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Prominent pathological hypotheses for schizophrenia include auditory processing deficits and dysconnectivity within cerebral networks. However, most neuroimaging studies have focused on impairments in either resting‐state or task‐related functional connectivity in patients with schizophrenia. The aims of our study were to examine (1) blood oxygen level‐dependent (BOLD) signals during auditory steady‐state response (ASSR) tasks, (2) functional connectivity during the resting‐state and ASSR tasks and (3) state shifts between the resting‐state and ASSR tasks in patients with schizophrenia. To reduce the functional consequences of scanner noise, we employed resting‐state and sparse sampling auditory fMRI paradigms in 25 schizophrenia patients and 25 healthy controls. Auditory stimuli were binaural click trains at frequencies of 20, 30, 40 and 80 Hz. Based on the detected ASSR‐evoked BOLD signals, we examined the functional connectivity between the thalamus and bilateral auditory cortex during both the resting state and ASSR task state, as well as their alterations. The schizophrenia group exhibited significantly diminished BOLD signals in the bilateral auditory cortex and thalamus during the 80 Hz ASSR task (corrected p < 0.05). We observed a significant inverse relationship between the resting state and ASSR task state in altered functional connectivity within the thalamo‐auditory network in schizophrenia patients. Specifically, our findings demonstrated stronger functional connectivity in the resting state (p < 0.004) and reduced functional connectivity during the ASSR task (p = 0.048), which was mediated by abnormal state shifts, within the schizophrenia group. These results highlight the presence of abnormal thalamocortical connectivity associated with deficits in the shift between resting and task states in patients with schizophrenia. [ABSTRACT FROM AUTHOR]

Eco-evolutionary feedback can result in periodic shifts with long intervals between alternative community states. Simulations using a food chain model with three trophic levels, namely the resource-prey–predator system, with evolution of an anti-predator trait possessed by the prey (prey trait) have shown long-term oscillations that ecological dynamics alone cannot attain. The alternative community states are characterized by stable states slowly changing with prey trait evolution and fast cycles at the lower two trophic levels. This shift of community dynamical states with large intervals was governed by the evolution of the prey trait. The abrupt state shifts between long and intermittent stationary periods were caused by the interaction between community ecological dynamics and trait evolution. We further examined the effects of genetic variation on the stability of the community. A faster evolutionary rate with larger genetic variance tended to stabilize eco-evolutionary dynamics. [ABSTRACT FROM AUTHOR]

Although only representing 0.05% of global freshwater, or 0.001% of all global water, soil water supports all terrestrial biological life. Soil moisture behaviour in most models is constrained by hydraulic parameters that do not change. Here we argue that biological feedbacks from plants, macro-fauna and the microbiome influence soil structure, and thus the soil hydraulic parameters and the soil water content signals we observe. Incorporating biological feedbacks into soil hydrological models is therefore important for understanding environmental change and its impacts on ecosystems. We anticipate that environmental change will accelerate and modify soil hydraulic function. Increasingly, we understand the vital role that soil moisture exerts on the carbon cycle and other environmental threats such as heatwaves, droughts and floods, wildfires, regional precipitation patterns, disease regulation and infrastructure stability, in addition to agricultural production. Biological feedbacks may result in changes to soil hydraulic function that could be irreversible, resulting in alternative stable states (ASS) of soil moisture. To explore this, we need models that consider all the major feedbacks between soil properties and soil-plant-faunal-microbial-atmospheric processes, which is something we currently do not have. Therefore, a new direction is required to incorporate a dynamic description of soil structure and hydraulic property evolution into soil-plant-atmosphere, or land surface, models that consider feedbacks from land use and climate drivers of change, so as to better model ecosystem dynamics.

