Examination of the nitrogen limitation hypothesis in non‐cyclic populations of cotton rats (Sigmodon hispidus)

Abstract

Summary 0[ Nitrogen!containing nutrients have long been considered a frequently limiting resource to the growth of herbivore populations "nitrogen limitation hypothesis#[ To explore this hypothesis\ we examined the relationships between availability of essential amino acids and concentrations of phenolics in the diets of hispid cotton rats "Sigmodon hispidus# in central Oklahoma and the intrinsic characteristics of their non!cyclic populations[ We posited that lower quality proteins "i[e[ essential amino acid composition# and elevated phenolic levels "protein digestion inhibitors# in diets of cotton rats from low! compared to high!density populations\ especially during the breeding season\ would be supportive of the nitrogen limitation hypothesis[ Replicated low! and high!density populations were censused by live!trapping at 2!month intervals[ Samples of stomach digesta were collected from cotton rats in similar habitats adjacent to trapping grids to determine the botanical and nutrient composition of their diets[ 1[ During the breeding season\ concentrations of essential amino acids were as much as 32) greater in diets of cotton rats from high!density populations[ Dicots\ typically higher in protein than monocots\ were an important component of diets and were preferred forage in all seasonal collections[ Seeds and arthropods were frequently utilized by cotton rats as additional high!quality sources of essential amino acids[ Concentrations of total phenolics in the diet "greater in diets from low!density popu! lations# were consistent with the nitrogen limitation hypothesis[ 2[ Density was consistently higher in the high!density populations throughout the study[ Other demographic and body condition parameters were similar between low! and high!density populations in the non!breeding season\ but reproductive activity was greater in high!density populations during the breeding season[ Total number of juveniles recruited into the trappable population over the entire study was about _ve times greater in high! compared to low!density populations[ 3[ Our data did not refute the nitrogen limitation hypothesis where levels of essential amino acids and phenolic compounds in the diet during the breeding season may determine annual peak densities of cotton rats that can be supported in their habitat[ However\ we could not rule out the involvement of other environmental variables such as overhead cover "as well as other unmeasured variables# as contributing factors to determining annual peak densities[ Key!words] amino acids\ cotton rat\ food quality\ herbivore nutrition\ nitrogen limi! tation\ phenolics\ population dynamics\ Sigmodon hispidus[ Journal of Animal Ecology "0887# 56\ 694Ð610

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

“…We used an estimate of dietary nitrogen from field data collected at CSEAR for S. hispidus (3.16% N, n=52; Clark 2003) that was based on nitrogen analysis of stomach contents (samples collected in April and August 2000) coupled with regressions developed between stomach and dietary nitrogen (Clark et al 2003b). Our estimate was within the range of previously recorded estimates for S. hispidus in central Oklahoma (seasonal range 2.6-4.3% N; Schetter et al 1998). We obtained an estimate of dietary nitrogen from the literature for P. leucopus (4% N; Derting and Hornung 2003) and used this estimate for R. fulvescens, R. montanus, and P. maniculatus because diets of these species primarily comprise insects and seeds (Wilkins 1986;Stancampiano and Caire 1995).…”

“…For example, dietary quality is likely to be lower during dormant seasons (e.g., winter), which would cause variation in nitrogen consumption. However, Schetter et al (1998) found that nitrogen content of S. hispidus diets remained high (>2.5% N) throughout the year in central Oklahoma as a result of selective foraging.…”

Food resources and intestinal parasites as limiting factors for boreal vole populations during winter

“…For herbivores, forage quality is to a considerable degree determined by nitrogen content, which is often a primary limiting factor for the growth of populations (nitrogen limitation hypothesis [27][28][29][30]). Nitrogen levels in plants vary in response to a range of biotic and abiotic factors, such as weather, leading to both spatial and temporal variation in its availability to herbivores [31][32].…”

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

“…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).…”