**3. Results**

## *3.1. Rarity Patterns*

We found marked rarity patterns within NW pitvipers (Figure 1 and Table S4). Considering each component separately, most species have a narrow habitat breadth (78.7% of the species inhabit a single habitat type) or are locally common (79.5%), and around half of them (55.9%) are widely distributed (GR > 82,900 km2).

**Figure 1.** Number of species of New World pitvipers in each rarity cell (letters A to F after each number) of the method proposed by Rabinowitz [10]. The species depicted is *Bothrops pauloensis*, from southeastern Brazil.

Regarding the rarity types of Rabinowitz ([10]; cells A to H in Figure 1), one type does not occur in NW pitvipers (cell C in Figure 1; large GR, broad HB, and low LA; Table S4) and two types comprise less than 5% of the species, with 3.15% of species with small GR, broad HB, and high LA (cell E in Figure 1; Table S4) and 0.8% of species with small GR, broad HB, and low LA (cell G in Figure 1; Table S4). A grea<sup>t</sup> number of the NW pitvipers (30.7%) has large GR, narrow HB, and high LA (cell B in Figure 1; Table S4) and 28.3% of the species have small GR, narrow HB, and high LA (cell F in Figure 1; Table S4). Thus, cells B and F represent the majority (59%) of the rarity patterns characterizing the NW pitvipers (Figure 1; Table S4). Besides, 11.8% of the species are in cell H (small GR, narrow HB, and low LA) and 7.9% in cell D (large GR, narrow HB, low LA; Figure 1; Table S4). As for our rarity categories, 11.8% of the species are in the rarest category (cell H), 37.0% are in high intermediate (cells D, F, and G), 33.8% are in low intermediate (cells B, C, and E), and 17.3% are in the not rare category (cell A). Using log-linear models, we found significant, positive associations between GR and HB (χ<sup>2</sup> = 7.75, *p* = 0.005, 1 *df*) and between HB and LA (χ<sup>2</sup> = 5.66, *p* = 0.017, 1 *df*). This indicates that the most parsimonious model predicting the number of species in each rarity category includes the association between GR and HB and the association between HB and LA.

Species in the rarest category occur along the Pacific coast of Mexico, in southern Central America, especially in Costa Rica and Panamá, in the Andean region of Ecuador, and in a narrow area in eastern Brazil (Figure 2A). When both higher rarity categories (high intermediate and rarest) are considered together, rare pitvipers are found in the southwestern United States, throughout Central America from southwestern Mexico to Panamá, and in central and northern South America (Figure 2B). When the distribution of rare pitvipers (high intermediate and rarest; Figure 2A,B) is compared to pitviper richness hotspots throughout the Americas ("hottest" areas in Figure 2D), there is a relatively good congruence between them in North and Central America, but a generally low congruence in South America.

**Figure 2.** Maps depicting the species richness of New World pitvipers, according to different rarity and threat status categories. (**A**) Distribution of the rarest species (category RT); (**B**) distribution of rare species considering both higher rarity categories (HI and RT); (**C**) distribution of threatened species (IUCN (International Union for Conservation of Nature) categories critically endangered, endangered, and vulnerable); (**D**) species richness of all New World pitvipers.

In general, rarity patterns do not seem to be phylogenetically conserved across NW pitvipers (Figure 3) with the exception of Central American lineages (*Bothriechis*, *Cerrophidion*, *Mixcoatlus*, and *Ophryacus*), which show high concentration of rare species (High Intermediate and Rarest; Figure 3). In other lineages (e.g., *Bothrops*, *Crotalus*), rare species are frequently endemic to islands or to Central and North American mountains (Figure 3 and Figure S1).

**Figure 3.** Phylogeny of the New World pitvipers, with colors representing different rarity categories.
