Abstract
We compared growth curves for ramus length and diastema length from two autumn collections of mandibles of male Western Arctic Herd caribou in Alaska. We were primarily interested in determining if growth curves of caribou mandibles differed between caribou born during 1959-1967, after the herd had been high for several years and was probably declining in size, and those born during 1976-1988, when the herd was increasing in size. To compare these growth curves, we used a nonlinear model and used maximum likelihood estimates and likelihood ratio tests. We found that growth rates were similar between periods, but intercepts and variances of growth curves differed. From this we infer that calves were smaller in autumn during the 1960s and that significant compensatory growth did not occur later in life.
Highlights
Mandibles from many species of herbivores have been collected to assess population age structure, recruitment, mortality, and nutritional condition, especially where direct measures of these parameters have been lacking (Banfield, 1955; Alexander, 1958; Klein & Strandgaard, 1972; Lowe, 1972; Miller, 1972, 1974; Reimers, 1972; Doerr, 1979; Beninde, 1988)
Diastema length, and other skeletal measurements have been used to determine if body size has changed in populations over time
The primary objective of this study was to determine if nutrition was constraining the Western Arctic Herd during the 1960s w h e n the herd was high and probably declining compared to the late 1970s and 1980s w h e n it was increasing
Summary
Mandibles from many species of herbivores have been collected to assess population age structure, recruitment, mortality, and nutritional condition, especially where direct measures of these parameters have been lacking (Banfield, 1955; Alexander, 1958; Klein & Strandgaard, 1972; Lowe, 1972; Miller, 1972, 1974; Reimers, 1972; Doerr, 1979; Beninde, 1988). Diastema length, and other skeletal measurements have been used to determine if body size has changed in populations over time. In most analyses biologists have restricted comparisons to simple statistical tests (e.g., Mests) of mean jaw size of older animals that have finished growing or compared size only within age classes (Skoog, 1968; Doerr, 1979; Valkenburg et ai, RangiSer, 21 (1), 2001. The only available data from the earlier period were measurements of mandible length and diastema length. To compare growth rates of mandibles between periods, we used a nonlinear growth model that included all age classes to determine where the initial restriction in growth occurred, and whether there was compensatory growth. Because nonlinear statistical methods have not been routinely used in analyses of this kind, w e have included a detailed description of the statistical methodology
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