ABSTRACT
The Mexican transition zone is the area where the Neotropical and Nearctic regions overlap (Figure 4.1). In its broad sense, it comprises southwestern United States, Mexico, and most of Central America (Halffter, 1987; Zunino and Halffter, 1988; Gutiérrez-Velázquez et al., 2013). It is partially coincident with the areas named Megamexico 3 (Rzedowski, 1991) and biotic Mesoamerica (Ríos-Muñoz, 2013). The Mexican transition zone in the strict sense, which is followed in this book, corresponds to the moderate to high elevation highlands of Mexico, Guatemala, Honduras, El Salvador, and Nicaragua (Morrone, 2006, 2010b, 2014b, 2015c; Espinosa Organista et al., 2008).
