Investigating monarch butterfly (Danaus plexippus) movement ecology to inform conservation strategies

Abstract

The eastern North American monarch butterfly is at risk of quasi-extinction and determined to be a candidate species for listing under the Endangered Species Act due, in part, to the loss of breeding habitat in agricultural landscapes of the Midwest United States. Because the monarch is a vagile species, the spatial arrangement of milkweed in the landscape is expected to influence movement patterns, habitat utilization, and reproductive output. To help obtain the biggest impact of newly established habitat, monarch butterfly movement behavior should be considered. This dissertation aims to advance understanding of monarch movement ecology at the milkweed patch, landscape, and continental scales and provide information that supports conservation planning. In addition, the work presented here propels the field of insect movement ecology with the development of new insights and implementation of novel methods and techniques. At the milkweed patch scale explored in chapter 2, because of seemingly innate milkweed abandonment behavior and biomass consumption requirements, our results suggest milkweed patches containing at least two to four ramets of closely spaced common milkweed would provide sufficient biomass for development and increase the likelihood that larvae moving in random directions would encounter non-natal ramets to support complete development. Larval movement behavior and biomass requirements are critical aspects of monarch larval biology that should be considered in habitat restoration and maintenance plans, monitoring survey designs and protocols, and population modeling. Through five years of landscape-scale movement experiments (Chapters 3-6), we released 393 radio-tagged, sham-tagged, and untagged monarch butterflies in various land cover types. With the use of radio telemetry, we attained more information about monarch butterfly movement than was possible by visual observations only. We developed a new data collection system capable of estimating the location of a monarch butterfly in a sod field with a frequency 12 times faster than currently employed methods. We analyzed movement characteristics, including step length, directionality, and perceptual range. We employed novel approaches, specifically continuous-time movement models, to analyze monarch butterfly occurrence. Finally, we conclude by reporting that 50 m perceptual range and 30 m step length are appropriate parameter selections in a spatially explicit agent-based model reported by Grant et al. (2018). We found that turn angle was variable in relation to milkweed density, and therefore could be further explored for model parameterization. Additionally, parameters to simulate large dispersal steps should be included as this will greatly influence how monarchs move across the landscape. Chapter