Climate change affects many statistical descriptions of the environment. The impact
of changes in mean environmental conditions on animal populations has been widely
reported. The variability and autocorrelation of environmental variables are also
changing over time, yet less research has focussed on what impact these changes may
have on populations. Is the research focus on changes in mean conditions justified? How do changes in different statistical descriptions of climate change affect populations,
and how do the impacts compare? To answer these questions, we developed a simple
stochastic population model, explicitly linked to the environment, and compared the
impacts of changes in environmental mean and variability. We found, using both the
long-term stochastic growth rate and extinction risk as proxies for population fitness,
that changes in variability have a significant impact on population dynamics. The
main gradient along which the relative importance of changes in environmental mean
and variability varied was the population's distance from its ideal environment. We
also re-analysed existing population models to yield the sensitivity of the population to
changes in environmental mean and variability. Results support the findings from our
model, and confirm the importance of changes in variability for population dynamics.
Previous theoretical and laboratory studies concluded that the autocorrelation in the
environment in part affects the autocorrelation in population time series. So far, this
hypothesis has not been tested using empirical data. We used a database of population
time series to find that the autocorrelation in mean summer temperature is significantly correlated with the autocorrelation in population time series. Results also show that
environmental variables have become less autocorrelated in most geographical regions,
suggesting that populations' autocorrelation may also be changing. Autocorrelation in
population time series has been linked to extinction; these results may therefore have
important implications for animal populations.