Ecosystem Behavior Research Articles

A BLUEPRINT FOR ELEMENTARY REPRESENTATIVE WATERSHED SPECIFICATION

Provision of ecosystem services is necessary for our quality of life. In this vein, itis critical to develop a baseline to monitor the ecosystem behavior usingmonitoring, mapping, and modeling indicators of landscape condition. Therepresentative watersheds (RWs) can therefore be considered as such decisionblueprint to implement the best management practices to conserve andconsequently improve ecosystem services. There are few researches for theselection of RWs. However, the comprehensive and of course applicablemethodologies still are lacked particularly in developing countries whereconcentration and proper directing of conservation measures are further neededowing to investments constraints. Therefore, in the present study, an intensivewatershed selection process was undertaken to identify RW across the Gharesoo-Gorgan River Basin (ca. 12987 km2), Golestan Province, Iran. This study aimed toadopt the Laize’s approach in Gharesoo-Gorgan Watershed for identifying therepresentative sub-watershed. Towards this, four GIS-based layers of elevation,slope, rainfall erosivity and land use were selected for sub-watershedscharacterization. The representative watershed index (RWI) was then calculatedand mapped using MATLAB 2016 and ArcGIS 10.3 softwares, respectively. TheRWI was calculated pixel wise for all nine individual sub-watersheds and the entirewatershed as reference area with the help of matrix combinations of four studylayers. Ultimately, RWIs obtained from 21.3 to 62.6 with mean of 44.94±14.49 andcoefficient of variation of 32.25% were used for sub-watershed prioritization.Accordingly, the sub-watershed 8 in north east with RWI of 56.8 was proposed asthe final RW for the whole Gharesoo-Gorgan Watershed. The results of the study ishelpful to be used by authorities for launching monitoring systems in the RW tocollect behavioral indicators leading to designation of reasonable ecoenvironmentalrestoration strategies.

Biophysical effects on soil crack morphology in a faunally active dryland vertisol

Faunal behavior in dryland ecosystems may physically influence swelling soil hydrologic and pedologic processes due to its contributions to soil crack formation. In order to provide a physical link between this faunal activity and pedological processes, we use a resin visualization technique and X-ray imaging to characterize the biomechanical influences of biocompaction (mega/meso-herbivores) and bioturbation (termites) on 3D crack morphology and topology in a faunally active dryland vertisol system. Results show increased soil cracking intensity due to faunal influence. However, this increased cracking diverged by faunal influence: bioturbation creates “surficial” (shallow, extensive) crack networks while biocompaction creates “systematic” (deep, narrow) crack networks, compared to a reference soil. Biocompacted soils also exhibit a memory of past wetting and drying events via vertically layered crack morphologies. Despite differences in these crack magnitudes between the faunal influences, crack structures show morphological and topological similarity as a topological network. These persistent differences in field crack systems may potentially create convectively-driven “hotspots” of enhanced water and carbon gas transport in dryland ecosystems as a result of crack formation, highlighting the importance of considering fracture behavior in both an ecological, atmospheric, and pedologic context.

How well do meteorological drought indices predict live fuel moisture content (LFMC)? An assessment for wildfire research and operations in Mediterranean ecosystems

Live Fuel Moisture Content (LFMC) is a critical variable affecting fire ignition, behavior and severity in many ecosystems. Although the use of meteorological drought indices as proxies for LFMC is a straightforward and widespread approach, it is largely unknown whether it can provide reliable estimates of LFMC, either for local or spatial applications. We address this issue by evaluating the capacity of drought indices to predict LFMC quantitative variations and critical values. LFMC observations used for reference were measured on six different Mediterranean shrub species for 15 years in 20 different sites in Southern France. Six drought indices were evaluated: the Duff Moisture Code (DMC) and Drought Code (DC) of the Canadian Forest Fire Weather Index System, the Keetch-Byram Drought Index (KBDI), the Nesterov Index (NI) and the Relative Water Content (RWC) of the soil derived from a forest water balance model for low (80 mm) and high (160 mm) field capacities. The species were classified in two groups according to their seasonal variability: high and low responding species. We found large differences in the capacity of drought indices to predict LFMC, with indices that simulate long-term drought dynamics (DC, RWC and KBDI) generally performing better than others (NI and DMC). Once calibrated at stand scale, drought indices showed a good potential for predicting LFMC of high responding species, although large variations between sites were observed. In contrast, spatial predictability was limited with a RMSE and R2 on the order of 20% and 0.3, respectively (for high responding species). Our results suggest that drought indices should therefore be used with caution for spatial applications in wildfire research and operational fire management. Because they can explicitly consider environmental (soil, climate) and biological (species traits related to dehydration) factors, mechanistic indices have a great potential to improve LFMC predictions.

