Evolution of positive and negative 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.

Download Full-text

Immigration rates during population density reduction in a coral reef fish

10.1101/033274 ◽

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.

Download Full-text

Conspecific negative density dependence and why its study should not be abandoned

10.1101/2020.05.11.089334 ◽

2020 ◽

Author(s):

Joseph A. LaManna ◽

Scott A. Mangan ◽

Jonathan A. Myers

Keyword(s):

Density Dependence ◽

Latitudinal Gradient ◽

Null Model ◽

Statistical Bias ◽

Fitness Components ◽

Density Dependent ◽

Statistical Errors ◽

Negative Density Dependence ◽

Model Approach

AbstractRecent studies showing bias in the measurement of density dependence have the potential to sow confusion in the field of ecology. We provide clarity by elucidating key conceptual and statistical errors with the null-model approach used in Detto et al. (2019). We show that neither their null model nor a more biologically-appropriate null model reproduces differences in density-dependent recruitment between forests, indicating that the latitudinal gradient in negative density dependence is not an artefact of statistical bias. Finally, we suggest a path forward that combines observational comparisons of density dependence in multiple fitness components across localities with mechanistic and geographically-replicated experiments.

Download Full-text

When higher carrying capacities lead to faster propagation

10.1101/307322 ◽

2018 ◽

Cited By ~ 6

Author(s):

Marjorie Haond ◽

Thibaut Morel-Journel ◽

Eric Lombaert ◽

Elodie Vercken ◽

Ludovic Mailleret ◽

...

Keyword(s):

Carrying Capacity ◽

Invasion Biology ◽

Reaction Diffusion Equations ◽

Positive Density ◽

Allee Effects ◽

Demographic Stochasticity ◽

Positive Dependence ◽

Density Dependent ◽

Temporal Models ◽

Density Dependent Dispersal

AbstractThis preprint has been reviewed and recommended by Peer Community In Ecology (https://dx.doi.org/10.24072/pci.ecology.100004). Finding general patterns in the expansion of natural populations is a major challenge in ecology and invasion biology. Classical spatio-temporal models predict that the carrying capacity (K) of the environment should have no influence on the speed (v) of an expanding population. We tested the generality of this statement with reaction-diffusion equations, stochastic individual-based models, and microcosms experiments with Trichogramma chilonis wasps. We investigated the dependence between K and v under different assumptions: null model (Fisher-KPP-like assumptions), strong Allee effects, and positive density-dependent dispersal. These approaches led to similar and complementary results. Strong Allee effects, positive density-dependent dispersal and demographic stochasticity in small populations lead to a positive dependence between K and v. A positive correlation between carrying capacity and propagation speed might be more frequent than previously expected, and be the rule when individuals at the edge of a population range are not able to fully drive the expansion.

Download Full-text

MODELS OF PERIODIC INUNDATION OF PARASITOIDS FOR PEST CONTROL

The Canadian Entomologist ◽

10.4039/ent117705-6 ◽

1985 ◽

Vol 117 (6) ◽

pp. 705-716 ◽

Cited By ~ 11

Author(s):

Hugh J. Barclay ◽

Imre S. Otvos ◽

Alan J. Thomson

Keyword(s):

Density Dependence ◽

Pest Control ◽

Ecological Factors ◽

Host Population ◽

Density Dependent ◽

Density Dependent Mortality ◽

Inundative Releases ◽

Dependent Mortality

AbstractSeveral host–parasitoid models were examined to assess the feasibility of parasitoid inundation as a means of pest control or eradication. The approach is comparative, to assess independently the effects of various ecological factors on the ease of control by this means. For most of the models, there exists a critical inundation rate, I*, above which the host population is eradicated, provided inundative releases continue beyond the time of eradication. The existence of density-dependent mortality in the hosts reduces the time to eradication but does not affect I*. Density dependence in the parasitoids, however, usually increases I*. The existence of hyperparasitoids appears to have no effect on the ease of host eradication.

Download Full-text

Landscape connectivity alters the evolution of density-dependent dispersal during pushed range expansions

10.1101/2021.03.03.433752 ◽

2021 ◽

Author(s):

Maxime Dahirel ◽

Aline Bertin ◽

Vincent Calcagno ◽

Camille Duraj ◽

Simon Fellous ◽

...

