scholarly journals Identifying critical transitions in seasonal shifts of zooplankton composition in a confined coastal salt marsh

2021 ◽  
Vol 83 (4) ◽  
Author(s):  
Xavier D. Quintana ◽  
Maria Antón-Pardo ◽  
Maria Bas-Silvestre ◽  
Dani Boix ◽  
Xavier Casamitjana ◽  
...  
Keyword(s):  
Salt Marshes ◽  
Dominant Species ◽  
Resistance To Change ◽  
Alternative Stable States ◽  
Zooplankton Biomass ◽  
The Other ◽  
Stable States ◽  
Top Down ◽  
Bottom Up ◽  
Critical Transitions

AbstractZooplankton assemblages in the confined coastal lagoons of La Pletera salt marshes (Baix Ter wetlands, Girona, Spain) are dominated by two species: one calanoid copepod (Eurytemora velox) and the other rotifer (Brachionus gr. plicatilis). They alternate as the dominant species (more than 80% of total zooplankton biomass), with the former being dominant in winter and the latter in summer. Shifts between these taxa are sudden, and intermediate situations usually do not last more than 1 month. Although seasonal shifts between zooplankton dominant species appear to be related with temperature, other factors such as trophic state or oxygen concentration may also play an important role. Shifts between species dominances may be driven by thresholds in these environmental variables. However, according to the alternative stable states theory, under conditions of stable dominance a certain resistance to change may exist, causing that gradual changes might have little effect until a tipping point is reached, at which the reverse change becomes much more difficult. We investigated which are the possible factors causing seasonal zooplankton shifts. We used high-frequency temperature and oxygen data provided by sensors installed in situ to analyse if shifts in zooplankton composition are determined by a threshold in these variables or, on the other hand, some gradual change between stable states occur. Moreover, following the postulates of the alternative stable states theory, we looked at possible hysteresis to analyse if these seasonal zooplankton shifts behave as critical transitions between two different equilibriums. We also examined if top-down or bottom-up trophic interactions affect these zooplankton shifts. Our results show that shifts between dominant zooplankton species in La Pletera salt marshes are asymmetric. The shift to a Eurytemora situation is mainly driven by a decrease in temperature, with a threshold close to 19 °C of daily average temperature, while the shift to Brachionus does not. Usually, the decrease in water temperature is accompanied by a decrease in oxygen oscillation with values always close to 100% oxygen saturation. Moreover, oxygen and temperature values before the shift to calanoids are different from those before the reverse shift to Brachionus, suggesting hysteresis and some resistance to change when a critical transition is approaching. Top-down and bottom-up forces appear to have no significant effect on shifts, since zooplankton biomass was not negatively correlated with fish biomass and was not positively related with chlorophyll, in overall data or within shifts.

scholarly journals Different Roles of Top-Down and Bottom-Up Processes in the Distribution of Size-Fractionated Phytoplankton in Gwangyang Bay

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1682
Author(s):  
Yoonja Kang ◽  
Yeongji Oh
Keyword(s):  
Nutrient Availability ◽  
Fast Response ◽  
Nutrient Addition ◽  
The Other ◽  
Zooplankton Grazing ◽  
Top Down ◽  
Bottom Up ◽  
Phytoplankton Distribution ◽  
Summer Bloom ◽  
Gwangyang Bay

The interactive roles of zooplankton grazing (top-down) and nutrient (bottom-up) processes on phytoplankton distribution in a temperate estuary were investigated via dilution and nutrient addition experiments. The responses of size-fractionated phytoplankton and major phytoplankton groups, as determined by flow cytometry, were examined in association with zooplankton grazing and nutrient availability. The summer bloom was attributed to nanoplankton, and microplankton was largely responsible for the winter bloom, whereas the picoplankton biomass was relatively consistent throughout the sampling periods, except for the fall. The nutrient addition experiments illustrated that nanoplankton responded more quickly to phosphate than the other groups in the summer, whereas microplankton had a faster response to most nutrients in the winter. The dilution experiments ascribed that the grazing mortality rates of eukaryotes were low compared to those of the other groups, whereas autotrophic cyanobacteria were more palatable to zooplankton than cryptophytes and eukaryotes. Our experimental results indicate that efficient escape from zooplankton grazing and fast response to nutrient availability synergistically caused the microplankton to bloom in the winter, whereas the bottom-up process (i.e., the phosphate effect) largely governed the nanoplankton bloom in the summer.

