Title

Relative Importance of Host Abundance in Population Declines of S. adiaste

Poster Number

28

Lead Author Major

Pre-Denistry and Biological Sciences

Format

Poster Presentation

Faculty Mentor Name

Ryan Hill

Faculty Mentor Department

Biological Sciences

Abstract/Artist Statement

Populations of Speyeria species across North America are in decline. Possible reasons for these declines include human disturbance, loss of habitat, declines in violet host populations, drought and fire. S. adiaste is an imperiled species, being restricted to the southern California coast range, and having lost its southern-most subspecies to extinction. The purpose of this project was to study the link between violet hosts and abundance of the butterfly Speyeria adiaste clemencei to better understand its decline and aid in restoration of this and other Speyeria species. In order to assess the importance of the host plant, Viola purpurea quercetorum, in regulating adult abundance of S. a. clemecei, we compared adult population counts to projected population size given available host. We did this by combining field collected data for number of plants, number of leaves per plant, and leaf area per plant, with lab estimates of consumed leaf area to reach pupal stage. This results in an estimated average of 30,871 pupae for the 2013 Viola population on Chew’s Ridge, with 1.3% of the estimated distribution being less than 1000 pupae. In contrast the actual 2013 adult population estimate is less than 400 individuals. These results indicate that host abundance is not a strong predictor of adult abundance, although other aspects of host biology such as host density and spacing may be important. However factors totally unrelated to hosts, such as mortality from drought, predators, parasites, or disease may ultimately be driving population declines.

Location

DeRosa University Center, Ballroom

Start Date

26-4-2014 2:00 PM

End Date

26-4-2014 4:00 PM

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Apr 26th, 2:00 PM Apr 26th, 4:00 PM

Relative Importance of Host Abundance in Population Declines of S. adiaste

DeRosa University Center, Ballroom

Populations of Speyeria species across North America are in decline. Possible reasons for these declines include human disturbance, loss of habitat, declines in violet host populations, drought and fire. S. adiaste is an imperiled species, being restricted to the southern California coast range, and having lost its southern-most subspecies to extinction. The purpose of this project was to study the link between violet hosts and abundance of the butterfly Speyeria adiaste clemencei to better understand its decline and aid in restoration of this and other Speyeria species. In order to assess the importance of the host plant, Viola purpurea quercetorum, in regulating adult abundance of S. a. clemecei, we compared adult population counts to projected population size given available host. We did this by combining field collected data for number of plants, number of leaves per plant, and leaf area per plant, with lab estimates of consumed leaf area to reach pupal stage. This results in an estimated average of 30,871 pupae for the 2013 Viola population on Chew’s Ridge, with 1.3% of the estimated distribution being less than 1000 pupae. In contrast the actual 2013 adult population estimate is less than 400 individuals. These results indicate that host abundance is not a strong predictor of adult abundance, although other aspects of host biology such as host density and spacing may be important. However factors totally unrelated to hosts, such as mortality from drought, predators, parasites, or disease may ultimately be driving population declines.