scholarly journals Experimental demonstration of an Allee effect in microbial populations

2016 ◽  
Vol 12 (4) ◽  
pp. 20160070 ◽  
Author(s):  
RajReni B. Kaul ◽  
Andrew M. Kramer ◽  
Fred C. Dobbs ◽  
John M. Drake
Keyword(s):  
Allee Effect ◽  
Vibrio Fischeri ◽  
Microbial Populations ◽  
Critical Threshold ◽  
Initial Population ◽  
Positive Density ◽  
Allee Effects ◽  
Low Carbon ◽  
Positive Density Dependence ◽  
The Relationship

Microbial populations can be dispersal limited. However, microorganisms that successfully disperse into physiologically ideal environments are not guaranteed to establish. This observation contradicts the Baas-Becking tenet: ‘Everything is everywhere, but the environment selects’. Allee effects, which manifest in the relationship between initial population density and probability of establishment, could explain this observation. Here, we experimentally demonstrate that small populations of Vibrio fischeri are subject to an intrinsic demographic Allee effect. Populations subjected to predation by the bacterivore Cafeteria roenbergensis display both intrinsic and extrinsic demographic Allee effects. The estimated critical threshold required to escape positive density-dependence is around 5, 20 or 90 cells ml −1 under conditions of high carbon resources, low carbon resources or low carbon resources with predation, respectively. This work builds on the foundations of modern microbial ecology, demonstrating that mechanisms controlling macroorganisms apply to microorganisms, and provides a statistical method to detect Allee effects in data.

scholarly journals A cryptic Allee effect: spatial contexts mask an existing fitness–density relationship

2015 ◽  
Vol 2 (6) ◽  
pp. 150034 ◽  
Author(s):  
Akira Terui ◽  
Yusuke Miyazaki ◽  
Akira Yoshioka ◽  
Shin-ichiro S. Matsuzaki
Keyword(s):  
Allee Effect ◽  
Local Level ◽  
Freshwater Mussel ◽  
Fertilization Rate ◽  
Positive Density ◽  
Allee Effects ◽  
Flow Conditions ◽  
Conspecific Density ◽  
Sperm Density ◽  
Density Relationship

Current theories predict that Allee effects should be widespread in nature, but there is little consistency in empirical findings. We hypothesized that this gap can arise from ignoring spatial contexts (i.e. spatial scale and heterogeneity) that potentially mask an existing fitness–density relationship: a ‘cryptic’ Allee effect. To test this hypothesis, we analysed how spatial contexts interacted with conspecific density to influence the fertilization rate of the freshwater mussel Margaritifera laevis . This sessile organism has a simple fertilization process whereby females filter sperm from the water column; this system enabled us to readily assess the interaction between conspecific density and spatial heterogeneity (e.g. flow conditions) at multiple spatial levels. Our findings were twofold. First, positive density-dependence in fertilization was undetectable at a population scale (approx. less than 50.5 m 2 ), probably reflecting the exponential decay of sperm density with distance from the sperm source. Second, the Allee effect was confirmed at a local level (0.25 m 2 ), but only when certain flow conditions were met (slow current velocity and shallow water depth). These results suggest that spatial contexts can mask existing Allee effects.

scholarly journals Pushed beyond the brink: Allee effects, environmental stochasticity, and extinction

2014 ◽  
Author(s):  
Gregory Roth ◽  
Sebastian Schreiber
Keyword(s):  
High Probability ◽  
Geometric Mean ◽  
Environmental Stochasticity ◽  
Initial Population ◽  
Positive Density ◽  
Allee Effects ◽  
Population Densities ◽  
Density Dependent ◽  
Environmental Fluctuations ◽  
Predation Rates

To understand the interplay between environmental stochasticity and Allee effects, we analyze persistence, asymptotic extinction, and conditional persistence for stochastic difference equations. Our analysis reveals that persistence requires that the geometric mean of fitness at low densities is greater than one. When this geometric mean is less than one, asymptotic extinction occurs with high probability for low initial population densities. Additionally, if the population only experiences positive density-dependent feedbacks, conditional persistence occurs provided the geometric mean of fitness at high population densities is greater than one. However, if the population experiences both positive and negative density-dependent feedbacks, conditional persistence only occurs if environmental fluctuations are sufficiently small. We illustrate counter-intuitively that environmental fluctuations can increase the probability of persistence when populations are initially at low densities, and can cause asymptotic extinction of populations experiencing intermediate predation rates despite conditional persistence occurring at higher predation rates.

scholarly journals Widespread density dependence of bacterial growth under acid stress