5. Simple complex questions

2020 ◽  
pp. 73-93
Author(s):  
Jaboury Ghazoul
Keyword(s):  
Tropical Forest ◽  
Tree Species ◽  
Dominant Species ◽  
Environmental Changes ◽  
Top Down ◽  
Simple Complex ◽  
Bottom Up ◽  
Biological Richness

‘Simple complex questions’ contrasts top-down and bottom-up approaches to ecological puzzles. For example, plants evade herbivores with physical defences that render them toxic or unpalatable, and the predators then evolve their own defences. How can a tropical forest support over 1,000 different tree species in a 50-hectare plot? When trees in the same forest differ in their response to environmental changes, can we still describe their environment as a niche? In species-rich systems, is there stability in complexity? Do we need so many species? Even when answering this question, we might benefit from a less human-centred approach. Earth’s biological richness has resonance beyond the dominant species.

Wired for Warmth

2012 ◽  
Vol 2 (3) ◽  
pp. 17-28
Author(s):  
Alan E. Singer
Keyword(s):  
Ethical Behavior ◽  
The Other ◽  
Computer Engineering ◽  
Top Down ◽  
Moral Consciousness ◽  
Bottom Up ◽  
The Real ◽  
Moral Agents ◽  
Artificial Moral Agents ◽  
The Relationship

An aspect of the relationship between philosophy and computer engineering is considered, with particular emphasis upon the design of artificial moral agents. Top-down vs. bottom-up approaches to ethical behavior are discussed, followed by an overview of some of the ways in which traditional ethics has informed robotics. Two macro-trends are then identified, one involving the evolution of moral consciousness in man and machine, the other involving the fading away of the boundary between the real and the virtual.

scholarly journals The Global Laboratory of Investment Law Reform Alternatives

AJIL Unbound ◽  
2018 ◽  
Vol 112 ◽  
pp. 237-243
Author(s):  
Wolfgang Alschner
Keyword(s):  
Real Life ◽  
Analytical Framework ◽  
The Other ◽  
Law Reform ◽  
Institutional Choice ◽  
Top Down ◽  
Policy Goal ◽  
Bottom Up ◽  
Investment Law ◽  
Institutional Choices

There are two ways of thinking about institutional choice in the context of multilateral investment law reform. One starts from abstract principles, asking what policy goal investment law is supposed to achieve and what institutional choice most effectively advances that goal. The other draws on practical experimentation, asking what institutional choices states are making and how these choices perform in real life. Sergio Puig and Gregory Shaffer present a compelling analytical framework for the former, top-down approach to investment law reform. In this essay, I will scrutinize their analysis and argue that the latter, bottom-up approach is more promising.

Dishabituation of Laser-evoked EEG Responses: Dissecting the Effect of Certain and Uncertain Changes in Stimulus Modality

2011 ◽  
Vol 23 (10) ◽  
pp. 2822-2837 ◽  
Author(s):  
Elia Valentini ◽  
Diana M. E. Torta ◽  
André Mouraux ◽  
Gian Domenico Iannetti
Keyword(s):  
Explicit Knowledge ◽  
Sensory Modality ◽  
The Other ◽  
Subjective Perception ◽  
Top Down ◽  
Stimulus Modality ◽  
Bottom Up ◽  
Relative Contribution ◽  
Brain Responses ◽  
Response Habituation

The repetition of nociceptive stimuli of identical modality, intensity, and location at short and constant interstimulus intervals (ISIs) determines a strong habituation of the corresponding EEG responses, without affecting the subjective perception of pain. To understand what determines this response habituation, we (i) examined the effect of introducing a change in the modality of the repeated stimulus, and (ii) dissected the relative contribution of bottom–up, stimulus-driven changes in modality and top–down, cognitive expectations of such a change, on both laser-evoked and auditory-evoked EEG responses. Multichannel EEG was recorded while participants received trains of three stimuli (S1–S2–S3, a triplet) delivered to the hand dorsum at 1-sec ISI. S3 belonged either to the same modality as S1 and S2 or to the other modality. In addition, participants were either explicitly informed or not informed of the modality of S3. We found that introducing a change in stimulus modality produced a significant dishabituation of the laser-evoked N1, N2, and P2 waves; the auditory N1 and P2 waves; and the laser- and auditory-induced event-related synchronization and desynchronization. In contrast, the lack of explicit knowledge of a possible change in the sensory modality of the stimulus (i.e., uncertainty) only increased the ascending portion of the laser-evoked and auditory-evoked P2 wave. Altogether, these results indicate that bottom–up novelty resulting from the change of stimulus modality, and not top–down cognitive expectations, plays a major role in determining the habituation of these brain responses.

