The relationship between home range area and body size of terrestrial mammals is reconsidered in light of the concept of biological time. Biological time is an internal, body-massdependent, time scale to which the durations (or rates) of biological events are entrained. These events range from purely physiological (e.g., muscle contraction time) to purely ecological (e.g., time to traverse home range).Evidence is presented that home range size scales linearly to body mass for carnivores as it does for herbivores. This scaling supports the hypothesis that animals select their home range areas to meet metabolic demands integrated over biologically critical periods. Confounding variables in the home range-body mass regression include habitat productivity and methods of location. Data on home ranges derived from telemetry studies of terrestrial carnivores are presented and used to derive allometric equations for home range area. The exponents of these equations are shown to approximate 1.0, although intercept values vary with latitude and, presumably, habitat productivity. Social organization and behavior may also influence the relationship of home range area to metabolic needs for different sex and age categories within a species.

Interspecific killing is a key determinant of the abundances and distributions of carnivores, their prey, and nonprey community members. Similarity of body size has been proposed to lead competitors to seek similar prey, which increases the likelihood of interference encounters, including lethal ones. We explored the influence of body size, diet, predatory habits, and taxonomic relatedness on interspecific killing. The frequency of attacks depends on differences in body size: at small and large differences, attacks are less likely to occur; at intermediate differences, killing interactions are frequent and related to diet overlap. Further, the importance of interspecific killing as a mortality factor in the victim population increases with an increase in body size differences between killers and victims. Carnivores highly adapted to kill vertebrate prey are more prone to killing interactions, usually with animals of similar predatory habits. Family-level taxonomy influences killing interactions; carnivores tend to interact more with species in the same family than with species in different families. We conclude that although resource exploitation (diet), predatory habits, and taxonomy are influential in predisposing carnivores to attack each other, relative body size of the participants is overwhelmingly important. We discuss the implications of interspecific killing for body size and the dynamics of geographic ranges.

Summary 1.A major paradigm shift is occurring in the approach of ecologists to statistical analysis. The use of the traditional approach of null-hypothesis testing has been questioned and an alternative, model selection by information-theoretic methods, has been strongly promoted and is now widely used. For certain types of analysis, information-theoretic approaches offer powerful and compelling advantages over null-hypothesis testing. 2. The benefits of information-theoretic methods are often framed as criticisms of null-hypothesis testing. We argue that many of these criticisms are neither irremediable nor always fair. Many are criticisms of the paradigm's application, rather than of its formulation. Information-theoretic methods are equally vulnerable to many such misuses. Care must be taken in the use of either approach but users of null-hypothesis tests, in particular, must greatly improve standards of reporting and interpretation. 3. Recent critiques have suggested that the distinction between experimental and observational studies defines the limits of the utility of null-hypothesis testing (with the paradigm being applicable to the former but not the latter). However, we believe that there are many situations in which observational data are collected that lend themselves to analysis under the null-hypothesis testing paradigm. We suggest that the applicability of the two analytical paradigms is more accurately defined by studies that assess univariate causality (when null-hypothesis testing is adequate) and those that assess multivariate patterns of causality (when information-theoretic methods are more suitable). 4. Synthesis and applications . Many ecologists are confused about the circumstances under which different inferential paradigms might apply. We address some of the major criticisms of the null-hypothesis testing paradigm, assess those criticisms in relation to the information-theoretic paradigm, propose methods for improving the use of null-hypothesis testing, and discuss situations in which the use of null-hypothesis testing would be appropriate. We urge instructors and practitioners of statistical methods to heighten awareness of the limitations of null-hypothesis testing and to use informationtheoretic methods whenever prior evidence suggests that multiple research hypotheses are plausible. We contend, however, that by marginalizing the use of null-hypothesis testing, ecologists risk rejecting a powerful, informative and well-established analytical tool.

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