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Publications (10 of 27) Show all publications
Zhang, L., Thibert-Plante, X., Ripe, J., Svanback, R. & Brännström, Å. (2019). Biodiversity loss through speciation collapse: Mechanisms, warning signals, and possible rescue. Evolution, 73(8), 1504-1516
Open this publication in new window or tab >>Biodiversity loss through speciation collapse: Mechanisms, warning signals, and possible rescue
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2019 (English)In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 73, no 8, p. 1504-1516Article in journal (Refereed) Published
Abstract [en]

Speciation is the process that generates biodiversity, but recent empirical findings show that it can also fail, leading to the collapse of two incipient species into one. Here, we elucidate the mechanisms behind speciation collapse using a stochastic individual-based model with explicit genetics. We investigate the impact of two types of environmental disturbance: deteriorated visual conditions, which reduce foraging ability and impede mate choice, and environmental homogenization, which restructures ecological niches. We find that: (1) Species pairs can collapse into a variety of forms including new species pairs, monomorphic or polymorphic generalists, or single specialists. Notably, polymorphic generalist forms may be a transient stage to a monomorphic population; (2) Environmental restoration enables species pairs to reemerge from single generalist forms, but not from single specialist forms; (3) Speciation collapse is up to four orders of magnitude faster than speciation, while the reemergence of species pairs can be as slow as de novo speciation; (4) Although speciation collapse can be predicted from either demographic, phenotypic, or genetic signals, observations of phenotypic changes allow the most general and robust warning signal of speciation collapse. We conclude that factors altering ecological niches can reduce biodiversity by reshaping the ecosystem's evolutionary attractors.

Keywords
Assortative mating, hybridization, speciation, species diversity, warning signals
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:umu:diva-163080 (URN)10.1111/evo.13736 (DOI)000482092600001 ()30980527 (PubMedID)
Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-14Bibliographically approved
Ge, J., Lin, L. & Zhang, L. (2017). A DIFFUSIVE SIS EPIDEMIC MODEL INCORPORATING THE MEDIA COVERAGE IMPACT IN THE HETEROGENEOUS ENVIRONMENT. Discrete and continuous dynamical systems. Series B, 22(7), 2763-2776
Open this publication in new window or tab >>A DIFFUSIVE SIS EPIDEMIC MODEL INCORPORATING THE MEDIA COVERAGE IMPACT IN THE HETEROGENEOUS ENVIRONMENT
2017 (English)In: Discrete and continuous dynamical systems. Series B, ISSN 1531-3492, E-ISSN 1553-524X, Vol. 22, no 7, p. 2763-2776Article in journal (Refereed) Published
Abstract [en]

To explore the impact of media coverage and spatial heterogeneity of environment on the prevention and control of infectious diseases, a spatial-temporal SIS reaction-diffusion model with the nonlinear contact transmission rate is proposed. The nonlinear contact transmission rate is spatially dependent and introduced to describe the impact of media coverage on the transmission dynamics of disease. The basic reproduction number associated with the disease in the heterogeneous environment is established. Our results show that the degree of mass media attention plays an important role in preventing the spreading of infectious diseases. Numerical simulations further confirm our analytical findings.

Place, publisher, year, edition, pages
AMER INST MATHEMATICAL SCIENCES-AIMS, 2017
Keywords
Diffusive SIS model, heterogeneous environment, nonlinear contact transmission rate, basic production number, media coverage
National Category
Mathematics
Identifiers
urn:nbn:se:umu:diva-137028 (URN)10.3934/dcdsb.2017134 (DOI)000402309200012 ()
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2018-06-09Bibliographically approved
Tian, C., Lin, L. & Zhang, L. (2017). Additive noise driven phase transitions in a predator-prey system. Applied Mathematical Modelling, 46, 423-432
Open this publication in new window or tab >>Additive noise driven phase transitions in a predator-prey system
2017 (English)In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 46, p. 423-432Article in journal (Refereed) Published
Abstract [en]

