Evolving ecological communities in changing environments
Sammanfattning: This thesis consists of theoretical studies of the evolutionary consequences of environmental change in ecological communities. Paper I and II are concerned with the origin of diversity, i.e. how a single lineage can split into two, under the influence of selection induced by competitive interactions (evolutionary branching). In paper I we find that environmental fluctuations may affect the likelihood of such a split. In particular, if correlation in species environment decreases quickly during divergence, stochastic fluctuations can impede or delay the branching process. In paper II we study this process more in detail in a scenario where population fluctuations are derived mechanistically from environmental fluctuations affecting prey growth rates. We find that high autocorrelation in combination with low or negative correlation in environmental fluctuations can block the branching process. The fluctuating environment may also cause cycles of branching and extinction. In paper III I study the role of competition for adaptation in a changing environment. The environmental change is envisioned as gradual shifts of the resource landscape. I find that competitive interactions decrease the rate of adaptation considerably due to an ecological effect of the environmental change (an increase in population size of the species favoured by the change). As a result a coalition of two species can only adapt to a slowly changing resource landscape, whereas a single species can adapt to much more variable environments. In paper IV we investigate the long term effects of extinctions on ecological communities, and especially if inherent evolutionary dynamics, i.e. gradual evolution in combination with evolutionary branching can restore an ecological community after extinctions of constituent species. Interestingly, even if an ESS can be constructed, or attained, from a single precursor species it is not certain that evolution will lead back to it after extinctions. We discuss how such irreversible evolution may lead to Humpty-Dumpty effects and community closure on an evolutionary time scale. In sum, the findings illustrate that if ecological feedback is taken into account for evolutionary responses to environmental changes and extinctions, rather complex patterns of community evolution can be anticipated. With very few assumptions in the description of the ecological and evolutionary model, environmental perturbations may cause delays in community radiation, evolutionarily driven extinctions, patterns of repeated branching and shifts of ESS impeding restoration. The inclusion of ecological feedback also reveals how evolutionary responses to a changing environment can be modified and slowed down by interactions which even may lead to patterns of stasis and mass extinctions.
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