Browsing by Subject "community perturbations"

The purpose of this thesis was to study the antibiotic perturbations in bacterial populations. Perturbations are common in ecosystems and they can change the composition and functionality of a community substantially. The response of a community is governed by ecological and evolutionary factors: perturbations change the competitive ability of species in the community, but rapid evolution can further affect species fate. This thesis focuses more on the ecological effects. Understanding the community response to a disturbance would be interesting both from a general point of view and from the more practical approach of understanding natural communities under perturbations caused by antibiotics but also, for example, by climate change or chemicals. Thus far, most studies have been performed in one- or two-species systems, not taking into account the effects communities have on the fate of a single species. To study antibiotic perturbations, a multi-species bacterial community was exposed to a streptomycin pulse of three different levels concentrations. Changes in community composition were studied in the end of the pulse (ecological resistance) and after a recovery period (resilience) from the antibiotic perturbation comparing to the pre-perturbed communities. Further, the presence of species flow was manipulated to examine if it could enhance community resistance and resilience. Based on the analysis, even low antibiotic concentrations can have a long-lasting effect on community composition, but the magnitude of the effect is dependent on the concentration. Community diversity was recovered better than the composition, especially after the weaker perturbations. Species flow aids in community recovery but does not affect resistance. The results were relatively reproducible between replicate communities, and species traits steered the species fate in, pointing to deterministic ecological processes driving the community response. However, repeatability decreased in communities perturbed with the highest antibiotic concentration, which could point to evolution.