Search Results

This chapter presents size-based analyses of aquatic food webs, where body size rather than species identity is the principle descriptor of an individual's role in the food web, provides insights into food web structure and function that complement, and extends those from species-based analyses. Focus is given to body size because it underpins predator-prey interactions and dictates how the biological properties of individuals change with size. Thus, size-based food web analyses offer an approach for integrating community and ecosystem ecology with energetic and metabolic theory.

This chapter explores the pattern of sexual size dimorphism (SSD) in mammals and the processes that underlie its evolution. Most mammalian orders have male-biased SSD, although some orders are not sexually-dimorphic for body size or show significantly female-biased SSD. In general, SSD increases with body size across mammals (Rensch's rule). Male-biased dimorphism relates to sexual selection on males through male-male competition for females, since sexual selection as indicated by mating systems is positively correlated with male-biased SSD. Selection pressure on female mass, identified in that age at weaning, is higher in polygynous species. However, the reproductive rate is lower for large females, indicating that fecundity selection selects small females. Although these patterns hold across mammals as a whole, the data presented in the chapter also reveal considerable variation across orders.

This chapter introduces the dramatis personae of contemporary wild canids, along with some of their features. Topics discussed include interspecific variation; intraspecific variation; phylogenetic baggage; communicative canids; dispersal, disease, and body size; sympatry and interspecific relations; and canid geography. A vignette account of all thirty-six canid taxa (including dingoes, here listed as a grey wolf subspecies Canis lupus dingo) is also presented.

This chapter describes studies on two common dung fly species with contrasting sexual size dimorphism (SSD): females are the larger sex in Sepsis cynipsea but the smaller sex in Scathophaga stercoraria. In both species, there is overwhelming evidence for sexual and fecundity selection favouring large body size, but only sparse evidence for selection favouring small size in either sex. The absence of evidence of net balancing selection on either sex does not support the differential equilibrium model of SSD. For the yellow dung fly, S. stercoraria, the efforts taken to detect selection against large individuals were substantial, including multiple viability selection estimates covering a wide and representative range of environmental conditions and artificial extension by artificial selection of the body size range available. Therefore, undetected selection favouring small size is unlikely. Phylogenetic, genetic, or developmental constraints are also unlikely to be responsible for lack of support of the differential equilibrium model in dung flies, but physiological constraints have not yet been properly addressed.

Most studies interpret reptilian sexual size dimorphism (SSD) as a means to reducing resource competition by way of sexual selection, fecundity selection, and natural selection. This chapter assesses the importance of these processes using data on 832 species of snakes, lizards, and turtles. The data reveal allometry consistent with Rensch's rule in most, but not all reptilian taxa, and support the hypothesis that sexual selection for large male size has influenced the evolution of reptile SSD. However, more data on male combat and territoriality are needed to test more fully this hypothesis. Although fecundity increases with female body size in many reptiles, comparative data provide only weak support for the fecundity advantage of large female size. The chapter concludes that further progress in assessing the relative importance of different selective processes in reptiles will require studies that more fully integrate evolutionary hypotheses with knowledge of proximate physiological and developmental mechanisms.

This chapter integrates the major conclusions from the book. It focuses on how much is known about variation in insect physiology from the phylogenetic and geographic perspectives, raising the issue of the extent of work done on non-model organisms and a dearth of studies in the southern hemisphere, despite likely differences in broad-scale patterns among hemispheres. The significance of body size and of cross-resistance are further explored in the context of poor reporting, such as of body size in studies of development rate. The chapter concludes by identifying the significant areas in which physiological ecology has a role to play in promoting an understanding how insects will respond to global climate change, including both temperature change and the effects of global change-type drought.

