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This chapter shows that organizational ecology is much more sociological and less biological than many critics of organizational ecology think. It argues that organizational ecology and its theory of competition rests heavily on the seminal work of Emile Durkheim on the division of labour, and on the thoughts of Amos Hawley on human ecology. It suggests that the expressions used by the agents of organizational ecology are ‘Darwinian’ but that the theoretical argumentation is ‘Durkheimian’. The chapter highlights the theoretical foundations of organizational ecology and emphasizes that competition — and not the biological aspects of evolution — forms the core of the organizational ecology theory. The most the most important sub-concepts of organizational ecology that deal with competition and market formation are also discussed: density dependence and resource partitioning. The first concept deals with the impact of the number of competitors on the survival and founding chances of organizations. The latter is concerned with the influence of market concentration on the vital rates of specialist and generalist organizations.

This chapter describes the mechanisms by which an Allee effect can arise. For each mechanism, the chapter discusses how it works in theory, and then presents current evidence for, and examples of, the mechanisms in practice. It begins with reproductive mechanisms, including fertilization efficiency in broadcast spawners, pollen limitation, mate finding, sperm limitation, reproductive facilitation by conspecifics, and female choice. It then moves on to mechanisms related to survival: environmental conditioning and particularly predation, both via the dilution effect and via group ‘behaviour’, such as flocking, coloniality, and group vigilence. Finally, the chapter discusses Allee effects in social and cooperative species, where group size is important for both reproduction and survival.

The total density dependence in a life history is defined as the negative elasticity of population growth rate per generation with respect to population density. This chapter analyzes a stage-structured life history model with age at maturity α, and adult annual mortality and reproductive rates independent of age, with all density dependence exerted by the adult age class on all the vital rates. For small or moderate fluctuations in adult population size around an equilibrium or average size, a linear autoregressive equation is derived with time delays from 1 to α years. This demonstrates that a nonzero autoregression coefficient at a given time delay does not generally measure delayed density dependence, but also can be produced by intrinsic delays in the life history. The total density dependence in the life history can be estimated using the sum of the autoregression coefficients. Applying this theory to time series of terrestrial vertebrate populations reveals that, despite evidence for strong density dependence in some components of the life history, the expected dynamics of adult population size are undercompensated, γ less than 1. Thus, near equilibrium a proportional increase in adult population density is expected to produce a smaller proportional decrease in λ. Inspection of model autocorrelation functions and power spectra calculated by fitting population time series to the stage-structured life history shows that the expected dynamics are usually smoothly damped rather than cyclic or chaotic. Long autocorrelation and a red-shifted power spectrum are produced by a combination of weak density dependence and long generation times.

The problems faced by a hypothetical planet with only one species strongly suggest that any functioning ecological system must have organisms from at least two major ecological guilds: autotrophs and decomposers. While conventional predators do not seem to be crucial to planetary ecologies it is likely that parasites will quickly evolve, and through density dependent processes help to regulate population sizes. Density dependence may be crucial in preventing the runaway population growth of a species, leading to it monopolizing a planet's ecology. While density independent processes (be they a cold winter on a local scale, or the impact of a large meteorite at the planetary scale) can greatly affect abundance, they cannot provide regulation; this requires the ‘thermostat’ like behaviour of density dependence. As such, both multiple guilds and the presence of parasites are likely to have positive Gaian effects in most biospheres.

This chapter reviews the basic mathematics of population growth as described by the exponential growth model and the logistic growth model. These simple models of population growth provide a foundation for the development of more complex models of species interactions covered in later chapters on predation, competition, and mutualism. The second half of the chapter examines the important topic of density-dependence and its role in population regulation. The preponderance of evidence for negative density-dependence in nature is reviewed, along with examples of positive density dependence (Allee effects). The study of density dependence in single-species populations leads naturally to the concept of community-level regulation, the idea that species richness or the total abundance of individuals in a community may be regulated just like abundance in a single-species population. The chapter concludes with a look at the evidence for community regulation in nature and a discussion of its importance.

Winter elk numbers on the northern range have been counted through most of its history, with ground counts up to 1956 (except 1935) and aerial counts up to the present. Several sightability bias tests have indicated that the censuses count approximately 70-75% of the herd. Regression of annual, instantaneous rates of change (r) between censuses of years t and t+1 on censuses of years t produces an inverse correlation with r reaching zero (equilibrium) at 16,800 (22,000-25,000 corrected for the sightability bias), and indicating density dependence. Below 16,800, the herd increased or held its numbers when hunting kills outside the park and park removals fell below 15-20%, but declined when removals exceeded this magnitude. While evidence of equilibration supports one tenet of the population aspect of the natural-regulation hypothesis, the 6x increase from a census of 3,172 in 1968 to 18,913 in 1988 (‘eruption’) falsifies two of the population tenets of the hypothesis.

