| Paulette
Bierzychudek -- research on Viola adunca and Speyeria
zerene hippolyta |
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| Cascade
Head is a Nature Conservancy preserve on the Oregon coast,
north of Lincoln City. This remnant grassland supports one of
only 5 extant populations of the threatened Oregon silverspot
butterfly, Speyeria zerene hippolyta, as well as several rare plant species. Speyeria's larval foodplant is Viola adunca, a small early-successional perennial. Viola adunca is a poor competitor, easily outshaded by the tall non-native grasses that have replaced the native fescue at Cascade Head, a legacy of the site's grazing history. My early work at Cascade Head focused on the demographic responses of Viola adunca to burning and mowing. In an experiment comparing Viola's performance after fire with control treatments, we learned that fire greatly stimulates Viola seed germination. On the basis of this finding, the Nature Conservancy began a program of controlled burning at Cascade Head. However, since fire also stimulates seed germination by undesirable nonnative species, TNC researchers have also investigated ways to minimize such invasion. In the meantime, the butterfly population is supported by a captive rearing program. In collaboration with the Nature Conservancy and the Oregon Zoo, Lewis & Clark students have reared butterflies in the laboratory from egg to pupation. Pupae are released at Cascade Head, where the adults join the resident individuals. Captive rearing allows the silverspot population to survive until the grassland is able to support them. |
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Because Viola adunca's seedbank at Cascade Head is sparse, achieving high densities may require additional intervention. In the future we plan to transplant adult violets to Cascade Head into sites that have been cleared of invasive competitors. Before designing this restoration scheme, we need to know: what hostplant density is needed for foraging larvae to locate violets successfully? and should we/can we supplement the Cascade Head violet population with genotypes from other populations? The presence of captively-reared individuals in the lab has created the opportunity to learn crucial information about the movement behavior of foraging larvae. Greenhouse experiments in semi-natural environments have verified the importance of violet density to larval survival. In field studies, we have learned that silverspot larvae cannot sense their hostplants from a distance, and thus search for food by moving randomly through the vegetation until they make contact with a plant. We have quantified their movement behavior, and are using these data to develop a model that will allow us to predict larval success in different densities and spatial patterns of violets, to guide restoration efforts. We are also investigating the potential of different Viola adunca source populations to serve as suitable restoration material. Sasha Stortz '07 did a genetic analysis of multiple coastal populations of V. adunca using microsatellite markers, detecting only modest amounts of genetic differentiation. Anne McHugh '10 reared silverspot larvae on food from different source populations and learned that their growth and survival rates did not vary with food source. We have transplanted seedlings from different poppulations at Cascade Head to see if there is a home site advantage. Created
by: P. Bierzychudek |