Monarch (Danaus plexippus) larval records in the western U.S

Species distributions are driven by abiotic and biotic factors, but the importance of variation in the availability and quality of critical resources is poorly understood. Disentangling the relative importance of these factors – abiotic environment, availability of critical resources, and resource quality– will be important to modeling species current distributions and responses to projected climate change. We address these questions using species distribution models (SDMs) for the western monarch butterfly population (Danaus plexippus), whose larvae feeds exclusively on Asclepias species known for their heterogeneously distribution and variation in host-quality. We modeled the distribution of 24 Asclepias species to compare three monarch distribution models with increasing levels of complexity: (i) a null model using only environmental factors (climate envelope model), (ii) a model using environmental factors and Asclepias availability estimated as species richness, (iii) and a model u...