Non-equilibrium dynamics shaped by temporal changes in biotic interactions

Background/Question/Methods

Substantial research during the last century has shown that biotic interactions play a fundamental role in the maintenance of biodiversity and in the sustainable provision of multiple ecosystem services critical for human well-being. However, such knowledge considers that biotic interactions such as competition or pollination are not temporally variable, which contradict recent work documenting that temporal variation of biotic interactions (TVBI) is a common phenomenon. Because of this limitation, we poorly understand which are the main drivers of TVBI and their consequences for the persistence of ecological communities. To address this gap of knowledge, we first estimated from long term field observations (7 years) in Mediterranean grasslands, the intrinsic ability to grow and the strength of intra and interspecific interactions of 16 annual plant species following a spatial explicit design. We then combined such information with recent advances in the field of non-autonomous systems to explore the role of climate and species characteristics in shaping TVBI, and in determining the ability of the system to maintain species diversity under different community assemblages.

Results/Conclusions

The structure of interactions (matrix) containing the occurrence, sign and strength between pairs of species significantly varied across years, and there were not two years alike. Moreover, climate conditions and in particular winter rainfall strongly determined the variability of species interactions within years. Either very dry or very wet winters limited the ability of species to respond to competition. Regarding species characteristics, we did not observed that particular species played a disproportional role in the community. This means that the observed structure of species interactions did not differ from a null model shuffling species position in the interaction matrix. Overall, these different lines of evidence suggest that the high diversity of the system ensures a functional redundancy of species interactions within years but climatic conditions produce an overall change of species interactions across years. As a consequence of this observed pattern, stressful climatic conditions (either very dry or very wet winters) reduced the frondosity of the community assembly landscapes (a metric that account for the number of feasible local equilibria compared to the total) and the maximum number of species that are predicted to coexist at the global stability point. These results show how to adopt a TVBI perspective.