Many animals move more slowly in high-resource environments. This behavior means that populations are able to persist longer in high-resource environments, but also that high-resource habitat types may not be optimal in terms of patch connectivity. In this talk, I explore these issues using data for movement of monarch butterflies (Danaus plexippus) during the summer breeding season in eastern Massachusetts. During summer 2016, we tracked flight paths of 22 female and 11 male monarch butterflies. Movement observations were divided into steps that were within one meter of their larval host plant, milkweed (Asclepias spp), and steps that were not near host plants. I used these data to calculate diffusion coefficients in homogeneous environments with and without milkweed, and in fine-grained heterogeneous environments with sparse milkweed densities. I will combine these data with published estimates of vital rates (Flockhart et al. 2015) to explore how differences in movement rates might translate to differences in landscape-scale population dynamics.
Results/Conclusions
Monarch butterflies moved more slowly near milkweed plants. The estimated diffusion coefficient was 1.0 m2/sec near milkweed plants, and 6.9 m2/sec in the same areas, but not near milkweed plants. This result corroborates a pioneering experimental study (Zalucki and Kitching 1982) of movement in Australian populations of monarch butterflies; both studies report slower movement near milkweed patches, and faster movement away from patches. Because diffusion coefficients are high, butterflies would need large patches to persist, unless there are mechanisms of long-distance attraction to host plants that are not captured by these simple models. In addition, the relationship between plant density and patch residence time is approximately linear (the relationship is asymptotic, but this only shows up in very large patches.) I will explore the extent to which simple diffusion models are a reasonable starting place for assessing habitat use by monarchs during breeding season, and implications for habitat restoration.