Understanding ecosystem responses to compound disturbance regimes and the influence of specific sequences of events in determining ecosystem shifts remains a challenge. We use a modelling framework for Mediterranean-type ecosystems to assess the effects of fire–drought interactions on long-term vegetation dynamics and to identify disturbance-driven changes in trait composition (tree seeder vs. tree resprouter prevalence) and ecosystem state (forest vs. non-forest). Changes in tree seeder and the tree resprouter dominance show nonlinear, threshold-type trends over gradients of increasing compound disturbance frequency. Vegetation composition thresholds mostly occur in a narrow range of the compound fire–drought disturbance space. Additionally, trait compositional switches and the likelihood of sudden changes in ecosystem state are promoted by fire-drought interactions. Distinct sequences of disturbance events cause vegetation transitions, disrupting ecosystem resilience, even under moderate recurrence of individual disturbances. An extreme drought year followed by one or two large fire events promotes shifts from resprouter- to seeder dominance. Contrastingly, a large crown fire followed by an extreme drought promotes changes from seeder to resprouter dominance. This disturbance sequence is also a mechanism strong enough to trigger sudden shifts in ecosystem state (from forest to non-forest). Synthesis. Thresholds of change in vegetation composition occur over a narrow range of the modelled gradients of compound fire-drought recurrence, and the loss of ecosystem resilience is contingent on particular sequences of disturbance events. Overall, our findings highlight that disturbance interactions define the relative location of tipping points in ecosystem state, and that effects and feedbacks of compound disturbance regimes increase the long-term likelihood of sudden ecosystem shifts and, therefore, uncertainty in predicting vegetation state.

Abstract Ecological systems can exist under multiple stable states for a specific set of environmental conditions. Perturbations can shift ecosystems to alternative stable states, and these changes are difficult to reverse. This is a concept known as hysteresis. Current management methods for system recovery require considerable effort. A model for system recovery that requires small changes in a target community would be of high value for ecosystem restoration. In this study, we focused on rocky reefs that exhibit two alternative stable states: one dominated by macroalgae and another dominated by sea urchins and crustose coralline algae. Community recovery requires a state shift. To better understand the state shift, we simulated the ecosystem using a lattice model incorporating local interactions, rather than equations representing homogenized spaces. Using spatial information and simulating conditions in the target ecosystem, we concluded that a shift to an alternative stable state is possible by adjusting the spatial arrangement of the organisms. These results indicate that spatial arrangements are significant in systems exhibiting hysteresis and that the spatial manipulation of organisms may be useful for ecosystem management and restoration.

Ecological systems can exist under multiple stable states for a specific set of environmental conditions. Perturbations can shift ecosystems to alternative stable states, and these changes are difficult to reverse. This is a concept known as hysteresis. Current management methods for system recovery require considerable effort. A model for system recovery that requires small changes in a target community would be of high value for ecosystem restoration. In this study, we focused on rocky reefs that exhibit two alternative stable states: one dominated by macroalgae and another dominated by sea urchins and crustose coralline algae. Community recovery requires a state shift. To better understand the state shift, we simulated the ecosystem using a lattice model incorporating local interactions, rather than equations representing homogenized spaces. Using spatial information and simulating conditions in the target ecosystem, we concluded that a shift to an alternative stable state is possible by adjusting the spatial arrangement of the organisms. These results indicate that spatial arrangements are significant in systems exhibiting hysteresis and that the spatial manipulation of organisms may be useful for ecosystem management and restoration. [ABSTRACT FROM AUTHOR]

High mountain lakes provide essential ecosystem services and have a high conservation value. Therefore, understanding how glacier retreat will affect their ecological functioning and water quality is crucial. Here, we tested how shallow high mountain lakes having different glacial influences differ in their abiotic main features and food web structure using a multiple ecological indicator approach. We identified 13 functional groups within the planktonic and littoral communities, each one representing a biotic indicator and a node in a simplified food web network. The abiotic environment and most functional groups differed significantly as a consequence of the glacial influence. In general, runoff from glacial meltwaters resulted in highly simplified food webs. Considering that many turbid glacially fed lakes are losing their hydrological connection with disappearing/retreating glaciers and shifting to a clear state, our results suggest that this shift could enhance food web complexity, but at the cost of losing specific habitats. Further, retreat of large glaciers will form new glacially fed lakes, but it remains unclear whether this will buffer the expected habitat and biodiversity loss. [ABSTRACT FROM AUTHOR]

