Looking back to the future: Four decades of global-change forcing on small-mammal assemblage dynamics

In many regions on Earth, past and current changes in temperature, rainfall patterns, and snow cover are concomitant with changes in atmospheric pollution, probably causing interactive but overlooked impacts on ecosystems. However, in global-change ecology, we often study the interactive effects of climate changes (mainly temperature warming) and chemical pollution experimentally at short spatio-temporal scales and in controlled conditions. As a result, how these global change factors interact to shape long-term population dynamics in natural ecosystems, remains little known. As a key example, the European Black Triangle — the region at the borders of former Czechoslovakia, Germany, and Poland — was heavily air polluted in the 1970s and 1980s due to emissions from coal power plants, resulting in high loads of toxic element deposition (e.g., lead). In the Ore Mountains, within the Black Triangle region, we collected during 40 years (twice a year in June and October) the abundances of six small-mammal species belonging to three trophic guilds (omnivores, insectivores, and herbivores). We complemented this dataset with atmospheric pollution (SO₂, NO_x, and total Particulate Matter), temperature, snow cover, and runoff (snowmelt and rainfall) historical data. Firstly, we studied the local stability (Lyapunov local stability) of the global change factors and small-mammal multivariate time series, respectively, and identified that periods of instability in climate and atmospheric pollution were preceding periods of small-mammal assemblage instability. Secondly, we used Bayesian Multivariate (Dynamic) Generalized Additive Models (MDGAMs) to test contrasting hypotheses on how different climate factors (snow cover, runoff, and temperature) may interact with temporal changes in pollution in a trophic-guild-specific manner. We showed evidence for guild-specific effects of climatic variables and atmospheric pollution. For instance, the strength of the negative interaction between runoff and atmospheric pollution on population dynamics depended on the trophic guild, with stronger negative effects on omnivores. We finish by discussing the implications of our findings on how global change factors contribute to community dynamics, and what this entails for species coexistence and biodiversity conservation amid ongoing changes in climate and atmospheric chemical composition.