Salafism pushes Muslim communities to conservatism

2018 ◽  
Keyword(s):  
Public Discourse ◽  
The State ◽  
The Other ◽  
Top Down ◽  
Bottom Up ◽  
Content Type ◽  
The Core ◽  
Conservative Ideology ◽  
Three Generations ◽  
Muslim Communities

Subject Salafism impact on Muslim societies. Significance Salafism (‘ancestralism’) is an ultra-conservative ideology adopted by a variety of Muslim individuals and organisations. It claims to reveal the authentic Islam of the first three generations of ‘pious forefathers’ (Arabic: al-salaf al-salih) from the time of the Prophet Mohammed. Salafis seek to 'purify' and thereby change other Muslims’ behaviour. These aims can be pursued by ‘top-down’ methods of engaging the state via activist struggle (jihad), or by ‘bottom-up’ strategies of engaging society via quietist proselytisation (da‘wa): that is, with or without violence. Impacts The core salafi doctrine of (‘loyalty [to Muslims] and disavowal [of non-Muslims]’) encourages its followers’ isolation from wider society. Competition for authenticity will further divide Muslim communities by ‘condemning the other’. Salafi-inspired organisations will seek to dominate public discourse and definitions of Islam.

scholarly journals Disentangling the Role of Cortico-Basal Ganglia Loops in Top–Down and Bottom–Up Visual Attention: An Investigation of Attention Deficits in Parkinson Disease

2015 ◽  
Vol 27 (6) ◽  
pp. 1215-1237 ◽  
Author(s):  
Giorgio Tommasi ◽  
Mirta Fiorio ◽  
Jérôme Yelnik ◽  
Paul Krack ◽  
Francesca Sala ◽  
...  
Keyword(s):  
Visual Attention ◽  
Parkinson Disease ◽  
Attentional Capture ◽  
Motor Response ◽  
Response Selection ◽  
The Other ◽  
Top Down ◽  
Movement Initiation ◽  
Bottom Up ◽  
Brain Functions

It is solidly established that top–down (goal-driven) and bottom–up (stimulus-driven) attention mechanisms depend on distributed cortical networks, including prefrontal and frontoparietal regions. On the other hand, it is less clear whether the BG also contribute to one or the other of these mechanisms, or to both. The current study was principally undertaken to clarify this issue. Parkinson disease (PD), a neurodegenerative disorder primarily affecting the BG, has proven to be an effective model for investigating the contribution of the BG to different brain functions; therefore, we set out to investigate deficits of top–down and bottom–up attention in a selected cohort of PD patients. With this objective in mind, we compared the performance on three computerized tasks of two groups of 12 parkinsonian patients (assessed without any treatment), one otherwise pharmacologically treated and the other also surgically treated, with that of a group of controls. The main behavioral tool for our study was an attentional capture task, which enabled us to tap the competition between top–down and bottom–up mechanisms of visual attention. This task was suitably combined with a choice RT and a simple RT task to isolate any specific deficit of attention from deficits in motor response selection and initiation. In the two groups of patients, we found an equivalent increase of attentional capture but also comparable delays in target selection in the absence of any salient distractor (reflecting impaired top–down mechanisms) and movement initiation compared with controls. In contrast, motor response selection processes appeared to be prolonged only in the operated patients. Our results confirm that the BG are involved in both motor and cognitive domains. Specifically, damage to the BG, as it occurs in PD, leads to a distinct deficit of top–down control of visual attention, and this can account, albeit indirectly, for the enhancement of attentional capture, reflecting weakened ability of top–down mechanisms to antagonize bottom–up control.

Trends in Macroergonomics Applications for Improved Work Systems

2019 ◽  
pp. 242-260
Author(s):  
Karina Cecilia Arredondo ◽  
Arturo Realyvásquez ◽  
Guadalupe Hernández-Escobedo
Keyword(s):  
The Other ◽  
System Structure ◽  
Work Processes ◽  
Top Down ◽  
Bottom Up ◽  
Work Systems ◽  
Work System ◽  
Analysis Design ◽  
A Company ◽  
General Work

Macroergonomics is the subdiscipline of ergonomics that is concerned with the analysis, design, and evaluation of work systems. It means, macroergonomics focuses on harmonizing the organizational structure of a company and not only one workstation or one task, as microergonomics does. Macroergonomics is a top-down, middle-out, and bottom-up approach. In the top-down approach, the overall general work system structure may be prescribed to match the organization's sociotechnical characteristics. On the other hand, the middle-out approach focuses on the analysis of subsystems and work processes, which can be assessed both up and down the organizational hierarchy from intermediate levels, and also, up and down some changes may be done to ensure the work system design is harmonized. Finally, the bottom-up approach comprises an extensive participation of employees in the identification of problems. Currently, macroergonomics is considered an emergent subdiscipline, and there is the need to promote current theories and methods and propose new ones.

