Study site
We conducted the fieldwork in the Pedregal de San Angel Ecological Reserve (PSAER or REPSA for its name in Spanish; 237 ha). This reserve belongs to the National Autonomous University of Mexico and is located on its main campus in Mexico City (19°18’-19°19’ N, 99°10’-99°11’ W). In this reserve the most common vegetation type is a native xeric shrubland dominated by Pittocaulon praecox Cav. (Rzedowski 1954, Cano-Santana 1994). The climate is temperate sub-humid with summer rainfall (Castillo-Argüero et al. 2004). We report the temperature and rainfall during the study year in Supplemental Materials I.