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Saunders S.P., Ries L., Oberhauser K.S., Thogmartin W.E., & Zipkin E.F. (2018) Local and cross-seasonal effects of climate and land-use on migratory monarch butterflies. Ecography. 41: 278-290.

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Sarah P. Saunders, Leslie Ries, Karen S. Oberhauser, Wayne E. Thogmartin, and Elise F. Zipkin

Ecography

Please contact the first author for questions about the code or data: Sarah P. Saunders (sarahpsaunders@gmail.com)


Abstract

Quantifying how climate and land use factors drive population dynamics at regional scales is complex because it depends on the extent of spatial and temporal synchrony among local populations, and the integration of population processes throughout a species’ annual cycle. We modeled weekly, site‐specific summer abundance (1994–2013) of monarch butterflies Danaus plexippus at sites across Illinois, USA to assess relative associations of monarch abundance with climate and land use variables during the winter, spring, and summer stages of their annual cycle. We developed negative binomial regression models to estimate monarch abundance during recruitment in Illinois as a function of local climate, site‐specific crop cover, and county‐level herbicide (glyphosate) application. We also incorporated cross‐seasonal covariates, including annual abundance of wintering monarchs in Mexico and climate conditions during spring migration and breeding in Texas, USA. We provide the first empirical evidence of a negative association between county‐level glyphosate application and local abundance of adult monarchs, particularly in areas of concentrated agriculture. However, this association was only evident during the initial years of the adoption of herbicide‐resistant crops (1994–2003). We also found that wetter and, to a lesser degree, cooler springs in Texas were associated with higher summer abundances in Illinois, as were relatively cool local summer temperatures in Illinois. Site‐specific abundance of monarchs averaged approximately one fewer per site from 2004–2013 than during the previous decade, suggesting a recent decline in local abundance of monarch butterflies on their summer breeding grounds in Illinois. Our results demonstrate that seasonal climate and land use are associated with trends in adult monarch abundance, and our approach highlights the value of considering fine‐resolution temporal fluctuations in population‐level responses to environmental conditions when inferring the dynamics of migratory species.

Data (proprietary, described here for context)

SiteEffects_IL94to14.csv - Site-level data for sites where monarchs were surveyed in Illinois. The rows contain the data for each of the 263 sites in the study area. The columns contain 1) Latitudes and Longitudes of each site (first 2 columns); 2) Site IDs; 3) the percent of each site considered 'open' habitat (% Open column; see main text for description of this covariate; 4) average growing degree days (GDD) measured during weeks 10-28 (avgGDD10-28NEW) at each site; and 5) amount of crop cover (determined from Cropland Data Layer) at each site (acres).

SiteYear_IL94to14_09max.csv - Site-year-level data for each site-year combination. Each row is a site-year combination (columns 1 and 2) and the additional columns contain: 1) accumulated GDD during weeks 10-28 in each year at each site; 2) several variables describing glyphosate application at each site (columns 4-7); 3) acres of corn and soybeans at each site; and 4) acreage of other crop types at each site.

SurveyData_IL94to14_MaxCts.csv - This file contains all survey-specific information (i.e. for each observation). This file is the raw data that were later manipulated to yield the sum total of monarchs observed at each site during a given survey (i.e. column SumofMonarchCount).

YearEffects_IL94to14.csv - Each row of this datasheet is a year of the study period (indicated in column 1). The remaining columns are: 1) accumulated GDD during spring in weeks 4-9 (second column); 2) average PDSI during weeks 4-9; 3) total average spring precipitation in Texas; 4) colony size in early winter on overwintering grounds in Mexico each year; 5) colony size in early winter on overwintering grounds in Mexico in prior year; 6) early winter colony size in Mexico (replicate of prior column except with 0 recorded in years where late winter colony data available); and 7) late winter colony size in Mexico, collected since 2005.

Weeks_IL94to14.csv - This file was used in data manipulation to note which sites were surveyed each week in each year.

Code

Ecography 2017_Git code_SaundersSP.R - R code to manipulate data and fit the models described in the main text of the published paper, including creation of whiskerplots.

About

Saunders S.P., Ries L., Oberhauser K.S., Thogmartin W.E., & Zipkin E.F. (2018) Local and cross-seasonal effects of climate and land-use on migratory monarch butterflies. Ecography. 41: 278-290.

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