ALBERT

Description: The interface between climate and ecosystem structure and function is incompletely understood, partly because few ecological records start before the recent warming phase. Here, we analyse an exceptional 100-yr long record of the great tit (Parus major) population in Switzerland in relation to climate and habitat phenology. Using path analysis, we demonstrate an uninterrupted cascade of significant influences of the large-scale atmospheric circulation (North-Atlantic Oscillation, NAO, and North-sea – Caspian Pattern, NCP) on habitat and breeding phenology, and further on fitness-relevant life history traits within animal populations. We then apply the relationships of this analysis to reconstruct the circulation-driven component of fluctuations in great tit breeding phenology and population dynamics on the basis of new seasonal NAO and NCP indices back to 1500 AD. According to the path model, the multi-decadal oscillation of the atmospheric circulation likely led to substantial variation in habitat phenology, and consequently, tit population minima during the "Maunder Minimum" (1650–1720) and the Little Ice Age Type Event I (1810–1850). The warming since 1975 was not only related with a quick shift towards earlier breeding, but also with the highest productivity since 1500, and thus, an unprecedented increase of the population. A verification of the structural equation model against two independent data series corroborates that the retrospective model reliably depicts the major long-term NAO/NCP impact on ecosystem parameters. The results suggest a complex cascade of climate effects beginning at a global scale and ending at the level of individual life histories. This sheds light on how large scale climate conditions substantially affect major life-history parameters within a population, and thus influence key ecosystem parameters at the scale of centuries.