The application of resilience concepts in palaeoecology

The concept of resilience has become increasingly important in ecological and socio-ecological literature. With its focus on the temporal behaviour of ecosystems, palaeoecology has an important role to play in developing a scientific understanding of ecological resilience. We provide a critical review of the ways in which resilience is being addressed by palaeoecologists. We review ~180 papers, identifying the definitions or conceptualisations of ‘resilience’ that they use, and analysing the ways in which palaeoecology is contributing to our understanding of ecological resilience. We identify three key areas for further development. First, the term ‘resilience’ is frequently defined too broadly to be meaningful without further qualification. In particular, palaeoecologists need to distinguish between ‘press’ vs ‘pulse’ disturbances, and ‘ecological’ vs ‘engineering’ resilience. Palaeoecologists are well placed to critically assess the extent to which these dichotomies apply in real (rather than theoretical) ecosystems, where climate and other environmental parameters are constantly changing. Second, defining a formal ‘response model’ – a statement of the anticipated relationships between proxies, disturbances and resilience properties – can help to clarify arguments, especially inferred causal links, since the difficulty of proving causation is a fundamental limitation of palaeoecology for understanding ecosystem drivers and responses. Third, there is a need for critical analysis of the role of scale in ecosystem resilience. Different palaeoenvironmental proxies are differently able to address the various temporal and spatial scales of ecological change, and these limitations, as well as methodological constraints on inherently noisy proxy data, need to be explored and addressed.

From theory to experimental design-Quantifying a trait-based theory of predator-prey dynamics.

Successfully applying theoretical models to natural communities and predicting ecosystem behavior under changing conditions is the backbone of predictive ecology. However, the experiments required to test these models are dictated by practical constraints, and models are often opportunistically validated against data for which they were never intended. Alternatively, we can inform and improve experimental design by an in-depth pre-experimental analysis of the model, generating experiments better targeted at testing the validity of a theory. Here, we describe this process for a specific experiment. Starting from food web ecological theory, we formulate a model and design an experiment to optimally test the validity of the theory, supplementing traditional design considerations with model analysis. The experiment itself will be run and described in a separate paper. The theory we test is that trophic population dynamics are dictated by species traits, and we study this in a community of terrestrial arthropods. We depart from the Allometric Trophic Network (ATN) model and hypothesize that including habitat use, in addition to body mass, is necessary to better model trophic interactions. We therefore formulate new terms which account for micro-habitat use as well as intra- and interspecific interference in the ATN model. We design an experiment and an effective sampling regime to test this model and the underlying assumptions about the traits dominating trophic interactions. We arrive at a detailed sampling protocol to maximize information content in the empirical data obtained from the experiment and, relying on theoretical analysis of the proposed model, explore potential shortcomings of our design. Consequently, since this is a “pre-experimental” exercise aimed at improving the links between hypothesis formulation, model construction, experimental design and data collection, we hasten to publish our findings before analyzing data from the actual experiment, thus setting the stage for strong inference.

Impact of Corn Earworm (Lepidoptera: Noctuidae) on Field Corn (Poales: Poaceae) Yield and Grain Quality.

