Brian K. McNab

Bioenergetics and the Determination of Home Range Size

The size of the home range is examined in mammals. It is determined, mainly, by the amount of energy expended by the species, and, therefore, the home range area may vary according to the direct and indirect influences of weather and climate on the animal. But the kind of food that is utilized will also influence home range size. Those species that must hunt for their food need larger areas for food gathering than those species that feed on the vegetation. As a result the largest hunters appear to have their food habits regulated by considerations of the efficient use of the food materials in their home range. Finally, the home range size affects population density, which in turn influences the behavior in the population.

On the Ecological Significance of Bergmann's Rule

A positive correlation of weight with latitude in homoiotherms (Bergmanns rule) cannot normally depend upon the physics of heat exchange. Most latitudinally widespread mammals in North America do not follow this rule. Those that do are usually carnivores or granivores; a change in their body size reflects a change in the size of their prey. A latitudinal change in the size of available prey is due either to the distribution of the prey species or to the distribution of other predators utilizing the same prey species. Only the smallest species of a set of similar predators normally will conform to Bergmanns rule, and then only beyond the limits of distribution of the largest species. These changes in size seem to be another example of character displacement. See full-text article at JSTOR

Food Habits, Energetics, and the Population Biology of Mammals

Data presented in this paper suggest that a complex interaction occurs between the physiological parameters of mammals and the growth and fluctuation of their populations: The Malthusian parameter rm increases with rate of metabolism, which in turn varies with body size and food habits. It can be concluded that it behooves all mammals to have as high a rate of metabolism as can be sustained by the quantity and quality of their food resources in space and time, because this adjustment will permit them to maximize their reproductive efforts. These interactions raise many questions, one of which concerns the temporal variation in reproductive strategies. Thus, Coady (1975) showed that the basal rate in the brown lemming (Lemmus trimucronatus) may be especially high during a winter in which the snow cover is reduced. Does a seasonal variation in the rate of metabolism therefore have a significant influence on seasonal variation in reproduction and therefore in population size? Whatever the correct answer to this question may be, it is clear that the physiological and populational characteristics of mammals are more intimately related than hitherto suspected.

On estimating thermal conductance in endotherms

Thermal conductance is a measure of the ease with which heat is exchanged between a body and the environment. It may include or exclude evaporative heat loss. If evaporative heat loss is included, conductance in endotherms should be used only at temperatures below thermoneutrality because evaporation is of little importance only at these temperatures. The slope of the curve of metabolism on air temperature equals conductance if and only if the curve extrapolates to body temperature when the rate of metabolism is zero. Slopes fitted by the method of least squares (Cf) usually are less than the mean minimal conductance (Cm) calculated from individual measurements of metabolism below thermoneutrality, because most endotherms mix physical and chemical thermoregulation at temperatures below thermoneutrality. The extent to which an extrapolation of the fitted curve overestimates body temperature (δT) is related to the error by which fitted slopes estimate mean minimal conductance: Cm/Cf = 0.060(δT) + 1.0. This relation can be used to correct fitted slopes in the literature to mean minimal conductances, as long as the mean air temperature at which minimal conductance is being estimated falls between 12 and 20 C and mean body temperature falls between 32 and 38 C.

Body Temperature and Metabolism in Subspecies of Peromyscus from Arid and Mesic Environments

