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Evolution's Wedge: Competition and the Origins of Diversity

David W. Pfennig
Karin S. Pfennig
Copyright Date: 2012
Edition: 1
Pages: 320
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  • Book Info
    Evolution's Wedge
    Book Description:

    Evolutionary biology has long sought to explain how new traits and new species arise. Darwin maintained that competition is key to understanding this biodiversity and held that selection acting to minimize competition causes competitors to become increasingly different, thereby promoting new traits and new species. Despite Darwin’s emphasis, competition’s role in diversification remains controversial and largely underappreciated. In their synthetic and provocative book, evolutionary ecologists David and Karin Pfennig explore competition's role in generating and maintaining biodiversity. The authors discuss how selection can lessen resource competition or costly reproductive interactions by promoting trait evolution through a process known as character displacement. They further describe character displacement’s underlying genetic and developmental mechanisms. The authors then consider character displacement’s myriad downstream effects, ranging from shaping ecological communities to promoting new traits and new species and even fueling large-scale evolutionary trends. Drawing on numerous studies from natural populations, and written for a broad audience, Evolution’s Wedge seeks to inspire future research into character displacement’s many implications for ecology and evolution.

    eISBN: 978-0-520-95404-5
    Subjects: Ecology & Evolutionary Biology

Table of Contents

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  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-viii)
    (pp. ix-xiv)
    (pp. 1-28)

    In a frequently heard—and perhaps apocryphal—story, the evolutionary biologist J. B. S. Haldane, when asked to comment on what could be inferred about the Creator based on the creation, is reported to have said, “He must have had an inordinate fondness of beetles” (Farrell 1998). Whyarethere so many species of beetles (Figure 1.1A)? For that matter, why are there so many different kinds of living things generally?

    As it turns out, living things are amazingly diverse. As one measure of this diversity, conservative estimates place the number of species alive today at 8 to 10 million...

    (pp. 29-56)

    In chapter 1, we defined “character displacement” as trait evolution that arises as an adaptive response to resource competition or deleterious reproductive interactions between species. Left unaddressed in that chapter, however, were thecausesof resource competition or deleterious reproductive interactions between species. Specifically, how do such interactions come about, why are they costly, and—in the absence of character displacement—what is the ultimate fate of populations that experience such interactions? In other words,whydoes character displacement occur?

    In this chapter, we examine the selective bases of character displacement. As we describe, regardless of whether competitive interactions occur...

    (pp. 57-80)

    In the previous two chapters, we examined how character displacement arises as an adaptive response to resource competition or deleterious reproductive interactions between species. A key unresolved issue, however, is why some populations and species are more likely to undergo character displacement as opposed to the alternative outcomes of competitive exclusion or reproductive exclusion (Schluter 2000; Rice and Pfennig 2007). In this chapter, we address this issue by consideringwhencharacter displacement occurs.

    We begin by discussing six general factors that facilitate character displacement. Like other forms of local adaptation, character displacement is more likely to occur when various proximate...

    (pp. 81-104)

    Recall from chapter 3 that a key facilitator of character displacement is the presence of standing phenotypic variation on which competitively mediated selection can act. Yet, relatively little is known about the source(s) of such variation or how different sources affect character displacement’s tempo and mode. In this chapter, we address these issues by examining the underlying proximate (that is, genetic and developmental) mechanisms of character displacement.

    We begin by considering whether character displacement comes about strictly through genetically canalized change (that is, change that reflects allelic or genotype frequency changes and that is relatively insensitive to the environment) or...

    (pp. 105-132)

    Most species exhibit a striking amount of phenotypic variation. Indeed, in some cases, trait variation between different members of the same species is as great as that normally seen between different species (see, for example, Figure 1.1B, C). Here we consider the role of competitively mediated selection in generating and maintaining such diversity within species.

    In explaining this variation, we shift our focus in this chapter to intraspecific competition, which contrasts with previous chapters, where the focus was oninterspecific competition. Compared with interspecific competition, intraspecific competition is probably more common and frequently stronger (Gurevitch et al. 1992; Dybzinski and...

    (pp. 133-156)

    Having focused on the causes of character displacement in the first half of the book, we now explicitly examine some of the consequences of character displacement, starting with its ecological consequences. In this chapter, we consider how the study of character displacement provides a unifying framework for understanding the maintenance, abundance, and distribution of biodiversity.

    We begin by discussing how character displacement contributes to species coexistence by promoting niche differences among interacting species. In particular, we describe how competitively mediated selection can promote niche differences, either by causing species to diverge and assume new resource-use or reproductive traits, or by...

    (pp. 157-178)

    In chapter 6, we examined the ecological ramifications of character displacement. For the remainder of the book, we discuss character displacement’s evolutionary implications, starting with its implications for sexual selection.

    Identifying the factors that can influence sexual selection is critical for understanding the causes of diversification, for at least two reasons. First, traits produced through sexual selection—such as the striking sexually dimorphic features observed in many organisms—provide some of the most dramatic examples of diversity within species (for example, see Figure 5.8). Second, sexual selection may drive speciation (Figure 7.1; reviewed in Andersson 1994; Butlin and Ritchie 1994;...

    (pp. 179-204)

    Understanding how species arise (“speciation”) is essential for explaining the origins of diversity. Until this point in the book, we have only briefly mentioned the possible contribution of character displacement to speciation. Here, we explicitly consider character displacement’s role in the formation of new species.

    Specifically, we discuss how character displacement potentially promotes speciation via three routes: (1) by finalizing speciation following contact between already divergent populations (Figure 8.1 at the arrow labeled a); (2) by initiating speciation between conspecific populations in sympatry with a heterospecific, which have undergone character displacement, versus those in allopatry, which have not undergone character...

    (pp. 205-232)

    Macroevolution is large-scale evolutionary change, ranging from the origin of species and major new features (such as novel traits or even new body plans) to long-term evolutionary trends (Stanley 1979; Erwin 2000; Levinton 2001; Gould 2002; Futuyma 2009). Beginning with Darwin, many evolutionary scientists have held that macroevolution reflects the long-term accumulation of small-scale evolutionary change occurring within species; that is, macroevolution is the sum ofmicroevolution over time (Mayr 2001). From this perspective, the processes that cause microevolution (such as selection, drift) are also thought to propel macroevolution. Yet, because macroevolutionary change typically unfolds over long periods of time...

    (pp. 233-242)

    At the outset of this book, we emphasized that a longstanding problem in both evolutionary biology and ecology is to explain why there are so many different kinds of living things and why even closely related organisms tend to differ from one another phenotypically (for example, see Figure 1.1). We described how Darwin (1859 [2009]) addressed this problem by advancing his principle of divergence of character. According to this principle, the origin of species and the evolution of phenotypic differences between them stem ultimately from divergent selection acting to minimize competitive interactions between initially similar groups of individuals. We also...

    (pp. 243-290)
  15. INDEX
    (pp. 291-303)
  16. Back Matter
    (pp. 304-304)