Sex differences in diet, ranging, and activity budgets (‘ecology’) can have two plausible, non-exclusive causes: differential needs due to reproduction in females and differences in body size, as well as sex differences in sociosexual strategies, usually because males are forced to travel more widely or minimize feeding time relative to females. The authors of this chapter evaluated these two hypotheses by examining sex differences in the ecology of orangutans inhabiting a Sumatran swamp forest, using two different methods. The greater reproductive burden on females is reflected in their spending more time per day feeding overall, more time foraging on insects, and less time resting, but females did not engage more in tool-assisted foraging or less in acquiring vertebrate meat. Despite the large range of body sizes, the influence of body size on time budgets, diet and the toughness and elasticity of food items was minor. However, larger males spent more time feeding on fruit than smaller ones. The other differences between unflanged males and flanged males were more compatible with different sociosexual strategies: unflanged males moved more and travelled faster than flanged males, and had shorter feeding bouts. Thus, the overall pattern of differences largely reflects sex differences in requirements due to reproduction and male sociosexual strategies. The effects of body size on diet may be so small because tooth morphology rather than body strength determine food choice.

This chapter examines food webs at the landscape scale by focusing on the large-scale food web architecture that is deeply constrained by space. It begins with a discussion of how variability in space, time, and food web structure, coupled with the ability of organisms to rapidly respond to variation, affect the maintenance of the food web and its functions. It then explains how individual traits such as body size and foraging behavior relate to food web structure in space and time. It also considers the role of spatial constraints on food webs and how the existence of fast–slow pathways coupled by mobile adaptive predators gives rise to spatial asynchrony in the resources. The chapter concludes with a review of some empirical examples to show that some food webs display the bird feeder effect and that resource coupling of distinct habitats appears to stabilize food webs.

Studies on streams provide some of the most detailed and best resolved webs yet available, and provide a means to test food web theory. These systems can be used to test patterns in connectance webs and the effect of sampling on the patterns evident. The role of body-size in stream webs is reviewed. This chapter deals with attempts to quantify food webs by measures of energy flow and interaction strengths, and to characterize the circumstances leading to the presence or absence of trophic cascades in food webs. Streams are strongly linked through their food webs with surrounding systems, such as ground water and flood plains, and such cross-system subsidies is considered. The effect of natural and anthropogenic disturbances on food web attributes is addressed. Finally, the relationship between biodiversity/ecosystem functions in stream webs is addressed in the context of environmental stress.

Birds show a number of structural and functional adaptations that are characteristic of the group as a whole and independent of the ability to fly. This chapter explores some basic physical and physiological principles and structural variables, which help us understand how birds ‘work’. Many of these physiological principles are fundamental to all vertebrates (and in some cases to all metazoans), but some are unique to the avian group. The discussion is focused on gas and heat exchanges, energy flow, and water and ion fluxes. Budget modelling and analysis of the effects of body size on function are indispensable tools to understand some basic principles. When pertinent, and whenever relationships with environmental adaptations can be established, typical bird examples, to illustrate some of the topics treated in this chapter, are included.

This chapter uses recent experimental and observational studies of birds to explore patterns of sex-specific offspring vulnerability (increased mortality and reduced fledging mass under poor conditions) in relation to sexual size dimorphism (SSD). The results show size-dependent modulation of male fledgling mass but size-independent mass reduction in females. Overall, growth is more phenotypically plastic in males than in females. Comparisons of fledging mass reached in ‘good’ and ‘poor’ environments suggest that having to grow large is mainly disadvantageous when coupled with the male phenotype. Differences in environmental sensitivity between the two sexes during ontogeny, either in the form of increased mortality or reduced body size, will tend to reduce dimorphism during development, affecting adult SSD. These results suggest that environmental conditions during ontogeny contribute significantly to variation in SSD within bird species, particularly when comparisons are made among environments or between generations.

Fighting success and dominance in crayfish depends on a variety of extrinsic and intrinsic factors. Most intrinsic factors studied to date are related to the physical size of the crayfish. Larger crayfish or those with larger chelae often have advantages in agonistic interactions. Age, sex, and reproductive status can influence the physical size of the carapace and major chelae. These and other factors (e.g., social history) may also influence the intrinsic neurochemistry of individuals. Extrinsic factors that lead to increased dominance include the availability of resources, signal transmission properties, and status pheromones in the environment. Presently, it is largely unknown how these factors interact together to produce dominance. From an ultimate perspective, the evolutionary consequence of aggression and dominance is assumed to be tied to reproductive success or increased resource holding potential. This chapter uses a multidisciplinary and multilevel approach to address the question “what makes a crayfish dominant?”

