Nitrogen dynamics and nutritional ecology of the plains pocket gopher, Geomys bursarius illinoensis

David Henry Thorne, Purdue University

Abstract

The nutritional ecology of the plains pocket gopher, Geomys bursarius illinoensis, was studied to gain information on pocket gopher physiology and ecology in grassland habitats. An examination of 26 tallgrass prairie plants for nutritional content and secondary plant compound content indicated that no digestive-reducing or toxic compounds were present at levels that could influence diet choice of plains pocket gophers. A study of the distribution and habitat of the plains pocket gopher in Indiana during 1987-1989 suggested that human-induced disturbance is the primary factor influencing the current range, population size, and habitat occupied by pocket gophers. Pocket gophers were found in only two areas in Indiana that contained relict prairie vegetation. Only two population groups were on publicly-owned land. It is predicted that population groups and numbers of plains pocket gophers in Indiana will decline in the future as more areas of grassland are developed or modified through agricultural practices and residential development. A latin square total collection balance trial was conducted to determine the nitrogen requirement of plains pocket gophers. Six diets, ranging in protein content from 1% to 8%, were fed to six nonreproductive adult females during six time periods. A minimum daily nitrogen excretion rate of 422 mg kg$\sp{-1}$ (body mass) day$\sp{-1}$ (CV = 13.3%) was calculated from the metabolic balance data by fitting regression equations to nitrogen intake and fecal and urinary nitrogen excretion rates. Metabolic fecal nitrogen was determined to be 191 mg kg$\sp{-1}$ (body mass) day$\sp{-1}$ (CV = 15.2%) or 6.22 g nitrogen kg$\sp{-1}$ (dry-matter intake), and endogenous urinary nitrogen was determined to be 231 mg kg$\sp{-1}$ (body mass) day$\sp{-1}$ (CV = 16.5%). The null hypotheses that allometric equations, based on the scaling of body mass, could accurately predict plains pocket gopher metabolic fecal nitrogen and endogenous urinary nitrogen could not be rejected. The nutritional health of plains pocket gophers in existing grassland habitats was evaluated by collecting morphological data and whole blood and plasma samples from pocket gophers in old-field, roadside right-of-way, and sand savanna habitats. No differences in any parameters were apparent. Densities of populations in the old-field and roadside grassland rights-of-way were higher, reflecting the higher levels of soil fertility and greater density of vegetation in those habitats, compared to sand savannas.

Degree

Ph.D.

Advisors

Weeks, Purdue University.

Subject Area

Forestry|Zoology|Ecology

COinS