Corn earworm, Helicoverpa zea (Boddie), commonly infests field corn, Zea mays (L.). The combination of corn plant biology, corn earworm behavior in corn ecosystems, and field corn value renders corn earworm management with foliar insecticides noneconomical. Corn technologies containing Bacillus thuringiensis (Bt) Berliner (Bacillales: Bacillaceae) were introduced that exhibit substantial efficacy against corn earworm and may reduce mycotoxin contamination in grain. The first generation Bt traits in field corn demonstrated limited activity on corn earworm feeding on grain. The pyramided corn technologies have greater cumulative protein concentrations and higher expression throughout the plant, so these corn traits should provide effective management of this pest. Additionally, reduced kernel injury may affect physical grain quality. Experiments were conducted during 2011-2012 to investigate corn earworm impact on field corn yield and grain quality. Treatments included field corn hybrids expressing the Herculex, YieldGard, and Genuity VT Triple Pro technologies. Supplemental insecticide treatments were applied every 1-2 d from silk emergence until silk senescence to create a range of injured kernels for each technology. No significant relationship between the number of corn earworm damaged kernels and yield was observed for any technology/hybrid. In these studies, corn earworm larvae did not cause enough damage to impact yield. Additionally, no consistent relationship between corn earworm damage and aflatoxin contamination was observed. Based on these data, the economic value of pyramided Bt corn traits to corn producers, in the southern United States, appears to be from management of other lepidopteran insect pests including European and southwestern corn borer.

From Petri Dishes to Model Ecosystems.

Model ecosystems could provide significant insight into the evolution and behavior of real ecosystems. We discuss the advantages and limitations of common approaches like mesocosms. In this context, we highlight recent breakthroughs that allow for the creation of networks of organisms with independently controlled environments and rates of chemical exchange.

Implications of tristability in pattern-forming ecosystems.

Many ecosystems show both self-organized spatial patterns and multistability of possible states. The combination of these two phenomena in different forms has a significant impact on the behavior of ecosystems in changing environments. One notable case is connected to tristability of two distinct uniform states together with patterned states, which has recently been found in model studies of dryland ecosystems. Using a simple model, we determine the extent of tristability in parameter space, explore its effects on the system dynamics, and consider its implications for state transitions or regime shifts. We analyze the bifurcation structure of model solutions that describe uniform states, periodic patterns, and hybrid states between the former two. We map out the parameter space where these states exist, and note how the different states interact with each other. We further focus on two special implications with ecological significance, breakdown of the snaking range and complex fronts. We find that the organization of the hybrid states within a homoclinic snaking structure breaks down as it meets a Maxwell point where simple fronts are stationary. We also discover a new series of complex fronts between the uniform states, each with its own velocity. We conclude with a brief discussion of the significance of these findings for the dynamics of regime shifts and their potential control.

The One Health Concept: 10 Years Old and a Long Road Ahead.

Over the past decade, a significant increase in the circulation of infectious agents was observed. With the spread and emergence of epizootics, zoonoses, and epidemics, the risks of pandemics became more and more critical. Human and animal health has also been threatened by antimicrobial resistance, environmental pollution, and the development of multifactorial and chronic diseases. This highlighted the increasing globalization of health risks and the importance of the human–animal–ecosystem interface in the evolution and emergence of pathogens. A better knowledge of causes and consequences of certain human activities, lifestyles, and behaviors in ecosystems is crucial for a rigorous interpretation of disease dynamics and to drive public policies. As a global good, health security must be understood on a global scale and from a global and crosscutting perspective, integrating human health, animal health, plant health, ecosystems health, and biodiversity. In this study, we discuss how crucial it is to consider ecological, evolutionary, and environmental sciences in understanding the emergence and re-emergence of infectious diseases and in facing the challenges of antimicrobial resistance. We also discuss the application of the “One Health” concept to non-communicable chronic diseases linked to exposure to multiple stresses, including toxic stress, and new lifestyles. Finally, we draw up a list of barriers that need removing and the ambitions that we must nurture for the effective application of the “One Health” concept. We conclude that the success of this One Health concept now requires breaking down the interdisciplinary barriers that still separate human and veterinary medicine from ecological, evolutionary, and environmental sciences. The development of integrative approaches should be promoted by linking the study of factors underlying stress responses to their consequences on ecosystem functioning and evolution. This knowledge is required for the development of novel control strategies inspired by environmental mechanisms leading to desired equilibrium and dynamics in healthy ecosystems and must provide in the near future a framework for more integrated operational initiatives.

