Vegetation and foraging ecology of the Vancouver Island marmot (Marmota vancouverensis)
Date
1984
Authors
Milko, Robert Joseph
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Abstract
The foraging ecology of the Vancouver Island Marmot (Marmota vancouverensis) was studied in the field to determine its degree of patch-type selection and diet breadth. Vegetation analysis of the intensively studied Haley Lake site and two additional sites produced six community types in the summer. In addition, three vegetation types were classified from four sites in the spring, a period when early stages of plant development precluded recognition of plant community types derived from the late summer. These types provided a framework for analysis of patch type selection. Combining cover values of plant species from taxa which were difficult to identify did not affect the classification.
The six community types are: Phlox-moss, Anaphalis-Aster, Ribes-Heuchera, Pteridium aquilinum, Senecio-Veratrum and Vaccinium-Carex.
The Haley Lake site showed sharply delineated plant communities, while Bell Creek, the other floristically similar low elevation site, farmed more of a vegetational continuum. Vegetation similarities allowed examination and comparison of marmot patch type selection at these two sites. Gemini Peak, the high elevation site, was floristically distinct and showed a more advanced stage of plant succession affecting its relatively homogeneous meadow vegetation.
The plant communities studied were compared with those described for other subalpine regions of the Pacific Northwest and explanations for the described vegetation patterns are proposed.
In the spring, patch-type select ion was found with a low variability between sites. In the summer, the highest selection was for the Anaphalis-Aster community type, most notably at the site with the most distinct patch definition. In the spring, four plant species accounted for 87. 2% of the marmot's diet. Mean grazing of those four species was constant in all patch types independent of their mean availability, although examination of those species in individual sampling quadrats showed a variable response of use to availability.
Except Phlox diffusa, species availability was low. Incidence of use indicated the strongest selection for grasses. Diet composition shifted from graminoids at early phenological stages, to forbs, with a continuous summer preference for five plant species. Results indicated a strong conformity to herbivore diet selection models.
Patch type selection in spring or summer was not predictable by the relative abundance of the preferred forage species. Analyses suggested that the risk of predation in tall vegetation most strongly influenced patch type selection, although the benefits of greater food abundance appeared to balance the cost of risk. Distance from burrows and a high frequency of Golden Eagle presence are proposed as risk factors affecting patch type selection in the spring.
Plant succession and other aspects of the vegetation are discussed with respect to the possible constraints they may have on the marmot population.