Principios de Taxonomia

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80j 4 What are Traits in Taxonomy? Hawaii is designated as the subspecies wyvilliana, and the Pintail in the Kerguelen Islands as subspecies eatoni (del Hoyo, Elliott, and Sargatal, 1992). These examples make clear that in some species the species identification traits are only of local importance. They are not valid for all organisms of the species. Such traits are useless as recognition traits for the species as a whole. 4.7 A Species cannot be Defined by Traits As explained in other parts of this book, a species cannot be defined by its traits for many reasons. It is hard to actually define what a trait is. The number of traits is almost infinite, and a choice has to be made as to which traits permit acceptance of a species as a species; however, every choice is subjective. No single species recognition trait is essential for the species because no trait is sufficient and necessary to define an organism as belonging to a species (Chapter 3). The membership of an organism in one species can only be determined by the covariation of several traits. However, if a species cannot be defined by even a single essential trait, then the characterization of a species by a catalog of covarying traits is at best an operational definition. An operational definition does not tell us anything about what a species is, but only how to distinguish a species from another species (Mahner and Bunge, 1997). It only tells us which properties a species has (Chapter 2). However, trait recognition is different from defining criteria for a species. Traits are symptoms of a species, so to speak (de Queiroz, 1999). If one s limbs are aching, this is a symptom of the flu. However, this limb pain does not define what the flu is. It is tempting to equate similarity in traits with species membership, because in several cases members of the same species indeed resemble each other in traits. There are biological reasons why organisms of common descent or the members of a gene-flow community have similar traits. Ancestors pass on their traits to descendants, and because of this, the descendants resemble their parents and grandparents. Because of kinship, the descendants (the siblings) also resemble each other. However, this resemblance continuously declines over the course of evolution. The sibling branches continue to lose resemblance over time due to mutations and adaptations to local conditions. They all still belong to same descent community, although their trait similarity may have considerably declined over the course of time. Also the biological principles behind the species as a gene-flow community explain why the traits of members of a gene-flow community resemble each other. Mutual sexual contact among the organisms generates trait similarity among the organisms. To a limited extent, biparental sexual recombination of even distant organisms causes a homogenization of traits, even between individuals that previously diverged in their trait resemblance. Many species have trait similarity because their organisms continually mix through genetic recombination and are thus kept homogeneous (see Section Why do the individuals of a species resemble each other? in Chapter 6). However, if the geographical distance between the members of a species exceeds a
4.7 A Species cannot be Defined by Traitsj81 certain limit, homogenization of traits by genetic recombination declines, and local races arise (Chapter 5). Trait similarity and trait differences are certainly phenomena that are causally connected to biological rules. Similarity of traits could be the result of both common descent (the species concept of kinship) and sexual gene exchange (the species concept of the reproductive community). If species are grouped by kinship or as gene flow communities, similarity in traits has a certain probability. However, the trait similarities among the members of a descent community, as well as the trait similarities among the members of a gene-flow community, can be substantially weakened. Furthermore, the similarities, or rather the dissimilarities, of traits can also have other causes (see several of the Color Plates). Thus, it should not be a principle to treat the members of a species as equivalent with regard to their traits because often, they are not equivalent in this manner. The inference of status as a species from trait equivalence has the merit only of an initial suspicion (Mahner and Bunge, 1997). In discovering two groups of organisms with different traits, one can only claim a lower or higher probability for the assumption that these groups are two different species. Trait similarity in general is not a criterion of species membership. It is not possible to establish a species definition based on criteria that apply only by the majority of examples, but not by all. Since the organisms of different species are distinguished from each other by their traits, but the organisms within a species are also distinguished by their traits, the question arises of whether intraspecific differences (that is, differences between organisms of the same species) are based on trait qualities that are different in type from interspecific differences (that is, differences between the organisms of different species). Basically, there are three lines of thought on this issue: 1) A species has fewer intraspecific differences than there are interspecific differences between related species. This relationship could be true, but it does not have to be true in all cases. With respect to DNA sequence traits, which have the advantage, compared to morphological traits, that they can be counted, individuals of the same species could differ more from each other than the members of different species (Avise, Walker, and Johns, 1998; Verheyen et al., 2003). Thus, it is not admissible, at least in the case of evolutionarily young species, to elevate the extent of trait differences to a species criterion, in the sense that small differences indicate the same species, whereas more pronounced differences must indicate a different species (see the criticism of barcoding below). 2) The differences between species rely on special trait qualities, whereas intraspecific differences have different trait qualities. Is there any type of trait that marks a species as a species, as in chemistry, where the number of protons determines the identity of a specific element? Can we simply choose a morphological trait (e.g., the number of limbs) and divide the animal kingdom accordingly into groups in a law-like manner, similar to a chemist compiling a table of elements? This approach has certainly been attempted in the past in taxonomy research (Chen, 2002). The modern response,
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Werner Kunz Do Species Exist?
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Werner Kunz Do Species Exist? Princ
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Contents Foreword XI Preface XV Col
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5.5 Are Carrion Crow and Hooded Cro
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7.8 Gene Trees are not Species Tree
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XIIj Foreword formed out in various
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Preface What is water? You would no
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Color Plates Do Species Exist? Prin
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Color PlatesjXIX
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Color PlatesjXXI
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Color PlatesjXXIII
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Color PlatesjXXV
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Color PlatesjXXVII
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Color PlatesjXXIX
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Color PlatesjXXXI
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Color PlatesjXXXIII
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230j Scientific Terms Autapomorphy
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232j Scientific Terms Gene-flow com
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234j Scientific Terms Monophylum A
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236j Scientific Terms barriers prev
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238j Scientific Terms Universal Uni
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2j Introduction would be sufficient
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4j Introduction A number of the col
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6j 1 Are Species Constructs of the
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2 Why is there a Species Problem? 2
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2.2 Can Species be Defined and Deli
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2.3 What Makes Biological Species s
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These conclusions indeed sound para
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2.4 Species: To Exist, or not to Ex
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If the species concept is, or even
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2.6 The Constant Change in Evolutio
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2.7 Can a Scientist Work with a Spe
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2.8 The Species as an Intuitive Con
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Contrary to this, it is always auto
Page 70 and 71: 2.9 Taxonomy s Status as a Soft or
Page 72 and 73: 2.11 Sociological Consequences of a
Page 74 and 75: Races are not populations of indivi
Page 76 and 77: 2.12 Species Pluralism: How Many Sp
Page 78 and 79: 2.12 Species Pluralism: How Many Sp
Page 80 and 81: 2.13 It is One Thing to Identify a
Page 82 and 83: 2.14 The Dualism of the Species Con
Page 84 and 85: 2.14 The Dualism of the Species Con
Page 86 and 87: 3 Is the Biological Species a Class
Page 88 and 89: 3.2 Class Formation and Relational
Page 90 and 91: 3.3 Is the Biological Species a Uni
Page 92 and 93: 3.4 The Difference Between a Group
Page 94 and 95: 3.4 The Difference Between a Group
Page 96 and 97: 3.5 Artificial Classes and Natural
Page 98 and 99: 3.6 The Biological Species Cannot b
Page 100 and 101: 3.7 The Biological Species as a Hom
Page 102 and 103: 3.9 The Linnaean System is Based on
Page 104 and 105: 3.10 Comparison of the System of Or
Page 106 and 107: 3.11 The Relational Properties of t
Page 108 and 109: 68j 4 What are Traits in Taxonomy?
Page 134 and 135: 94j 5 Diversity within the Species:
Page 140 and 141: 100j 5 Diversity within the Species
Page 168 and 169: 128j 6 Biological Species as a Gene
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130j 6 Biological Species as a Gene
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7 The Cohesion of Organisms Through
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7.2 The Problem of Displaying the P
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level of organisms with the next-hi
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Figure 7.4 Classification of organi
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7.4 How is a Cladistic Bifurcation
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7.5 Descent is not the Same Thing a
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Figure 7.7 Paraphyletic classificat
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7.6 Why are Paraphyla used Despite
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Figure 7.8 Phylogenetic trees at di
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Figure 7.10 Gene trees are not spec
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7.9 The Concepts of Monophyly and P
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7.10 Paraphyly and Anagenesis are M
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7.11 The Cladistic Bifurcation of a
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7.12 The Phylocode j213 Thus, if th
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7.12 The Phylocode j215 Figure 7.13
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8 Outlook What is a species? The an
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Index a aberration 96 Acinonyx juba
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essence 45, 46, 56, 58, 64, 65 esse
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Old World Ruddy Duck 150 Old World
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v vague boundaries 21, 184 vaguenes
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