Scale, Heterogeneity, and the Structure and Diversity of Ecological Communities

Scale, Heterogeneity, and the Structure and Diversity of Ecological Communities

Copyright Date: 2010
Pages: 232
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  • Book Info
    Scale, Heterogeneity, and the Structure and Diversity of Ecological Communities
    Book Description:

    Understanding and predicting species diversity in ecological communities is one of the great challenges in community ecology. Popular recent theory contends that the traits of species are "neutral" or unimportant to coexistence, yet abundant experimental evidence suggests that multiple species are able to coexist on the same limiting resource precisely because they differ in key traits, such as body size, diet, and resource demand. This book presents a new theory of coexistence that incorporates two important aspects of biodiversity in nature--scale and spatial variation in the supply of limiting resources.

    Introducing an innovative model that uses fractal geometry to describe the complex physical structure of nature, Mark Ritchie shows how species traits, particularly body size, lead to spatial patterns of resource use that allow species to coexist. He explains how this criterion for coexistence can be converted into a "rule" for how many species can be "packed" into an environment given the supply of resources and their spatial variability. He then demonstrates how this rule can be used to predict a range of patterns in ecological communities, such as body-size distributions, species-abundance distributions, and species-area relations. Ritchie illustrates how the predictions closely match data from many real communities, including those of mammalian herbivores, grasshoppers, dung beetles, and birds.

    This book offers a compelling alternative to "neutral" theory in community ecology, one that helps us better understand patterns of biodiversity across the Earth.

    eISBN: 978-1-4008-3168-5
    Subjects: Ecology & Evolutionary Biology

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-vi)
  3. Acknowledgments
    (pp. vii-x)
  4. CHAPTER ONE Community Ecology Lives
    (pp. 1-14)

    Understanding what controls the structure and diversity of ecological communities has invoked the intellectual firepower of ecologists since at least the time of Charles Darwin (1859, p. 125).

    In the case of every species, many different checks, acting at different periods of life, and during different seasons or years, probably come into play; some one check or some few being the most potent, but all concurring in determining the average number or even the existence of the species. . . . When we look at the plants and bushes clothing an entangled bank, we are attempted to attribute their proportional...

  5. CHAPTER TWO The Geometry of Heterogeneity
    (pp. 15-31)

    In this book, I explicitly incorporate spatial heterogeneity into mathematical models of niche boundaries, species coexistence and species richness. The first step is to define heterogeneity explicitly and quantitatively (Wiens et al. 1993). Dozens of studies now show that the physical environment, and the habitat and resources located within it, very often exhibit fractal-like geometry. This assumption generates the scale or size-dependence of resource acquisition that produces most of the major qualitative predictions and quantitative tests in this book. In this chapter, I present a tutorial of fractal geometry to show how it captures heterogeneity and its scale-dependent properties. I...

  6. CHAPTER THREE Scaling Relationships for the Consumption of Resources
    (pp. 32-55)

    To persist in an environment, organisms must find enough resources to meet their requirements to produce enough offspring to replace themselves in their lifetime. They must avoid being eaten by other organisms, find mates (if they are sexual) and not experience intolerable physical conditions. If organisms are mobile, they can actively search the environment, while sedentary organisms must have resources delivered to them by the physical movement of the medium in which they live, such as water, or by the movement of potential prey. Other organisms, such as plants, search the environment by building permanent structures, such as plant roots,...

  7. CHAPTER FOUR Food, Resources, and Scale-Dependent Niches
    (pp. 56-83)

    Thus far I have considered resources as if they were consumed directly, such as when phytoplankton take up dissolved nitrate or phosphate from a water column or when plants harvest photons of light. However, many limiting resources, such as proteins and carbohydrates for animals, are not consumed directly. Instead, they are “packaged” in other material that, for lack of a better term, can be calledfood(Ritchie and Olff 1999) Organisms therefore must consume “food” in order to obtain limiting resources. For example, carnivores eat other animals and herbivores eat plant tissue, seeds, sap, fruits, etc. in order to consume...

  8. CHAPTER FIVE Size Structure in Ecological Guilds
    (pp. 84-121)

    Three fundamental and inter-related characteristics of ecological guilds, or communities of species that use the same resources, are the number of species of different sizes, the abundance of different-sized species (Hutchinson and MacArthur 1959; Morse et al. 1985; Damuth 1991; Blackburn and Gaston 1999; Brown et al. 1993; Brown 1995; Siemann et al. 1996) and the limit to similarity in species traits (Hutchin son 1959; Abrams 1975; Pacala and Tilman 1994; Belovsky 1997; Kinzig et al. 1999). Defined more generally as the size structure of guilds, these two characteristics may reflect the outcome of competitive interactions within guilds, although other...

  9. CHAPTER SIX Heterogeneity and Patterns of Species Diversity
    (pp. 122-147)

    Predicting species diversity and its major patterns from underlying mechanisms of organism births, deaths, dispersal, and resource consumption, to name a few, has perhaps been the “Holy Grail” of community ecology since the 1950s. Beginning in the 1960s, classical Lotka-Volterra models of competition and predation (Lotka 1925; Volterra 1926) published 30 years earlier began to be employed to understand how species coexist. By the beginning of the 1970s, ecologists were excited about constructing “community matrices” of interactions among sets of competitor or predator-prey species to predict species diversity and its patterns across different environments (MacArthur 1969, 1972; Vandermeer 1972; Strobeck...

  10. CHAPTER SEVEN Biodiversity Conservation in Fractal Landscapes
    (pp. 148-169)

    The spatial scaling model of consumer-resource interactions yields qualitative predictions about the richness and body size, or other morphological traits of species, in environments that differ in the amount and spatial pattern of resources. Consequently the spatial scaling model can be used to address some questions relevant to the conservation of biodiversity. One consequence of environmental changes on communities that can be uniquely addressed with this model is the effect of habitat fragmentation on species’ populations and community species richness for particular guilds that use the same resources in the same habitats.

    A major question faced by conservationists is how...

  11. CHAPTER EIGHT Testing the Model
    (pp. 170-178)

    Now that the reader is armed (and potentially dangerous!) with the spatial scaling model, he or she might ask, how do I test it? I have tested the major assumptions and predictions of the model at virtually every opportunity throughout this book, and while these datasets are certainly not exhaustive, the limited number of studies that simultaneously measure size, resource consumption, abundance and species richness strongly constrain tests at this time. Nevertheless, these tests represent just the beginning of what needs to be done to validate the model for situations where its assumptions apply, and to compare its qualitative predictions...

  12. CHAPTER NINE Perspectives, Caveats, and Conclusions
    (pp. 179-202)

    The past four chapters present a series of models that, when combined, form the “spatial scaling model” of community structure. This model explores how heterogeneity in the distribution and packaging (as food) of a resource might influence individuals, populations, and communities of consumers whose fitness is limited by that resource. The assumption of heterogeneous resources generates the basis for selective foraging, resource partitioning, and competitive coexistence of community structure: as I mention repeatedly, this model collapses to the classic consumer-resource models of Tilman (1976, 1982) and Chase and Leibold (2003) if resources are distributed randomly rather than heterogeneously. However, there...

  13. Appendix Summary of Model Parameters
    (pp. 203-206)
  14. References
    (pp. 207-226)
  15. Index
    (pp. 227-230)
  16. Back Matter
    (pp. 231-233)