Seeds are an important food resource for many rodents.  One of the specializations that many granivorous rodents exhibit to increase their efficiency in harvesting seeds is cheek pouches.  However, many rodent species lack cheek pouches.  We propose that the presence or absence of cheek pouches is related to seed size and the productivity of the habitat where those rodents reside. 

Location  North America – United States and Canada.

Taxon  Granivorous rodents.

We divided granivorous rodents into those species with and without cheek pouches. We then compiled a list of plant species (n = 389) that are known or suspected to be dispersed by these rodents via scatter hoarding the seeds in soil and compared the richness distributions of small (≤10 mm) and large seeds (>10 mm) to the distributions of rodents with and without cheek pouches.  Large seeds are generally too large to fit into cheek pouches so they are usually carried one at a time with the incisors. Most rodents with cheek pouches live in the arid southwestern North America, whereas most rodents that lack cheek pouches live in the mesic southeastern North America. The richness distribution of rodents with cheek pouches was more similar to the richness distribution of small seeds, and the richness distribution of rodents that lack cheek pouches was more similar to the richness distribution of large seeds (nuts), although details of these distributions differed significantly.  The body mass of rodents with cheek pouches (mean = 59.5 g) was significantly less than the body mass of rodents that lack cheek pouches (592.6 g). Large rodents that lack cheek pouches live mostly in the more productive southeastern portion of North America where there are many trees that produce large nuts.  Small rodent with cheek pouches live mostly in the less productive southwestern portion of North America where there are many shrubs, forbs, and grasses that produce small seeds.

Data was enumerated by using program R to count the number of overlapping animal and plant species across 197 sites in the United States and Canada. Unmanipulated data can be found from the International Union for Conservation of Nature (IUCN 2019) and Vander Wall and Moore 2016.

IUCN. (2019). The IUCN Red List of Threatened Species Version 2019-6.2. https://www.iucnredlist.org. Downloaded on January 17^th, 2020.

Vander Wall, S. B. & Moore, C.M.  (2016).  Interaction diversity of North American seed-dispersal mutualisms.  Global Ecology and Biogeography 25, 1377-1386.