their dispersal capacity, thus facilitating the transition from desert to fertile soil. We show that small modifications enhancing cooperative loops can effectively modify the aridity level of the critical transition found at increasing soil degradation rates, also identifying a stronger protection against soil degradation by using the D -terraformation strategy. The same results are found in a mean-field model providing insights into the transitions and dynamics tied to these terraformation strategies. The potential consequences and extensions of these models are discussed.

Analytical Electron Microscopy of Surface-Modified Ceramics

1985 ◽  
Vol 43 ◽  
pp. 276-279
Author(s):  
P. S. Sklad
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Theoretical Models ◽  
Ceramic Materials ◽  
Solute Concentration ◽  
Second Phase ◽  
Analytical Electron ◽  
Implantation Techniques ◽  
Lattice Damage ◽  
Surface Modified

Over the past several years, it has become increasingly evident that materials for proposed advanced energy systems will be required to operate at high temperatures and in aggressive environments. These constraints make structural ceramics attractive materials for these systems. However it is well known that the condition of the specimen surface of ceramic materials is often critical in controlling properties such as fracture toughness, oxidation resistance, and wear resistance. Ion implantation techniques offer the potential of overcoming some of the surface related limitations.While the effects of implantation on surface sensitive properties may be measured indpendently, it is important to understand the microstructural evolution leading to these changes. Analytical electron microscopy provides a useful tool for characterizing the microstructures produced in terms of solute concentration profiles, second phase formation, lattice damage, crystallinity of the implanted layer, and annealing behavior. Such analyses allow correlations to be made with theoretical models, property measurements, and results of complimentary techniques.

On the Relationship Between General Auditory Sensitivity and Speech Perception: An Examination of Pitch and Lexical Tone Perception in 4- to 6-Year-Old Children

2020 ◽  
Vol 63 (2) ◽  
pp. 487-498
Author(s):  
Puisan Wong ◽  
Man Wai Cheng
Keyword(s):  
Speech Perception ◽  
Theoretical Models ◽  
Developmental Trajectory ◽  
Auditory Sensitivity ◽  
Pitch Discrimination ◽  
Lexical Tone ◽  
Perceptual Training ◽  
Lexical Tones ◽  
Tone Perception ◽  
Tone Discrimination

Purpose Theoretical models and substantial research have proposed that general auditory sensitivity is a developmental foundation for speech perception and language acquisition. Nonetheless, controversies exist about the effectiveness of general auditory training in improving speech and language skills. This research investigated the relationships among general auditory sensitivity, phonemic speech perception, and word-level speech perception via the examination of pitch and lexical tone perception in children. Method Forty-eight typically developing 4- to 6-year-old Cantonese-speaking children were tested on the discrimination of the pitch patterns of lexical tones in synthetic stimuli, discrimination of naturally produced lexical tones, and identification of lexical tone in familiar words. Results The findings revealed that accurate lexical tone discrimination and identification did not necessarily entail the accurate discrimination of nonlinguistic stimuli that followed the pitch levels and pitch shapes of lexical tones. Although pitch discrimination and tone discrimination abilities were strongly correlated, accuracy in pitch discrimination was lower than that in tone discrimination, and nonspeech pitch discrimination ability did not precede linguistic tone discrimination in the developmental trajectory. Conclusions Contradicting the theoretical models, the findings of this study suggest that general auditory sensitivity and speech perception may not be causally or hierarchically related. The finding that accuracy in pitch discrimination is lower than that in tone discrimination suggests that comparable nonlinguistic auditory perceptual ability may not be necessary for accurate speech perception and language learning. The results cast doubt on the use of nonlinguistic auditory perceptual training to improve children's speech, language, and literacy abilities.

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