Predicting monarch butterfly (Danaus plexippus) movement and egg-laying with a spatially-explicit agent-based model: The role of monarch perceptual range and spatial memory

Abstract

An ~80% decline in the eastern population of the monarch butterfly (Danaus plexippus) has prompted conservation efforts to increase summer reproductive success in the Midwest United States. Implementation of conservation practices will create a patchwork of milkweed (mainly Asclepias spp.) habitat within agricultural landscapes dominated by corn and soybean production. Since the monarch butterfly is a vagile species, reproductive success is, in part, a function of both the amount and spatial arrangement of habitat patches in a fragmented landscape. To inform conservation planning we developed a spatially-explicit, agentbased model for summer breeding, non-migratory female monarch butterfly movement and egg-laying on an Iowa, USA landscape. Our model employs a unique movement algorithm when monarch agents encounter habitat edges that incorporates monarch perceptual range to their host plant and spatial memory of previously visited habitat. These behavioral factors are rarely incorporated into animal movement algorithms; however, they can influence estimates of resource utilization. Model exploration assessed the distribution and density of eggs laid on a spatially-explicit 148,665 ha landscape comprised of 17 land cover classes with varying milkweed densities. Uncertainty analysis was undertaken by sampling 25 combinations of perceptual range, spatial memory, flight step length and flight directionality parameters from a total of 256 (44) possible combinations. Movement paths simulated with our new movement algorithm show preferential use of high density milkweed areas that would not be simulated using a correlated random walk. Increasing perceptual range caused a decrease in the area used by monarch agents and caused a skewed egg distribution where most eggs were laid in relatively few habitat patches. Increasing spatial memory caused an increase in the area used but decreased the median number of eggs laid in roadside habitat. Current national and regional monarch conservation goals assume a uniform distribution of milkweed in different land cover classes. Translating these goals into spatially-explicit, heterogeneous habitat patches is essential for predicting realized fecundity in the landscape. Our model provides the foundation to link national and regional monarch conservation goals to fine scale spatial configurations of habitat patches in defined landscapes.

Monarch Butterfly Distribution and Breeding Ecology in Idaho and Washington

“…Although monarch breeding habitat is delimited by distributions of its obligate milkweed host plants, not all milkweed sites support breeding monarchs (Grant et al, 2018;Pitman et al, 2018). The relatively coarse scale of our study did not allow inferences about microsite attributes or preferred spatial configurations of habitat at monarch natal habitats.…”

The importance of including habitat-specific behaviour in models of butterfly movement

“…These measures are notably affected by the size of the study area (Schneider 2003) and, consequently, the lowest of those estimates may result from small study sites influenced by edge effects not included in our model. It would be beneficial to include edge effects in future work studying dispersal in landscapes consisting of small and fragmented habitat patches and these movement rules can be incorporated in IBMs (Grant et al 2018;Evans et al 2019b). An additional limitation of our study is the simple dichotomy between resource-rich and resource-poor habitat, to understand how butterflies respond to a gradient of resource levels may require a better understanding of how motivation and perception interact to drive changes in local movements.…”

Assessing Field‐Scale Risks of Foliar Insecticide Applications to Monarch Butterfly (Danaus plexippus) Larvae

“…In 2016 and 2017, the US Department of Agriculture's National Resources Conservation Service's (2016) Monarch Butterfly Wildlife Habitat Evaluation Guide discouraged placement of monarch breeding habitat within 38 m of crop fields treated with herbicides or insecticides. Employing a “no habitat buffer” of this size would significantly reduce the area of land available for establishing breeding habitat and hectares of small habitat patches (e.g., 0.4–2.0 ha) that are crucial for supporting increased monarch egg densities across the landscape (Zalucki et al 2016; Grant et al 2018). For example, in Story County, Iowa, USA, a 38‐m buffer around conventional maize and soybean fields represents approximately 84% of rural roadside rights‐of‐way and 38% of grassland, Conservation Reserve Program land, pastures, railroad rights‐of‐way, riparian corridors, and wetlands.…”