Interaction of Climate Change and Eutrophication - Climate Change Impacts on Freshwater Ecosystems - page 134

responses to temperature increase in this species, in terms of both survival and key
life-history traits such as age at reproduction or number of offspring. Changes at
the within-species level are then buffering against changes at the among-species
level (Van Doorslaer et al . 2007).
All mesocosms in the UK second experiment were inoculated in March 2006
with the same, genetically well-characterized Daphnia magna population,
consisting of 150 clones hatched from the dormant egg bank of a local population.
The fate of these populations was monitored until the experiment ended in
September 2007. We studied dynamics of the populations establishing in the
different treatments, characterized their genetic structure using neutral DNA
markers and carried out life-table experiments in the laboratory using clones
isolated from mesocosms exposed to different temperatures. In addition, we
carried out enclosure and competition experiments in the tanks to quantify the
degree to which populations in differently heated mesocosms were locally
adapted to their new environment (Van Doorslaer et al . 2009).
Key observations were that the populations exposed to a higher temperature
indeed differed genetically from control populations for life-history traits and
that these differences translated into differences in competitive strength at higher
temperatures. The most striking result was that adaptation to heated mesocosms
made the UK genotypes better than the control genotypes at competing with
clones isolated from Southern France, mimicking immigration by southern
genotypes. Although the French clones were still competitively stronger at the
higher temperature than even the warm-adapted UK clones, the difference was
substantially smaller than when French clones competed with the initial UK
populations. These results suggest that evolutionary responses may rapidly reduce
the vulnerability for invasion by southern genotypes. Yet, 1 year of evolutionary
change proved insufficient to increase the fitness of UK clones to a level exceeding
the fitness of southern immigrant clones (Van Doorslaer et al . 2009).
Overall, our results indicate potential for rapid evolutionary change. This
suggests that there is potential for interaction between evolutionary dynamics
and ecological processes, including population dynamics, community assembly
and ecosystem functioning. These interactions have hardly been explored (Urban
et al . 2008), even though they may change our perspective on ecological responses
to anthropogenic environmental changes such as climate warming. They might,
for example, explain the negligible apparent effects of temperature increase on
the phytoplankton communities during the first UK mesocosm experiment,
where a mere two of over ninety species showed declines and a further two
increased their abundance in response to warming (Moss et al . 2003). It must be
borne in mind, however, that algae and zooplankton undergo many generations
in a year. Evolutionary response may be much slower for organisms that reproduce
only annually or less frequently, such as fish.
Stream and wetland experiments at paired sites
Studies in controlled mesocosms have the advantage that many factors such as
temperature and nutrient availability can be experimentally controlled. The
disadvantage is that the systems are relatively small compared with natural ecosystems