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Research
   
 
Research Summary
Dr. Sarah Reichard and her students are researching several rare plant species
at the Center for Urban Horticulture.
Astragalus sinuatus
Hackelia venusta

Fritillaria camschatcensis
 

Sidalcea oregana var. calva
Castilleja levisecta

Astragalus sinuatus

Insect herbivory is common and has been shown to drastically limit the reproductive success of many plant species. Most research examining the affects of herbivory has focused on common plants, while very little attention has been given
to understanding how herbivory impacts the reproductive success of rare plant species.

Astragalus sinuatus is a Washington endangered plant species. Its entire distribution is restricted to an 8km square area in the shrub-steppe habitat of Eastern Washington. Ms. Julie Combs's Master's Degree research determined that in areas of high Bromus tectorum cover, A. sinuatus is most likely limited by B. tectorum, an invasive annual grass. However, in areas of low B. tectorum cover, A. sinuatus is more likely limited by insect seed predators.

 

Julie Combs removes insect with aspirator
Julie Combs uses an aspirator to manually remove
a specialist insect herbivore.

     

Astragalus sinuatus
Astragalus sinuatus.
Aim your mouse at this photo
to see Bombus sp. pollinating Astragalus sinuatus
flowers, with Bromus tectorum, a non-native annual
grass, growing in the background.

 






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To examine whether competition with B. tectorum inhibits seedling germination and survivorship of A. sinuatus, seeds were added to plots with and without B. tectorum. Overall seedling germination did not differ between control and removal treatments. But overall seedling and juvenile establishment after the two-year monitoring period was significantly higher in plots where B. tectorum was removed. These results show that insect herbivores may strongly affect demographic processes of A. sinuatus.

Primary seed predators were tortricid moth larvae and two species of specialist beetles: the seed weevil, Tychius semisquamosus LeConte, and the seed beetle, Acanthoscelides fraterculus Horn. An insect reduction experiment using insecticide and manual removal techniques suppressed insect herbivores, resulting in 164-345% greater viable seed production. Insect herbivory indirectly led to a seven- to eleven-fold greater incident of fungal attack on plants exposed to herbivores. These results show that insect herbivores directly and indirectly decrease viable seed output of A. sinuatus.

     

In her dissertation work, Ms. Combs is investigating the hypothesis that rare plants are more susceptible to insect damage compared to more widespread, co-occurring, congeneric species. Some researchers have suggested that herbivory may be one causal factor of rarity; however, there is very little empirical evidence to either support or discard this hypothesis. The few studies that are published show conflicting results. To investigate this question, Ms. Combs is using rare-common, co-occurring pairs within the genus Astragalus (Fabaceae) to investigate the degree to which herbivory may limit rare plant populations. In addition, she is also investigating how pollination affects reproductive failure (seed loss) and success (seed-set) in a rare-common sympatric, congeneric pair. She is using several field sites located in the shrub-steppe plant communities of eastern Washington and Oregon where common and rare Astragalus species co-occur. Ms. Combs will finish her dissertation in 2011.

 
Recording flower production data
Field assistant Kelley Craig records flower production data
     
More Research    

Hackelia venusta
Fritillaria camschatcensis
Sidalcea oregana var. calva

Castilleja levisecta

 
     

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