Small Mammal Activity Alters Above- and Below-Ground Community Structure and Function in an Old-Field Ecosystem.

Abstract:

Herbivores shape ecosystems by altering plant community composition, inducing plant defenses, and redistributing nutrients via waste inputs. However, few studies have focused exclusively on how small mammal herbivores contribute to these processes. Using an established small mammal manipulation experiment we determined how exclusion of small mammal herbivores altered the structure and function of an old-field ecosystem. Specifically, we tested whether small mammal herbivores can alter plant community composition, can change belowground community structure, and can influence belowground functioning and nutrient cycling. We hypothesized (i) small mammals would directly alter plant composition through selective feeding pressure, (ii) indirectly change soil microbial structure, (iii) indirectly change soil microbial function, and (iv) indirectly alter N cycling.

Results:

Exclusion of small mammal herbivores did not change plant species composition (F _pseudo= 1.51, P_perm = 0.151) but it did alter the functional plant composition. Exclusion of small mammal herbivores caused a shift in the plant community from a woody and legume -dominated community to one comprised primarily of C₃ and C₄ grasses (F_pseudo = 3.92, P_perm = 0.018). Total aboveground standing biomass was significantly greater in exclosure than access plots (F = 3.76, p = 0.068). Belowground, mammal herbivores had minimal effects on bacterial and fungal abundance (F = 2.91, p = 0.105; F = 2.1, p = 0.164), but had larger effects on potential extracellular enzyme activity. The potential enzyme activity of carbon degrading enzymes, a-glucosidase, cellobiohydrolase, and phenol oxidase are higher when mammals are absent. The absences of small mammal herbivores also caused a 42% increase in potential nitrogen. Taken together, these data indicate small mammal herbivores impact ecosystem processes through changing above- and belowground community structure and function.