Lianas escape self-thinning: Experimental evidence of positive density dependence in temperate lianas Celastrus orbiculatus and C. scandens

2011 ◽  
Vol 13 (3) ◽  
pp. 163-172 ◽  
Author(s):  
Stacey A. Leicht-Young ◽  
Andrew M. Latimer ◽  
John A. Silander
Keyword(s):  
Density Dependence ◽  
Experimental Evidence ◽  
Positive Density ◽  
Celastrus Orbiculatus ◽  
Positive Density Dependence

scholarly journals The winner takes it all: how semelparous insects can become periodical

2018 ◽  
Author(s):  
Odo Diekmann ◽  
Robert Planqué
Keyword(s):  
Density Dependence ◽  
Initial Conditions ◽  
Short Note ◽  
Leslie Matrix ◽  
Positive Density ◽  
Simple Explanation ◽  
Large Classes ◽  
Full Life Cycle ◽  
Positive Density Dependence ◽  
One Year

AbstractThe aim of this short note is to give a simple explanation for the remarkable periodicity of Magicicada species, which appear as adults only every 13 or 17 years, depending on the region. We show that a combination of two types of density dependence may drive, for large classes of initial conditions, all but one year class to extinction. Competition for food leads to negative density dependence in the form of a uniform (i.e., affecting all age classes in the same way) reduction of the survival probability. Satiation of predators leads to positive density dependence within the reproducing age class. The analysis focuses on the full life cycle map derived by iteration of a semelparous Leslie matrix.

scholarly journals Restoration of eastern oyster populations with positive density dependence

2018 ◽  
Vol 28 (4) ◽  
pp. 897-909 ◽  
Author(s):  
Jacob L. Moore ◽  
Brandon J. Puckett ◽  
Sebastian J. Schreiber
Keyword(s):  
Density Dependence ◽  
Eastern Oyster ◽  
Positive Density ◽  
Positive Density Dependence

Switching from negative to positive density-dependence among populations of a cobble beach plant

Oecologia ◽  
2008 ◽  
Vol 158 (3) ◽  
pp. 473-483 ◽  
Author(s):  
William M. Goldenheim ◽  
Andrew D. Irving ◽  
Mark D. Bertness
Keyword(s):  
Density Dependence ◽  
Positive Density ◽  
Positive Density Dependence ◽  
Cobble Beach

scholarly journals A conceptual model for migratory tundra caribou to explain and predict why shifts in spatial fidelity of breeding cows to their calving grounds are infrequent

Rangifer ◽  
2012 ◽  
pp. 259-267 ◽  
Author(s):  
Anne Gunn ◽  
Kim G. Poole ◽  
John S. Nishi
Keyword(s):  
Density Dependence ◽  
Conceptual Model ◽  
Rangifer Tarandus ◽  
Curvilinear Relationship ◽  
Positive Density ◽  
Adaptive Use ◽  
Individual Fitness ◽  
Positive Density Dependence

Calving grounds of migratory tundra caribou (Rangifer tarandus) have two prominent characteristics. Firstly, the cows are gregarious, and secondly, the annual calving grounds spatially overlap in consecutive years (spatial fidelity). The location of consecutive annual calving grounds can gradually shift (either rotationally or un-directional) or more rarely, abruptly (non-overlapping). We propose a mechanism to interpret and predict changes in spatial fidelity. We propose that fidelity is linked to gregariousness with its advantages for individual fitness (positive density-dependence). Our argument is based on a curvilinear relationship between the density of cows on the calving ground (which we use to index gregariousness) and spatial fidelity. Extremely high or low densities are two different mechanisms which can lead to reduced spatial fidelity to annual calving grounds and reflect the caribou’s adaptive use of its calving ranges.

scholarly journals Restoration of Eastern oyster populations with positive density dependence

2017 ◽  
Author(s):  
Jacob L Moore ◽  
Brandon Puckett ◽  
Sebastian J Schreiber
Keyword(s):  
Density Dependence ◽  
Single Point ◽  
Eastern Oyster ◽  
Stock Enhancement ◽  
Positive Density ◽  
Integral Projection Model ◽  
Projection Model ◽  
Positive Density Dependence ◽  
Restoration Strategies ◽  
Habitat Enhancement

ABSTRACTPositive density dependence can create a threshold of population states below which extinction of the population occurs. The existence of this threshold, which can often be a complex, multi-dimensional surface, rather than a single point, is of particular importance in degraded populations for which there is a desire for successful restoration. Here, we incorporated positive density dependence into a closed, size- and age-structured integral projection model parameterized with empirical data from an Eastern oyster, Crassostrea virginica, population in Pamlico Sound, North Carolina. To understand the properties of the threshold surface, and implications for restoration, we introduced a general method based on a linearization of the threshold surface at its unique, unstable equilibrium. We estimated the number of oysters of a particular age (i.e. stock enhancement), or the surface area of hard substrate required (i.e. habitat enhancement), to move a population from an extinction trajectory to a persistent trajectory. The location of the threshold surface was strongly affected by changes in the amount of local larval retention. Traditional stock enhancement with oysters less than a year old (i.e. spat) required three times as many oysters relative to stock enhancement with oysters between ages three and seven, while the success of habitat enhancement depended upon the initial size distribution of the population. The methodology described here demonstrates the importance of considering positive density dependence in oyster populations, and also provides insights into effective management and restoration strategies when dealing with a high dimensional threshold separating extinction and persistence.

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.

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