Cultivation of medicinal and aromatic plants (MAPs) is persistently increasing due to excessive demands of naturals. Agricultural land and its microbial diversity are primarily adapted to conventional crops, and introduction of MAP and their continuous monocropping may disturb the ecological stability of soil microbiome. Here, the effect of cultivation of MAPs on soil microbial diversity was studied. The aim of the study is to examine the effects of cultivation of MAPs on the possible shift in soil microbial diversity and to restore such impacts by using organic amendments or intercropping. Terminal restriction fragments polymorphism (TRFLP) and next-generation sequencing (NGS) studies showed that of the various selected MAPs, maximal modulation in the soil microbial diversity patterns was noticed in fields of Mentha arvensis and Artemisia annua, and the traces of essential oil/phytochemicals were detected in bulk and rhizospheric soil. In both Artemisia- and Mentha-cultivated soil, the total operating taxonomic unit (OTU) declined in both bulk and rhizospheric soil in comparison to control (Zea mays), but the bacterial richness of Mentha soil was slightly higher than that of control. However, cultivation of Mentha improved the evenness of the microbial community. The inclusion of crops like Sesbania and Chlorophytum and the application of vermicompost (VC) enhanced the microbial richness and evenness, thereby restoring the soil microbial state shift and resulting in higher productivity in the continuously Mentha cropped field. Our study concludes that long-term cultivation of some MAPs may affect the richness but promote the evenness of microbial diversity. The state shift could be restored to some extent, and crop productivity could be enhanced by the inclusion of selected crops and organic manures in cropping systems.

Cultivation of medicinal and aromatic plants (MAPs) is persistently increasing due to excessive demands of naturals. Agricultural land and its microbial diversity are primarily adapted to conventional crops, and introduction of MAP and their continuous monocropping may disturb the ecological stability of soil microbiome. Here, the effect of cultivation of MAPs on soil microbial diversity was studied. The aim of the study is to examine the effects of cultivation of MAPs on the possible shift in soil microbial diversity and to restore such impacts by using organic amendments or intercropping. Terminal restriction fragments polymorphism (TRFLP) and next-generation sequencing (NGS) studies showed that of the various selected MAPs, maximal modulation in the soil microbial diversity patterns was noticed in fields of Mentha arvensis and Artemisia annua , and the traces of essential oil/phytochemicals were detected in bulk and rhizospheric soil. In both Artemisia - and Mentha -cultivated soil, the total operating taxonomic unit (OTU) declined in both bulk and rhizospheric soil in comparison to control (Zea mays), but the bacterial richness of Mentha soil was slightly higher than that of control. However, cultivation of Mentha improved the evenness of the microbial community. The inclusion of crops like Sesbania and Chlorophytum and the application of vermicompost (VC) enhanced the microbial richness and evenness, thereby restoring the soil microbial state shift and resulting in higher productivity in the continuously Mentha cropped field. Our study concludes that long-term cultivation of some MAPs may affect the richness but promote the evenness of microbial diversity. The state shift could be restored to some extent, and crop productivity could be enhanced by the inclusion of selected crops and organic manures in cropping systems. [ABSTRACT FROM AUTHOR]

