species. An apparent advantage to group living in the great
gerbil is the detection of predators and warning of group
members via a complex system of alarm signals. Group size
and composition are flexible and vary with availability of
vegetation and subsequent changes in population density.
Another group of semifossorial rodents, kangaroo rats (Di-
podomys), provides a model system for understanding
social behavior of solitary rodents. Kangaroo rats are philo-
patric, show a range of social tolerance, and have well-
developed means of communication by scent marking and
footdrumming. Social tolerance varies on a social contin-
uum from the most to the least tolerant species. Because
behavioral flexibility seems important to survival and re-
production in both solitary and social desert rodents, so-
cial flexibility may be common in desert rodents. Caution,
therefore, should be exercised when generalizing about their
social behavior.Environmental Constraints and the Evolution of Sociality in Semifossorial Desert Rodents 379