Climate, competition, and soil type: interactions controlling the success of endemic plants (Going)
Plant species that are specialized to particular substrates, such as serpentine endemics, are major contributors to local, regional, and global biodiversity. Serpentine plant endemics are species with more than 85% of their known occurrence on serpentine soil, an abiotically harsh soil that is low in nutrients (N, P, K, Ca), high in heavy metals (Mg, Ni, Fe) and has a low water holding capacity. In California, serpentine endemics occur in two narrow north-south bands in the Sierra Nevada and Coast Ranges, yet they comprise nearly 15% of the species endemic to the state. Recent statistical models suggest narrowly distributed species, such as serpentine endemics, may be more vulnerable to extinction due to climate change than species with wide distributions. Losses of these species could profoundly alter plant diversity in California. Barbara Going, in collaboration with Susan Harrison, have begun an examination of the factors influencing the success of serpentine endemics and how these species may respond to changing climatic patterns.
One hypothesis for why serpentine endemics are not found off of serpentine is competitors exclude non-endemic species on more fertile soils. However, recent work by Susan Harrison has revealed that serpentine endemic richness in California is strongly and positively correlated with the state’s precipitation gradient. Therefore, an alternative hypothesis is that the distribution of serpentine endemics is controlled by a three way interaction between climate (i.e. precipitation), competition and soil type. Under this hypothesis the response of serpentine endemics to precipitation would depend on the relative strength of the direct effects of precipitation and the indirect effects precipitation via competition on serpentine and normal soils. To test this hypothesis, we are studying how climate, specifically precipitation, and competition influence the performance of serpentine endemics in a serpentine and a non-serpentine grassland.