Contents xv 



Species Swarms in Fishes 220 



Sibling Species of Alpine Butterflies 220 



The Galapagos Finches 224 

 Host Preference in Parasitic Organisms 229 

 Discussion of Observed Patterns 230 



Geographic Variation in Selection Pressures 280 

 Exchange of Genetic Information 234 

 Cessation of Gene Exchange 236 

 Isolation 237 



Fusion of Populations 238 



Meeting with No Gene Exchange 238 



Limited Gene Exchange 240 



Selection against Hybrids 242 

 Patterns of Differentiation 243 



The Galapagos Finches and African Cichlids 243 



Sibling Butterfly Species 244 



Differentiation of Parasites 245 

 Allopatric Speciation 247 

 Sympatric Speciation 247 

 Summary 248 

 References 249 



Chapter 11 ( Major Patterns of Variation 250 



Extinction and Biogeographic Provincialism 251 



Extinction 251 



Biogeographic Provincialism 256 



Reticulate Variation 258 

 The Fossil Record 258 



Modes of Evolution 259 



Rates of Evolution 261 

 Major Evolutionary Patterns 264 



Adaptive Radiation 264 



Differing Rates of Evolution and Adaptive Zones 266 



Competition 270 



Convergence 270 

 Higher Categories 272 

 Evolutionary Trends 274 



Increase in Size 274 



Increase in Complexity 275 

 Summary 276 

 References 277 