2021 ◽  
Author(s):  
Francesca Fiegna ◽  
Samay Pande ◽  
Hansrainer Peitz ◽  
Gregory J Velicer
Keyword(s):  
Density Dependence ◽  
Allee Effect ◽  
Social Protection ◽  
Bacterial Species ◽  
Acid Stress ◽  
Local Environment ◽  
High Density ◽  
Positive Density ◽  
Fruiting Body Formation ◽  
Positive Density Dependence

Benefits of cooperation intrinsically depend on density because biological interaction requires organismal proximity. Microbial cooperative traits are common, yet systematic tests for a shared cooperative phenotype across diverse species are rare, as are direct tests for the Allee effect - positive density dependence of fitness. Here we test for positive density dependence of growth under acid stress in five phylogenetically widespread bacterial species - three Gram-negative and two Gram-positive - and find the Allee effect in all five. However, social protection from acid stress appears to have evolved by different mechanisms across species. In Myxococcus xanthus, the acid-stress Allee effect is found to be mediated by pH-regulated secretion of a diffusible molecule present in supernatants of high-density cultures. In contrast, growth from low density under acid stress by the other species was not enhanced by high-density supernatant. Additionally, density dependence of Myxococcus fruiting-body formation during starvation is found to increase with acid stress, suggesting that abiotic stresses other than starvation shape the evolution of aggregative development. Our findings suggest that high cell density may protect against acid stress in most bacterial species and in Myxococcus may promote predation on microbes that acidify their local environment by secretion of metabolic byproducts.

scholarly journals Does Revitalizing the Center of Mid-Sized French Cities Reduce GHG Emissions from Commuting?

2021 ◽  
Vol 13 (4) ◽  
pp. 1851
Author(s):  
Alexis Poulhès ◽  
Angèle Brachet
Keyword(s):  
Land Use Planning ◽  
Statistical Models ◽  
Total Population ◽  
Ghg Emissions ◽  
Low Carbon ◽  
Trip Distance ◽  
Working People ◽  
Shrinking City ◽  
The Relationship ◽  
Positive Effect

Mid-sized cities are usually considered in the literature to be shrinking cities. Some policies promote right-sizing and others promote revitalization. The relationship between land-use planning and mobility having been established, the present research issue is focused on whether a policy of revitalizing the centers of mid-sized cities is favorable to low-carbon mobility. Our study investigates commuting trips through two indicators: commuting trip distance and car modal share. The increase in total population, the increase in the number of jobs per resident, the decrease in the unemployment rate, the increase in the rate of executives, the increase in the rate of working people in the population and the decrease in the residential vacancy rate all come from the censuses of 2006 and 2016. Statistical models based on individuals in 113 mid-sized cities, in which sociodemographic variables are introduced, show that at the level of agglomerations, no indicator has a simultaneously positive effect in the center and in the urban periphery. No indicator is entirely positive or negative on GHG emissions from commuting trips. While the increase in GHG emissions from commuting trips between 2006 and 2016 is significant in mid-sized cities (18%), a shift toward shrinking city centers is insufficient to change this trajectory.

scholarly journals The influence of density in population dynamics with strong and weak Allee effect

2021 ◽  
Vol 29 (1) ◽  
Author(s):  
Kamrun Nahar Keya ◽  
Md. Kamrujjaman ◽  
Md. Shafiqul Islam
Keyword(s):  
Population Dynamics ◽  
Allee Effect ◽  
Global Bifurcation ◽  
Reaction Diffusion ◽  
Logistic Growth ◽  
Allee Effects ◽  
Reaction Diffusion Model ◽  
Positive Steady States ◽  
The Stability ◽  
The Impact

AbstractIn this paper, we consider a reaction–diffusion model in population dynamics and study the impact of different types of Allee effects with logistic growth in the heterogeneous closed region. For strong Allee effects, usually, species unconditionally die out and an extinction-survival situation occurs when the effect is weak according to the resource and sparse functions. In particular, we study the impact of the multiplicative Allee effect in classical diffusion when the sparsity is either positive or negative. Negative sparsity implies a weak Allee effect, and the population survives in some domain and diverges otherwise. Positive sparsity gives a strong Allee effect, and the population extinct without any condition. The influence of Allee effects on the existence and persistence of positive steady states as well as global bifurcation diagrams is presented. The method of sub-super solutions is used for analyzing equations. The stability conditions and the region of positive solutions (multiple solutions may exist) are presented. When the diffusion is absent, we consider the model with and without harvesting, which are initial value problems (IVPs) and study the local stability analysis and present bifurcation analysis. We present a number of numerical examples to verify analytical results.

