Growth of rodents in response to dietary nitrogen
Neonatal growth and survival of rodents in response to variation in maternal dietary nitrogen: life history strategy vs dietary niche
Nitrogen (N) enrichment of terrestrial ecosystems dramatically changes ecosystem diversity and structure of plant communities. Research designed to elucidate effects of nitrogen addition on mammalian assemblages is rare.
We investigated nitrogen requirements of hispid cotton rats (Sigmodon hispidus) and fulvous harvest mice (Reithrodontomys fulvescens), small mammals native to the tallgrass prairie of the southern Great Plains, USA, to better understand population responses of these species to nitrogen enrichment. We studied reproductive requirements by measuring growth of offspring under varying levels of dietary nitrogen. We predicted that dietary niche would dictate nitrogen requirements, such that the larger herbivore (S. hispidus) would have a lower dietary need for nitrogen per unit mass than the small omnivore/granivore (R. fulvescens). Reproductive output (measured as mass gain of litters and offspring) was responsive to varying nitrogen in cotton rats but not in harvest mice. Nitrogen intake that supported 50% survival of juvenile harvest mice (1.34% dietary nitrogen) also was adequate for maximum growth (1.29%). Cotton rats potentially drew on maternal nutrient stores to support litter growth at low levels of dietary nitrogen (as low as 1.08%). Overall, nitrogen requirements for maximum reproduction were greater (2.31% dietary nitrogen) for cotton rats. We conclude that life history characteristics and body size constraints rather than dietary niche explain the differential species response to variation in dietary nitrogen. Our results imply that nitrogen enrichment in old-field succession in the southern Great Plains may lead to dominance by cotton rats and a reduction in diversity of the small-mammal assemblage. Consumers with similar abilities to take advantage of increased environmental nitrogen may likewise dominate other ecosystems.