Data and code: Microgeographic variation in demography and thermal regimes stabilize regional abundance of a widespread freshwater fish

Predicting the persistence of species under climate change is an
increasingly important objective in ecological research and management.
However, biotic and abiotic heterogeneity can drive asynchrony in
population responses at small spatial scales, complicating species-level
assessments. For widely distributed species consisting of many fragmented
populations, such as brook trout (Salvelinus fontinalis), understanding
drivers of asynchrony in population dynamics can improve predictions of
range-wide climate impacts. We analyzed demographic time-series from
mark-recapture surveys of eleven natural brook trout populations in
eastern Canada over 13 years to examine the extent, drivers, and
consequences of fine-scale population variation. The focal populations
were genetically differentiated, occupied a small area (~25 km2) with few
human impacts, and experienced similar climate conditions. Recruitment was
highly asynchronous, weakly related to climate variables, and showed
population-specific relationships with other demographic processes,
generating diverse population dynamics. In contrast, individual growth was
mostly synchronized among populations and driven by a shared positive
relationship with stream temperature. Outputs from population-specific
models were unrelated to four of five hypothesized drivers (recruitment,
growth, reproductive success, phylogenetic distance), but variation in
groundwater inputs strongly influenced stream temperature regimes and
stock-recruitment relationships. Finally, population asynchrony generated
a portfolio effect that stabilized regional species abundance. Our results
demonstrate that population demographic and habitat diversity at
microgeographic scales can play a significant role in moderating species
responses to climate change. Moreover, we suggest that the absence of
human activities within study streams preserved natural habitat variation
and contributed to asynchrony in brook trout abundance, while the small
study area eased monitoring and increased the likelihood of detecting
asynchrony. Therefore, anthropogenic habitat degradation, landscape
context, and spatial scale must be considered when developing management
strategies to monitor and maintain populations that are diverse, stable,
and resilient to climate change.