We explore the impact of additive noise on phase transitions in a predator-prey system, which is formulated by stochastic partial differential equations (SPDEs). The system is observed to experience twice phase transitions under certain level of additive noise. We extend the multiple scaling approach from single SPDE to multiple SPDEs and find a necessary and sufficient condition to excite the occurrence of the first transition from a spatially homogeneous state to a spatially regular spiral wave. Numerical experiments show the second phase transition from the regular spatial pattern to spiral turbulence. We conclude that additive noise has a destabilising effect on population dynamics by triggering the onset of Hopf bifurcation.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Additive noise, Phase transitions, Spatial patterns, Predator-prey system, Stochastic partial differential equations
National Category
Mathematics
Identifiers
urn:nbn:se:umu:diva-137646 (URN)10.1016/j.apm.2017.01.087 (DOI)000403742000027 ()
Available from: 2017-07-18 Created: 2017-07-18 Last updated: 2018-06-09Bibliographically approved
Zhang, L., Takahashi, D., Hartvig, M. & Andersen, K. H. (2017). Food-web dynamics under climate change. Proceedings of the Royal Society of London. Biological Sciences, 284(1867), Article ID 20171772.
Open this publication in new window or tab >>Food-web dynamics under climate change
2017 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1867, article id 20171772Article in journal (Refereed) Published
Abstract [en]

Climate change affects ecological communities through its impact on the physiological performance of individuals. However, the population dynamic of species well inside their thermal niche is also determined by competitors, prey and predators, in addition to being influenced by temperature changes. We use a trait-based food-web model to examine how the interplay between the direct physiological effects from temperature and the indirect effects due to changing interactions between populations shapes the ecological consequences of climate change for populations and for entire communities. Our simulations illustrate how isolated communities deteriorate as populations go extinct when the environment moves outside the species' thermal niches. High-trophic-level species are most vulnerable, while the ecosystem function of lower trophic levels is less impacted. Open communities can compensate for the loss of ecosystem function by invasions of new species. Individual populations show complex responses largely uncorrelated with the direct impact of temperature change on physiology. Such complex responses are particularly evident during extinction and invasion events of other species, where climaticallywell-adapted species may be brought to extinction by the changed food-web topology. Our results highlight that the impact of climate change on specific populations is largely unpredictable, and apparently well-adapted species may be severely impacted.

Place, publisher, year, edition, pages
Royal Society, 2017
Keywords
population dynamics, Arrhenius, community ecology
National Category
Ecology Climate Research
Identifiers
urn:nbn:se:umu:diva-143600 (URN)10.1098/rspb.2017.1772 (DOI)000416391400010 ()
Available from: 2018-01-04 Created: 2018-01-04 Last updated: 2018-06-09Bibliographically approved
Zhang, L., Liu, J. & Banerjee, M. (2017). Hopf and steady state bifurcation analysis in a ratio-dependent predator-prey model. Communications in nonlinear science & numerical simulation, 44, 52-73
Open this publication in new window or tab >>Hopf and steady state bifurcation analysis in a ratio-dependent predator-prey model
2017 (English)In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 44, p. 52-73Article in journal (Refereed) Published
Abstract [en]

In this paper, we perform spatiotemporal bifurcation analysis in a ratio-dependent predator prey model and derive explicit conditions for the existence of non-constant steady states that emerge through steady state bifurcation from related constant steady states. These explicit conditions are numerically verified in details and further compared to those conditions ensuring Turing instability. We find that (1) Turing domain is identical to the parametric domain where there exists only steady state bifurcation, which implies that Turing patterns are stable non-constant steady states, but the opposite is not necessarily true; (2) In non-Turing domain, steady state bifurcation and Hopf bifurcation act in concert to determine the emergent spatial patterns, that is, non-constant steady state emerges through steady state bifurcation but it may be unstable if the destabilising effect of Hopf bifurcation counteracts the stabilising effect of diffusion, leading to non-stationary spatial patterns; (3) Coupling diffusion into an ODE model can significantly enrich population dynamics by inducing alternative non-constant steady states (four different states are observed, two stable and two unstable), in particular when diffusion interacts with different types of bifurcation; (4) Diffusion can promote species coexistence by saving species which otherwise goes to extinction in the absence of diffusion.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Prey-predator model, Turing instability, Pattern formation, Spatiotemporal bifurcation, Non-constant eady state
National Category
Mathematics Physical Sciences
Identifiers
urn:nbn:se:umu:diva-130075 (URN)10.1016/j.cnsns.2016.07.027 (DOI)000386744400005 ()
Available from: 2017-01-13 Created: 2017-01-11 Last updated: 2018-06-09Bibliographically approved
Tian, C., Ling, Z. & Zhang, L. (2017). Nonlocal interaction driven pattern formation in a prey-predator model. Applied Mathematics and Computation, 308, 73-83
Open this publication in new window or tab >>Nonlocal interaction driven pattern formation in a prey-predator model
2017 (English)In: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 308, p. 73-83Article in journal (Refereed) Published
Abstract [en]

