Climate can shape the nature of plant—animal interactions. The yellow pine chipmunk (Tamias amoenus), which occupies semi-arid pine forests of western North America, engages in mutualistic relationships with its food plants by dispersing seeds. These chipmunks scatter hoard seeds during spring, summer, and early autumn in soil; unrecovered seeds germinate in the spring. The eastern chipmunk (Tamias striatus) of eastern North America occupies mesic deciduous forests. These chipmunks primarily larder hoard seeds and nuts. Seeds in burrow larders cannot establish seedlings, so these chipmunks have not been documented to be involved in mutualistic plant—animal interactions. The differences in behaviour and the roles that these 2 species play in their communities appear to be caused by differences in precipitation. Scattered caches are more secure from pilferers in the dry western environment because olfaction is moisture dependent. In the more mesic eastern forests, scattered caches are quickly pilfered, causing chipmunks to store most food in larders, which they defend. Climate (i.e., amount of precipitation) also influences many other aspects of the ecology of these species, including home range size, the size and role of the home burrow, mode of foraging, and diet.