An Index of Home Range Size

Abstract

The relationship between the number of times an animal is captured c and the number of grid stations at which it has been captured So is represented by the function Sc = S. (1-e-kc). In such cases it is possible to compute an index of home range size S. that does not depend on sample size and is free of assumptions regarding home range shape and the distribution of activity within the home range. J. WILDL. MANAGE. 38(3):546-551 In his review of the study of mammal movements, Sanderson (1966) encouraged mammalogists to direct more attention to the causal bases of movement patterns and their variations. However, this excellent suggestion is often difficult to achieve because of the limitations of livetrapping which, in spite of recent advances such as telemetry, remains the most economical way of obtaining reasonable quantities of movement data for populations of small mammals. One of livetrapping's wellknown limitations is that appropriate measures of home range size vary with factors other than true differences in home range size. Three such factors are home range shape, the distribution of records (and, by inference, activity) within the home range, and the number of location records (Jennrich and Turner 1969, Metzgar 1972). It is well-known that as observations of an animal accumulate the area where it has been observed increases asymptotically (Hayne 1949, Stickel 1954, Odum and Kuenzler 1955). This asymptote represents the total area within which the animal can be observed (home range size). This curve's usefulness has been limited because most studies of small mammals provide insufficient captures per animal to reveal the asymptote. We describe a method for computing this asymptote. The senior author is indebted to F. C. Evans for his advice and for making the facilities of the University of Michigan E. S. George Reserve available to him. D. Rittshoff and R. Humphrey provided field assistance and the field work was supported by the following: NSF Summer Fellowship No. 34618; NIH Predoctoral Fellowship No. 1-Fl-GM-34, 301-01; The Edwin S. George Reserve Scholarship Fund, and the University of Michigan Department of Zoology. INDEX OF HOME RANGE SIZE We use the number of stations at which an animal would be recorded after an infinite number of observations S, as an index of home range size. (This number is the asymptotic value approached by field data.) The shape of the curve of home range area S, against number of captures c is shown inl Fig. 1 and by Hayne (1949), Stickel (1954), and Odum and Kuenzler (1955). This shape suggests the function Se = S, (1e-) (1) where e-k is a constant computed from the data. We use this function to represent the behavior of home range data. If it fits such data adequately, its parameters can be estimated and So used as a measure of home range size. Solving Equation (1) for the number of stations revealed after one additional capture (S,,1) yields the linear equation 546 J. Wildl. Manage. 38(3):1974 This content downloaded from 157.55.39.83 on Sun, 12 Jun 2016 05:14:57 UTC All use subject to http://about.jstor.org/terms INDEX OF HOME RANGE * Metzgar and Sheldon 547