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

Abstract

The monarch butterfly is one of the most easily recognized and frequently studied insects in the world, and has recently come into the spotlight of public attention and conservation concern because of declining numbers of individuals associated with both the eastern and western migrations. Historically, the larger eastern migration has received the most scientific attention, but this has been changing in recent years, and here we report the largest-ever attempt to map and characterize non-overwintering habitat for the western monarch butterfly. Across the environmentally and topographically complex western landscape, we include 8,427 observations of adults and juvenile monarchs, as well as 20,696 records from 13 milkweed host plant species. We find high heterogeneity of suitable habitats across the geographic range, with extensive concentrations in the California floristic province in particular. We also find habitat suitability for the butterfly to be structured primarily by host plant habitat associations, which are in turn structured by a diverse suite of climatic variables. These results add to our knowledge of range and occupancy determinants for migratory species and provide a tool that can be used by conservation biologists and researchers interested in interactions among climate, hosts and host-specific animals, and by managers for prioritizing future conservation actions at regional to watershed scales.

Climate Change and Local Host Availability Drive the Northern Range Boundary in the Rapid Expansion of a Specialist Insect Herbivore, Papilio cresphontes

“…Recent climatic shifts, particularly warmer, wetter temperatures during breeding season and warmer temperatures during pupal overwintering season, have allowed P. cresphontes to rapidly expand northward to now match or even surpass the slower moving northward range expansion of the northernmost host plant, Z. americanum, with further northward expansion of P. cresphontes now limited by host plant range, not climate (Figure 4). Our results highlight the importance of including biotic interactions (and interactions between herbivorous insects and host plants in particular) in examinations of range shifts and their speed, an idea often highlighted, (Urban et al, 2016) but infrequently implemented (Lemoine, 2015;Dilts et al, 2019;Svancara et al, 2019). Poleward range shifts in herbivorous insects, particularly butterflies, have been documented for a number of species (Parmesan et al, 1999;Warren et al, 2001;Pöyry et al, 2009;Breed et al, 2012).…”

Are eastern and western monarch butterflies distinct populations? A review of evidence for ecological, phenotypic, and genetic differentiation and implications for conservation

“…Summer‐breeding monarchs in western North America are typically found in areas with a broader range of daytime high temperatures, despite having a more compact geographic range (Figure 2a; see Data S1). Western monarchs also occur in areas with limited summer precipitation (Figure 2b), which may determine milkweed availability and explain why western monarch occurrence records are biased toward areas with surface water (Dingle, Zalucki, Rochester, & Armijo‐Prewitt, 2005) and particular land cover patterns (Dilts et al, 2019). This pattern applies to both adult and larval monarch records (Data S1).…”

Climate change and local host availability drive the northern range boundary in the rapid northward expansion of the eastern giant swallowtail butterfly

“…4). Our results highlight the importance of including biotic interactions (and interactions between herbivorous insects and host plants in particular) in examinations of range shifts, an idea often highlighted, (Urban et al , 2016) but infrequently implemented (Lemoine, 2015;Dilts et al , 2019;Svancara et al , 2019) .…”