Principios de Taxonomia

Recommendations

Info

132j 6 Biological Species as a Gene-Flow Community Figure 6.2 Isolation by distance (a) and ring species (b). To understand the cohesion among the individuals of a gene flow community, it is sufficient to consider only the immediate neighbors. Race A is connected with B, and both races exchange alleles. The same is true for B and C, but the geographically distant races C and A do not necessarily exchange alleles and may not necessarily be cross-fertile. Many alleles that arose in A may never be observed in C and vice versa. A ring species (b) is not a taxonomic peculiarity, not to mention a kind of super-species. It is nothing more than the frequently observed phenomenon of isolation by distance, distinguished only by the peculiarity that distant races encounter each other again under natural conditions. Reduction in gene flow has consequences. Genetic compatibility between distant races of a species may become reduced. Although studies on this subject are few, it is likely that the crossing of distant individuals of a species in many cases does not result in completely viable and fertile offspring, at least in the case of large geographical distances (Ford, 1954; Irwin et al., 2005). This means that distant organisms of a species do not belong to a potential reproductive community. A potential reproductive community is made up of distant or isolated groups of individuals that could successfully reproduce together if they were to encounter each other (Mayr, 2000) (see below). For this reason, the traditional term reproductive community (Mayr, 2000) does not reflect the nature of the group connection as it is defined in this book; the term reproductive community conveys the impression that all members of this community reproduce with each other, at least in the course of evolutionary time. This assumption, however, often does not hold. In some animals and plants, geographically distant organisms of a species never exchange alleles, even though they are considered to belong to the same gene-flow community. However, distant organisms of a species are still connected by uninterrupted gene flow, even when they have lost their reproductive compatibility (Figure 2.7). For this reason, in this book, the more precise term gene-flow community replaces the conventional term reproductive community (Mayr, 2000).
6.4 A Species Concept Requires Both Connection and Delimitationj133 The logic behind this consideration is as follows: local adaptation requires the alteration of many different traits that are genetically determined. These genes must function concertedly in the organism. If two organisms with very different adaptive traits crossbreed with each other, the genes of these adaptive traits will lose their chromosomal linkage when they recombine. Consequently, the offspring of such crosses should be intermediate with respect to their adaptive traits. It is unlikely that these hybrids would be fit enough to compete successfully with pure-bred organisms, at least not in those cases where the local adaptations involve an array of cooperating genes that would be disrupted by recombination. Despite this loss of reproductive connection, however, such distant populations are connected via stepwise gene flow. They are joined via intermediate organisms in the connecting regions (regions of clinal transition). Thus, all organisms form a common gene-flow community, even if individual alleles do not migrate over the entire distribution area of the species. The gene-flow community also includes distant populations whose members have even lost their potential reproductive compatibility. The distant organisms in a gene-flow community are only incrementally connected to each other; for example, a human s foot is connected to his head, without the foot being in direct contact with the head. 6.4 A Species Concept Requires Both Connection and Delimitation Taxonomy is the science of group connection; however, groups are not only defined by connection of the conspecific individuals but also by delimitation against unrelated individuals. Those characteristics that connect organisms as groups and separate them from other organisms define a natural taxon (Mishler and Brandon, 1987; Ereshefsky, 1999). In contrast to most