Lofflin, Diana , Kephart, Susan .
The role of outbreeding and seedling establishment in natural and reintroduced populations of Silene.
Habitat loss has fragmented populations of many species relative to their original ranges, placing species at risk from factors such as small population size, inbreeding, and low pollinator visitation. Silene douglasii (Caryophyllaceae) includes three varieties found in isolated montane and coastal prairies in western Oregon. We compared seedling establishment in multiple populations of the widespread var. douglasii relative to var. oraria, a rare endemic that persists on only three coastal headlands. Natural seedling densities were lowest in plots of oraria, which also had significantly fewer juveniles than detected in other varieties, indicating that seedling survival may limit new plant establishment. Thus, we also evaluated the genetic and demographic consequences of transplant and seed reintroduction as a restoration tools for oraria. Transplant survival declined 88% over five years, but plant fitness was significantly higher for outbred than inbred transplants. Additionally, 75% of established seedlings detected in the reintroduction site occurred near surviving cross-pollinated progeny. For reintroduced versus natural populations of oraria, pollinator visitation did not differ, but plants in the more diverse natural population produced significantly more fruits than in the reintroduced population (P = 0.001). Fitness values for most other traits (e.g. flowering levels, seed set) were also higher in the natural population. In contrast, natural seedling densities in the reintroduced site were significantly greater than in the natural prairie, despite a higher frequency of invasives. This level of seedling establishment could potentially sustain the population over time, but few seedlings apparently survived to become juveniles at either site, a factor that may contribute to rarity in oraria. In conclusion, the existing reintroductions of oraria show low survival and fitness relative to natural populations. The observed levels of inbreeding depression further imply that future reintroductions of oraria will have a greater probability of success if they include outbred progeny.
1 - Willamette University, Biology, 900 State Street, Salem, Oregon, 97301, USA
Presentation Type: Poster
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM