Long-Term Experimental Analysis of Ecological and Evolutionary Processes at a Species’ Range Limit

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Cross, Regan
ecology , evolution , range limits , transplant experiment , plants
Many species’ ranges have remained stable in space through time, but they may shift as climate change and other anthropogenic impacts alter habitats in their historic ranges. Successful range expansion can be prevented by limited dispersal or poor establishment if beyond-range habitat is outside the species’ niche. To conserve species with limited dispersal, they can be planted beyond their ranges in “assisted colonization”, but it is unclear whether central or peripheral populations are best suited to beyond-range habitats, and whether beyond-range populations will adapt after colonization. Restoration efforts to re-plant degraded habitats within species’ ranges often use local genotypes, but long-term comparisons of local vs. multi-source introduced populations are lacking. Here, I review the current state of the field of range limits and provide a novel long-term test of whether a species’ range is limited by its niche. I execute a transplant experiment to examine whether central or edge populations perform best beyond the range, and whether beyond-range populations adapt to their environment over ten generations. Finally, I test whether local or mixed-genotype populations perform best to inform planting efforts for restoration. After ~ 10 generations beyond the range, populations of coastal dune plant Camissoniopsis cheiranthifolia had high reproductive fitness and tripled in population size, suggesting that beyond-range habitat is not outside its niche. Peripheral populations had higher fruit production than central populations in beyond-range environments, but this didn’t result in higher rates of population growth. When transplanted back at home and at another beyond-range site, beyond-range populations did not outperform those from within the range, indicating that persistence did not require adaptation to beyond-range conditions. Local vs. genetically mixed populations did not differ in fitness at within-range sites, but genetically mixed populations sometimes had higher plant density after ten generations, indicating possible increased adaptive capacity. My thesis will improve our understanding of the factors preventing range expansion and the eco-evolutionary processes at play during range shifts, and inform population selection for conservation efforts like assisted migration and habitat restoration.
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