The Role of Epiphytic Algae and Grazing Snails in Stable States of Submerged and of Free-Floating Plants

Ecosystems ◽  
2021 ◽  
Author(s):  
Gergő Koleszár ◽  
Zoltán Nagy ◽  
Edwin T. H. M. Peeters ◽  
Gábor Borics ◽  
Gábor Várbíró ◽  
...  
2008 ◽  
Vol 363 (1504) ◽  
pp. 2745-2754 ◽  
Author(s):  
Euan G Nisbet ◽  
R. Ellen R Nisbet

Rubisco I's specificity, which today may be almost perfectly tuned to the task of cultivating the global garden, controlled the balance of carbon gases and O 2 in the Precambrian ocean and hence, by equilibration, in the air. Control of CO 2 and O 2 by rubisco I, coupled with CH 4 from methanogens, has for the past 2.9 Ga directed the global greenhouse warming, which maintains liquid oceans and sustains microbial ecology. Both rubisco compensation controls and the danger of greenhouse runaway (e.g. glaciation) put limits on biological productivity. Rubisco may sustain the air in either of two permissible stable states: either an anoxic system with greenhouse warming supported by both high methane mixing ratios as well as carbon dioxide, or an oxygen-rich system in which CO 2 largely fulfils the role of managing greenhouse gas, and in which methane is necessarily only a trace greenhouse gas, as is N 2 O. Transition from the anoxic to the oxic state risks glaciation. CO 2 build-up during a global snowball may be an essential precursor to a CO 2 -dominated greenhouse with high levels of atmospheric O 2 . Photosynthetic and greenhouse-controlling competitions between marine algae, cyanobacteria, and terrestrial C3 and C4 plants may collectively set the CO 2  : O 2 ratio of the modern atmosphere (last few million years ago in a mainly glacial epoch), maximizing the productivity close to rubisco compensation and glacial limits.


Hydrobiologia ◽  
2015 ◽  
Vol 778 (1) ◽  
pp. 167-178 ◽  
Author(s):  
Franco Teixeira-de Mello ◽  
Valdeci Antonio de Oliveira ◽  
Simoni Maria Loverde-Oliveira ◽  
Vera Lucia M. Huszar ◽  
José Barquín ◽  
...  

2020 ◽  
Author(s):  
Peter Ditlevsen

<p>Paleoclimatic records show that under glacial boundary conditions the climate has jumped irregularly between two different climate states. These are the stadial and interstadial climates characterized by extremely abrupt climate change, the Dansgaard-Oeschger events. The irregularity and the fact that no known external triggering is present indicate that these are induced by internal noise, so-called n-tipping. The high resolution record of dust from Greenland icecores, which is a proxy of the state of the atmosphere, can be well fitted by a non-linear 1D stochastic process. But in order to do so the noise process needs to be an alpha-stable process, which is characterized by heavy tails violating the central limit theorem.  I will discus how extreme events can influence the transition from one climate state to the other.</p>


2008 ◽  
Vol 18 (06) ◽  
pp. 1607-1626 ◽  
Author(s):  
ULRIKE FEUDEL

The coexistence of several stable states for a given set of parameters has been observed in many natural and experimental systems as well as in theoretical models. This paper gives an overview over the wide range of applications in different disciplines of science. Furthermore, different system classes possessing multistability are analyzed in terms of the appearance of coexisting attractors and their basins of attraction. It is shown that multistable systems are very sensitive to perturbations leading to a noise-induced hopping process between attractors. The role of chaotic saddles in the escape from attractors in multistable systems is discussed.


2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Letizia Milli

AbstractDuring the last decade, the advent of the Web and online social networks rapidly changed the way we were used to search, gather and discuss information of any kind. These tools have given everyone the chance to become a news medium. While promoting more democratic access to information, direct and unfiltered communication channels may increase our chances to confront malicious/misleading behavior. Fake news diffusion represents one of the most pressing issues of our online society. In recent years, fake news has been analyzed from several perspectives; among such vast literature, an important theme is the analysis of fake news’ perception. In this work, moving from such observation, I propose a family of opinion dynamics models to understand the role of specific social factors on the acceptance/rejection of news contents. In particular, I model and discuss the effect that stubborn agents, different levels of trust among individuals, open-mindedness, attraction/repulsion phenomena, and similarity between agents have on the population dynamics of news perception. To discuss the peculiarities of the proposed models, I tested them on two synthetic network topologies thus underlying when/how they affect the stable states reached by the performed simulations.


