Studying the history of diversity involves trying to explain variation among taxa in their rates of extinction and speciation (e.g., Simpson 1953; Stanley 1975; Sepkoski 1992b; Cracraft 1992; Gilinsky and Good 1991). For species or genera within particular groups, correlates of either or both of these rates include physical traits such as body size (Stanley 1987; Jablonski 1991), temperature tolerance (Jablonski et al. 1985), or armor (Vermeij 1987b); ecological traits such as the degree of trophic specialization (Vrba 1980); and environmental variables such as productivity (Vermeij 1993), latitude (Jablonski 1991), or ocean depth (Jackson 1974; Jablonski and Lutz 1983; Signor...

That which biologists measure as biological diversity is the consequence of a great number of complicated processes operating over numerous spatial and temporal scales. One important component of biological diversity is species richness, or the number of species found in a given place during a specific period of time. Species richness is measured at a variety of scales, from that of the local community in a given season to an entire continent over evolutionary time. In the past, it has been somewhat difficult to relate processes occurring in local communities to those operating on much larger scales, but recently a...

The Oxford English Dictionary defines diversity as “the condition or quality of being different in character or quality.” Biodiversity is, in simple terms, a catchall for describing levels of being biologically different or variable. Biodiversity is a reflection of certain patterns of turnover, as measured by differential speciation and extinction. Ecological aspects of turnover are related to specific ecological characteristics such as geographic range, life histories, or habitat structure. Evolutionarily, the questions are, how do these characteristics vary at different taxonomic levels such as populations, species, and so forth, and do they seemingly have an impact on biodiversity and turnover?...

Could the diversity of species have been caused by simple random processes of speciation and extinction? This question, asked repeatedly in recent decades (Raup et al. 1973; Gould et al. 1977; Stanley et al. 1981; Raup 1985; Hey 1992; Nee et al. 1992) and in this chapter, might seem irrelevant to investigators of specific cases of speciation or extinction. Clearly, every case of speciation or extinction has ecological, biogeographic, and genetic causes, and the idea of “random causes” may have little meaning to students of the mechanisms of speciation and extinction. However, scientists have few tools to study the causes...

America spread west in the mid to late nineteenth century. In our own century, the story of the mass migration has been told and retold in countless ballads and novels. And in now-classic movie westerns, it has been epitomized in scenes of long wagon trains winding across the prairie toward the setting sun.

Census data from that period confirm the demographic aspect of the story: the mean location of Americans—the country’s center of gravity, so to speak—shifted westward. However, the data also show that from two broad belts occupying the middle third of the country, the west-central states...

The diversity of life is composed of two parts. In part it is made up of species diversity, which is the number of discrete evolutionary lineages. Over 4700 species of mammals are known to science, for example, and new forms, even new genera, are being described routinely (Wilson and Reeder 1993). Diversity is also reflected in the tremendous variety of characteristics that these organisms exhibit. This is particularly true with respect to features of structure and function. One particularly important characteristic, and the most visible feature of living organisms, is body size. The variation in body sizes is impressive: it...

How are biodiversity dynamics developmentally constrained at various hierarchical levels? Patterns of diversity and associated process theories have conventionally been treated in extrinsic, particularly ecological, terms, and development has not been sufficiently integrated into discussions of diversity change (e.g., Rosenzweig 1995). This may be due, in part, to a reluctance of many students of development or ecology to delve into the interplay between allegedly ahistorical principles of form generation and their historical realization in the process of evolution. It was not until recently, when the reality of the Cambrian explosion of metazoan body plans became clear, that developmental explanations have...

This chapter is principally about evolutionary turnover at a high level of taxonomic organization, specifically, turnover among families within orders and turnover among orders themselves. To the extent that characteristics of family-level turnover within orders are correlated with processes of species-level turnover, a view urged by Bambach and Sepkoski (1992) and others (Allison and Briggs 1993; Sepkoski et al. 1981), the chapter is also about turnover at the species level. And to the extent that processes of species-level turnover can be understood by reference to ecological properties of organisms, populations, and environments, the chapter is also about the links—just...

It is a common practice in field geology to examine an outcrop in close detail only after getting the “big picture.” One gains this broader perspective by backing off a suitable distance so that the whole (or most) of the exposed section is within the field of view. The reason? We get closer to understanding the whole by considering its parts at more than one scale.

Like an outcrop, an ecosystem is formed from a hierarchy of processes and must therefore be defined relative to time and space. Communicating ideas using these definitions is often made more difficult by the...