Grazing can significantly impact spatial heterogeneity and conservation value of ecosystems. Earlier work revealed that overgrazing may stimulate persistent vegetation collapse in low‐productivity environments where vegetation survives by concentrating scarce resources within its local environment. However, it remains unclear whether grazer fluctuations may cause persistent vegetation changes in high‐productivity systems where dense stands facilitate their own survival by hampering grazer access.Here, we experimentally tested how the release from grazing by greylag geese (Anser anser) affects spatial vegetation structure in a highly productive, brackish marsh in which dense reed (Phragmites australis) stands and bare roosting areas coexist. Next, we assessed the resilience of the change in vegetation patterning by reintroducing the geese after a 2‐year exclosure period.During herbivore exclusion, vegetation rapidly colonized the bare areas, while reintroduction of herbivores generated a clear species‐specific response. Specifically, the pioneer species, Bolboschoenus maritimus, was immediately eradicated, while the dense and high structure of P. australis facilitated its own persistence by limiting grazer access. Surface accretion (~1 cm/year) during herbivore exclusion further amplified this herbivore‐inhibiting feedback, because greylag geese primarily rely on waterlogged conditions for grubbing.Synthesis and applications. Our results indicate that temporary reductions in herbivore numbers may induce persistent unfavourable changes in the spatial structure of a high‐productivity system. It is therefore important to first assess whether vegetation changes are naturally reversible or persistent. If state shifts are indeed persistent, sufficiently high grazer densities must be maintained to warrant the favourable heterogeneous system. If changes in vegetation structure negatively impact grazer densities, active management such as sod cutting or mowing may be required to restore ecosystem structure and functions. Our results indicate that temporary reductions in herbivore numbers may induce persistent unfavourable changes in the spatial structure of a high‐productivity system. It is therefore important to first assess whether vegetation changes are naturally reversible or persistent. If state shifts are indeed persistent, sufficiently high grazer densities must be maintained to warrant the favourable heterogeneous system. If changes in vegetation structure negatively impact grazer densities, active management such as sod cutting or mowing may be required to restore ecosystem structure and functions. [ABSTRACT FROM AUTHOR]

Understanding ecosystem responses to compound disturbance regimes and the influence of specific sequences of events in determining ecosystem shifts remains a challenge.We use a modelling framework for Mediterranean‐type ecosystems to assess the effects of fire–drought interactions on long‐term vegetation dynamics and to identify disturbance‐driven changes in trait composition (tree seeder vs. tree resprouter prevalence) and ecosystem state (forest vs. non‐forest).Changes in tree seeder and the tree resprouter dominance show nonlinear, threshold‐type trends over gradients of increasing compound disturbance frequency. Vegetation composition thresholds mostly occur in a narrow range of the compound fire–drought disturbance space. Additionally, trait compositional switches and the likelihood of sudden changes in ecosystem state are promoted by fire‐drought interactions.Distinct sequences of disturbance events cause vegetation transitions, disrupting ecosystem resilience, even under moderate recurrence of individual disturbances. An extreme drought year followed by one or two large fire events promotes shifts from resprouter‐ to seeder dominance. Contrastingly, a large crown fire followed by an extreme drought promotes changes from seeder to resprouter dominance. This disturbance sequence is also a mechanism strong enough to trigger sudden shifts in ecosystem state (from forest to non‐forest).Synthesis. Thresholds of change in vegetation composition occur over a narrow range of the modelled gradients of compound fire‐drought recurrence, and the loss of ecosystem resilience is contingent on particular sequences of disturbance events. Overall, our findings highlight that disturbance interactions define the relative location of tipping points in ecosystem state, and that effects and feedbacks of compound disturbance regimes increase the long‐term likelihood of sudden ecosystem shifts and, therefore, uncertainty in predicting vegetation state. [ABSTRACT FROM AUTHOR]

Vegetation structure and patchiness are central controllers of ecohydrological function in semiarid regions. The feedback interactions between vegetation patchiness and water redistribution make semiarid ecosystems sensitive to state-shifts, where nonlinearities appear in the structure-function correlations. Hydrological connectivity of runoff sources is functionally important for source-sink interactions over a range of spatial scales and plays a key role in ecosystem state-shifts. Accordingly, the study of the functional responses of ecosystems to changes in connectivity is important for assessing the system's resilience in response to drivers of degradation. We used runoff data collected over 18 years in experimentally manipulated plots to study both the primary functional response to the manipulations and the changes in both structure and function over two decades. By comparing simultaneous changes in woody and herbaceous cover, biocrust cover and connectivity, and runoff yield, we examined the interactions among the different cover classes and assessed the functional consequences of these interactions. The manipulated changes in vegetation and biocrust cover caused large differences in runoff yields, with positive correlation between biocrust cover and runoff. However, changes in vegetation patterns reduced these differences, as the spread of herbaceous plant cover, at the expense of biocrust and woody cover, caused a shift in the cover-runoff relationship. The landscape was resilient to degradation due to rapid shrub growth in locations of high biocrust cover. On the other hand, a positive feedback of herbaceous plant cover replacing shrub cover caused a state-shift, likely driven by a combination of drought recurrence and cessation of grazing. [ABSTRACT FROM AUTHOR]