Contrasting terrestrial carbon cycle responses to the 1997/98 and 2015/16 extreme El Niño events

Abstract. Large interannual atmospheric CO2 variability is dominated by the response of the terrestrial biosphere to El Niño–Southern Oscillation (ENSO). However, the behavior of terrestrial ecosystems differs during different El Niños in terms of patterns and biological processes. Here, we comprehensively compare two extreme El Niños (2015/16 and 1997/98) in the context of a multi-event “composite” El Niño. We find large differences in the terrestrial carbon cycle responses, even though the two events were of similar magnitude. More specifically, we find that the global-scale land–atmosphere carbon flux (FTA) anomaly during the 1997/98 El Niño was 1.64 Pg C yr−1, but half that quantity during the 2015/16 El Niño (at 0.73 Pg C yr−1). Moreover, FTA showed no obvious lagged response during the 2015/16 El Niño, in contrast to that during 1997/98. Separating the global flux by geographical regions, we find that the fluxes in the tropics and extratropical Northern Hemisphere were 1.70 and −0.05 Pg C yr−1 during 1997/98, respectively. During 2015/16, they were 1.12 and −0.52 Pg C yr−1, respectively. Analysis of the mechanism shows that, in the tropics, the widespread drier and warmer conditions caused a decrease in gross primary productivity (GPP; −0.73 Pg C yr−1) and an increase in terrestrial ecosystem respiration (TER; 0.62 Pg C yr−1) during the 1997/98 El Niño. In contrast, anomalously wet conditions occurred in the Sahel and East Africa during 2015/16, which caused an increase in GPP, compensating for its reduction in other tropical regions. As a result, the total 2015/16 tropical GPP and TER anomalies were −0.03 and 0.95 Pg C yr−1. GPP dominance during 1997/98 and TER dominance during 2015/16 accounted for the phase difference in their FTA. In the extratropical Northern Hemisphere, the large difference occurred because temperatures over Eurasia were warmer during the 2015/16, as compared with the cooling seen during the 1997/98 and the composite El Niño. These warmer conditions enhanced GPP and TER over Eurasia during the 2015/16 El Niño, while these fluxes were suppressed during 1997/98. The total extratropical Northern Hemisphere GPP and TER anomalies were 0.63 and 0.55 Pg C yr−1 during1997/98, and 1.90 and 1.45 Pg C yr−1 during 2015/16, respectively. Additionally, wildfires played a less important role during the 2015/16 than during the 1997/98 El Niño.

Improving Silvofishery Management Through Seedling Growth – Environment Quality Dynamic Relation Analysis

<p>Mangrove plants are sensitive to environment condition. This research aimed to analyze the linkages of mangrove growth and environment dynamics and to estimate the growth of mangrove along with the environment dynamics. The research was conducted through the field experiment by the plantation of A. marina in silvofishery pond canals. Data collection was conducted for 18 months with 3 months observation interval. The environment variables observed including temperature, salinity, turbidity, pH, dissolved oxygen, TSS, sediment organic matter, nitrogen and phosphorus, and the growth of mangrove seedling. Analysis was conducted through regression and modelling with Powersim software. The result showed that the height growth was affected by dissolved oxygen, temperature, salinity, turbidity and pH, while the diameter growth was affected by TSS concentration. Inversely, the growth of mangrove also had a significant effect on temperature, change of organic matter and nutrient sediment concentration. Simulation showed that the height and diameter growth rates of A. marina seedling were dynamically changed among periods. Simulated seedling growth for one year forecast resulted in the rate of 0.115024 to 0.282294 cm/day for height and 0.001287 to 0.006031 cm/day for diameter. The simulation also indicated the continuous accumulation of organic matter and nitrogen over time. This research concluded that under limited environment dynamic, the growth of mangrove could be estimated. This model is a novelty in ecological studies. This research might initiates the more advanced ecological studies. Systematic estimation of ecosystem behaviour could be applied to formulate the best management practices, particularly in the silvofishery activities.</p>

