Date of Award:

5-1973

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Department name when degree awarded

Wildlife Science

Committee Chair(s)

Frederic H. Wagner

Committee

Frederic H. Wagner

Committee

David F. Balph

Committee

Kent W. Bridges

Committee

David W. Goodall

Committee

James A. MacMahon

Committee

Ivan G. Palmblad

Committee

Neil E. West

Abstract

The interrelations of black-tailed jackrabbits and the desert-shrub vegetation on which they were feeding were studied in Curlew Valley, Northern Utah. The vegetation was described as a three-cornered continuum, the corners being types dominated respectively by Artemisia tridentata, Atriplex confertifolia, and Sarcobatus vermiculatus.

Jackrabbit diet was studied by microscopic analysis of plant fragments in stomachs from shot animals. The method was inaccurate, apparently because the ratio of identifiable tissues to all ingested tissues was very low, and varied between plant taxa, and seasonally. This problem seems intractable for desert shrub vegetation.

The diet was similar to that reported by other workers on this species, with perennial grasses and forbs most important in sprlng and summer, shrubs in autumn and winter. Features new to this vegetation were large percentages of Halogeton glomeratus, particularly in autumn and winter, and intense selection for Kochia americana. Attempts to explain the foods chosen ln terms of t heir nutrient contents were partically successful.

Diet selection by large generalist herbivores was conceptualized as optimization of nutrient intake, mediated by long-delay learning, and constrained by food availability only at very low levels of availability. Spatial variation in jackrabbit diets confirmed this "cut-off" response to availability.

Percentage utilization was estimated indirectly as jackrabbit density, times yearly food consumption per jackrabbit, times year-round percentage of each taxon in the diet, divided by available biomass of each taxon. Less abundant plants were more intensely used, which is expected if consumption does not vary continuously with availability. Perennial grasses, Kochia americana and possibly Grayia spinosa seemed to be under damaging pressure at high jackrabbit densities.

Kochia had almost disappeared from outside a sheep- and jackrabbit-proof exclosure since the 1950's. In other exclosures, the presence or absence of jackrabbits seemed to make no difference to the rate of vegetation recovery over 5-7 years after exclusion of sheep.

Jackrabbit use of a crested wheatgrass seeding was concentrated in a 300 m band around its edge.

Checksum

19fdebe6c586d48166d93e29b8d0fd9b

Download

Share

COinS

Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .