Joel Cracraft

Species Concepts and Speciation Analysis

Systematic biologists have directed much attention to species concepts because they realize that the origin of taxonomic diversity is the fundamental problem of evolutionary biology. Questions such as, What are the units of evolution? and, How do these units originate? thus continually capture the attention of many. It is probably no exaggeration to say that most believe the “systematic” aspects of the problem have been solved to a greater or lesser extent, whereas the task before us now is to understand the “genetic” and “ecologic” components of differentiation, i. e., those aspects often perceived to constitute the “real mechanisms” of speciation: nA study of speciation is, to a considerable extent, a study of the genetics and evolution of reproductive isolating mechanisms (Bush, 1975, p. 339). n n... a new mechanistic taxonomy of speciation is needed before population genetics, which deals with evolutionary mechanisms, can be properly integrated with speciation theory; that is, the various modes of speciation should be characterized according to the various forces and genetic mechanisms that underly [sic] the evolution of isolating barriers (Templeton 1980, p. 720).

THE SPECIES OF THE BIRDS‐OF‐PARADISE (PARADISAEIDAE): APPLYING THE PHYLOGENETIC SPECIES CONCEPT TO A COMPLEX PATTERN OF DIVERSIFICATION

Abstract The phylogenetic species concept is applied for the first time to a major radiation of birds, the birds‐of‐paradise (Paradisaeidae) of Australasia. Using the biological species concept, previous workers have postulated approximately 40–42 species in the family. Of these, approximately 13 are monotypic and 27 are polytypic with about 100 subspecies. Phylogenetic species are irreducible (basal) clusters of organisms (terminal taxa) that are diagnosably distinct from other such clusters. Within the context of this concept, approximately 90 species of paradisaeids are postulated to have diversified within Australasia. The phylogenetic species concept more accurately describes evolutionary diversity within the family and provides a better theoretical and empirical framework for analysing speciation, historical biogeography and patterns of morphological, behavioral and ecological diversification within this group than does the biological species concept.

DNA Hybridization and Avian Phylogenetics

The phylogenetic relationships of birds are currently being studied from a number of different perspectives. Not only are distinct types of data being employed, but so, too, are alternative methods of analysis, including phenetics, evolutionary systematics, and cladistics. The last decade has seen more advance in our knowledge of avian relationships than perhaps during any other comparable period, and given the growing number of systematists, we can expect our understanding to continue developing in the years to come.

Species as Entities of Biological Theory

Species play a central role in evolutionary biology. They are generally the locus of most discussions of taxonomic and structural diversity. Species are said to be the active participants in a host of postulated processes. Thus, species speciate, go extinct, compete, interact, disperse, predate, or are selected.

The Significance of Phylogenetic Classifications for Systematic and Evolutionary Biology

Systematic biologists have engaged in a long-standing debate over the purposes and methods of classification. Many nonsystematic biologists probably look upon the resulting contentiousness with amusement, if they look upon it at all, for if we are honest about the present condition of systematic biology, we have to admit that classification is often seen as little more than the description and cataloging of nature, as stamp collecting in the minds of many. And when one looks objectively at the debate among the phylogeneticists, evolutionists, and pheneticists, much of it must seem as being highly irrelevant to a nonsystematist. While we might expect this reaction from molecular or cell biologists, its ubiquity also within the field of evolutionary biology is surprising. This apathy towards systematics can be attributed to two factors. First, systematic biologists have done an inadequate job of conveying the importance of classification, and thus the necessity and relevance of systematic studies for biology as a whole. If systematics has something to contribute, then systematists themselves must take some responsibility for communicating that contribution. The second reason is simply that many evolutionary biologists are intellectually lazy, and lack curiosity or desire to investigate for themselves what systematics might have to offer. If population ecologists, they may claim to be interested in the ecological analysis of evolutionary mechanisms: what, they might ask, could classification contribute to that? If population geneticists, they may claim to be concerned with the mechanisms of population change or of speciation: what could classification contribute to that? If physiologists, behaviorists, or biochemists, they may be interested in how organisms adjust evolutionarily to their environments: what could classification contribute to that?

Conceptual and Methodological Aspects of the Study of Evolutionary Rates, with some Comments on Bradytely in Birds

The analysis of evolutionary rates has received scant attention within ornithology. The primary reason would seem to be the nature of the avian fossil record: If an understanding of rates depends upon having a time dimension, which most paleontologists believe can only be extracted from fossil data, how can we hope to study rates using the notoriously poor record of birds? No one would deny that the avian record is less complete than other vertebrates or many groups of non vertebrates, yet this cannot be the entire story, for there are easily over a thousand paleospecies of birds known, some of which provide information about rates. Another contributing factor, probably, is our relatively poor knowledge of avian phylogenetic relationships. All assessments of rates, whether absolute or relative, depend upon some hypothesis about the phylogenetic relationships of the taxa being studied.