Ecological surprise: concept, synthesis, and social dimensions

AbstractAs the extent and intensity of human impacts on ecosystems increase and the capacity of ecosystems to absorb these impacts dwindles, unanticipated behavior in ecological systems—or surprises—is likely to become more common. The concept of ecological surprise is broadly applied but seldom explicitly developed in ecological literature, and ecologists can employ diverging language, frameworks, and interpretations of surprise. Here, we synthesize what ecological surprise has meant to ecologists studying these events and review the development and use of the concept in ecology. We define ecological surprise as a situation where human expectations or predictions of natural system behavior deviate from observed ecosystem behavior. This can occur when people (1) fail to anticipate change in ecosystems; (2) fail to influence ecosystem behavior as intended; or (3) discover something about an ecosystem that runs counter to accepted knowledge. We develop a conceptual model that captures the interactions between social and ecological processes that lead to these events and examine two types of drivers that contribute to surprise: underlying driving forces and proximate causes. Our definition of ecological surprise inherently acknowledges that, to be surprising, there must be human observers to the ecological occurrence who have expectations about ecosystem behavior. To explore this dimension, we draw on social science perspectives to understand the ways in which human expectations of ecosystems are influenced by social networks, heuristics, and mental models. We use a case study to demonstrate how our integrated conceptualization of ecological surprise provides a systematic way of examining these events. Our integration of these perspectives enables us to better synthesize social and ecological knowledge of these events, and encourages ecologists to critically reflect on how they, as scientists, formulate and reformulate expectations of ecosystem behavior.

Black Carbon (Biochar) In Water/Soil Environments: Molecular Structure, Sorption, Stability, and Potential Risk.

Black carbon (BC) is ubiquitous in the environments and participates in various biogeochemical processes. Both positive and negative effects of BC (especially biochar) on the ecosystem have been identified, which are mainly derived from its diverse physicochemical properties. Nevertheless, few studies systematically examined the linkage between the evolution of BC molecular structure with the resulted BC properties, environmental functions as well as potential risk, which is critical for understanding the BC environmental behavior and utilization as a multifunctional product. Thus, this review highlights the molecular structure evolution of BC during pyrolysis and the impact of BC physicochemical properties on its sorption behavior, stability, and potential risk in terrestrial and aqueous ecosystems. Given the wide application of BC and its important role in biogeochemical processes, future research should focus on the following: (1) establishing methodology to more precisely predict and design BC properties on the basis of pyrolysis and phase transformation of biomass; (2) developing an assessment system to evaluate the long-term effect of BC on stabilization and bioavailability of contaminants, agrochemicals, and nutrient elements in soils; and (3) elucidating the interaction mechanisms of BC with plant roots, microorganisms, and soil components.

BIAM: a new bio-inspired analysis methodology for digital ecosystems based on a scale-free architecture

Today we live in a world of digital objects and digital technology; industry and humanities as well as technologies are truly in the midst of a digital environment driven by ICT and cyber informatics. A digital ecosystem can be defined as a digital environment populated by interacting and competing digital species. Digital species have autonomous, proactive and adaptive behaviors, regulated by peer-to-peer interactions without central control point. An interconnecting architecture with few highly connected nodes (hubs) and many low connected nodes has a scale- free architecture. A new bio-inspired analysis methodology (BIAM) environment, an investigation strategy for information flow, fault and error tolerance detection in digital ecosystems based on a scale-free architecture is presented in this paper. In order to extract the information about modules and digital species role, the analysis methodology, inspired by metabolic network working, implements a set of three interacting techniques, i.e., topological analysis, flux balance analysis and extreme pathway analysis. Highly connected nodes, intermodule connectors and ultra-peripheral nodes can be identified by evaluating their impact on digital ecosystems behavior and addressing their strengthen, fault tolerance and protection countermeasures. Two real case studies of ecosystems have been analyzed in order to test the functionalities of the proposed (BIAM) environment and the goodness of this approach.

