Using structured decision making to guide habitat restoration for butterflies: a case study of Oregon silverspots

Doll CF, Converse SJ, Edwards CB, and Schultz CB

Journal of Insect Conservation

DOI:

Please contact the first author for questions about the code or data: Cassandra F. Doll (cassandra.doll@wsu.edu)

Citation:

Doll CF, Converse SJ, Edwards CB, and Schultz CB. Under Review. Using structured decision making to guide habitat restoration for butterflies:a case study of Oregon silverspots. Journal of Insect Conservation.

Abstract:

Introduction When making decisions about how to restore habitat for at-risk species, land managers must balance multiple competing objectives in the face of uncertainty about the impacts of management actions on at-risk populations. The Oregon silverspot (Speyeria = Argynnis zerene hippolyta) is a federally threatened butterfly, and uncertainty exists about the effects of proposed management.

Aims/Methods We used structured decision making (SDM) to guide restoration for Oregon silverspots. Managers identified persistence as their primary objective and further identified effects of herbicides as a key uncertainty. We developed a model of population dynamics incorporating management actions and parameterized the model based on experiments with a surrogate subspecies, the Zerene silverspot (S. z. zerene). Herbicide application may directly harm Oregon silverspots by increasing larval mortality, while indirectly benefiting silverspots by reducing the competition faced by their host plant. In this system, potential herbicide treatments include grass-specific fluazifop-P-butyl or forb-specific clopyralid applied with Agri-Dex^® or Nu-Film^® IR adjuvants.

Results We found that Oregon silverspot population growth rate is greatest with clopyralid and fluazifop-p-butyl when combined with Nu-Film^® IR than other alternatives (including no treatment) considering only direct effects or in combination with indirect effects.

Discussion An adaptive management program would benefit Oregon silverspots by promoting exploration of management alternatives while allowing managers to act quickly to arrest steep declines. Uncertainty remains regarding how well our results will generalize in field conditions.

Implications for insect conservation SDM, in combination with experiments to parameterize models, provides a powerful tool for evaluating risks from management actions relative to conservation benefits.

Code

1. Model - Fig. 2.Rmd: R script to generate and analyze Oregon silverspot population simulaiton data described in the manuscript.

2. 2019 A. B. James - Fig. S1.Rmd: R script to create Fig. S1 in the manuscript.

Data

1. 1990-2002 Index Counts.csv: Data for estimating e, from the U.S. Fish and Wildlife Service (USFWS) annual index counts for Oregon silverspot abundance at Mt. Hebo.

2. 2018 Herbicide Exposure - Offspring Survival & Development Time.csv: Data for estimating s₁, from Doll et al. (in press).

3. 2018 Herbicide Exposure.csv: Data for estimating s₃, s₄, and f from Doll et al. (in press).

4. 2019 A. B. James.csv: Data for estimating b, from A. B. James, Washington State University (WSU).

5. 2019 Oviposition Behavior - Offspring Survival.csv: Data for estimating s₂, from Doll et al. (in press).

Results

1. Model Results.csv: Results used for Table 5 and Fig. 2 in the manuscript.

2. Raw Means.RDS: Results of the means.

Figures

1. Fig. 2.jpg: Fig. 2 in the manuscript.

2. Fig. S1.jpg: Fig. S1 in the manuscript.