The term “inertia” was first used in population ecology in relation to the property of overshooting equilibria due to any one of a variety of causes. This chapter tries to flesh out the details of a general account of inertia in population growth that can accommodate a number of possible mechanisms. To motivate this discussion, the chapter considers a couple of difficulties for the maternal effect. Both difficulties concern the inadequacy of existing data and require a little technical detail.

This chapter focuses on a generalization of a classic consumer-resource model with a single population embedded in a community. It develops this physiologically structured consumer-resource model by extending the static model in Chapter 4. The chapter then studies how density dependence emerges in the model, and how it changes the population size spectrum. Finally, the chapter explores how some of the standard fisheries impact assessments from Chapter 5 are changed when density dependence is in the form of competition or cannibalism. Specifically, it shows how the appearance of late-life density dependence rocks one of the cornerstones of contemporary fisheries management: that we should fish only the largest fish. In some cases, it turns out that yield is instead maximized by fishing juveniles.

This chapter reviews the ecological processes that define and limit the distributions and abundances of many odonate species across ecological environments. Distributions of species among standing bodies of water seem to be limited mainly by the distributions of their predators in the larval stage (e.g., larger dragonflies and fish). Although species also show restricted distributions among flowing water habitats, much less is known about the ecological processes that constrain their distributions. Many different types of species interactions (e.g., resource abundances, competitors, predators, parasites) contribute to the limitation of local abundances. Directions for potential future research are suggested.

Historically, studies of the population ecology of mutualism have been largely divorced from the key principles (e.g., density dependence, functional responses, consumer–resource theory) that have shaped our understanding of the dynamics of predation and competition. The population ecology of mutualism has been slow to mature, largely due to unrealistic Lotka–Volterra theory. This chapter summarizes shortcomings of such historical models that stifled theory for decades, reviews the new generation of consumer–resource theory for the population dynamics of mutualism, synthesizes empirical studies of the density dependence of mutualism, and proposes future research directions. Contemporary advances in theory are emphasized, including mechanisms for the density dependence of mutualism for which research at the interface of theory and empiricism will be critical to future progress. The chapter builds a foundation for future theoretical and empirical work to enhance our understanding of the short-term transient dynamics and long-term stability properties of mutualistic interactions.

The non-equilibrium dynamics of biological invasions has revived the debate on the balance of nature and mechanisms for population regulation. Invasive species in novel environments, whether experiencing the quasi-equilibrium of halted expansion during the lag phase or undergoing fast expansion to fulfil the opportunity niche, face a multitude of stabilizing and destabilizing forces that affect their population dynamics—from positive (Allee effects) and negative density dependence to rapidly shifting niches during invasion; these have major effects on population variability and spatial dynamics. The temporal and spatial dynamics are also intertwined, which means that the spatial structures of species distributions are potentially indicative of the invasiveness and population trends of target species. Time-series analysis for depicting the temporal population dynamics can be extended to capture the spatial synchrony dynamics of multiple local populations. Spatial autoregressive models further advance species distribution models to unveil the drivers of non-equilibrium dynamics of invasive species.

Nutritional research on northern-range elk and park-wide bison shows catabolic decline and mortality increase through winters, and as functions of population size and winter severity, collectively indicating usurpation of the range resource and intraspecific competition. Bighorn sheep numbers declined from the 1920s until about the 1960s, increased during and immediately after the elk population low, and then declined again in the 1980s and 1990s when they occurred at low population viability. Contrary to one hypothesis, the bison population increased steadily from the 1960s, except for slight population reductions in the 1980s and 1990s, until it reached ~3,000 when animals began leaving the park. Mule deer declined from the early 1900s to 1958-1970, and increased substantially by the 1980s and 1990s when they began wintering outside the park. Pronghorns, numbering in the thousands in early park years, now exist at low population viability. With speculative estimates, elk numbers and biomass increased 3.2x between park establishment and the 1990s; the other four species together declined 67% in numbers and 40% in biomass.

Although we must understand the mechanical nuts and bolts of inheritance, evolution occurs through changes in the population frequencies of traits, trait values, and genes in time and space, values that depend at least as much on the dynamics of populations as on the mechanics of inheritance. This chapter demonstrates the crucial roles of ecology in evolutionary change. There are two major types of dynamics that are essential to model evolution. The chapter develops the principles of strategy dynamics to examine the processes responsible for the success and failure of some traits, and trait values, over others. Different traits and their values represent competing strategies to be tested by adaptive evolution. The success of each strategy depends on the spatial and temporal dynamics of populations, and their respective influences on those dynamics. The chapter merges strategy and population dynamics to evaluate the evolutionary stability of competing strategies.