Biogeographic patterns of terrestrial vertebrates in the Southwest Pacific

Abstract A unified biogeographic history of the Southern Hemisphere biota is beginning to emerge, and vertebrates, invertebrates, and plants are seen to exhibit many similarities in the patterns of their phylogenetic relationships. Terrestrial vertebrate biogeographic patterns are reviewed based on present knowledge of phylogenetic relationships; the major patterns (generalized tracks) and their taxonomic components include: (1) Australia—South America: leptodactyloid-like frogs, possibly hylid frogs; meiolaniid and chelid turtles; ratite, galliform, anseriform, and caprimulgiform birds; marsupials, possibly monotremes; (2) New Zealand-South America: leiopelmatid frogs; ratite, sphenisciform, and gruiform birds; (3) New Caledonia-New Zealand: gekkonid and scincid lizards; gruiform birds; (4) New Zealand (+ New Caledonia)-Australia/Southeast Asia: gekkonid and scincid lizards; most birds; vespertilionid bats; (5) Australia-Southeast Asia: ranid, microhylid frogs; agamid, scincid, varanid lizards; pythonine, colubrid, elapid snakes; many non-passeriform and passeriform birds; murid rodents. In most cases generalized tracks are best interpreted as vicariance of an ancestral biota into two or more descendant biotas. Dispersal across geographic or climatic barriers is less efficacious as an explanation for generalized tracks than is vicariance; post-vicariance dispersal is a hypothesis difficult to test. Centers of origin and pathways of dispersal of component elements of a generalized track prior to vicariance can be investigated using cladistic analysis.

The Measurement of Biological Shape and Shape Change.

One. Introduction: On the Absence of Geometry from Morphometrics.- First Part. The Measurement of Biological Shape.- Two. Shapes and Measures of Shape.- A. Properties of the Euclidean Plane and Euclidean Space.- B. Outlines and Homologous Landmarks.- C. Definitions of Shape, Shape Change, Shape Measurement.- D. Shapes as Data.- Three. Critique of an Applied Field: Conventional Cephalometrics.- A. Landmarks, Curvature, and Growth.- B. Registration.- Four. New Statistical Methods for Shape.- A. Analysis of the Tangent Angle Function.- 1. History.- 2. Sampling from the tangent angle function.- 3. Conic replacement curves and their estimation Fit of a conic to a point - Geometric interpretation - Estimator for a circle - Estimation for the general conic - Computation of the extremum -Linear constraints.- 4. Conic splining Joint conic fitting under constraint -An example - Application - Analysis of parameters.- B. Extension to Three Dimensions: A Sketch.- C. Skeletons Definition - A multivariate statistical method - Bibliographic note.- Second Part. The Measurement of Shape Change Using Biorthogonal Grids.- Five. The Study of Shape Transformation after DArcy Thompson.- A. The Original Method.- 1. Thompsons own work.- 2. Later examples.- 3. Difficulties.- B. Analysis of Growth Gradients.- C. Simulations.- D. Other Morphometric Schemes Vector displacements - Multivariate morphometrics.- Six. The Method of Biorthogonal Grids.- A. Representation of Affine Transformations.- B. General Lines of Growth and Biorthogonal Grids.- C. Summarizing the Grids.- Technical Note 1. Existence and Form of Biorthogonal Grids.- Technical Note 2. Interpolation from Landmark Locations and Arcs The measure of roughness - The vector space and its associated functions - Interpolation from boundary values - Interpolation from boundary values and interior points - Note on computation.- Technical Note 3. Construction of Integral Curves.- Technical Note 4. On Homologous Points.- Seven. Examples of Biorthogonal Analysis.- A. Comparison of Square and Biorthogonal Grids: Thompsons Diodon Figure.- B. Phylogeny and Ontogeny of Primate Crania.- 1. Functional craniology and craniometrics.- 2. Data for this exercise.- 3. Two types of transformations.- 4. Comparative ontogeny of the apes and man.- Eight. Future Directions for Transformation Analysis.- A. Statistical Methods The symmetric tensor field - Concordance -Linear methods.- B. Computation Other kinds of information about homology -Three dimensions.- C. Likely Applications Computed tomography - Orthodontics - Developmental biology.- Nine. Envoi.- Literature Cited.