INTRODUCTION The faunas of our southwestern deserts are rich in small birds and mammals. These homeotherms must have established a harmonious balance between their requirements and the problems presented by the extreme conditions in such an environment. A scarcity of water coupled with high environmental temperatures accentuates the difficulty of thermoregulation in exposed animals, since regulation with a small differential in temperature between the body and the environment is dependent upon evaporative cooling. Estivation (Howell, 1938; Bartholomew and Cade, 1957; Lyman and Chatfield, 1955; Bartholomew and MacMillen, 1961), burrowing (Sumner, 1925, Vorhies, 1945; Schmidt-Nielsens, 1951), and nocturnal activity (Sumner, 1925, Vorhies, 1945; Schmidt-Nielsens, 1951; Dawson, 1955) are considered as physiological and behavioral adaptations exhibited by desert homeotherms allowing a resident to evade the most extreme conditions. Another desert adaptation is the production of a concentrated urine, demonstrated in Dipodomys (Schmidt-Nielsens, 1951) and to a lesser extent in Citellus leucufrus (Hudson, 1960), which at its extreme may permit a desert species to live entirely on the water produced by oxidation. Other species like the wood rat, Neoto ma albigula, depend upon succulent vegetation for their water supply (Vorhies, 1945; Schmidt-Nielsen, 1948). But adaptative modifications of the body temperature and metabolism to desert conditions have not been extensively sought for. Temperature in most mammals is maintained relatively independent of moderate changes in environmental temperature. These body temperatures are not

An analysis of the factors that influence the level and scaling of mammalian BMR

The factors influencing the basal rate of metabolism (BMR) in 639 species of mammals include body mass, food habits, climate, habitat, substrate, a restriction to islands or highlands, use of torpor, and type of reproduction. They collectively account for 98.8% of the variation in mammalian BMR, but often interact in complex ways. The factor with the greatest impact on BMR, as always, is body mass (accounting for 96.8% of its variation), the extent of its impact reflecting the 10(6.17)-fold range of mass in measured species. The attempt to derive mathematically the power relationship of BMR in mammals is complicated by the necessity to include all of the factors that influence BMR that are themselves correlated with body mass. BMR also correlates with taxonomic affiliation because many taxa are distinguished by their ecological and behavioral characteristics. Phylogeny, reflecting previous commitments, may influence BMR either through a restriction on the realized range of behaviors or by opening new behavioral and ecological opportunities. A new opportunity resulted from the evolution by eutherians of a type of reproduction that permitted species feeding on high quality resources to have high BMRs. These rates facilitated high rates of gas, nutrient, and waste exchange between a pregnant eutherian and her placental offspring. This pattern led to high rates of reproduction in some eutherians, a response denied all monotremes and marsupials, thereby permitting eutherians to occupy cold-temperate and polar environments and to dominate other mammals in all environments to which ecologically equivalent eutherians had access.

The economics of temperature regulation in neutropical bats

Abstract 1. 1. The level and effectiveness of thermoregulation in bats is determined by the interaction of weight, basal rate of metabolism and thermal conductance. 2. 2. Conductances in tropical bats are greater than expected from weight. 3. 3. Basal rates of metabolism are higher than expected by weight in nectar-, fruit- and meat-eating bats, lower than expected in insectivorous species and intermediate in vampires, this correlation depending upon the seasonal stability of food resources in the environment. 4. 4. Therefore, nectar-, fruit- and meat-eating bats are effective thermoregulators, vampires are marginal regulators and insectivorous species readily enter torpor. 5. 5. Torpor evolved in the tropics in response to the high cost of thermoregulation at a small weight.

The Influence of Body Size on the Energetics and Distribution of Fossorial and Burrowing Mammals

The energetics of four fossorial mammals, Spalacopus cyanus, Cannomys radius, Aplodontia rufa, and Scalopus aquaticus, are examined and compared to data available in the liter- ature. Basal rates of metabolism are lower than expected from mass if fossorial mammals weigh >80 g, but they are higher than expected if they weigh 100 g. Small burrowers may have low basal rates unrelated to burrowing habits. Minimal thermal conductances in fossorial and burrowing mammals are usually near the expected values at masses 1 kg have high minimal conductances. The temperature differential maintained at the lower limit of thermoneutrality and at temperatures above thermoneutrality is proportional to the ratio of basal rate to minimal conductance. Adaptations to a burrowing habit include (1) maintaining a small temperature differential independent of mass, which is accomplished by matching the mass sensitivity of the basal rate to that of the minimal conductance, (2) reducing basal rate, (3) increasing minimal conductance, and (4) reducing mass. The limits that exist to a reduction in mass and a reduction in basal rate of metabolism and to an increase in minimal conductance result in geographical limits to the distribution of fossorial mammals, but not necessarily to the distribution of other burrowing mammals.

