Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

A graphical method is discussed which allows a specification of the optimal diet of a predator in terms of the net amount of energy gained from a capture of prey as compared to the energy expended in searching for the prey. The method allows several predictions about changes in the degree of specialization of the diet as the numbers of different prey organisms change. For example, a more productive environment should lead to more restricted diet in numbers of different species eaten. In a patchy environment, however, this will not apply to predators that spend most of their time searching. Moreover, larger patches are used in a more specialized way than smaller patches.

On Optimal Use of a Patchy Environment

To understand resource partitioning, essentially a community phenomenon, we require a holistic theory that draws upon models at the individual and population level. Yet some investigators are still content mainly to document differences between species, a procedure of only limited interest. Therefore, it may be useful to conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way. 1) What is the mechanism of competition? What is the relative importance of predation? Are differences likely to be caused by pressures toward reproductive isolation? 2) Are niches (utilizations) regularly spaced along a single dimension? 3) How many dimensions are important, and is there a tendency for more dimensions to be added as species number increases? 4) Is dimensional separation complementary? 5) Which dimensions are utilized, how do they rank in importance, and why? How do particular dimensions change in rank as species nuimber increases? 6) What is the relation of dimensional separation to difference in phenotypic indicators? To what extent does the functional relation of phenotype to resource characteristics constrain partitioning? 7) What is the distance between mean position of niches, what is the niche standard deviation, and what is the ratio of the two? What is the niche shape?

https://science.sciencemag.org/content/sci/185/4145/27.full.pdf

Resource Partitioning in Ecological Communities

Natural history is replete with observations on feeding, yet only recently have investigators begun to treat feeding as a device whose performance­ as measured in net energy yield/feeding time or some other units assumed commensurate with fitness-may be maximized by natural selection (44, 1 13, 135, 156, 181) . The primary task of a theory of feeding strategies is to specify for a given animal that complex of behavior and morphology best suited to gather food energy in a particular environment. The task is one, therefore, of optimization, and like all optimization problems, it may be tri­ sected: 1. Choosing a currency: What is to be maximized or minimized? 2. Choosing the appropriate cost-benefit functions: What is the mathematical form of the set of expressions with the currency as the dependent variable? 3. Solving for the optimum: What computational technique best finds ex­ trema of the cost-benefit function? In this review, most of the following section is devoted to possible answers to the first problem. Then four key aspects of feeding strategies will be considered: (a) the optimal diet, (b) the optimal foraging space, (c) the optimal foraging period, and (d) the optimal foraging-group size. For each, possible cost-benefit formulations will be discussed and compared, and predictions derived from these will be matched with data from the literature on feeding. Because the third problem is an aspect of applied mathematics, it will be mostly ignored. Throughout, emphasis will be placed on strategic aspects of feeding rather than on what Holling (75) has called "tactics."

Theory of Feeding Strategies

The principles of classification and a classification of mammals. Bulletin of the AMNH ; v. 85

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.

Bioenergetics and the Determination of Home Range Size

A positive correlation of weight with latitude in homoiotherms (Bergmann's 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

On the Ecological Significance of Bergmann's Rule

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 t...

Food Habits, Energetics, and the Population Biology of Mammals

The level of energy expenditure in eutherian mammals is correlated with the type of food consumed, especially in medium—sized to large species; some foods (including vertebrates, herbs, and nuts) permit high basal rates, while other foods (including invertebrates, fruit, and the leaves of woody plants) require low basal rates. Various properties of a food, including a low digestibility, a high content of plant secondary compounds, the inability to separate food from non—nutritive particles, and a seasonal reduction in availability, may require a consumer to have a low basal rate of metabolism; all of these factors are exaggerated in importance by the high food intake of large mammals. In small species most foods, except flying insects and seed crops in the desert, permit high basal rates and effective endothermy. Climatic factors modify these relationships to a limited extent, while a specialization in moderately—sized species to arboreal habits leads to reduced activity, smaller muscle mass, and lower basal rate than is found in terrestrial species using the same food resources. Mixed diets generally produce basal rates intermediate to those expected from the component specialist diets. The correlation of basal rate with food habits has the following demonstrable consequences for mammals. (1) The scaling of basal rate usually follows the Kleiber relation, unless food habits require low basal rates, or temperature regulation requires high rates. (2) Mammals that feed on foods associated with high basal rates have a higher reproductive output than mammals of similar size that use foods requiring low basal rates. (3) Predator avoidance is correlated with level of energy expenditure and food habits, terrestrial species with low rates of metabolism relying principally on burrows or passive integumental structures, such as shells, plates, or spines. (4) Most living "conservative" mammals use foods that require low basal rates of metabolism, a condition that protects conservative species from replacement by "advanced" eutherians, which are also required by these foods to have low basal rates.

The Influence of Food Habits on the Energetics of Eutherian Mammals

Temperature regulation and rate of metabolism were studied in five species of fossorial rodents: Geomys pinetis, Spalax leucodon, Tachyoryctes splendens, Heliophobius kapeti, and Heterocephalus glaber. The burrows of these rodents are in well—drained soils of poor water—holding capacity. Burrow atmospheres have an oxygen concentration of 15 to 20%, a carbon dioxide concentration of 0.5 to 2.0%, and limited temperature fluctuations; they are saturated with water vapor. Body temperature are somewhat low (35 to 37°C) in four species; temperature regulation is good in these species at ambient temperature down to 5 or 10°C. Heterocephalus, however, has a much lower body temperature (about 32°C) and the poorest capacity for thermoregulation of any known mammal. Fossorial rodents have low basal rates of metabolism, high conductances, and high ranges of thermoneutrality. Lethal ambient temperatures are inversely proportional to the normal levels of body temperature. Analysis of basal rates of metabolism (M), conductances (C), and body temperature suggests that the first two are determined in relation to environmental characteristics, and that body temperature, "goodness" of thermoregulation, midpoint of thermoneutrality, and lethal ambient temperature are dependent upon the ratio M/C. It is concluded that the lowest body temperature in homoiotherms compatible with good thermoregulation is about 35°C. A comparison of Heterocephalus and lizards illustrates the energetic similarities and differences between endotherms and ectotherms. The reduction of M and the increase of C in fossorial rodents are directly related to the mean burrow temperatures. These modifications reduce the probability of overheating in an environment where evaporative and convective cooling are greatly reduced. Tachyoryctes and Heliophobius use forced evaporative cooling for emergency thermoregulation, in spite of the saturated burrow atmosphere. Heterocephalus facilitates heat loss during heat stress by increasing peripheral circulation over its naked body; Geomys does this by increasing the circulation to its naked tail and, possibly, naked feet. Geomys may lose up to 30% of its heat production via its tail. As a result of these modifications, the lethal ambient temperature is proportional to the mean burrow temperature. Geomys responds to geographic variation in heat loading either by a decrease in body size or by an increase in tail length. The smaller size of nonpregnant, female gophers helps to maintain their heat production during pregnancy below the limits established by the environment for males. Gopher distribution appears to be limited to soils with high rates of gas exchange. Interaction among species of gophers has, to some extent, a physiological basis. It is suggested that the physiological characters concerned with energetics are readily modified, in an evolutionary sense, to conform to the requirements imposed by the environment.

Brian K. McNab

Papers

Bioenergetics and the Determination of Home Range Size

On the Ecological Significance of Bergmann's Rule

Food Habits, Energetics, and the Population Biology of Mammals

The Influence of Food Habits on the Energetics of Eutherian Mammals

The Metabolism of Fossorial Rodents: A Study of Convergence