Nitrogen outputs from fecal and urine deposition of small mammals: implications for nitrogen cycling

Abstract

The contribution of small mammals to nitrogen cycling could have repercussions for the producer community in the maintaining or perhaps magnifying of nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of small mammals in an old-field ecosystem and estimate the amount of fecal and urinary nitrogen deposited annually. To address this objective, we used models from laboratory studies and combined these with data from field studies to estimate dietary nitrogen and monthly and annual nitrogen outputs from fecal and urine deposition of five rodent species. The models accounted for monthly fluctuations in density and biomass of small-mammal populations. We estimated that the minimal amount of nitrogen deposited by rodents was 1.0 (0.9-1.1) and 2.7 (2.6-2.9) kg Nha(-1) year(-1) from feces and urine, respectively, for a total contribution of 3.7 (3.5-4.0) kg Nha(-1) year(-1). Hispid cotton rats (Sigmodon hispidus) accounted for >75% of the total nitrogen output by small mammals. Our estimates of annual fecal and urinary nitrogen deposited by rodents were comparable to nitrogen deposits by larger herbivores and other nitrogen fluxes in grassland ecosystems and should be considered when assessing the potential effects of herbivory on terrestrial nitrogen cycles.

Ecological correlates of small mammal assemblage structure at different spatial scales in the savannah biome of South Africa

“…Rodents and shrews play important ecological roles by sustaining multiple terrestrial and aerial predators (Andersson and Erlinge 1977) and by contributing to the cycling of nutrients (Clark et al 2005). Furthermore, they act as useful indicators of ecological integrity and can be used to predict environmental change (Avenant and Cavallini 2007).…”

Protein Nutrition of Southern Plains Small Mammals: Immune Response to Variation in Maternal and Offspring Dietary Nitrogen

“…Our results indicate that, contrary to our a priori assumptions, at higher dietary nitrogen, individuals may face increasing energetic demands from the excretion of excess nitrogenous compounds, which may lead to decreased immune function. Although we did not measure metabolic rate or nitrogen excretion during this study, a concurrent study from the same lab measured nitrogen excretion in the same species (Parsons 2001;Clark et al 2005). Parsons (2001) found that changes in liver and gut morphology were associated with both maternal and offspring dietary nitrogen.…”

“…Parsons (2001) found that changes in liver and gut morphology were associated with both maternal and offspring dietary nitrogen. Clark et al (2005), using results from Parsons (2001), found that increasing dietary nitrogen is associated with increased urinary nitrogen output and that with increasing dietary nitrogen, harvest mice increase nitrogen output faster than cotton rats. This provides indirect support for the hypothesis that the energy needed to eliminate excess nitrogen may reduce energy available for immunity.…”

“…We chose two of the most common species in the southern prairie, the hispid cotton rat (Sigmodon hispidus; Cameron and Spencer 1981) and the fulvous harvest mouse (Reithrodontomys fulvescens; Spencer and Cameron 1982), because of their dominant position by biomass and numbers within the ecosystem (Schetter et al 1998;Brady and Slade 2001;Clark et al 2005) and the difference in their diets. Cotton rats are primarily herbivores, consuming a mixture of monocots and dicots (Randolph et al 1991), whereas the harvest mouse is an omnivore with a substantial insect component (Meserve 1976;Vasquez et al 2004).…”

Modeling nitrogen flux by larval insect herbivores from a temperate hardwood forest

“…A complementary approach to estimating frass N inputs is to scale individual N flux to the community level using general models of individual flux and information about community structure. This strategy has been used to study N flux by a variety of aquatic (Peters and Rigler 1973;Ejsmont-Karabin 1984;Grimm 1988;Wen and Peters 1994;Vanni et al 2002) and mammalian herbivores (Clark et al 2005), but this approach has not been used with herbivorous insects.…”