A widely observed scenario in ecological systems is that populations interact not only with those living in the same spatial location but also with those in spatially adjacent locations, a phenomenon called nonlocal interaction. In this paper, we explore the role of nonlocal interaction in the emergence of spatial patterns in a prey-predator model under the reaction-diffusion framework, which is described by two coupled integro-differential equations. We first prove the existence and uniqueness of the global solution by means of the contraction mapping theory and then conduct stability analysis of the positive equilibrium. We find that nonlocal interaction can induce Turing bifurcation and drive the formation of stationary spatial patterns. Finally we carry out numerical simulations to demonstrate our analytical findings.

National Category
Mathematics
Identifiers
urn:nbn:se:umu:diva-134685 (URN)10.1016/j.amc.2017.03.017 (DOI)000399591500006 ()
Available from: 2017-06-22 Created: 2017-06-22 Last updated: 2018-06-09Bibliographically approved
Zhang, L., Dieckmann, U. & Brännström, Å. (2017). On the performance of four methods for the numerical solution of ecologically realistic size-structured population models. Methods in Ecology and Evolution, 8(8), 948-956
Open this publication in new window or tab >>On the performance of four methods for the numerical solution of ecologically realistic size-structured population models
2017 (English)In: Methods in Ecology and Evolution, ISSN 2041-210X, E-ISSN 2041-210X, Vol. 8, no 8, p. 948-956Article in journal (Refereed) Published
Abstract [en]

1. Size-structured population models (SSPMs) are widely used in ecology to account for intraspecific variation in body size. Three characteristic features of size-structured populations are the dependence of life histories on the entire size distribution, intrinsic population renewal through the birth of new individuals, and the potential accumulation of individuals with similar body sizes due to determinate or stunted growth. Because of these three features, numerical methods that work well for structurally similar transport equations may fail for SSPMs and other transport-dominated models with high ecological realism, and thus their computational performance needs to be critically evaluated.

2. Here, we compare the performance of four numerical solution schemes, the fixed-mesh upwind (FMU) method, the moving-mesh upwind (MMU) method, the characteristic method (CM), and the Escalator Boxcar Train (EBT) method, in numerically solving three reference problems that are representative of ecological systems in the animal and plant kingdoms. The MMU method is here applied for the first time to SSPMs, whereas the three other methods have been employed by other authors.

3. Our results show that the EBT method performs best, except for one of the three reference problems, in which size-asymmetric competition affects individual growth rates. For that reference problem, the FMU method performs best, closely followed by the MMU method. Surprisingly, the CM method does not perform well for any of the three reference problems.

4. We conclude that life-history features should be carefully considered when choosing the numerical method for analyzing ecologically realistic size-structured population models.

Keywords
asymmetric competition, characteristic curve, Escalator Boxcar Train, life history, moving mesh, size-structured population, upwind scheme
National Category
Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-138680 (URN)10.1111/2041-210X.12741 (DOI)000406916200006 ()
Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2018-06-09Bibliographically approved
Liu, J. & Zhang, L. (2016). Bifurcation analysis in a prey-predator model with nonlinear predator harvesting. Journal of the Franklin Institute, 353(17), 4701-4714
Open this publication in new window or tab >>Bifurcation analysis in a prey-predator model with nonlinear predator harvesting
2016 (English)In: Journal of the Franklin Institute, ISSN 0016-0032, E-ISSN 1879-2693, Vol. 353, no 17, p. 4701-4714Article in journal (Refereed) Published
Abstract [en]

In this paper, the spatiotemporal dynamics of a delayed diffusive prey predator model with nonlinear predator harvesting is investigated. Through mathematical analysis, we obtain the conditions for Turing and Hopf bifurcation. Numerical simulations display a variety of spatial patterns including spots, strips, mixture of spots and strips, spiral, patchy structure, and chaos. The delay is found to have significant influence on the emergent spatial patterns, such as changing arm length and direction of strips, and accelerating the transformation of spatial patterns. 