Dynamic response of NDVI to soil moisture variations during different hydrological regimes in the Sahel region

ABSTRACTOver the last few decades, the African Sahel has become the focus of many studies regarding vegetation dynamics and their relationships with climate and people. This is because rainfall limits the production of biomass in the region, a resource on which people are directly dependent for their livelihoods. In this study, we utilized a remote-sensing approach to answering the following two questions: (1) how does the dynamic relationship between soil moisture and plant growth vary across hydrological regimes, and (2) are vegetation-type-dependent responses to soil moisture availability detectable from satellite imagery? In order to answer these questions, we studied the relationship between monthly modelled soil moisture as an indicator for water availability and the remotely sensed normalized difference vegetation index (NDVI) as a proxy for vegetation growth between a “recovery rainfall period” (1982 to 1997) and a “stable rainfall period” (1998 to 2013), at different time lags across the Sahel region. Using windowed cross-correlation, we find a strong significant positive relationship between NDVI and soil moisture at a concurrent time and at NDVI lagging behind soil moisture by 1 month for grassland, cropland, and deciduous shrubland vegetation – the dominant vegetation classes in the Sahel. South of the Sahel (the Sudanian and Guinean areas), we find longer optimal lags (soil moisture lagged by 1–3 months) in association with mixed forest and deciduous shrubland. We find no major significant change in optimal lag between the recovery and stable periods in the Sahelian region; however, in the Sudanian and Guinean areas, we observe a trend towards shorter time lags. This change in optimal lag suggests a vegetation change, which may be a response to a climatic shift or land-use change. This approach of identifying spatiotemporal trends in optimal lag correlations between modelled soil moisture and NDVI could prove to be a useful tool for mapping vegetation change and ecosystem behaviour, in turn helping inform climate change mitigation approaches and agricultural planning.

Enantioselective bioaccumulation following exposure of adult zebrafish (Danio rerio) to epoxiconazole and its effects on metabolomic profile as well as genes expression

Although epoxiconazole is the worldwidely used fungicide, limited information is known about its toxic effects and bioaccumulation behavior in freshwater ecosystems. In this study, zebrafish were exposed to epoxiconazole at concentrations of 100 and 1000 μg L−1 for 21 d. 1H NMR-based metabolomics analysis showed that low- and high-dose epoxiconazole exposure resulted in two similar but not identical patterns for the change of endogenous metabolites related to energy, lipid and amino acid metabolism. The expression of genes associated with mitochondrial respiratory chain, ATP synthesis and fatty acid β-oxidation were further measured to explore the reason for the disturbed energy metabolism, finding epoxiconazole had an inhibition effect on the genes expression of the above ways. Significant enantioselectivity was observed with (+)-epoxiconazole enrichment in the bioaccumulation process. These results will be of great importance in understanding the toxic effects induced by epoxiconazole and provide important basis for its comprehensive environmental assessment.

Secular change and inter-annual variability of the Gulf Stream position, 1993–2013, 70°−55°W

The Gulf Stream (GS) is the northeastward-flowing surface limb of the Atlantic Ocean's meridional overturning circulation (AMOC) “conveyer belt” that flows towards Europe and the Nordic Seas. Changes in the GS position after its separation from the coast at Cape Hatteras, i.e., from 75°W to 50°W, may be key to understanding the AMOC, sea level variability and ecosystem behavior along the east coast of North America. In this study we compare secular change and inter-annual variability (IAV) of the Gulf Stream North Wall (GSNW) position with equator-ward Labrador Current (LC) transport along the southwestern Grand Banks near 52°W using 21 years (1993–2013) of satellite altimeter data. Results at 55°, 60°, and 65°W show a significant southward (negative) secular trend for the GSNW, decreasing to a small but insignificant southward trend at 70°W. IAV of de-trended GSNW position residuals also decreases to the west. The long-term secular trend of annual mean upper layer (200m) LC transport near 52°W is positive. Furthermore, IAV of LC transport residuals near 52°W along the southwestern Grand Banks are significantly correlated with GSNW position residuals at 55°W at a lag of +1-year, with positive (negative) LC transport residuals corresponding to southward (northward) GSNW positions one year later. The Taylor-Stephens index (TSI) computed from the first principal component of the GSNW position from 79° to 65°W shows a similar relationship with a more distal LC index computed along altimeter ground track 250 located north of the Grand Banks across Hamilton Bank in the western Labrador Sea. Increased (decreased) sea height differences along ground track 250 are significantly correlated with a more southward (northward) TSI two years later (lag of +2-years). Spectral analysis of IAV reveals corresponding spectral peaks at 5–7 years and 2–3 years for the North Atlantic Oscillation (NAO), GSNW (70°−55°W) and LC transport near 52°W for the 1993–2013 period suggesting a connection between these phenomena. An upper-layer (200m) slope water volume calculation using the LC IAV rms residual of +1.04Sv near 52°W results in an estimated GSNW IAV residual of 79km, or 63% of the observed 125.6km (1.13°) rms value at 55°W. A similar upper-layer slope water volume calculation using the positive long-term, upper-layer LC transport trend accounts for 68% of the mean observed secular southward shift of the GSNW between 55° and 70°W over the 1993–2013 period. Our work provides additional observational evidence of important interactions between the upper layers of the sub-polar and sub-tropical gyres within the North Atlantic over both secular and inter-annual time scales as suggested by previous studies.

