Restrictions on roaming Until the past century or so, the movement of wild animals was relatively unrestricted, and their travels contributed substantially to ecological processes. As humans have increasingly altered natural habitats, natural animal movements have been restricted. Tucker et al. examined GPS locations for more than 50 species. In general, animal movements were shorter in areas with high human impact, likely owing to changed behaviors and physical limitations. Besides affecting the species themselves, such changes could have wider effects by limiting the movement of nutrients and altering ecological interactions. Science , this issue p. 466

Of the blazars detected by EGRET in GeV γ rays, 3C 279 is not only the best-observed by EGRET, but also one of the best-monitored at lower frequencies. We have assembled eleven spectra, from GHz radio through GeV γ rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial γ-ray contribution to the total luminosity of the object; in a high state, the γ-ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and γ-ray bands.The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton + external Compton γ-ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low γ-ray intensity.Subject headings: quasars: individual (3C 279)

Population viability is driven by individual survival, which in turn depends on individuals balancing energy budgets. As carnivores may function close to maximum sustained power outputs, decreased food availability or increased activity may render some populations energetically vulnerable. Prey theft may compromise energetic budgets of mesopredators, such as cheetahs and wild dogs, which are susceptible to competition from larger carnivores. We show that daily energy expenditures (DEE) of cheetahs were similar to sizebased predictions and positively related to distance travelled. Theft at 25% only requires cheetahs to hunt for an extra 1.1h/day, increasing DEE by just 12%. Therefore, not all mesopredators are energetically constrained by direct competition. Other factors that increase DEE, such as those that increase travel, may be more important for population viability.The acquisition and expenditure of energy by animals unifies physiology with population ecology and viability, although interactions between energetics, ecology and survival can be complex (1,2). Indeed, of the studies that have investigated how energetic factors affect population dynamics, most are concerned with the effects of changes in abiotic conditions such as ambient temperature (3), with few examining the effects of changes in biotic conditions, such as the abundance and distribution of prey and competitors (1,4).Although recent human activities have driven declines in large mammalian predators (5), intraguild interactions may also shape carnivore communities. One persistent hypothesis suggests that, because carnivores may be routinely working close to maximum sustained power outputs, decreases in food availability or increases in activity may push them over an energetic precipice (6). Kleptoparasitism, the theft of prey captured by another animal, is one critical element in this interaction, particularly for mesopredators such as wild dogs Lycaon pictus and cheetahs Acinonyx jubatus, which are prone to competition with and displacement by larger more dominant carnivores such as lions Panthera leo, and spotted hyaenas Crocuta crocuta (7-11). The details of such intraguild interactions with respect to energetic implications are, however, poorly understood.Carnivores hunt using a combination of sit-and-wait, stalk, ambush and charge, or extended coursing strategies (12-15). While the short-term energetic consequences of hunting (i.e. the ways which predators chase and subdue prey) are profoundly different (2,16), the longterm costs such as the energy required to locate prey and avoid predators are rarely considered. These costs may be pivotal in determining the viability of different hunting strategies, particularly as it relates to prey abundance, accessibility and loss (2,6,17).We combined behavioral observations of 14 cheetahs from the Kgalagadi Transfrontier Park ("Kalahari") with measurements of daily energy expenditure (DEE) to estimate the energetic cost of foraging. We also obtained DEE measurements of five free-ranging cheetahs fr...

Latitudinal gradients in species diversity represent, perhaps, one of the longest recognized and most discussed biogeographical phenomena. Simpson (1964) studied the species density pattern of the mammals of North America and found a trend toward increased species density in the tropics; Terent'ev (1963) found similar results in the U.S.S.R. Simpson points out that the increase does not occur in all of the mammals, but in certain groups. The purpose of this paper is to begin the analysis of different mammalian taxa, and to show the significance of topographic relief and climate on which Simpson did not calculate statistics. METHODSThe material for this paper conforms as much as possible to that used by Simpson (1964) . A grid of quadrats 150 miles square (22,500 square miles) centered at 40 0N, 1000W was imposed on a map of Lambert's azimuthal equal-area projection (Goode's series by Henry M. Leppard, ed., The University of Chicago Press) of North America to the Panama-Colombia border.Species lists were generated for each quadrat using the species distribution maps in Hall and Kelson (1959) for mainland species. Whenever Hall and Kelson suspected two species were only subspecies of the same species, I recorded them as one species. In all, species lists were made for 445 quadrats with a total of 671 species of mammals, which were the basis for all analyses. A copy of these species lists is included in Wilson (1972).