Woody plant encroachment is affecting vegetation composition in arid grasslands worldwide and has been associated with a number of environmental drivers and feedbacks. It has been argued that the relatively abrupt character (both in space and in time) of grassland‐to‐shrubland transitions observed in many drylands around the world might result from positive feedbacks in the underlying ecosystem dynamics. In the case of the Chihuahuan Desert, we show that one such feedback could emerge from interactions between vegetation and microclimate conditions. Shrub establishment modifies surface energy fluxes, causing an increase in nighttime air temperature, particularly during wintertime. The resulting change in winter air temperature regime is important because the northern limit of the dominant shrub in the northern Chihuahuan Desert, Larrea tridentata, presently occurs where minimum temperatures are sufficiently low to be a potential source of mortality. Using freezing responses from published studies in combination with observed temperature records, we predict that a small warming can yield meaningful changes in plant function and survival. Moreover, we also suggest that the effect of the change in air temperature on vegetation depends on whether plants experience drought during winter. Thus, in the Chihuahuan region a positive feedback exists between shrub encroachment and changes in microclimate conditions, with implications for the response of this ecosystem to regional changes in temperature and precipitation.

Questions: Climate change-type drought (the combination of drought and heatwave) has become a widely documented driver of forest dieback yet, to date, limited measurement of post-event forest dynamics has been reported. Can climate change-type drought trigger structural and/or compositional changes in a forest type which is usually highly resilient to other disturbances? Location: Mixed Eucalyptus forest in southwestern Australia. Methods: Forest areas that were severely and minimally affected by drought were measured repeatedly at 3, 6, 16, 26 and 49 mo post-event for changes in forest structure and composition of the two dominant tree species (Eucalyptus marginata/ Corymbia calophylla). Means and dispersal from pre-drought conditions were analysed for each structural variable among drought severity classes and between measurement periods. Resprouting, the predominant resilience mechanism in Eucalyptus, was assessed at 6 and 16 mo, while regeneration type and density were determined at 16 mo post-drought. Results: Structural changes were observed after 49 mo on plots severely but not minimally affected by drought, including a 30% increase in stem density (P < 0.0001) and reduction in tree diameter (23%; P < 0.01), basal area (33%; P < 0.0001), canopy height (40%; P < 0.0001) and live biomass (36%; P = 0.01). On severely affected plots, all structural variables plateaued at levels different from pre-drought conditions. Large, old trees on severely affected plots were replaced by high densities of small stems (1-10 cm DBH). Resprouting among drought affected trees (P < 0.001) and tree regeneration (P = 0.02) were higher on severely affected plots. No significant shifts in the proportional abundance of the two dominant species, E. marginata and C. calophylla, were observed for structural attributes or regeneration after 49 mo. Conclusion: Climate change-type drought can cause structural shifts in a resproutingmediterranean-type forest, providing evidence for a shift to an alternate state, particularly with repeated disturbance. While the study area showed low structural resistance and resilience, tree species composition was resilient to change, as E. marginata is likely to remain dominant in the future due to its resprouting capacity. Findings support the view that climate change-type drought will drive replacement of large trees with short,multi-stemmed individuals, transforming ecosystem structure. [ABSTRACT FROM AUTHOR]