National Category
Mathematics
Identifiers
urn:nbn:se:umu:diva-129924 (URN)10.1016/j.jfranklin.2016.09.005 (DOI)000387200900018 ()
Available from: 2017-01-10 Created: 2017-01-10 Last updated: 2018-06-09Bibliographically approved
Lindh, M., Falster, D., Zhang, L., Dieckmann, U. & Brännström, Å. (2016). Evolution of tree crown shape and the influence of productivity, incident sun angle, and latitude.
Open this publication in new window or tab >>Evolution of tree crown shape and the influence of productivity, incident sun angle, and latitude
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2016 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Across the globe, large variations are observed in plant architecture, from bushes in tundra and semi desert, to high top-heavy trees in boreal and tropical forests. Despite recent advances in large scale monitoring of forests, little is known about how crown architecture varies with environmental conditions. We investigate how shading from the plant on itself, and the shading from the forest influence growth, using a dynamic size-structured crown architecture model with mean-field shading and self-shading, based on an established model. We evolve the two traits crown top-heaviness and crown width-to-height ratio.

We report the following findings: (1) Tree crowns are shaped by trade-offs. Top-heavy crowns intercept light well as they can reach high up in the vertical light gradient, but they have low crown-rise efficiency. Wide crowns have a low leaf density per volume giving low self-shading, but a large cost for branches. (2) When coevolving the two traits we find a single evolutionarily stable strategy, far away from the strategy maximizing net primary production. (3) When only sun angle decreases with latitude, both crown width-to-height ratio and crown top-heaviness are decreasing with latitude. When both sun angle and light assimilation response to canopy openness decreases with latitude, crown width-to-height ratio is decreasing significantly only at sites with low productivity, while crown top-heaviness decreases for all sites independent of productivity. Crown top-heaviness increases with increasing site productivity, as a result of a darker forest caused by an increasing density of plants. (4) When varying latitude and sun angle over large ranges we find that crown width-to-height ratio has a maximum at intermediate net primary production or leaf area index, while crown top heaviness is saturating for high net primary production or leaf area index.

Our model approach makes it possible to study evolving crown shapes in high detail, and we can identify trade-offs for crown shape. As expected crown top-heaviness is increasing with site productivity and net primary production, but crown width-to-height ratio has a rich and a more unexpected response due to interactions of self-shading and mean-field-shading.

Keywords
forest, plant architecture, ecology
National Category
Ecology
Research subject
Mathematics
Identifiers
urn:nbn:se:umu:diva-119541 (URN)
Available from: 2016-04-22 Created: 2016-04-22 Last updated: 2018-06-07
Meng, X. & Zhang, L. (2016). Evolutionary dynamics in a Lotka–Volterra competition model with impulsive periodic disturbance. Mathematical methods in the applied sciences, 39(2), 177-188
Open this publication in new window or tab >>Evolutionary dynamics in a Lotka–Volterra competition model with impulsive periodic disturbance
2016 (English)In: Mathematical methods in the applied sciences, ISSN 0170-4214, E-ISSN 1099-1476, Vol. 39, no 2, p. 177-188Article in journal (Refereed) Published
Abstract [en]

In this paper, we develop a theoretical framework to investigate the influence of impulsive periodic disturbance on the evolutionary dynamics of a continuous trait, such as body size, in a general Lotka–Volterra-type competition model. The model is formulated as a system of impulsive differential equations. First, we derive analytically the fitness function of a mutant invading the resident populations when rare in both monomorphic and dimorphic populations. Second, we apply the fitness function to a specific system of asymmetric competition under size-selective harvesting and investigate the conditions for evolutionarily stable strategy and evolutionary branching by means of critical function analysis. Finally, we perform long-term simulation of evolutionary dynamics to demonstrate the emergence of high-level polymorphism. Our analytical results show that large harvesting effort or small impulsive harvesting period inhibits branching, while large impulsive harvesting period promotes branching.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
adaptive dynamics, critical function analysis, periodic disturbance, singular strategy, speciation
National Category
Mathematical Analysis
Identifiers
urn:nbn:se:umu:diva-101199 (URN)10.1002/mma.3467 (DOI)000368798900002 ()
Available from: 2015-03-24 Created: 2015-03-24 Last updated: 2018-06-07Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2409-7348

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