Climatic Niche Model for Overwintering Monarch Butterflies in a Topographically Complex Region of California

Abstract

We use climatic conditions that are associated with known monarch butterfly overwintering groves in California to build a Maxent model, and focus on the fine scale probability of overwintering grove occurrence in a topographically complex region of the state (Santa Barbara County). Grove locations are known from recent and historical surveys and a long-term citizen science database. The climatic niche model performs well, predicting that overwintering habitat is most likely to occur along the coast and at low elevations, as shown by empirical data. We then use climatic variables in conjunction with climate change scenarios to model the future location of overwintering habitat, and find a substantial shift in the predicted distribution. Under a plausible scenario, the probability of occurrence of overwintering habitat directly reflects elevation, with coastal regions having a reduced probability relative to today, and higher elevation sites increasing in probability. Under a more extreme scenario, high probability sites are only located along ridgelines and in mountaintop regions of the county. This predicted shift in distribution is likely to have management implications, as sites that currently lack monarchs may become critical to conservation in the future. Our results suggest that estimating the size of the western overwintering population in the future will be problematic, unless annual counts compensate for a shift in the distribution and a potential change in the number and location of occupied sites.

Spatio-Temporal Distribution of Monarch Butterflies Along Their Migratory Route

“…The HSM showed concordance with the identified overwintering zones in the west, both in California (USA) (Fisher et al, 2018) and in Baja California (Mexico). However, the model for March predicted a migratory route from the overwintering sites to the north of Mexico and south of the USA.…”

Host Plants and Climate Structure Habitat Associations of the Western Monarch Butterfly

“…Such field studies could be combined with gridded environmental covariates to make predictive maps that could be compared with the maps produced from this study. Future efforts could also incorporate more complete habitat associations for the most widespread milkweeds (extending beyond our focal western states), as well as the mapping of habitat suitability for the California overwintering sites, which was beyond the scope of our present efforts (but see Fisher et al, 2018). In summary, it is our hope that the results presented here both advance our basic understanding of the biology of a widespread and relatively well-studied insect, as well as provide an important tool for conservation biologists and land managers.…”

Modeling Current and Future Potential Distributions of Milkweeds and the Monarch Butterfly in Idaho

“…Species distribution models (SDMs) are increasingly used to assess the current "climate envelope" for species and project the potential effects of changes in those climate variables under different future scenarios (Porfirio et al, 2014). To date, broad-scale modeling efforts suggest milkweed and monarch distributions in the eastern United States (US) will expand northward during summer months (Batalden et al, 2007;Lemoine, 2015) while fine-scale modeling of western population overwintering sites in California indicate shifts upward in elevation and inland (Fisher et al, 2018). Such modeling efforts, however, are often limited due to a mismatch between the spatial resolution of climate data available (e.g., 1-30 km) and the scale relevant to the species of interest (e.g., 10-100 m), especially in areas of complex terrain (Randin et al, 2009;Austin and Van Niel, 2011;Suggitt et al, 2011;Franklin et al, 2013).…”