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Tadeas Priklopil, University of Helsinki

Title: On the evolution of magic traits and speciation

We study the adaptive dynamics of a so-called magic trait, which is under natural selection and which also serves as a cue for mating. We derive general results on the monomorphic evolutionary singularities. Next, we study the long-term evolution of single-locus genetic polymorphisms under different forms and strengths of mating preferences in a version of Levene's soft selection model, where natural selection favours different values of a continuous trait within two habitats. If adaptive dynamics leads to a polymorphism with sufficiently different alleles, then the corresponding homozygotes cease to interbreed so that speciation occurs.

Philip Gerlee, Niels Bohr Institute

Title: The effect of space on the war of attrition

In the game-theoretic model 'war of attrition' the strategy of a player consists of a single real number which corresponds to how long the agent is willing to wait. In the two-contestant game, the winner is the player with the longest waiting time (WT). The winner collects a unit award, while the loser receives a consolation prize of k < 1. It has previously been shown that a population of agents playing this game (with an implicit time-cost, i.e. players with long waiting times play fewer games), can exhibit both stationary and oscillatory distribution of WT depending on the value of k. We consider the effect of space on the dynamics, and analyse a coarse-grained version of the model, which is formally equivalent to a stochastic cellular automata. The results show that the system exhibits a phase-transition in the WT-distribution, where for small k the long WTs dominate, while for large k short WTs are most abundant. However, when the spatial component is removed and the model is well-stirred this effect disappears and co-existence is prominent.

Alexander Sadykov, University of Oslo

Title: Epidemiology of conspecific community

Point of view on the population as on an intrinsically organized conspecific community of diverse individuals requires a revision of the basic epidemiological models with taking into account heterogeneity among individuals and underlying physiology of host. We introduce a new analytical platform to modelling epidemics, which combines nutrition-depended physiology and nutrition-depended immunity with differences among individuals. This approach allows to investigate the spread of epidemics in conspecific communities, which consist of varying by their immunocompetence of individuals, as well as to reveal the link between resource fluctuations and epidemic outbreaks. Using a simple SIS model as an example, we show that heterogeneity among individuals plays a key role in determining the dynamics of epidemics, while the traditional parameters such as population size or average physical condition of the host are of secondary importance, in the sense that they do not allow to give unambiguous evaluation of epidemic thresholds.

Mikael Pontarp, Lund University

Title: Evolutionary and ecological processes structure marine bacterial communities across the globe

Natural communities are the products of historical contingencies and current ecological processes. Incorporating phylogentic data into studies of community assemblage provide a framework for inferring the importance of these processes. E.g. phylogenetic structure of a community can inform us about the processes shaping them. For the first time a combination of phylogenetic structure analysis and data on species abundance, geographical distribution and habitat characteristics are used to interpret non-random phylogenetic signals to elucidate ecological and evolutionary mechanisms dictating the assemblage of nine globally distributed marine bacterial communities. We recognize that results and interpretations from these methods are scale dependent. Consequently, the analyses were done on different geographical and phylogenetic scales. We show that community assemblage is phylogenetically different in natural marine bacterioplancton communities distributed around the globe. A large proportion of the communities are clustered, i.e., the recruitment to these communities has a strong bias towards phylogenetically similar organisms. Thus, the local communities are assembled non-randomly from the global pool of available bacterioplankton. We also find a correlation between phylogenetic structure and temperature at sample sight. These results indicate that habitat filtering probably plays a dominating role in community assemblage. Nevertheless, this does not rule out local inter-specific competition at other geographical and temporal scales, although we cannot from data pick up a conclusive signal. We conclude that, dependent on what scale is studied, bacterial communities can be structured in similar ways as macro-organisms by habitat filtering and intra-specific interactions.

Thanate Dhirasakdanon, University of Helsinki

Title: Coexistence of vertically and horizontally transmitted parasite
strains in a simple SI type model

We study an SI type endemic model with one host and two parasite strains with complete cross protection between the strains. We assume that one strain is exclusively vertically transmitted and the other strain is horizontally (and possibly also vertically) transmitted. We also assume reduced fertility and increased mortality of infected hosts. Our model, which consists of three ordinary differential equations, has some
remarkable properties. The first is the paradox that the ratio of horizontal to vertical transmission decreases if the coefficient of
horizontal transmission increases [1]. The second is that the vertically
transmitted strain that would go extinct by itself can persist by
protecting the host against the more virulent horizontally transmitted
strain [2]. Finally, if the horizontal transmission is of
density-dependent (mass-action) type, the endemic equilibrium is always
locally asymptotically stable, but if the horizontal transmission is of
frequency-dependent (standard) type, the endemic equilibrium can become
unstable and undamped oscillations can occur [3].

[1] Stanley H. Faeth, Karl P. Hadeler, and Horst R. Thieme.
An apparent paradox of horizontal and vertical disease transmission.
Journal of Biological Dynamics, 1(1):45-62, 2007.
[2] Thanate Dhirasakdanon and Horst R. Thieme.
Persistence of vertically transmitted parasite strains which protect
against more virulent horizontally transmitted strains.
In Z. Ma, Y. Zhou, and J. Wu, editors, Modeling and Dynamics of
Infectious Diseases, 187-215, World Scientific, 2009.
[3] Thanate Dhirasakdanon and Horst R. Thieme.
Stability of the endemic coexistence equilibrium for one host and two
Mathematical Modelling of Natural Phenomena, 5(6):109-138, 2010.

Valerio Bartolino

Title: Scale-dependent depletion of natural resource

In ecology certain processes dominate others at particular scales, and
the response of populations to exogenous and endogenous forces are
typically scale-dependent. In spite of this central role played by
scale, the temporal and spatial scales of human impacts on ecosystems
and populations remain almost unknown. We used a spatially explicit
model to detect the depletion scales of a natural population of fish in
relation to fisheries exploitation. Applying a multiscale regression
analysis, and integrating harvesting and monitoring data, we
investigated the spatiotemporal scales which characterize the depletion
of a large fish population in the eastern Bering Sea. We found that
harvest-induced depletion processes act simultaneously at local and
regional scales. At the local scale harvesting produced a negative
effect on local fish densities, particularly in those areas and periods
of fish aggregation, when both the vulnerability of the fish and the
targeting behaviour of the fleet increase. In contrast, at the regional
scale harvesting was characterized by a diffused effect on the whole
fish population across seasons and years. We findings demonstrate how
human activities can simultaneously operate over a wide range of
ecological scales which are not necessarily correlated with each other,
with consequent limited possibilities of up-scaling human-induced
depletion processes.

Page Manager: Lisa Sundqvist|Last update: 9/27/2010

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