scholarly journals Positive density dependence acting on mortality can help maintain species-rich communities

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Thomas G Aubier
Keyword(s):  
Density Dependence ◽  
Species Coexistence ◽  
Equilibrium Points ◽  
Positive Density ◽  
Extrinsic Mortality ◽  
Positive Density Dependence ◽  
Negative Density Dependence ◽  
Competitive Species ◽  
Dependent Growth ◽  
Globally Stable

Conspecific negative density dependence is ubiquitous and has long been recognized as an important factor favoring the coexistence of competing species at local scale. By contrast, a positive density-dependent growth rate is thought to favor species exclusion by inhibiting the growth of less competitive species. Yet, such conspecific positive density dependence often reduces extrinsic mortality (e.g. reduced predation), which favors species exclusion in the first place. Here, using a combination of analytical derivations and numerical simulations, I show that this form of positive density dependence can favor the existence of equilibrium points characterized by species coexistence. Those equilibria are not globally stable, but allow the maintenance of species-rich communities in multispecies simulations. Therefore, conspecific positive density dependence does not necessarily favor species exclusion. On the contrary, some forms of conspecific positive density dependence may even help maintain species richness in natural communities. These results should stimulate further investigations into the precise mechanisms underlying density dependence.

scholarly journals Immigration rates during population density reduction in a coral reef fish

2015 ◽  
Author(s):  
Katrine Turgeon ◽  
Donald L. Kramer
Keyword(s):  
Density Dependence ◽  
Local Density ◽  
Empirical Studies ◽  
Limited Area ◽  
Positive Density ◽  
Density Dependent ◽  
Novel Approach ◽  
Positive Density Dependence ◽  
Wide Range ◽  
Negative Density Dependence

AbstractAlthough the importance of density-dependent dispersal has been recognized in theory, few empirical studies have examined how immigration changes over a wide range of densities. In a replicated experiment using a novel approach allowing within-site comparison, we examined changes in immigration rate following the gradual removal of territorial damselfish from a limited area within a much larger patch of continuous habitat. In all sites, immigration occurred at intermediate densities but did not occur before the start of removals and only rarely as density approached zero. In the combined data and in 5 of 7 sites, the number of immigrants was a hump-shaped function of density. This is the first experimental evidence for hump-shaped, density-dependent immigration. This pattern may be more widespread than previously recognized because studies over more limited density ranges have identified positive density dependence at low densities and negative density dependence at high densities. Positive density dependence at low density can arise from limits to the number of potential immigrants and from behavioral preferences for settling near conspecifics. Negative density dependence at high density can arise from competition for resources, especially high quality territories. The potential for non-linear effects of local density on immigration needs to be recognized for robust predictions of conservation reserve function, harvest impacts, pest control, and the dynamics of fragmented populations.

Positive density-dependent growth supports costs sharing hypothesis and population density sensing in a manipulative parasite

Parasitology ◽  
2017 ◽  
Vol 144 (11) ◽  
pp. 1511-1518 ◽  
Author(s):  
MIKHAIL GOPKO ◽  
VICTOR N. MIKHEEV ◽  
JOUNI TASKINEN
Keyword(s):  
Growth Rate ◽  
Rainbow Trout ◽  
Population Density ◽  
Cost Sharing ◽  
Positive Density ◽  
Diplostomum Pseudospathaceum ◽  
Instance Theory ◽  
Positive Density Dependence ◽  
Study Support ◽  
Dependent Growth

SUMMARYParasites manipulate their hosts’ phenotype to increase their own fitness. Like any evolutionary adaptation, parasitic manipulations should be costly. Though it is difficult to measure costs of the manipulation directly, they can be evaluated using an indirect approach. For instance, theory suggests that as the parasite infrapopulation grows, the investment of individual parasites in host manipulation decreases, because of cost sharing. Another assumption is that in environments where manipulation does not pay off for the parasite, it can decrease its investment in the manipulation to save resources. We experimentally infected rainbow trout Oncorhynchus mykiss with the immature larvae of the trematode Diplostomum pseudospathaceum, to test these assumptions. Immature D. pseudospathaceum metacercariae are known for their ability to manipulate the behaviour of their host enhancing its anti-predator defenses to avoid concomitant predation. We found that the growth rate of individual parasites in rainbow trout increased with the infrapopulation size (positive density-dependence) suggesting cost sharing. Moreover, parasites adjusted their growth to the intensity of infection within the eye lens where they were localized suggesting population density sensing. Results of this study support the hypothesis that macroparasites can adjust their growth rate and manipulation investment according to cost sharing level and infrapopulation size.

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 Evolution of positive and negative density-dependent dispersal

2014 ◽  
Vol 281 (1791) ◽  
pp. 20141226 ◽  
Author(s):  
António M. M. Rodrigues ◽  
Rufus A. Johnstone
Keyword(s):  
Density Dependence ◽  
Habitat Heterogeneity ◽  
Temporal Stability ◽  
Ecological Factors ◽  
Positive Density ◽  
Density Dependent ◽  
High Dispersal ◽  
Variable Environments ◽  
Negative Density Dependence ◽  
Density Dependent Dispersal

Understanding the evolution of density-dependent dispersal strategies has been a major challenge for evolutionary ecologists. Some existing models suggest that selection should favour positive and others negative density-dependence in dispersal. Here, we develop a general model that shows how and why selection may shift from positive to negative density-dependence in response to key ecological factors, in particular the temporal stability of the environment. We find that in temporally stable environments, particularly with low dispersal costs and large group sizes, habitat heterogeneity selects for negative density-dependent dispersal, whereas in temporally variable environments, particularly with high dispersal costs and small group sizes, habitat heterogeneity selects for positive density-dependent dispersal. This shift reflects the changing balance between the greater competition for breeding opportunities in more productive patches, versus the greater long-term value of offspring that establish themselves there, the latter being very sensitive to the temporal stability of the environment. In general, dispersal of individuals out of low-density patches is much more sensitive to habitat heterogeneity than is dispersal out of high-density patches.

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.

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