title: The shift from plant-plant facilitation to competition under severe water deficit is spatially explicit.
abstract: The stress-gradient hypothesis predicts a higher frequency of facilitative interactions as resource limitation increases. Under severe resource limitation, it has been suggested that facilitation may revert to competition, and identifying the presence as well as determining the magnitude of this shift is important for predicting the effect of climate change on biodiversity and plant community dynamics. In this study, we perform a meta-analysis to compare temporal differences of species diversity and productivity under a nurse plant (Retama sphaerocarpa) with varying annual rainfall quantity to test the effect of water limitation on facilitation. Furthermore, we assess spatial differences in the herbaceous community under nurse plantsin situduring a year with below-average rainfall. We found evidence that severe rainfall deficit reduced species diversity and plant productivity under nurse plants relative to open areas. Our results indicate that the switch from facilitation to competition in response to rainfall quantity is nonlinear. The magnitude of this switch depended on the aspect around the nurse plant. Hotter south aspects under nurse plants resulted in negative effects on beneficiary species, while the north aspect still showed facilitation. Combined, these results emphasize the importance of spatial heterogeneity under nurse plants for mediating species loss under reduced precipitation, as predicted by future climate change scenarios. However, the decreased water availability expected under climate change will likely reduce overall facilitation and limit the role of nurse plants as refugia, amplifying biodiversity loss.
authors.affiliation: Estación Experimental de Zonas Áridas Consejo Superior de Investigaciones Científicas Almería Spain.
authors.forename: Michael J
authors.identifier: 0000-0003-0943-8423
authors.initials: MJ
authors.lastname: O'Brien
authors.affiliation: Estación Experimental de Zonas Áridas Consejo Superior de Investigaciones Científicas Almería Spain.
authors.forename: Francisco I
authors.initials: FI
authors.lastname: Pugnaire
authors.affiliation: Estación Experimental de Zonas Áridas Consejo Superior de Investigaciones Científicas Almería Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Armas
authors.affiliation: Centre for Functional Ecology Department of Life Sciences University of Coimbra Coimbra Portugal.
authors.forename: Susana
authors.initials: S
authors.lastname: Rodríguez-Echeverría
authors.affiliation: Department of Evolutionary Biology and Environmental Studies University of Zurich Zurich Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Schöb
keywords: biodiversity; competition; plant community diversity; plant–climate interactions; spatial variability; stress‐gradient hypothesis; water limitation