Résumé
Environmental fluctuations are important for parasite spread and
persistence. However, the effects of the spatial and temporal structure of
environmental fluctuations on host–parasite dynamics are not well
understood. Temporal fluctuations can be random but positively
autocorrelated, such that the environment is similar to the recent past
(red noise), or random and uncorrelated with the past (white noise). We
imposed red or white temporal temperature fluctuations on experimental
metapopulations of Paramecium caudatum, experiencing an epidemic of the
bacterial parasite Holospora undulata. Metapopulations (two subpopulations
linked by migration) experienced fluctuations between stressful (5°C) and
permissive (23°C) conditions following red or white temporal sequences.
Spatial variation in temperature fluctuations was implemented by exposing
subpopulations to the same (synchronous temperatures) or different
(asynchronous temperatures) temporal sequences. Red noise, compared with
white noise, enhanced parasite persistence. Despite this, red noise
coupled with asynchronous temperatures allowed infected host populations
to maintain sizes equivalent to uninfected populations. It is likely that
this occurs because subpopulations in permissive conditions rescue
declining subpopulations in stressful conditions. We show how patterns of
temporal and spatial environmental fluctuations can impact parasite spread
and host population abundance. We conclude that accurate prediction of
parasite epidemics may require realistic models of environmental noise.