Complex natural systems with eroded resilience, such as populations, ecosystems and socio-ecological systems, respond to small perturbations with abrupt, discontinuous state shifts, or critical transitions. Theory of critical transitions suggests that such systems exhibit fold bifurcations featuring folded response curves, tipping points and alternate attractors. However, there is little empirical evidence of fold bifurcations occurring in actual complex natural systems impacted by multiple stressors. Moreover, resilience of complex systems to change currently lacks clear operational measures with generic application. Here, we provide empirical evidence for the occurrence of a fold bifurcation in an exploited fish population and introduce a generic measure of ecological resilience based on the observed fold bifurcation attributes. We analyse the multivariate development of Barents Sea cod ( Gadus morhua), which is currently the world's largest cod stock, over six decades (1949-2009), and identify a population state shift in 1981. By plotting a multivariate population index against a multivariate stressor index, the shift mechanism was revealed suggesting that the observed population shift was a nonlinear response to the combined effects of overfishing and climate change. Annual resilience values were estimated based on the position of each year in relation to the fitted attractors and assumed tipping points of the fold bifurcation. By interpolating the annual resilience values, a folded stability landscape was fit, which was shaped as predicted by theory. The resilience assessment suggested that the population may be close to another tipping point. This study illustrates how a multivariate analysis, supported by theory of critical transitions and accompanied by a quantitative resilience assessment, can clarify shift mechanisms in data-rich complex natural systems. [ABSTRACT FROM AUTHOR]

Ecosystem dynamics may exhibit alternative stable states induced by positive feedbacks between the state of the system and environmental drivers. Bistable systems are prone to abrupt shifts from one state to another in response to even small and gradual changes in external drivers. These transitions are often catastrophic and difficult to predict by analyzing the mean state of the system. Indicators of the imminent occurrence of phase transitions can serve as important tools to warn ecosystem managers about an imminent transition before the bifurcation point is actually reached. Thus, leading indicators of phase transitions can be used either to prepare for or to prevent the occurrence of a shift to the other state. In recent years, theories of leading indicators of ecosystem shift have been developed and applied to a variety of ecological models and geophysical time series. It is unclear, however, how some of these indicators would perform in the case of systems with a delay. Here, we develop a theoretical framework for the investigation of precursors of state shift in the presence of drivers acting with a delay. We discuss how the effectiveness of leading indicators of state shift based on rising variance may be affected by the presence of delays. We apply this framework to an ecological model of desertification in arid grasslands. [ABSTRACT FROM AUTHOR]

Taking the macrophytes remaining area in Dahong Harbor of Gehu Lake as test object, this paper studied the phosphorus threshold for the shift between grass-and algae-stable states under natural conditions. The correlation analysis on the environmental factors showed that the total phosphorous in water body had better liner relationships with phytoplankton chlorophyll a and Secchi depth, and principal component analysis indicated that total phosphorous and nitrogen in the water body were the two main components affecting the water quality, among which, total phosphorous was the maximum weight source and played a determinant role in the shift between grass-and algaestable states. The Harbor was in grass-stable state in winter, shifted to grass-algae intermediate state in spring, and kept the intermediate state in summer and autumn. The total phosphorous threshold for grass-stable state shifting to grass-algae intermediate state was 61 μg·L-1,and that for grass-algae intermediate state shifting to algae-stable state was 115 μg·L-1. In order to make the ecosystem shift from algae-stable state to grass-stable state, some measures such as cutting and controlling the Lake's nutrient sources, removing the sediment rich in organic matter, and constructing submerged macrophytes areas should be adopted to make the total phosphorous threshold in the water body dropped to below 61 μg·L-1. [ABSTRACT FROM AUTHOR]

