How does spatial heterogeneity buffer plant species against climate change?

Background/Question/Methods

Spatial heterogeneity plays a critical role in driving many ecological patterns and processes, including species coexistence, biological invasions, and patterns of alpha and beta diversity.  Recently, spatial heterogeneity has been implicated as an important factor responsible for buffering fish and plant communities against climatic variability and change.  However, the specific mechanism by which spatial environmental heterogeneity confers temporal stability remains unclear.  We propose that in communities structured by competitive interactions, spatial heterogeneity could buffer communities by creating opportunities for niche partitioning and weakening the strength of interspecific interactions.  In this study, we use a novel design to examine the response of two annual plant species to experimental drought (50% reduction in ambient precipitation) in the presence and absence of competition in heterogeneous or homogeneous soil textures (clay, sand, or a mixture of clay and sand).  At the end of each season we measure biomass and seed production of our two focal species, Plantago erecta and Salvia columbariae.  In this talk we report the results from the first year of the experiment.

Results/Conclusions

Rain out shelters reduced ambient precipitation by 11% on average.  Clay soils had higher soil moisture than sand soils, while heterogeneous soils were intermediate between clay and sand.  Although we did not detect significant treatment effects for per capita biomass and seed production, there were interesting patterns in total biomass production.  Plantago biomass was reduced by the presence of Salvia, while Salvia performance depended on a three-way interaction between precipitation, soil texture, and competition with Plantago.  Heterogeneous soil texture buffered the effects of competition for Salvia, but only under ambient precipitation.  Interestingly, sand soils altered the direction of the interactions under drought conditions; monoculture biomass was lower on sand under drought and higher under ambient precipitation.  While our preliminary results do not support our original hypothesis, they do suggest that soil texture can play an important role in mediating species responses to changes in rainfall and the competitive environment.