Document Type

Thesis - University Access Only

Award Date

2004

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Charles D. Dieter

Abstract

Aspects of beaver (Castor canadensis) ecology were investigated during 2000 and 2001 along a section of the Big Sioux River in eastern South Dakota. Grazed and ungrazed habitat quadrats were sampled for tree species, diameter of trees at breast height (DBH), beaver damage to trees, and distance from water of trees and damage. Grazed habitat comprised 80.l % of the quadrats, while ungrazed habitat accounted for 19.9%. Green ash (Fraxinus pennsylvanica) (23.5%), peachleaf willow (Salix amygdaloides) (17.8%), and boxelder (Acer negundo) (13.1 %) were the dominant trees species throughout the river system. Silver maple (19.2%) was only found in the lower end of the study area.

The actual density of trees was significantly higher in ungrazed habitat (1067 trees/ha) than in grazed habitat (529 trees/ha). Total basal area was significantly higher in ungrazed habitat (2.4 x 108 square cm/ha) than in grazed habitat (2.9 x 107 square cm/ha). Trees in grazed habitat were larger (52% having a DBH greater than 30. l cm) than trees in ungrazed habitat (72% having a DBH less than 30 cm).

Beavers cut trees in equal proportions between grazed (17.4%) and ungrazed habitats (15.4%). The number of trees cut/ha was greater in ungrazed habitat (164.5 trees cut/ha) than in grazed habitat (97.1 trees cut/ha). Beaver activity was evident on 85 of 527 (16%) trees sampled. Green ash, peachleaf willow, and American elm were selected for by beavers. The mean DBH for trees cut (30.82 cm) was significantly smaller than that of uncut trees (42.23 cm). The mean distance from the water of cut trees (20.34 m) was less than that of uncut trees (26.86 m).

I examined 103 beaver carcasses for age and sex. The age ratio was 32% (33) kits, 22.3% (23) yearlings, and 45.6% (47) adults. There was no significant difference in the sex ratio of from the 1: 1 ratio in the entire population or between age classes. The age and sex ratio is similar to other beaver populations that are characterized as exploited yet increasing in population.

I also examined the beaver carcasses for the presence of an internal Nematode parasite, Dracunculus insignis. None of the beaver carcasses examined (103) were infested by Dracunculus insignis.

Library of Congress Subject Headings

Beavers -- Ecology -- South Dakota.

Publisher

South Dakota State University

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Rights Statement

In Copyright