Evolution of phenotypic plasticity and ecological specialization in temporally varying environments
The patterns of spatial and temporal heterogeneity in a population’s environment drive selection for dispersal, plasticity, and ecological specialization. Today, anthropogenic activities are modifying the variance regime in natural systems. We are investigating how changes to historical patterns of environmental variance influence the ecological and evolutionary trajectories of plant populations that occupy ephemeral wetlands in the California Floristic Province of western North America. In this system, habitat loss and creation have modified the spatial distribution of wetland habitat within landscapes, and the temporal variability in hydrology within pools. We used molecular markers to define the spatial scale of gene flow and population connectivity in vernal pool endemic plant species, and then quantified the extent of spatial and temporal variability experienced by these populations in natural and artificially created wetland complexes. Next, we conducted transplant experiments across depth gradients in natural and created wetlands to evaluate plant fitness across hydrological gradients within individual pools and among contrasting hydrological profiles of different pools. Finally, we used these data to predict the responses of these populations to changing patterns of hydrological variability due to changing precipitation conditions associated with climate change.
Patterns of population genetic structure in vernal pool endemic plants indicate that gene flow occurs beyond the limits of individual pools, but within the boundaries of vernal pool complexes. At this scale, natural and created wetlands exhibit contrasting patterns of habitat availability: natural vernal pool complexes contain pools that are less densely packed and more variable in size and shape compared to those that occur in artificially created wetland complexes. The temporal variation in hydrology also differs between natural and created vernal pools, with created vernal pools lacking the hydrological dynamics that characterize the natural wetlands. The transplant experiment revealed that temporal hydrological variability within pools significantly influences the fitness of the resident plant populations, and provides insight into how these populations will respond to changing precipitation conditions associated with climate change. Collectively, our results indicate that artificially created vernal pool complexes may be imposing different patterns of selection for dispersal and plasticity that historically shaped the evolution of vernal pool plant lineages. These conclusions point toward a need to explicit consider spatial and temporal environmental variability when designing strategies that aim to conserve wetland specialists in the face of habitat loss and climate change.