other species concepts, the concept of the geneflow community satisfies both conditions. Gene-flow connection includes both connection and delimitation. The organisms of a gene-flow community are joined by the exchange of genes and delimited by the barriers to this gene flow. Most other species concepts are incomplete, because they do not contain the criteria of delimitation. The barriers between two gene-flow communities inhibit gene flow and prevent (or allow only to a limited extent) gene flow from one species into another. Barriers such as these are natural boundaries between two groups, not human-made delimitations. This point is not changed by the discovery that gene-flow communities are, in many cases, leaky. The fact that boundaries are vague does not contradict the fact that boundaries exist. A partially permeable boundary is still a boundary (Figure 2.7). Several other species concepts include only the criteria for inclusion; they do not tell us by what criteria one species is delimited from another. A gene-flow community is demarcated by barriers; a descent community is not (Chapter 7). While a descent community does have a real (genealogical) connection, the line between species is not defined by descent, but is set by artificial borderlines (Mallet, 1995).
Page 2 and 3:
Werner Kunz Do Species Exist?
Page 4 and 5:
Werner Kunz Do Species Exist? Princ
Page 6 and 7:
Contents Foreword XI Preface XV Col
Page 8 and 9:
5.5 Are Carrion Crow and Hooded Cro
Page 10 and 11:
7.8 Gene Trees are not Species Tree
Page 12 and 13:
XIIj Foreword formed out in various
Page 14 and 15:
Preface What is water? You would no
Page 16 and 17:
Color Plates Do Species Exist? Prin
Page 18 and 19:
Color PlatesjXIX
Page 20 and 21:
Color PlatesjXXI
Page 22 and 23:
Color PlatesjXXIII
Page 24 and 25:
Color PlatesjXXV
Page 26 and 27:
Color PlatesjXXVII
Page 28 and 29:
Color PlatesjXXIX
Page 30 and 31:
Color PlatesjXXXI
Page 32 and 33:
Color PlatesjXXXIII
Page 34 and 35:
230j Scientific Terms Autapomorphy
Page 36 and 37:
232j Scientific Terms Gene-flow com
Page 38 and 39:
234j Scientific Terms Monophylum A
Page 40 and 41:
236j Scientific Terms barriers prev
Page 42 and 43:
238j Scientific Terms Universal Uni
Page 44 and 45:
2j Introduction would be sufficient
Page 46 and 47:
4j Introduction A number of the col
Page 48 and 49:
6j 1 Are Species Constructs of the
Page 50 and 51:
2 Why is there a Species Problem? 2
Page 52 and 53:
2.2 Can Species be Defined and Deli
Page 54 and 55:
2.3 What Makes Biological Species s
Page 56 and 57:
These conclusions indeed sound para
Page 58 and 59:
2.4 Species: To Exist, or not to Ex
Page 60 and 61:
If the species concept is, or even
Page 62 and 63:
2.6 The Constant Change in Evolutio
Page 64 and 65:
2.7 Can a Scientist Work with a Spe
Page 66 and 67:
2.8 The Species as an Intuitive Con
Page 68 and 69:
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 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123: 82j 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
Page 222 and 223:
182j 6 Biological Species as a Gene
Page 224 and 225:
184j 6 Biological Species as a Gene
Page 226 and 227:
7 The Cohesion of Organisms Through
Page 228 and 229:
7.2 The Problem of Displaying the P
Page 230 and 231:
level of organisms with the next-hi
Page 232 and 233:
Figure 7.4 Classification of organi
Page 234 and 235:
7.4 How is a Cladistic Bifurcation
Page 236 and 237:
7.5 Descent is not the Same Thing a
Page 238 and 239:
Figure 7.7 Paraphyletic classificat
Page 240 and 241:
7.6 Why are Paraphyla used Despite
Page 242 and 243:
Figure 7.8 Phylogenetic trees at di
Page 244 and 245:
Figure 7.10 Gene trees are not spec
Page 246 and 247:
7.9 The Concepts of Monophyly and P
Page 248 and 249:
7.10 Paraphyly and Anagenesis are M
Page 250 and 251:
7.11 The Cladistic Bifurcation of a
Page 252 and 253:
7.12 The Phylocode j213 Thus, if th
Page 254 and 255:
7.12 The Phylocode j215 Figure 7.13
Page 256 and 257:
8 Outlook What is a species? The an
Page 258 and 259:
Index a aberration 96 Acinonyx juba
Page 260 and 261:
essence 45, 46, 56, 58, 64, 65 esse
Page 262 and 263:
Old World Ruddy Duck 150 Old World
Page 264:
v vague boundaries 21, 184 vaguenes
show all

Principios de Taxonomia

Create successful ePaper yourself

Delete template?

Save as template?