scholarly journals Evolution transforms pushed waves into pulled waves

2018 ◽  
Author(s):  
Philip Erm ◽  
Ben L. Phillips
Keyword(s):  
Invasive Species ◽  
Genetic Structure ◽  
Allee Effect ◽  
Evolutionary Dynamics ◽  
Low Density ◽  
Allee Effects ◽  
Invasion Speed ◽  
Invasion Dynamics ◽  
Invasion Front ◽  
Invasion Fronts

AbstractUnderstanding the dynamics of biological invasions is crucial for managing numerous phenomena, from invasive species to tumours. While Allee effects (where individuals in low-density populations suffer lowered fitness) are known to influence both the ecological and evolutionary dynamics of invasions, the possibility that an invader’s susceptibility to the Allee effect might itself evolve on an invasion front has received almost no attention. Since invasion fronts are regions of perpetually low population density, selection should favour vanguard invaders that are resistant to Allee effects. Evolution in response to this pressure could cause invasions to transition from pushed waves, propelled by dispersal from behind the invasion front, to pulled waves, driven by the invasion vanguard. To examine this possibility, we construct an individual-based model in which a trait that governs resistance to the Allee effect is allowed to evolve during an invasion. We find that vanguard invaders rapidly evolve resistance to the Allee effect, causing invasions to accelerate. This also results in invasions transforming from pushed waves into pulled waves, an outcome with consequences for predictions of invasion speed, the population’s genetic structure, and other important behaviours. These findings underscore the importance of accounting or evolution in invasion forecasts, and suggest that evolution has the capacity to fundamentally alter invasion dynamics.

scholarly journals Anomalous invasion dynamics due to dispersal polymorphism and dispersal-reproduction trade-offs

2020 ◽  
Author(s):  
Vincent A. Keenan ◽  
Stephen J. Cornell
Keyword(s):  
Life History Theory ◽  
Invasion Speed ◽  
Complex Behaviour ◽  
Trade Off ◽  
Invasion Dynamics ◽  
Population Growth Rates ◽  
Trade Offs ◽  
Invasion Fronts ◽  
Wide Range ◽  
Dispersal Polymorphism

AbstractDispersal polymorphism and mutation play significant roles during biological invasions, potentially leading to evolution and complex behaviour such as accelerating or decelerating invasion fronts. However, life history theory predicts that reproductive fitness — another key determinant of invasion dynamics – may be lower for more dispersive strains. Here, we use a mathematical model to show that unexpected invasion dynamics emerge from the combination of heritable dispersal polymorphism, dispersal-fitness trade-offs, and mutation between strains. We show that the invasion dynamics are determined by the trade-off relationship between dispersal and population growth rates of the constituent strains. We find that invasion dynamics can be “anomalous” (i.e. faster than any of the strains in isolation), but that the ultimate invasion speed is determined by the traits of at most two strains. The model is simple but generic, so we expect the predictions to apply to a wide range of ecological, evolutionary or epidemiological invasions.

scholarly journals Anomalous invasion dynamics due to dispersal polymorphism and dispersal–reproduction trade-offs

2021 ◽  
Vol 288 (1942) ◽  
pp. 20202825
Author(s):  
Vincent A. Keenan ◽  
Stephen J. Cornell
Keyword(s):  
Life History Theory ◽  
Invasion Speed ◽  
Complex Behaviour ◽  
Trade Off ◽  
Invasion Dynamics ◽  
Population Growth Rates ◽  
Trade Offs ◽  
Invasion Fronts ◽  
Wide Range ◽  
Dispersal Polymorphism

Dispersal polymorphism and mutation play significant roles during biological invasions, potentially leading to evolution and complex behaviour such as accelerating or decelerating invasion fronts. However, life-history theory predicts that reproductive fitness—another key determinant of invasion dynamics—may be lower for more dispersive strains. Here, we use a mathematical model to show that unexpected invasion dynamics emerge from the combination of heritable dispersal polymorphism, dispersal-fitness trade-offs, and mutation between strains. We show that the invasion dynamics are determined by the trade-off relationship between dispersal and population growth rates of the constituent strains. We find that invasion dynamics can be ‘anomalous’ (i.e. faster than any of the strains in isolation), but that the ultimate invasion speed is determined by the traits of, at most, two strains. The model is simple but generic, so we expect the predictions to apply to a wide range of ecological, evolutionary, or epidemiological invasions.

scholarly journals The genetic Allee effect: A unified framework for the genetics and demography of small populations

2016 ◽  
Author(s):  
Gloria M. Lucque ◽  
Chloé Vayssade ◽  
Benoît Facon ◽  
Thomas Guillemaud ◽  
Franck Courchamp ◽  
...  
Keyword(s):  
Genetic Structure ◽  
Population Size ◽  
Allee Effect ◽  
Small Populations ◽  
Allee Effects ◽  
Unified Framework ◽  
Fitness Components ◽  
Individual Fitness ◽  
Heated Debate ◽  
Underlying Mechanisms

AbstractThe Allee effect is a theoretical model predicting low growth rates and the possible extinction of small populations. Historically, studies of the Allee effect have focused on demography. As a result, underlying processes other than the direct effect of population density on fitness components are not generally taken into account. There has been heated debate about the potential of genetic processes to drive small populations to extinction, but recent studies have shown that such processes clearly impact small populations over short time scales, and some may generate Allee effects. However, as opposed to the ecological Allee effect, which is underpinned by cooperative interactions between individuals, genetically driven Allee effects require a change in genetic structure to link the decline in population size with a decrease in fitness components. We therefore define the genetic Allee effect as a two-step process whereby a decrease in population size leads to a change in population genetic structure, and in turn, to a decrease in individual fitness. We describe potential underlying mechanisms, and review the evidence for this original type of component Allee effect, using published examples from both plants and animals. The possibility of considering demogenetic feedback in light of genetic Allee effects clarifies the analysis and interpretation of demographic and genetic processes, and the interplay between them, in small populations.

