LAUSR

Recent findings in forests worldwide have evidenced how directionality in the richness-abundance causality shifts along global climate gradients: The "More Species Hypothesis" (richness determines abundance) prevailed towards the most productive Earth's climates whereas the opposite, the "More Individuals Hypothesis" (abundance determines richness), was more likely towards climatically harsh conditions. Since temporal variability is the norm, a critical question remaining is to know if this directionality shift is also a function of temporal climatic fluctuations locally. Here, we analyze whether directionality in the richness-abundance relationship is contingent on temporal variability over 10 annual consecutive realizations in ephemeral plant assemblages. Our results support that the More Species Hypothesis prevailed in the most benign years whereas the More Individuals Hypothesis did so during less productive years, which were significantly linked to the warmest years. These results support the idea that rising temperatures can reverse directionality in the richness-abundance relationship in these annual plant communities, and, therefore, climate warming can have a significant influence on the relationship between diversity and ecosystem functions such as productivity, by altering the prevalence of primary mechanisms involved in species assembly. This article is protected by copyright. All rights reserved.