ON THE UTILITY OF UNIFORMITY IN THE DEFINITION OF BASAL RATE OF METABOLISM

the intensity of similar or dissimilar components of the energy Energy expenditure is often used as a basis of ecological theory budget of different species or of the same species in different (e.g., Gadgil and Bossert 1970; Charnov 1976; Sibly and Calow environments. From this view, field measurements of energy 1986), and its study has been a means of examining the adjustexpenditure, as interesting as they are theoretically, are the ments made by vertebrates to the environments in which they most subject to misinterpretation because they are the least live (see, e.g., McNab 1994). The view that energetics is a clearly defined. central component of the natural history of vertebrates, and One of the most convenient (i.e., easiest) rates to measure especially of endotherms, given their high rates of metabolism, is the ‘‘standard’’ rate of metabolism, which in endotherms is is usually justified by the conclusion that energy and nutrient the ‘‘basal’’ rate. Basal rate was defined for humans and codified resources have a limited availability in most environments (but by DuBois (1924, 1930); later it was applied to domestic mamsee King and Murphy [1985]). Vertebrates, most notably endomals by Kleiber (1932, 1961) and Benedict (1938). It is the therms, are therefore often required to adjust expenditures to rate (1) in the zone of thermoneutrality when the individuals reflect resource availability. All endotherms do not make the are (2) inactive, (3) postabsorptive, (4) adult (thereby eliminatsame adjustments to accommodate a seasonally or a chronically ing the cost of growth), (5) nonreproductive (eliminating the limited resource base: some remain active and modify energy cost of pregnancy, lactation, egg formation, or incubation), expenditure, some migrate, and others enter torpor. One pracand (6) regulating body temperature, and it is (7) measured tical difficulty with the use of energy as a basis for ecological during the inactive period (also see Aschoff and Pohl 1970). theory, as well as with its use in the narrower objective of These criteria are most specifically discussed by Benedict analyzing the adaptation of individuals and species to the envi(1938). With the extension of the study of energetics to endoronment, is the parameter, or parameters, of energy expenditherms other than humans, some criteria demand special attenture that should be used. tion as the physiological diversity of species being studied inThe rate of energy expenditure, often measured in terms of creases. For example, fermentation in ruminants delays or oxygen consumption, is highly variable because it is influenced prohibits entrance into a postabsorptive state, which raises the by many factors. Each rate must be clearly defined by the question of whether they can be characterized by a basal rate. conditions under which it is measured; this is what separates Furthermore, most biologists use an estimate of basal rate that one rate from another. Rates that characterize vertebrates incorresponds to the ‘‘normally’’ regulated body temperature of clude the cost of body maintenance; the cost of various behavthe species being studied, which is not the same in all mammals iors, such as feeding, territorial defense, courting, and reproand birds; a correction factor in rate of metabolism for the duction; and the minimal and maximal rates of metabolism. differences in body temperature is properly not made, except Each of these rates measures the intensity of a component of that rates associated with torpid states are excluded. Consethe energy budget of vertebrates and therefore is a rate of quently, a mammal or bird can be said to have a basal rate justifiable concern. only if it regulates body temperature by the internal generation The sensitivity of energy expenditure to internal and external of heat, that is, if it is an endothermic homeotherm. Nearly factors is both its strength and its weakness: its strength because the complete array of endotherms is now potentially available it is interactive with most aspects of the natural history of for study, which increasingly means that biologists will examine

Evolutionary Alternatives in the Physiological Ecology of Bats

Bats are often thought to have poor temperature regulation, to feed on insects, and to enter hibernation. This combination of characteristics is typical only of temperate species. In the last two decades intensive work in the tropics, especially in the New World, has shown the great ecological diversity existing among bats, which in turn permits us to place temperate species in their appropriate ecological and evolutionary perspective and to examine some of the physiological and ecological alternatives available to bats when living in a physically benign environment.