The decline of overwintering populations of monarch butterflies ( Danaus plexippus ) in central Mexico has raised concern worldwide. Recent evidence suggests that the fall migration is becoming disrupted by several factors, leading to a decreasing number of monarchs completing their journey to their overwintering sites in central Mexico. One potential factor assumes that there are suitable habitats for species of tropical milkweed as well as for eggs and larvae of monarchs (ELM) laid by adult individuals. We evaluated the current and future habitat suitability of ELM and species of milkweeds in Mexico using ecological niche modeling. We built a three-stage protocol for habitat suitability of ELM, including climatic, biological, and environmental suitability modeling, under two general circulation models (CanESM5 and MPI-ESM1–2-HR), three-time horizons (2030, 2050, and 2070), and the “Middle of the road” socioeconomic pathway (SSP 2 RCP 4.5). We found a consistent southward shift in suitable areas, with climate emerging as the most limiting factor. Climate change projections indicate contrasting potential reductions of 40% and 8% in suitable habitat by 2070, under the CanESM5 and MPI-ESM1–2-HR, respectively. While environmental suitability remained relatively stable—mainly due to the persistence and increase of rainfed agriculture—biological suitability, determined by the distribution of 46 perennial species of milkweed ( Asclepias ), also shifted southward. This trend suggests that monarchs may increasingly establish reproductive resident populations in northeastern to central Mexico rather than reaching their overwintering sites. Our findings underscore the need to expand similar multifactorial modeling efforts across the U.S. and Canada to have a transboundary collaboration that integrates conservation strategies for monarch migration, accounting for potential shifts in climatic, biological, and environmental suitability under climate change scenarios.
Sánchez-Cordero et al. (Wed,) studied this question.