*2.1. Occurrence Data*

Occurrence data were obtained from three different sources: (1) Historical populations identified according to Source Features (SF; observations) shapefiles and Element Occurrences (EO) provided by the Texas Natural Diversity Database (TXNDD) (TXNDD 2016). SF and EO are matched with shapes and shapefiles using key identificatory fields (IDs). The EO ID represents populations and contains the complete information that TXNDD has for *Manihot walkerae*. (2) Non-digital data in the form of reports, handwritten notes, pictures and maps obtained from the Texas Parks and Wildlife Department (TPWD). (3) Shapefiles provided by expert botanists that contain precise latitude and longitude data for parcels within the Lower Rio Grande Valley National Wildlife Refuge.

All gathered occurrences were converted into decimal degrees and after removing duplicates and outliers that lay outside the Tamaulipan thornscrub ecoregion study area, the total number of occurrences for *M. walkerae* was 399 (Figure 1). We reduced geographic autocorrelation for the occurrences using the "spatially rarefy occurrence data" tool in the SDM toolbox version 2.2 [36] at a distance of 4-km. The resulting number of spatially rarefied occurrences was 19 and these were used to generate models through MaxEnt (Figure 1).

**Figure 1.** Known occurrences for *Manihot walkerae* in Texas and Mexico within the Tamaulipan Thornscrub ecoregion study area. The yellow dots represent all 399 known occurrences for *M. walkerae*, and the red dots represent the 19 4 km spatially rarefied occurrences.

### *2.2. Study Area and Bioclimatic Variables*

The geographic potential distribution of *M. walkerae* was generated in the Tamaulipan thornscrub ecoregion, because it encompassed all *M. walkerae* historical occurrences (Figure 1). The Tamaulipan thornscrub is characterized by a subtropical, semi-arid vegetation type that occurs on either side of the Rio Grande delta [30]. Spiny shrubs and trees dominate, but grasses, forbs, and succulents are also prominent. It is located within the physiographical province known as the Coastal Gulf Plain [30]. The region originates in the eastern part of Coahuila, Mexico at the base of the Sierra Madre Oriental, and then proceeds eastward to encompass the northern half of the state of Tamaulipas, and into the United States through the southwestern side of Texas. Elevation increases northwesterly from sea level at the Gulf Coast to a base of about 300 m (1000 ft.) near the northern boundary of the ecoregion, from which a few hills and small mountains protrude [30]. Global ecoregion data was downloaded from The Nature Conservancy Geospatial Conservation Atlas for the Tamaulipan thornscrub ecoregion.

We predicted the distribution for *M. walkerae* at present and for the future using three general circulation models and two representative concentration pathways for the years 2050 and 2070. The three general circulation models and two representative concentration pathways were chosen following a method by Kurpis et al. (2019) [37]. Bioclimatic variables representing current and future conditions were downloaded from WorldClim, a database that provides climatic data derived from monthly temperature and precipitation collected from weather stations around the world, and interpolated onto a surface of approximately 1 km spatial resolution [38]. Nineteen bioclimatic variables representing current global climate data at a 30 arcseconds spatial resolution were downloaded along with the future bioclimatic variables for three general circulation models (GCM): HadGEM2 (Hadley Centre for

Climate Prediction and Research), CMIP5 (Coupled Model Intercomparison Project Phase 5), and CM3 (Geophysical Fluid Dynamic Laboratory), and for the two representative concentration pathways: 4.5 watts/m<sup>2</sup> and 8.5 watts/m2. These scenarios were developed by the International Panel on Climate Change (IPCC) based on levels of accumulation of greenhouse gas emissions, agriculture area, and air pollution [39,40]. The 4.5 RCP represents an intermediate emissions scenario where temperatures are predicted to increase by approximately 1.5 ◦C by the end of the 21st century, while the 8.5 RCP represents the most severe scenario with an expected increase of over 2 ◦C by the end of the 21st century [40].

The bioclimatic variables (Table 1) were cut to fit the Tamaulipan thornscrub ecoregion through ArcGIS [41]. Highly correlated environmental variables with a correlation value above 0.8 were excluded using the "remove highly correlated variables" tool in the SDM toolbox [36]. Ten of the nineteen bioclimatic variables were found as "not-highly" correlated and were used to create the models (Table 1).

**Table 1.** Available and used (bold) bioclimatic variables for modeling of the present and future potential suitable habitat of *M. walkerae*. The percent contribution of each of the low correlated variables to the present potential suitable habitat model is also included.