This chapter looks into the differences and similarities between the two groups of fish: the teleosts and the elasmobranchs. In the data analyses done so far in this volume, the fish most considered were the teleosts (Teleostei), which represent by far the dominant group, in terms of both biomass and living number of species. Second in line comes the cartilaginous fishes—the elasmobranchs (sharks, rays, skates, and sawfish). This chapter describes the differences between teleosts and elasmobranchs from a population dynamics perspective. It shows that the main difference between the two groups is in their offspring size strategy: teleosts make small offspring; elasmobranchs make large offspring. The chapter uses this difference to quantify the sensitivity of elasmobranchs to fishing relative to teleosts. It also develops an evolutionary explanation for why the offspring size strategy differs between teleosts and elasmobranchs.

Climate variation strongly influences fluctuations in size of avian populations. In this chapter, we show that it is difficult to predict how the abundance of birds will respond to climate change. A major reason for this is that most available time series of fluctuations in population size are in a statistical sense short, thus often resulting in large uncertainties in parameter estimates. We therefore argue that reliable population predictions must be based on models that capture how climate change will affect vital rates as well as including other processes (e.g. density-dependences) known to affect the population dynamics of the species in question. Our survey of examples of such forecast studies show that reliable predictions necessarily contain a high level of uncertainty. A major reason for this is that avian population dynamics are strongly influenced by environmental stochasticity, which is for most species, irrespective of their life history, the most important driver of fluctuations in population size. Credible population predictions must therefore assess the effects of such uncertainties as well as biases in population estimates.

Climate change is likely to impact all trophic levels, although the response of communities and ecosystems to it has only recently received considerable attention. Further, it is expected to affect the magnitude of species interactions themselves. In this chapter, we summarize why and how climate change could affect predator–prey interactions, then review the literature about its impact on predator–prey relationships in birds, and provide prospects for future studies. Expected effects on prey or predators may include changes in the following: distribution, phenology, population density, behaviour, morphology, or physiology. We review the currently available information concerning particular key topics: top-down versus bottom-up control, specialist versus generalist predators, functional versus numerical responses, trophic cascades and regime shifts, and lastly adaptation and selection. Finally, we focus our review on two well-studied bird examples: seabirds and raptors. Key future topics include long-term studies, modelling and experimental studies, evolutionary questions, and conservation issues.

Population dynamics of dipterocarps is determined not only by their reproduction, but also by the growth and survival of the juveniles. This itself often depends on rates of tree mortality and gap formation events. The natural disturbance regime is an important agent in creating opportunities for growth and recruitment into the canopy. There are many forms of natural disturbances, including drought, fire, windthrow, and landslides. The importance of these disturbances varies across the dipterocarp range, and with respect to local topography and climate. The variety of disturbances create different sizes and frequencies of canopy gap formation, which provide reproductive and growth opportunities that favour some species groups over others, often based on relative growth rates and light responses. This chapter addresses the dynamics of canopy trees, and that of seedlings, with a focus on density-dependence effects at local scales. The role of the natural disturbance regime in providing opportunities for recruitment and in shaping dipterocarp forest structure is also evaluated.

This chapter deals with the ecology of Tropical East Asia from a plant perspective. The life cycle of forest trees is covered in detail, including their vegetative and reproductive phenology, pollination, seed dispersal, seed predation, and the seedling, sapling, and adult stages. Other life forms, including lianas, ground herbs, epiphytes, hemi-epiphytes, and parasites are considered in less detail. Recent advances in plant community ecology are discussed, including the mechanisms responsible for the maintenance of species diversity in tropical forests (niche differentiation, growth–survival trade-offs, conspecific negative density-dependent mortality, neutral theory), and the influence of functional traits and phylogeny on community assembly. Forest succession is discussed in a regional context.

This chapter deals with the ecology of Tropical East Asia from a plant perspective. The life cycle of forest trees is covered in detail, including pollination, seed dispersal, seed predation, and the seedling, sapling, and adult stages. Other life forms, including lianas, ground herbs, epiphytes, and hemi-epiphytes, are considered in less detail. Recent advances in plant community ecology are discussed, including the mechanisms responsible for the maintenance of species diversity in tropical forests (growth–survival trade-offs, negative density dependence, Janzen–Connell effects, neutral theory), and the influence of functional traits and phylogeny on community assembly. Forest succession is discussed in a regional context.