Nutria Grazing Preference as a Function of Fertilization

In Louisiana, subsiding wetlands frequently receive diverted fresh river water, which contains nutrients, stimulates vegetative growth, and may increase vertical accretion via vegetative growth. When river water is introduced, varying nutrient and salinity concentrations are produced. These varying conditions within marshes probably influence the feeding habits of herbivorous animals because of a preference for vegetation high in nutrients and low in salinity. Nutria (Myocastor coypus), a large introduced rodent, can negatively affect wetlands. We speculate that, driven by a biological need for nitrogen, nutria may affect treated wetlands more than untreated wetlands. Therefore, we sought to determine if wild-captured nutria preferred fertilized versus unfertilized plants of the following species: Panicum hemitomon Schult., Sagittaria lancifolia L., and Spartina patens (Aiton) Muhl. Nutria showed a significant preference for fertilized over non-fertilized samples, potentially caused by nutrient-driven increases in the nitrogen concentrations of fertilized plants, changes in the carbon to nitrogen ratio within plant tissue, and the universal animal need for biologically available nutrients to maintain homeostasis. Preliminary findings may partially explain observations of reduced plant abundance where elevated levels of nutrients are introduced to nutrient-limited wetlands, possibly necessitating a re-examination of proposed diversion implications and focusing nutria control efforts in such places.