2021 ◽  
Author(s):  
◽  
Alison Duncan

<p>Small herbivorous invertebrates consume algal epiphytes, reducing negative effects (e.g. shading) on seagrass. Much research to date has focused on crustacean grazers, and comparatively little on gastropods. The aim of this research was to 1) examine seasonal and spatial variation in seagrass and associated gastropods in a large, tidal estuary and 2) examine the response of seagrass and epiphytic algae to nutrient enrichment and grazing pressure in a laboratory experiment.  Surveys were conducted in summer and winter of 2016 to assess the seasonal fluctuations in the associated gastropods and relationships with seagrass and epiphyte biomass within three sites in the Porirua Harbour. Seagrass, gastropods and epiphytic algae showed seasonal trends, including evidence of a loss of grazer control on epiphytes during winter. Potamopyrgus estuarinus, Notoacmea scapha, Diloma spp. and Micrelenchus spp. were the dominant gastropod grazers in the system in both seasons. The gastropod assemblage and seagrass characteristics differed between sites, likely in response to small scale differences in abiotic factors.  Seagrass from Elsdon (a site with elevated nutrient levels) and Browns Bay (a relatively pristine site) were used to investigate the role of select grazers and nutrient enrichment on epiphyte and seagrass growth. Nutrient treatments represented nitrate and phosphate concentrations of Elsdon (High), a 20% increase (High+) and a control (no addition). Little evidence was found for epiphyte regulation by gastropods, nor did epiphyte loads increase with nutrient addition. Seagrass from Browns Bay responded more strongly to High+ treatments than that of Elsdon. The results suggest that seagrass from Elsdon is adapted to the site’s high nutrient loads, where seagrass from Browns Bay is not. The results of this thesis support prior research findings of high variation in seagrass over a small scale, and adds to the currently lacking information on the role of micro-grazers in New Zealand’s seagrass meadows.</p>


Botany ◽  
2016 ◽  
Vol 94 (11) ◽  
pp. 1009-1014 ◽  
Author(s):  
Nicole J. Fenton

Canada’s boreal biome is a mosaic of forests and peatlands. These ecosystems have developed dynamically, periodically affected by disturbance events of significant spatial extent and variable severity, reducing ecosystem biomass. The same ecosystem types typically regenerate from biological legacies. However, concern is growing about the impact of these different anthropogenic disturbances, particularly compound disturbances including climate change, which open the door to shifts to alternate stable states. One strategy promoted to regulate anthropogenic disturbance is the “mitigation hierarchy” for development projects, where impacts on ecosystems are avoided, mitigated, restored, or compensated. This practical approach is not yet integrated into disturbance and resilience theory. Here, I develop an integrated view of the mitigation hierarchy, as well as resilience and disturbance theory, in a boreal context using ecosystem services to measure ecosystem state in a two-step process that first models loss of ecosystem function and then integrates the mitigation hierarchy and resilience theory. The application of this model is discussed in the context of restoration studies after different types of catastrophic anthropogenic disturbance. These studies, some of which are published in this special issue, highlight the important role of bryophytes and understory plants in setting restoration targets and developing criteria and indicators of success.


1998 ◽  
Vol 10 (1) ◽  
pp. 73-111 ◽  
Author(s):  
A. David Redish ◽  
David S. Touretzky

We suggest that the hippocampus plays two roles that allow rodents to solve the hidden-platform water maze: self-localization and route replay. When an animal explores an environment such as the water maze, the combination of place fields and correlational (Hebbian) long-term potentiation produces a weight matrix in the CA3 recurrent collaterals such that cells with overlapping place fields are more strongly interconnected than cells with nonoverlapping fields. When combined with global inhibition, this forms an attractor with coherent representations of position as stable states. When biased by local view information, this allows the animal to determine its position relative to the goal when it returns to the environment. We call this self-localization. When an animal traces specific routes within an environment, the weights in the CA3 recurrent collaterals become asymmetric. We show that this stores these routes in the recurrent collaterals. When primed with noise in the absence of sensory input, a coherent representation of position still forms in the CA3 population, but then that representation drifts, retracing a route. We show that these two mechanisms can coexist and form a basis for memory consolidation, explaining the anterograde and limited retrograde amnesia seen following hippocampal lesions.


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