Keyword(s):

Range Expansion ◽

Landscape Connectivity ◽

Positive Density ◽

Low Density ◽

Trichogramma Brassicae ◽

Biological Organization ◽

Density Dependent ◽

Spatial Sorting ◽

Edge Populations ◽

Density Dependent Dispersal

As human influence reshapes communities worldwide, many species expand or shift their ranges as a result, with extensive consequences across levels of biological organization. Range expansions can be ranked on a continuum going from pulled dynamics, in which low-density edge populations provide the "fuel" for the advance, to pushed dynamics in which high-density rear populations "push" the expansion forward. While theory suggests that evolution by spatial sorting, a common feature of range expansions, could lead pushed expansions to become pulled with time, empirical comparisons of phenotypic divergence in pushed vs. pulled contexts are lacking. In a previous experiment using Trichogramma brassicae wasps as a model, we showed that expansions were more pushed when connectivity was lower. Here we used descendants from these experimental landscapes to look at how the range expansion process and connectivity interact to shape phenotypic evolution. Interestingly, we found no clear and consistent phenotypic shifts, whether along expansion gradients or between treatments, when we focused on low-density trait expression. However, we found evidence of changes in density-dependence, in particular regarding dispersal: populations went from positive to negative density-dependent dispersal at the expansion edge, but only when connectivity was high. As positive density-dependent dispersal leads to pushed expansions, our results confirm predictions that evolution during range expansions may lead pushed expansions to become pulled, but add nuance by showing environmental context may slow down or cancel this process. This shows we need to jointly consider evolution and ecological context to accurately predict range expansion dynamics and their consequences.

Download Full-text

Direct evidence that density-dependent regulation underpins the temporal stability of abundant species in a diverse animal community

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.1336 ◽

2014 ◽

Vol 281 (1791) ◽

pp. 20141336 ◽

Cited By ~ 21

Author(s):

Peter A. Henderson ◽

Anne E. Magurran

Keyword(s):

Density Dependence ◽

Temporal Stability ◽

Feedback Regulation ◽

Abundant Species ◽

Species Number ◽

Transient Species ◽

Negative Feedback Regulation ◽

Density Dependent ◽

Core Species ◽

Animal Community

To understand how ecosystems are structured and stabilized, and to identify when communities are at risk of damage or collapse, we need to know how the abundances of the taxa in the entire assemblage vary over ecologically meaningful timescales. Here, we present an analysis of species temporal variability within a single large vertebrate community. Using an exceptionally complete 33-year monthly time series following the dynamics of 81 species of fishes, we show that the most abundant species are least variable in terms of temporal biomass, because they are under density-dependent (negative feedback) regulation. At the other extreme, a relatively large number of low abundance transient species exhibit the greatest population variability. The high stability of the consistently common high abundance species—a result of density-dependence—is reflected in the observation that they consistently represent over 98% of total fish biomass. This leads to steady ecosystem nutrient and energy flux irrespective of the changes in species number and abundance among the large number of low abundance transient species. While the density-dependence of the core species ensures stability under the existing environmental regime, the pool of transient species may support long-term stability by replacing core species should environmental conditions change.

Download Full-text

Individual variation in dispersal, and its sources, shape the fate of pushed vs. pulled range expansions

10.1101/2022.01.12.476009 ◽

2022 ◽

Author(s):

Maxime Dahirel ◽

Chloe Guicharnaud ◽

Elodie Vercken

Keyword(s):

Density Dependence ◽

Evolutionary Dynamics ◽

Simulation Models ◽

Dispersal Capacity ◽

Density Dependent ◽

Range Edge ◽

Individual Trait ◽

Edge Populations ◽

The Impact ◽

Density Dependent Dispersal

Ecological and evolutionary dynamics of range expansions are shaped by both dispersal and population growth. Accordingly, density-dependence in either dispersal or growth can determine whether expansions are pulled or pushed, i.e. whether expansion velocities and genetic diversity are mainly driven by recent, low-density edge populations, or by older populations closer to the core. Despite this and despite abundant evidence of dispersal evolution during expansions, the impact of density-dependent dispersal and its evolution on expansion dynamics remains understudied. Here, we used simulation models to examine the influence of individual trait variation in both dispersal capacity and dispersal density-dependence on expansions, and how it impacts the position of expansions on the pulled-pushed continuum. First, we found that knowing about the evolution of density-dependent dispersal at the range edge can greatly improve our ability to predict whether an expansion is (more) pushed or (more) pulled. Second, we found that both dispersal costs and the sources of variation in dispersal (genetic or non-genetic, in dispersal capacity versus in density-dependence) greatly influence how expansion dynamics evolve. Among other scenarios, pushed expansions tended to become more pulled with time only when density-dependence was highly heritable, dispersal costs were low and dispersal capacity could not evolve. When, on the other hand, variation in density-dependence had no genetic basis, but dispersal capacity could evolve, then pushed expansions tended to become more pushed with time, and pulled expansions more pulled. More generally, our results show that trying to predict expansion velocities and dynamics using trait information from non-expanding regions only may be problematic, that both dispersal variation and its sources play a key role in determining whether an expansion is and stays pushed, and that environmental context (here dispersal costs) cannot be neglected. Those simulations suggest new avenues of research to explore, both in terms of theoretical studies and regarding ways to empirically study pushed vs. pulled range expansions.

Download Full-text

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

eLife ◽

10.7554/elife.57788 ◽

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.

Download Full-text