Mosaic freshwater landscapes exhibit tree-dominated patches -or tree islands-interspersed in a background of marshes and wet prairies. In the Florida Everglades, these patterned landscapes provide habitat for a variety of plant and animal species and are hotspots of biodiversity. Even though the emergence of patchy freshwater systems has been associated with climate histories, fluctuating hydrologic conditions, and internal feedbacks, a process-based quantitative understanding of the underlying dynamics is still missing. Here, we develop a mechanistic framework that relates the dynamics of vegetation, nutrients and soil accretion/loss through ecogeomorphic feedbacks and interactions with hydrologic drivers. We show that the stable coexistence of tree islands and marshes results as an effect of their both being (meta-) stable states of the system. However, tree islands are found to have only a limited resilience, in that changes in hydrologic conditions or vegetation cover may cause an abrupt shift to a stable marsh state. The inherent non-linear and discontinuous dynamics determining the stability and resilience of tree islands should be accounted for in efforts aiming at the management, conservation and restoration of these features. [ABSTRACT FROM AUTHOR]

Abstract: The influence of extreme floods from the River Danube in 2006 on the species composition and vertical distributions of phytoplankton was studied in a shallow floodplain lake, Lake Sakadaš (Kopački Rit Nature Park, Croatia) which in the last few decades was in a turbid state characterised by high phytoplankton concentrations. As a consequence of extremely high floods, the whole floodplain area (approximately 16km2) became one lentic habitat with well developed macrophyte vegetation. Seasonal dynamics of chlorophyll a (Chl a) concentration in the lake had a characteristic pattern for the shallow lakes with dense macrophyte vegetation. Extremely low mean phytoplankton abundance and biomass were found in the conditions of very high nutrient concentrations. Dominant phytoplankton species were diatoms and chlorococcal green algae from the functional groups characteristic for a mixed environment. The canonical correspondence analysis (CCA) demonstrated that nutrients and temperature were significant environmental variables for their development. The sequence of phytoplankton seasonality, vertical distribution of phytoplankton, as well as the domination of rapidly acclimating phytoplankton forms (R-strategists) indicated clear, well-mixed conditions and a highly disturbed environment. Our results suggest that the occurrence of extreme flooding can be a stressor high enough for the transition from a turbid to a clear state of the floodplain lake. Possibly, cyclic shifts between alternative stable states in floodplain ecosystems can be expected as a consequence of the impact of extreme hydrological events induced by a climate change. [Copyright &y& Elsevier]

1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g−1 snail DW d−1. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m−2, forming a spongy pond scum in the no-apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out-competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out-competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co-dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re-introduce native snails which can control the development of filamentous algae. [ABSTRACT FROM AUTHOR]

The Homerian to Ludfordian interval of the mid to late Silurian Period was a time of significant changes in conodont communities, global climate, oceanographic patterns and biogeochemical cycles. The Mulde and the Lau events are preeminent examples of globally recognized conodont extinction episodes from this interval in Earth's history. The Silurian Baltic Basin is the most suitable locality, globally, for studying these perturbations to the ocean-atmosphere system, since there is an extensive record of conodont taxa occurrences, their communities, and their environments spanning across shore-face to open-ocean settings. In this study, we present new conodont and δ13C data from the upper Homerian to Ludlow interval from two core sections – Gėluva-99 and Gėluva-118, representing shelfal environments, and the numerical conodont data from the Viduklė-61 section, from deep-water settings, and compare them with patterns of conodont diversity change, as revealed in the data-rich Milaičiai-103 core section. For this purpose, we explored the stratigraphically tied time series of conodont diversity changes employing recurrence and cross-recurrence plots – the binary similarity matrices that are used for deciphering complex spatial and temporal dynamic patterns. The cross-recurrence plots were used as a means of synchronizing the geological sections by applying dynamic time warping and the newly described moving window median recurrence point search algorithms. The results revealed that the conodont community compositional data are sufficiently temporally and spatially coherent to be reasonably used for synchronizing geological records. Moreover, the sudden state transitions detected in the cross-recurrence plots suggest that the Lau Event was of great importance for conodont community evolution in the studied time slice. • Integrated stratigraphical model implies existence of a significant regression in the late Ludlow. • The Lau Event represented the only significant shift in conodont communities of the Ludlow. • Spatiotemporal conodont community coherence enables high resolution eco-correlation. [ABSTRACT FROM AUTHOR]