Technology Innovation Based on Environmental Kuznets Curve Hypothesis

2012 ◽  
Vol 573-574 ◽  
pp. 831-835 ◽  
Author(s):  
Yu Wei He ◽  
Jin Rong Jiang
Keyword(s):  
Energy Consumption ◽  
Environmental Kuznets Curve ◽  
Technology Innovation ◽  
Added Value ◽  
Kuznets Curve ◽  
Low Carbon ◽  
Low Carbon Economy ◽  
Environmental Kuznets Curve Hypothesis ◽  
The Relationship ◽  
Carbon Economy

Low-carbon economy was an inevitable choice in response to climate warming. With the deep analysis of the environmental Kuznets curve (EKC), this paper used two models to analyze the relationship between the growth of a country’s economic and the quantity of pollutants produced in the process. The empirical study compare the two groups of samples, which described energy consumption per unit of industrial added value, each group contains five symbolic provinces or municipalities in coastal and western areas. The outcome proved the positive significance of technology innovation.

The relationship between composition and toxicity of tannery wastewater

2004 ◽  
Vol 49 (1) ◽  
pp. 39-46 ◽  
Author(s):  
M. Cotman ◽  
J. Zagorc-Končan ◽  
A. Žgajnar-Gotvajn
Keyword(s):  
Activated Carbon ◽  
Daphnia Magna ◽  
Vibrio Fischeri ◽  
Organic Pollution ◽  
Tannery Wastewater ◽  
Organic Load ◽  
Short Term ◽  
Air Stripping ◽  
Luminescence Inhibition ◽  
The Relationship

Key toxic components have been identified in pre-treated tannery wastewater with fractionation of samples through chemical and physical means (filtration, air stripping, adsorption on activated carbon, …). The goal of each fractionation step was to reduce the toxicity due to a specific group of chemicals and compare the results to the toxicity present in the unaltered sample. Toxicity short-term tests with the invertebrate Daphnia magna and the bacterial luminescence inhibition test with Vibrio fischeri were used in combination with chemical analyses. During the toxicity identification and evaluation fractionation, a portion of the sample was pressure filtered. Treated samples contained less organic pollution and metals and were less toxic especially to Daphnia magna. For the removal of ammonia the second portion of sample was air-stripped at different pH levels. We removed 84% of ammonia at pH 11; the toxicity to both organisms decreased but ammonia did not have a deciding effect on the toxicity of tannery wastewater when the organic load was still present. The most successful procedure for toxicity removal was adsorption on powdered activated carbon. We removed organic pollution detected as COD, organic nitrogen compounds and part of the metals. Zeolite treatment was a little less successful for removing ammonia than air-stripping.

scholarly journals Response of Variation of Water and Sediment to Landscape Pattern in the Dapoling Watershed

2022 ◽  
Vol 14 (2) ◽  
pp. 678
Author(s):  
Chong Wei ◽  
Zhiqiang Zhang ◽  
Zhiguo Wang ◽  
Lianhai Cao ◽  
Yichang Wei ◽  
...  
Keyword(s):  
Landscape Pattern ◽  
Sediment Yield ◽  
Landscape Heterogeneity ◽  
Swat Model ◽  
Landscape Patterns ◽  
Land Resource ◽  
Low Carbon ◽  
Water And Sediment ◽  
The Relationship ◽  
Runoff And Sediment Yield

The relationship between water-sediment processes and landscape pattern changes has currently become a research hotspot in low-carbon water and land resource optimization research. The SWAT-VRR model is a distributed hydrological model which better shows the effect of land use landscape change on hydrological processes in the watershed. In this paper, the hydrological models of the Dapoling watershed were built, the runoff and sediment yield from 2006 to 2011 were simulated, and the relationship between landscape patterns and water-sediment yield was analyzed. The results show that the SWAT-VRR model is more accurate and reasonable in describing runoff and sediment yield than the SWAT model. The sub-basins whose soil erosion is relatively light are mostly concentrated in the middle reaches with a slope mainly between 0–5°. The NP, PD, ED, SPIIT, SHEI, and SHDI of the watershed increased slightly, and the COHESION, AI, CONTAG, and LPI showed a certain decrease. The landscape pattern is further fragmented, with the degree of landscape heterogeneity increasing and the connection reducing. The runoff, sediment yield and surface runoff are all extremely significantly negatively correlated with forest, which implies that for more complicated patch shapes of forest which have longer boundaries connecting with the patches of other landscape types, the water and sediment processes are regulated more effectively. Therefore, it can be more productive to carry out research on the optimization of water and soil resources under the constraint of carbon emission based on the SWAT-VRR model.

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