Some Problems of Applied Small Mammal Sampling in Western North America

Abstract

The study of mammal populations is still a relatively new field. It is natural that most investigations have been pursued under selected conditions that introduce the fewest complications. At the same time, applied knowledge of mammal density and distribution has been a necessity in a number of fields. Applied needs differ in that problems which are encountered largely dictate the area and conditions under which a study is undertaken. Without minimizing the value of continued fundamental approaches it is appropriate that attention also be devoted to methods that are particularly adapted to special applications. It is important to Westerners that methods of population study have largely been developed by ecologists working in extensive areas of uniform vegetation. Modifications of sampling methods are often necessary where abruptly shifting terrain and vegetation is the rule, as is typical of Western conditions. There is characteristically a striking variation in density and species composition of small mammals over small areas. Often these differences are between areas that appear to be fully equivalent. Further complications arise from the continuous variation between vegetation types so frequently found in areas of sharp relief. One may select distinct associations in which to trap, only to find that much of the surrounding area is intermediate in various combinations and will not be truly represented. The main implication here is that a large and thorough population study on a single site, however valuable it may be in some aspects, will not provide estimates of density and species occurrence which may safely be interpolated over larger areas. Therefore an ecologist, given an area to census, and assuming his time and facilities are limited, is better advised to use smaller sampling units and cover a wider range of the habitat and its variation. Knowledge of the home ranges of the species encountered …