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Abstract:
Traditional evolutionary theory often treats selective forces from the
environment and the adaptation of populations as independent of each other,
focusing on the effects of natural selection on population dynamics. The
fitness landscape is considered to be static, and adaptation is taken as a
process of optimisation. In this thesis, I intend to call attention to the interactions
between the environment and biological populations, emphasising the
feedbacks from the population to the environment that changes the direction,
rate and dynamics of the evolutionary process.
Two general approaches through which populations affect their environment
are studied in this thesis. The first one is via life history and demographic
architecture of the population. The second one is through interactions among
individuals of the same or different types in the population. These two approaches
are not inter-exclusive, but rather interact and reinforce each other.
Evolutionary game theory provides a convenient framework of modelling
interactions, but it usually takes no account of the life history aspects of
the organisms in the population. Demographic models, on the other hand,
emphasise the optimisation of life history traits, while neglecting interactions
among individuals in the population. One major innovation in this thesis
project is to build a system that takes into account both aspects and connects
the two theoretical frameworks. This is realised by defining age/life-stage
dependent strategies. The behaviours of individuals are conditioned on the
age/life-stage of the players involved in the interactions. The dynamics of the
system are studied under both deterministic and stochastic frameworks.
Besides an analytical and numerical study of abstract mathematical models,
this thesis also includes collaborative projects with experiments in real
biological systems. In one modelling project, we show how complex population
dynamics can emerge from a simple system of two bacteria species, under
frequency dependent selection. Preliminary experimental evidence suggests
that the infection and cross-infection of phages might have produced such
frequency dependent effects. We continue the investigation in a follow up
project.
Covering diverse subjects and employing various methods and mathematical
techniques, this thesis summarises my research in the last three years,
raises new questions, and opens up opportunities for future investigations.
