The Native Plants Journal recently published the results of research by the Institute for Applied Ecology that suggests that habitat fragmentation and reduced population size in Willamette daisy has led to loss of fitness in some populations and to population differentiation.  In outcrossing species, habitat fragmentation and reduced population size can lead to increased genetic drift, local adaptation, and (or) inbreeding.  The endangered Willamette daisy (Erigeron decumbens) is currently restricted to approximately 40 sites in prairies of Oregon's urbanized Willamette Valley.  More than half of the known populations have fewer than 100 individuals. In research funded by the Bureau of Land Management, we found a positive relationship between seed viability  and population size. In populations with 20 or fewer individuals, seed viability dropped to less than 2.5%.

In modified reciprocal transplant and common-garden experiments supported by the US Fish and Wildlife Service, we found that although there were some differences in survival, growth, and reproduction in transplants from 2 source populations, the effect of source varied depending on response variable, year of planting, year of monitoring, and habitat. Although plants were grown from seeds from wetland and upland sites, their progeny showed no consistent preference for one habitat or the other.  These results suggest that conservation of Willamette daisy will benefit from increasing the size and genetic diversity of existing populations and from reintroducing genetically diverse populations within the historic range of the species.  Read more...