This chapter considers the influence of species-level traits in the establishment success of exotic birds. Previous treatments of such traits have failed to find consistent associations between species traits and establishment success. However, framing the issue in terms of the small population problem again provides useful insights into the role of species-level traits, and allows some general conclusions to be drawn about the roles of population growth rates, the predisposition to Allee effects, and the ability to cope with novelty in aiding establishment. This approach to sorting through the influence of species' traits on establishment success should provide a suitable framework for similar explorations within other exotic taxa. The more widespread confusion over the importance of species' traits to establishment success may be a by-product of failing to view the influence of these traits within the context of the small population paradigm.

This chapter considers patterns of evolution in exotic bird populations. Evidence is presented that exotic birds have evolved in their phenotypes over the relatively short time spans in which they have been established in their new locations. Some of the shifts observed are entirely consistent with macroevolutionary patterns observed amongst native bird species; others are more curious and require reconsideration of some long-held views of evolutionary dynamics. The chapter notes the great potential for research on the evolution of exotic birds to provide insight into basic evolutionary theory and the role of evolution in the impacts of all invasive species.

Japanese raccoon dogs (Nyctereutes procyonoides viverrinus) have been isolated from populations (e.g., N. p. ussuriensis) on mainland Asia for about 12,000 years. Since the environment and climate of Japan differ greatly from that on mainland Asia, different selection pressures have affected the two populations. This chapter compares several features of Finnish (N. p. ussuriensis, originally from SE Russia) and Japanese raccoon dogs to evaluate the progress of the Japanese raccoon dog towards speciation. It reviews the chromosome number, skull and tooth morphology, body size and weight, the ability to hibernate, reproduction, home ranges, habitat use, and diet of Japanese and Finnish raccoon dogs.

This chapter addresses the uses of measures of body size and composition, with special emphasis on epidemiologic applications. It begins with an overview of weight and height, including their relationships to nutritional status, their use in epidemiologic studies, and the reproducibility and validity of these measurements. The concept of major body compartments is discussed, and methods of measuring them are considered. The main part of the chapter addresses the assessment of relative body composition, specifically fatness, using densitometry, combinations of weight and height, skinfold thicknesses, and the newer methods of bioelectric resistance and dual energy x-ray absorptiometry. Finally, the evaluation of body fat distribution is reviewed, and the use of such measurements in epidemiologic analyses is examined.

This chapter integrates existing literature on body dissatisfaction in a way that highlights possible pathways or trajectories that explain variation in body dissatisfaction at midlife. It focuses on three main questions: first, what is the extent or prevalence of body dissatisfaction in women beyond young adulthood, and what trends have there been over time? Second, what are the consequences of body dissatisfaction for health and well-being among older women? Third, what are the determinants of dissatisfaction at different stages of the life span that may be relevant in explaining midlife dissatisfaction? A life course perspective is considered in this third goal, and since this perspective is a new framework for the study of body image, identification of gaps in the literature is inevitable.

This chapter examines the macroecological patterns of body size in mammals across space and time. It addresses the following questions: How similar are overall body size distributions across individual continents and large islands? How similar are overall body size distributions across time in North America? Are present-day patterns warped? Is the relationship between body size and range size consistent across time and space? Are the shapes of body size distributions at the community level consistent across time and space? The results show gross similarities in macroecological patterns across land masses and throughout evolutionary time. Although there are unique aspects to the patterns on individual continents, the shapes of body size distributions and the moments of the distributions are remarkably similar despite their different evolutionary and geological histories.

The chapter summarizes the history of recent scientific understanding of food webs, particularly shallow water food webs. The chapter outlines a history of key papers ranging from Elton to the most recent synthetic studies of meta-analysis of multiple food webs in many ecosystems. Changes in general organizing principles over time and conflicts with recent understanding are emphasized including an outline of the considerable progress over time and hope for an emerging discipline that takes advantage of emerging multidisciplinary tools and collaborations.