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Physiological response of deer on ranges of varying quality. Klein, David R.

Abstract

Limited work has been done in the field of ecology to relate growth and development of wild ungulates to the quality of their natural forage. This study was conducted in Southeast Alaska during the summers of 1959, 1960 and 1961 to identify the factors of the environment which alter the plane of nutrition of deer (Odocoileus hemionus sitkensis) and result in variations in body size. Woronkofski and Coronation Islands, suspected to produce deer of wide contrast in body size, were chosen as study areas and qualitative and quantitative measurements were made of both the deer and the range on the two islands. A total of 63 deer specimens were collected, from which sex, age, weights and measurements were recorded and samples of rumen contents were collected and analysed. Specimens were examined to determine levels of parasitism. Sex and age status of deer that died from natural causes were utilized for additional data. The range was evaluated through the use of line intercept transects correlated with chemical analyses of major forage species. Results of quantitative analyses of vegetation on the two islands indicate that Woronkofski Island greatly outranks Coronation Island in: 1) plant density and species abundance in the forest (110 to 54 interceptions) and muskeg (297 to 242 interceptions) types, 2) total area of subalpine (4.72 to 1.82 sq.mi.) and alpine (5.00 to 0.24 sq.mi) types and total area of forest type on an equal density basis (13.05 to 11.64 sq.mi.), and 3) total vegetated area on an equal density basis (24.31 to 16.51 sq.mi.). Qualitative evaluation of forage species through the use of chemical analyses did not show significant differences between islands in comparisons of similar species under comparable site conditions. There were indications that alpine and muskeg vegetation was of higher quality than forest vegetation and alpine plants appeared of slightly higher quality than similar species growing on low elevation muskegs. The physiological stage of plant growth appeared to be the most important factor in determining nutritive quality of vegetation. Analyses of rumen samples enabled a clear separation between Woronkofski and Coronation Islands on the basis of range quality. Nitrogen content of both the gross and washed rumen samples was consistently higher in the Woronkofski group than in those from Coronation Island. An inverse relationship existed with respect to the fiber content. Other techniques of rumen contents analyses involving centrifuge fractionation of microorganisms, light transmittancy determinations of rumen liquor and microscope counts of protozoa supported the comparative evidence from the chemical analyses. Regression analyses of weights and skeletal measurements of the specimen deer showed growth differences between the two islands which are apparently attributable to differing levels in the annual nutritional regimens of the deer. Skeletal ratios were found to be more reliable than body weight as measures of growth differences because skeletal parts are less subject to short term fluctuations in the environment and they, therefore, more accurately reflect physiological age. The use of the femur/hind foot ratio supports the thesis that the larger size of deer on Woronkofski than on Coronation Island is the product of nutritional rather than genetic causes. No significant differences, that could be related to nutritional factors, were found in the levels of parasitism among the deer of the two islands. The sex and age composition of the deer populations on the two islands reflects the quality and quantity of forage present on the ranges. Conclusions of the study are that the larger size and more rapid rate of growth of deer on Woronkofski Island in comparison to those on Coronation Island are the result of the psysiological response of the deer on both islands to pronounced differences in the nutritive quality and quantity of their respective ranges. These nutritive factors are primarily operative during the summer period of growth of both the vegetation and the deer. The factors of the environment responsible for the differences in quality and quantity of forage present on the two islands are primarily differences in the degree of altitudinal and topographic Variation and in the relative proportions of alpine and subalpine areas and secondarily in the regional climatic differences and the presence or absence of predation.

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