A space for identity: the case of Lebanon’s naturalised Palestinians

2018 ◽  
Author(s):  
Hind Ghandour
Keyword(s):  
Human Rights ◽  
The Other ◽  
Top Down ◽  
National Belonging ◽  
Bottom Up ◽  
Paradigmatic Shift ◽  
Naturalized Citizens ◽  
National Discourses ◽  
The One

This chapter examines a segment of Palestinians who were granted citizenship in Lebanon through a process of tawtin, a naturalization strategy underpinned by notions of national belonging and identity. It draws upon interviews and observations with naturalized citizens and refugees to illustrate and reveal patterns of citizenship practice that challenge national discourses of tawtin, and suggest the emergence of a paradigm that posits citizenship-as-rights, and not identity.  Despite the dichotomous discourse that posits Palestinian identity in dialectic to citizenship, naturalized Palestinians constructed dynamic spaces for both to exist, somewhat harmoniously. Despite the globalization of human rights and the rise of universal personhood, access to rights remains inextricably bound and dependent upon access to citizenship. Analyses of citizenship practice remains, for the most part, conscripted to frameworks that posit citizenship-as identity on the one hand, and the subsequent emergence of citizenship-as-rights on the other. Belying these existing frameworks is a negotiation and re-negotiation of citizenship by individuals that inherently challenges them from within. This necessitates a paradigmatic shift from the top-down lens within which tawtin of Palestinians in Lebanon is presented, towards a bottom-up approach that explores the individuals’ agency in its conceptualization. 

scholarly journals Major role of marine vegetation on the oceanic carbon cycle

2005 ◽  
Vol 2 (1) ◽  
pp. 1-8 ◽  
Author(s):  
C. M. Duarte ◽  
J. J. Middelburg ◽  
N. Caraco
Keyword(s):  
Organic Carbon ◽  
Salt Marshes ◽  
Total Carbon ◽  
Organic Carbon Content ◽  
Top Down ◽  
Coastal Habitats ◽  
Bottom Up ◽  
Seagrass Meadows ◽  
Carbon Burial ◽  
Oceanic Carbon

Abstract. The carbon burial in vegetated sediments, ignored in past assessments of carbon burial in the ocean, was evaluated using a bottom-up approach derived from upscaling a compilation of published individual estimates of carbon burial in vegetated habitats (seagrass meadows, salt marshes and mangrove forests) to the global level and a top-down approach derived from considerations of global sediment balance and a compilation of the organic carbon content of vegeatated sediments. Up-scaling of individual burial estimates values yielded a total carbon burial in vegetated habitats of 111 Tmol C y-1. The total burial in unvegetated sediments was estimated to be 126 Tg C y-1, resulting in a bottom-up estimate of total burial in the ocean of about 244 Tg C y-1, two-fold higher than estimates of oceanic carbon burial that presently enter global carbon budgets. The organic carbon concentrations in vegetated marine sediments exceeds by 2 to 10-fold those in shelf/deltaic sediments. Top-down recalculation of ocean sediment budgets to account for these, previously neglected, organic-rich sediments, yields a top-down carbon burial estimate of 216 Tg C y-1, with vegetated coastal habitats contributing about 50%. Even though vegetated carbon burial contributes about half of the total carbon burial in the ocean, burial represents a small fraction of the net production of these ecosystems, estimated at about 3388 Tg C y-1, suggesting that bulk of the benthic net ecosystem production must support excess respiration in other compartments, such as unvegetated sediments and the coastal pelagic compartment. The total excess organic carbon available to be exported to the ocean is estimated at between 1126 to 3534 Tg C y-1, the bulk of which must be respired in the open ocean. Widespread loss of vegetated coastal habitats must have reduced carbon burial in the ocean by about 30 Tg C y-1, identifying the destruction of these ecosystems as an important loss of CO2 sink capacity in the biosphere.

Sign in / Sign up

Export Citation Format

Share Document