Large ecosystems in transition: Bifurcations and mass extinction

We propose a model of multispecies populations surviving on distributed resources. System dynamics are investigated under changes in abiotic factors such as the climate, as parameterized through environmental temperature. In particular, we introduce a feedback between species abundances and resources via abiotic factors. This model is apparently the first of its kind to include a feedback mechanism coupling climate and population dynamics. Moreover, we take into account self-limitation effects. The model explains the coexistence of many species, yet also displays the possibility of catastrophic bifurcations, where all species become extinct under the influence of abiotic factors. We show that as these factors change there are different regimes of ecosystem behavior, including a possibly chaotic regime when abiotic influences are sufficiently strong.

Alternative stable states in coastal intertidal wetland ecosystems of Yangtze estuary, China

Alternative stable states phenomenon widely exists in a variety of ecosystems and is closely related to ecosystem health and sustainable development. Although alternative stable states research has become the focus and hotspot of the ecology researches, only a few empirical evidences supported its behavior and mechanisms in coastal wetland ecosystems up to now. In our study, ta-king the intertidal wetland ecosystem in Chongming Dongtan Nature Reserve as study area, we aimed to: 1) test the existence of alternative stable states based on judgment conditions (bimodal characteristic and threshold effect) and determine the relative stable state types; 2) explore the formation mechanisms of alternative stable states by monitoring hydrological conditions, sediment accretion dynamics as well as vegetation growth parameters and analyzing the positive feedbacks between saltmarsh vegetation and sedimentary geomorphology. Our results showed that: 1) Normalized difference vegetation index (NDVI) frequentness distribution revealed obvious bimodality at saltmarsh pioneer zone. Propagule biomass threshold limited the establishment of plant patches representing the "saltmarsh" state. The presence of bimodality and biomass threshold demonstrated there are "mudflat" stable state and "saltmarsh" stable state with distinct structure and function in intertidal wetland ecosystem. 2) Current velocities, turbidities and direction perpendicular to the vegetation zone were the most important factors responsible for the sediments rapid accretion at saltmarsh pioneer zone in spring and summer. Sediments accretion significantly promoted the growth of saltmarsh plant. The positive feedbacks between plant growth and sediments accretion resulted in the formation of alternative stable states. 3) The expansion pattern of saltmarshes in the Chongming Dongtan intertidal wetland ecosystem also suggested that increases of sediments accretion could trigger the formation of "mudflat" stable state and "saltmarsh" stable state on landscape scale. The results from this study could enrich regime shift mechanisms researches and provide the scientific supports for coastal zone protection, restoration and comprehensive management, which could have important theoretical and practical meaning.

Spatial analogies pervade complex relational reasoning: Evidence from spontaneous gestures.

How do people think about complex phenomena like the behavior of ecosystems? Here we hypothesize that people reason about such relational systems in part by creating spatial analogies, and we explore this possibility by examining spontaneous gestures. In two studies, participants read a written lesson describing positive and negative feedback systems and then explained the differences between them. Though the lesson was highly abstract and people were not instructed to gesture, people produced spatial gestures in abundance during their explanations. These gestures used space to represent simple abstract relations (e.g., increase) and sometimes more complex relational structures (e.g., negative feedback). Moreover, over the course of their explanations, participants’ gestures often cohered into larger analogical models of relational structure. Importantly, the spatial ideas evident in the hands were largely unaccompanied by spatial words. Gesture thus suggests that spatial analogies are pervasive in complex relational reasoning, even when language does not.