Background and Question:
Climate changes include concurrent changes in environmental mean, variance and extremes, and it is challenging to understand their respective impact on wild populations. We ask how changes in mean and standard deviation of sea surface temperature (SST), frequency and magnitude of warm SST extreme climatic events (ECE) affect the stochastic population growth rate and age structure of a Black-browed albatross population.
Methods:
We constructed an age-structured stochastic population model in which young, middle-aged and old breeders respond differently to changes in SST. The stochastic population growth rate and stable age distribution are projected for various scenarios of change in SST distribution, hence frequency and magnitude of warm SST ECE.
Results/Conclusions
Results:
For changes in SST around historical levels observed since 1982, changes in standard deviation had a larger (threefold) and negative impact on population growth compared to changes in mean. By contrast, the mean had a positive impact. The historical SST mean was lower than the optimal SST value for which the population growth was maximized. Thus, a larger environmental mean increased the occurrence of SST close to this optimum that buffered the negative effect of ECE. This ‘climate safety margin’ (i.e. difference between optimal and historical climatic conditions) and the specific shape of the population growth rate response to climate for a species determine how ECE affect the population. Furthermore, increases in either mean or standard deviation of the SST distribution led to a younger population, with potentially important conservation implications for black-browed albatrosses.
Conclusions:
Our results indicate that a shift in environmental mean can buffer and even reverse the effects of ECE on stochastic population growth rate. Species might therefore be able to cope with ECE. This depends on the magnitude of climate shift and variation in relation to a species’ optimal environmental conditions.