Doctoral thesis investigates population movement models in competition for resources

Since populations of animals and plant communities are prototypical examples of complex systems – they comprise many heterogeneous individuals or species that interact and display diversified behaviors and spatial distributions –, the models and tools used in this thesis come from Statistical Physics and Complex Systems Theory. Part of my research consisted in the implementation of a stochastic numerical model that considers a heterogeneous population of individuals that move with diversified dispersal abilities, die, and reproduce, and compete for resources over a finite competition range affecting their demographic processes and thus survival.  

As initial conditions for the model two ecologically representative cases were considered: 1) a densely crowded environment, in which patch formation can play a crucial role and 2) a habitat consisting in a central and small crowded patch from which individuals can spread across the unoccupied space. In both cases, the initial population is characterized with a large variety of dispersal abilities. By performing many numerical realizations of the model with statistically equivalent initial conditions, the competitive outcome was analyzed obtaining the final probability distributions of the dispersal abilities and averages quantities of the relevant variables such as population size and diversity (number of different dispersal abilities remaining in the system).

With regards the first environment studied (1), the most interesting finding is the emergence of a range of optimal intermediates (not the most or least motile) values of the dispersal ability, suggesting that natural selection could act on this trait. Besides, such values can be related to the features of the periodic spatial distribution in which the organisms self-organize (a patchy environment). Besides, such an inhomogeneous environment can foster the coexistence of different dispersal abilities under suitable values of the model parameters (the average initial dispersal coefficient of the population). Concerning the second habitat studied (2), the case of invading populations, the results are radically different: although initially the most motile individuals can win the competition process because of their ability to colonize, due to finite size of the environment studied, in the long term, individuals with moderately low values of the dispersal ability could also give the competitive advantage.

The results of this thesis demonstrate the importance of dispersal in ecological competition. The study is particularly relevant for systems of micro-organisms such as bacteria but may give useful references also for the systems consisting of macro-organisms like animal populations or plant communities.

Doctoral student in School of Natural Sciences and Health David Navidad Maseo defended his doctoral thesis "Finite-range competition and natural selection in dispersal-structured populations" on September 19. Thesis supervisors were Senior Researcher at National Institute of Chemical Physics and Biophysics Els Heinsalu, Senior Researcher at National Institute of Chemical Physics and Biophysics Marco Patriarca and Associate Professor at Tallinn University Astrid Rekker. Opponents were Tenured Full Professor at the Tallinn University of Technology Jaan Kalda and Young Investigator Group Leader at Center for Advanced Systems Understan Ricardo Martínez-García,.