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.

Spatial genetic structure inMilicia excelsa(Moraceae) indicates extensive gene dispersal in a low-density wind-pollinated tropical tree

2009 ◽  
Vol 18 (21) ◽  
pp. 4398-4408 ◽  
Author(s):  
J.-P. BIZOUX ◽  
K. DAÏNOU ◽  
N. BOURLAND ◽  
O. J. HARDY ◽  
M. HEUERTZ ◽  
...  
Keyword(s):  
Genetic Structure ◽  
Spatial Genetic Structure ◽  
Tropical Tree ◽  
Low Density ◽  
Gene Dispersal

Locomotor performance in an invasive species: cane toads from the invasion front have greater endurance, but not speed, compared to conspecifics from a long-colonised area

Oecologia ◽  
2009 ◽  
Vol 162 (2) ◽  
pp. 343-348 ◽  
Author(s):  
John Llewelyn ◽  
Benjamin L. Phillips ◽  
Ross A. Alford ◽  
Lin Schwarzkopf ◽  
Richard Shine
Keyword(s):  
Invasive Species ◽  
Locomotor Performance ◽  
Invasion Front

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 Evidence for an Allee effect in a declining fur seal population

2021 ◽  
Vol 288 (1947) ◽  
Author(s):  
Rebecca Nagel ◽  
Claire Stainfield ◽  
Cameron Fox-Clarke ◽  
Camille Toscani ◽  
Jaume Forcada ◽  
...  
Keyword(s):  
Time Series Data ◽  
Poor Quality ◽  
Weight Of Evidence ◽  
Series Data ◽  
Low Density ◽  
Allee Effects ◽  
Wild Populations ◽  
Fur Seal ◽  
Parallel Body ◽  
Pup Mortality

Allee effects play an important role in the dynamics of many populations and can increase the risk of local extinction. However, some authors have questioned the weight of evidence for Allee effects in wild populations. We therefore exploited a natural experiment provided by two adjacent breeding colonies of contrasting density to investigate the potential for Allee effects in an Antarctic fur seal ( Arctocephalus gazella ) population that is declining in response to climate change-induced reductions in food availability. Biometric time-series data were collected from 25 pups per colony during two consecutive breeding seasons, the first of which was among the worst on record in terms of breeding female numbers, pup birth weights and foraging trip durations. In previous decades when population densities were higher, pup mortality was consistently negatively density dependent, with rates of trauma and starvation scaling positively with density. However, we found the opposite, with higher pup mortality at low density and the majority of deaths attributable to predation. In parallel, body condition was depressed at low density, particularly in the poor-quality season. Our findings shed light on Allee effects in wild populations and highlight a potential emerging role of predators in the ongoing decline of a pinniped species.

scholarly journals Population Genetic Structure of the Invasive Spotted Alfalfa Aphid Therioaphis trifolii (Hemiptera: Aphididae) in China Inferred From Complete Mitochondrial Genomes

2021 ◽  
Vol 9 ◽  
Author(s):  
Xinzhi Liu ◽  
Shuhua Wei ◽  
Zhenyong Du ◽  
Jia He ◽  
Xinyue Zhang ◽  
...  
Keyword(s):  
Invasive Species ◽  
Genetic Structure ◽  
Population Genetic ◽  
High Throughput Sequencing ◽  
Demographic History ◽  
Complete Mitochondrial Genome ◽  
Haplotype Diversity ◽  
Evolutionary Process ◽  
Invasion History ◽  
Ecosystem Integrity

Biological invasions represent a natural rapid evolutionary process in which invasive species may present a major threat to biodiversity and ecosystem integrity. Analyzing the genetic structure and demographic history of invaded populations is critical for the effective management of invasive species. The spotted alfalfa aphid (SAA) Therioaphis trifolii is indigenous in the Mediterranean region of Europe and Africa and has invaded China, causing severe damages to the alfalfa industry. However, little is known about its genetic structure and invasion history. In this study, we obtained 167 complete mitochondrial genome sequences from 23 SAA populations across China based on high-throughput sequencing and performed population genetic and phylogenomic analyses. High haplotype diversity and low nucleotide diversity were found in SAA populations in China with distinct genetic structures, i.e., all populations diverged into three phylogenetic lineages. Demographic history analyses showed a recent expansion of the SAA population, consistent with the recent invasion history. Our study indicated that SAA may have invaded through multiple introduction events during commercial trades of alfalfa, although this needs further validation by nuclear markers.

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