The flow of energy through an ecosystem is essential for the integrity of a system.  In desert ecosystems, small mammals are an important link between primary production and subsequent consumer levels. By making inter-site comparisons within the same ecosystem, we can further understand factors that affect energy flow through the small mammal community.  To that end, we compared the biomass of the major functional groups of small mammals (granivores and folivores) between two distant (750 km) areas in the Chihuahuan Desert (the Mapimi Biosphere Reserve in northern Mexico and the Jornada Experimental Range in New Mexico).  Specifically, we tested 1) whether total small mammal biomass differed between the two sites, 2) if the contribution of functional groups differed, and 3) if the species composition of the functional groups differed or change through time. To make these comparisons, we used concurrent 10 year data sets from the two areas.  Small mammals were trapped on both areas within two habitat types, grassland and shurbland, in identically designed trapping webs.  There were three replicates per habitat per area.  Trapping was done twice a year at approximately the same time in the two areas (March-April and November-December).

Results/Conclusions

Both Mapimi and the Jornada had a similar richness in small mammal species (14 vs. 15 respectively).  However, the areas only had 8 species in common.  Total biomass per hectare per year was also similar: Mapimi 1.4 ± 0.03 (SE) kg/ha/yr vs. Jornada 1.6 ± 0.02.  Both areas had 4 functional groups of small mammals: granivores, folivores, carnivores, and omnivores but the majority of the biomass was in the first two groups. Mapimi had a higher biomass of folivores than the Jornada (0.65 ± 0.01 vs 0.37 ± 0.008 kg/ha/yr).  The Jornada in turn, had a higher biomass of granivores (1.0 ± 0.02 vs. 0.65 ± 0.01 kg/ha/yr). We also found a high amount of asynchrony between the two sites with the maximum biomass in Mapimi being in 2005 (4.0 ± 0.02 kg/ha/yr) and for the Jornada it was in 1997 (2.2 ± 0.02 kg/ha/yr).  We conclude that although both desert sites had similar overall biomass of rodents, how it was partitioned among the functional groups and how it varied annually was strikingly different. We discuss the possible reasons for these differences and the implications relative to energy flow to the subsequent carnivore levels.