Influence of nitrogen and silica concentration on grass palatability and digestion in the meadow vole, Microtus pennsylvanicus

Background/Question/Methods

Field experiments are commonly used to investigate the effects of global change drivers such as warming and nitrogen deposition on plant productivity and community structure. Often overlooked in these studies is the potential for herbivores to concentrate feeding activity in preferred treatment plots, which could substantially influence plant responses to the treatments. In a previous study we observed that the exclusion of meadow voles from nitrogen fertilized plots had a significantly greater effect on grass biomass than did their exclusion from non-fertilized plots. The aim of our current study was to explore the potential mechanisms governing this response by determining how changes in forage quality would influence meadow vole feeding dynamics. Both foliar nitrogen and silica concentrations were manipulated in order to determine their individual, as well as interactive effects on grass palatability and digestibility.   

Results/Conclusions

Results from 4-choice palatability trials showed that nitrogen addition had no effect on vole diet choice, whereas silica addition had a marginally significant negative effect. There were no significant interactive effects, suggesting that increased nitrogen was not able to compensate for the low palatability of high-silica grasses. Bomb calorimetry results from the grass digestion trials revealed diet had no significant effect on fecal energy content. It was particularly interesting to find that silica addition had no effect on fecal energy content despite silica-rich material being avoided during palatability trials. Overall, our results suggest that silica may play an important role in vole diet choice in the field, but it does not appear to be a significant impediment to digestion.