Species are not distributed randomly across the face of the Earth. It is a fundamental observation in ecology that species occur in particular habitats, and that the occurrence of a species often correlates, positively or negatively, with the occurrence of other species. Describing and interpreting patterns of species occurrences—over different spatial scales and through time—are central concerns of ecology and paleoecology, as well as of their new cousin, macroecology (Brown 1995).

One simple and extremely common pattern of species distributions has been termed nested subsets by Patterson and Atmar (1986). Given a set of replicate habitats with biotas...

The study of diversity patterns has long been one of paleobiology’s principal preoccupations. Simpson (1944) was only one of many early workers to quantify diversity trends using paleontological data. Despite this, “taxon counting” has been plagued by enough practical difficulties to seriously undermine our confidence in statistical results. These difficulties are so profound that Benton (1995) ignored two decades of advances going back to MacArthur (1969) and boldly declared that “there is no need to assume equilibrium models of global diversity, nor to apply logistic models to the investigation of past diversification patterns.” Is this true? Can ecologists safely assume...

Three decades of intense paleobiological research have yielded a substantially improved calibration of global biodiversity trends throughout the Phanerozoic. The overall pattern among marine biotas, evaluated in numerous studies (e.g., Newell 1959; Valentine 1970, 1973b; Raup 1972, 1976a,b; Bambach 1977; Sepkoski 1976, 1978, 1979, 1981, 1984, 1993; Sepkoski et al. 1981; Signor 1990), is now understood with some confidence (but seeMiller and Foote 1996). Among the early highlights of Phanerozoic marine diversification were (1) an initial radiation in the Cambrian Period (the Cambrian explosion), when most phyla originated (Erwin et al. 1987) and the trilobite-dominated Cambrian evolutionary fauna flourished (Sepkoski...

Area is a pervasive and powerful influence on species diversity (Rosenzweig 1995). If we are to understand diversity, we must therefore understand its relationship to area. By the mid nineteenth century, Watson (1835) had described an important aspect of this relationship in terms that we would later understand as a power equation:

$ S = k{A^z} $ [1a]

where $ A $ is area and $ S $ is the number of species. ( $ S $ , species richness, is the only measure of species diversity I will use in this chapter.) Equation 1a is called the species—area curve, or SPAR.

To simplify their analyses, ecologists transformed equation 1a to...

Diversity—by which we mean here the multiplicity of taxonomic entities we call species—is one of the most conspicuous aspects of living systems. It is therefore remarkable that we know so little about its causes. Maybe this is because it is genuinely one of the most difficult problems in biology; maybe it is because we have not looked at it the right way; maybe it is some combination of these two.

It is not for lack of trying; there is no shortage of literature on diversity. Yet some of the most sweeping attempts at explanation of the diversity we...

In this chapter, I will argue for turnover as an underappreciated and underutilized property of all biological systems. Currently, study of turnover is piecemeal. Turnover is defined, measured, and modeled in many different ways, depending on the discipline, the scale of measurement, and whether this measurement is over time or space. Where models are similar, they seem to have been arrived at independently. I will demonstrate the following:

1. Turnover may be found in all biological systems.

2. Turnover can be measured in a similar way over time and space.

3. Turnover can be measured in a similar way at...

Mass extinctions are most parsimoniously explained by purely physical mechanisms (e.g., global temperature change, sea level fall, anoxia). Perhaps this is because from our own “organismic” perspective, it is “difficult for us to view processes at higher [ecosystem, biosphere] levels . . . as emerging out of results of processes at lower biotic . . . levels . . .” (Salthe 1985, p. 219; my italics; see also Valentine 1973a). These “ultimate” physical mechanisms have probably varied in relative importance depending on the particular tectonic, paleoceanographic, and paleoclimatic setting during each extinction episode (Cracraft 1992). But significant (“catastrophic”) changes in...

Most paleobiologists acknowledge that small-scale interactions between organisms can sum to produce large-scale patterns that directly reflect those individual interactions. Vermeij (1977, 1978, 1987a) popularized this idea by showing that increasing predation caused the morphology of gastropod shells to vary in predictable, similar ways on multiple scales of time and space. A growing body of evidence supports scale-independent, or fractal, models of biological interaction, diversification, and extinction (Burlando 1993; Aronson 1994; McKinney 1995; Perry 1995; Rosenzweig, chapter 14). In apparent opposition to this evidence is the concern that our perceptions of pattern and process depend on our scale of observation...