|dc.description.abstract||Climate change can have potentially catastrophic effects upon biodiversity and
food web structure and according to the fourth IPCC report, ambient
temperatures will rise by between 3.0 -5.0 °C over the next century, with already
an average increase in global surface temperature of ~0.74°C in the past 100
years. This has known implications in ecology from individuals to ecosystems.
The microbial loop consists of small organisms ranging in body size from
bacteria (1-15 μm), single-celled eukaryotes (10-1000 μm) and multicellular
organisms (250 – 1000 μm) that assimilate dissolved organic carbon into the
“classical food web”. !
The principal goal of this thesis was to assess how rising global
temperatures might impact the natural microbial assemblages in 20 mesocosms
under 2 treatments – 10 warmed (in line with IPCC predictions) and 10 ambient.
The abundance and body mass of 4 major microbial loop taxa (desmids,
flagellates, heterotrophic protists and meiofauna) were quantified at monthly
intervals over a 2-year period. Secondly, in a microcosm experiment, the
population dynamics of three pure cultures of ciliates were monitored across a
temperature gradient; the rate of population decline under starvation and
changes in body size were quantified.!
Results showed that (1) rising global temperatures alters the size
spectrum in the autotrophic protists, (2) temperature interacts with temporal and
spatial gradients, resulting in changes in phenology (3) these changes in
phenology are observable at both the community level and the population level
within the microbial assemblage of the mesocosms and (4) extinction rates and
body mass reduction in experimental microcosms were faster at warmer
temperatures and partially support predictions of the metabolic theory of
The implications of these findings are discussed in terms of (1) continued
research into the role that small organisms play in community and ecosystem
ecologyand (2) the use of these small organisms in experiments as models to
inform ecological theory by scaling up from microcosms and finally, (3) I discuss
future directions in freshwater microbial ecology, focusing on the increased use
of molecular techniques.||en_US