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

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

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

Evolution of positive and negative density-dependent dispersal

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.1226 ◽

2014 ◽

Vol 281 (1791) ◽

pp. 20141226 ◽

Cited By ~ 29

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.

Download Full-text

Dispersal and life-history traits in a spider with rapid range expansion

Movement Ecology ◽

10.1186/s40462-019-0182-4 ◽

2020 ◽

Vol 8 (1) ◽

Cited By ~ 3

Author(s):

Marina Wolz ◽

Michael Klockmann ◽

Torben Schmitz ◽

Stano Pekár ◽

Dries Bonte ◽

...

Keyword(s):

Climate Change ◽

Life History ◽

Environmental Conditions ◽

Range Expansion ◽

Life History Traits ◽

Winter Survival ◽

Model Organisms ◽

Spatial Sorting ◽

Theoretical Predictions ◽

Edge Populations

Abstract Background Dispersal and reproduction are key life-history traits that jointly determine species’ potential to expand their distribution, for instance in light of ongoing climate change. These life-history traits are known to be under selection by changing local environmental conditions, but they may also evolve by spatial sorting. While local natural selection and spatial sorting are mainly studied in model organisms, we do not know the degree to which these processes are relevant in the wild, despite their importance to a comprehensive understanding of species’ resistance and tolerance to climate change. Methods The wasp spider Argiope bruennichi has undergone a natural range expansion - from the Mediterranean to Northern Europe during the recent decades. Using reciprocal common garden experiments in the laboratory, we studied differences in crucial traits between replicated core (Southern France) and edge (Baltic States) populations. We tested theoretical predictions of enhanced dispersal (ballooning behaviour) and reproductive performance (fecundity and winter survival) at the expansion front due to spatial sorting and local environmental conditions. Results Dispersal rates were not consistently higher at the northern expansion front, but were impacted by the overwintering climatic conditions experienced, such that dispersal was higher when spiderlings had experienced winter conditions as occur in their region. Hatching success and winter survival were lower at the range border. In agreement with theoretical predictions, spiders from the northern leading edge invested more in reproduction for their given body size. Conclusions We found no evidence for spatial sorting leading to higher dispersal in northern range edge populations of A. bruennichi. However, reproductive investment and overwintering survival between core and edge populations differed. These life-history traits that directly affect species’ expansion rates seem to have diverged during the recent range expansion of A. bruennichi. We discuss the observed changes with respect to the species’ natural history and the ecological drivers associated with range expansion to northern latitudes.

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

Shifts from pulled to pushed range expansions caused by reduction of landscape connectivity

10.1101/2020.05.13.092775 ◽

2020 ◽

Cited By ~ 2

Author(s):

Maxime Dahirel ◽

Aline Bertin ◽

Marjorie Haond ◽

Aurelie Blin ◽

Eric Lombaert ◽

...

Keyword(s):

Genetic Diversity ◽

Evolutionary Dynamics ◽

Landscape Connectivity ◽

Empirical Studies ◽

Parasitoid Wasp ◽

Trichogramma Brassicae ◽

Relevant Today ◽

Current Context ◽

Edge Populations ◽

Evolutionary Consequences

Range expansions are key processes shaping the distribution of species; their ecological and evolutionary dynamics have become especially relevant today, as human influence reshapes ecosystems worldwide. Many attempts to explain and predict range expansions assume, explicitly or implicitly, so-called "pulled" expansion dynamics, in which the low-density edge populations provide most of the "fuel" for the species advance. Some expansions, however, exhibit very different dynamics, with high-density populations behind the front "pushing" the expansion forward. These two types of expansions are predicted to have different effects on e.g. genetic diversity and habitat quality sensitivity. However, empirical studies are lacking due to the challenge of generating reliably pushed vs. pulled expansions in the laboratory, or discriminating them in the field. We here propose that manipulating the degree of connectivity among populations may prove a more generalizable way to create pushed expansions. We demonstrate this with individual-based simulations as well as replicated experimental range expansions (using the parasitoid wasp Trichogramma brassicae as model). By analyzing expansion velocities and neutral genetic diversity, we showed that reducing connectivity led to pushed dynamics. Low connectivity alone, i.e. without density-dependent dispersal, can only lead to "weakly pushed" expansions, where invasion speed conforms to pushed expectations, but the decline in genetic diversity does not. In empirical expansions however, low connectivity may in some cases also lead to adjustments to the dispersal-density function, recreating "classical" pushed expansions. In the current context of habitat loss and fragmentation, we need to better account for this relationship between connectivity and expansion regimes to successfully predict the ecological and evolutionary consequences of range expansions.

Download Full-text