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 thirteen milkweed host plant species. We find high heterogeneity of suitable habitat 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.
Highlights
Species with exceptionally large geographic ranges are not often the focus of conservation and management attention, because large ranges typically encompass many populations or subpopulations, which buffer against stressors that are of concern in species with more restricted distributions (Brook et al, 2008)
Our study is the first peer-reviewed paper to apply maximum entropy habitat modeling to the western monarch and a majority of the important milkweed hosts in the western U.S
The geographic distribution of western monarch butterflies is characterized by high heterogeneity of suitable habitat (Figure 5), as has been seen with other wideranging species, in western North America (e.g., Lozier et al, 2013)
Summary
Species with exceptionally large geographic ranges are not often the focus of conservation and management attention, because large ranges typically encompass many populations or subpopulations, which buffer against stressors that are of concern in species with more restricted distributions (Brook et al, 2008). In at least some cases, migratory species are an exception in that they can be composed of a single population that covers a large geographic area, and may be uniquely exposed to stressors but without the resilience afforded by metapopulation structure (Drechsler et al, 2003). With such species, one of the central challenges is to understand habitat requirements or associations in different parts of the range so that. Maximum temperature of PRISM; Daly et al (2008)
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