Individual based models of plant fecundity often reveal that there are non-linear effects of neighbor density on seed production. Along with the abiotic environment, these complex species interactions compose the selective forces that a focal plant may experience during it’s life. Thus neighboring individuals can mediate selection pressures of the environment in non-linear and unexpected ways.
In a biodiversity hotspot for annual plants in Western Australia, we quantified the strength of selection on the traits of several plant species by using fecundity as a proxy for fitness. This experiment was performed in an extreme drought year, and a watering treatment was also implemented, allowing us to test how drought changes the selection regime experienced at the individual level. We investigated the interactions between environmental regime and neighbor density on selection.
Results/Conclusions
Here we show that species interactions between plants change with drought and neighbor density, resulting in more facilitation in drought environments and more diffuse species interactions as density increases. There were no significant differences in selection between drought and no drought environments. However, there was an interaction between drought and neighbor density, with weakening selection as density increases. This indicates that complex selection pressures are mediating community composition and diverse community interactions may slow down evolutionary responses to extreme weather events.