Historical Biogeography. Historical Biogeography. Systematics

Transcription

1 Historical Biogeography I. Definitions II. Fossils: problems with fossil record why fossils are important III. Phylogeny IV. Phenetics VI. Phylogenetic Classification Disjunctions debunked: Examples VII. Evolutionary Systematics vs. Phylogenetic Systematics VIII. Cladistics Assumptions Examples Criticisms Historical Biogeography is concerned with relationships among and between species the true genetic relationship of taxa. Systematics Classification of organisms into hierarchical groups (or taxa) that summarize patterns of similarities 1

2 Fossils are important because.. can give ages of taxon can document extinction from an area, or of a major group can aid in determining primitive features and evolutionary trends can give an idea of the diversity of early life Problems with the fossil record Known fossil record is incomplete animals lacking hard tissue and plants w/o durable chemicals in their cell walls are poorly represented fossil record is biased in favor of easily preserved organisms Fossils that are preserved may have actually been side branches of evolutionary tree that became extinct w/o giving rise to new species 2

3 Phylogeny the evolutionary relationship between an ancestor and all known descendants Three basic assumptions: evolution has occurred patterns of inheritance exist at least some features may be used to show relationships between taxa and determine evolutionary sequence Phenetics: Overall similarity of organisms Also called numerical taxonomy, Phenetics classifies organisms on the basis of overall morphological or genetic similarity. This mainly involves observable similarities and differences irrespective of whether or not the organisms are related LANTHANOTUS HELODERMATIDAE NOT A MONOPHYLETIC GROUP VARANIDAE 3

4 Old world: 8 GENERA g. Hystrix, g. Atherus New world: THREE GENERA g. Coendou, g. Erethizon NOT A MONOPHYLETIC GROUP

5 Taxonomy: naming things based on similarities and differences 1945 G.G. Simpson mammals 1960s angiosperms phylogeny Phylogeny of mammals 5

6 Evolutionary Systematics The method of reconstructing the evolutionary history (phylogeny) of a taxon by analyzing the evolution of major features along with the distribution of both shared primitive and shared derived characteristics 6

7 Some argue: Problems with evolutionary systematics Too much interpretation Statements too broad Not enough falsifiability Cladistics the method of reconstructing evolutionary history (phylogeny) of a taxon by identifying the branching sequences of differentiation through analysis of shared (nested) derived character states. Evolutionary systematics Cladistics 7

8 Assumptions of Cladistics speciation is allopatric in the majority of cases features analyzed are homologous parallel evolution of individual characteristics is rare organisms with derived characteristics generally do not rise to more primitive ones. Cladograms 8

9 Criticisms abound Convergent evolution Allopatric assumption Interspecific hybridization possible Dichotomous nature is too restrictive 9

10 Vicariance biogeography: study of distribution patterns of organisms that attempt to reconstruct historical events through cladistic methods (little or no attention to dispersal capabilities or ecological properties) Vicariants: two disjunct species that are most closely related to each other and that are assumed to have been created when an initial range of the ancestor was split by some historic event 10

11 Persistent issues Stochastic elements Assuming common patterns have common causes Stability of ranges 11

12 Other evolutionary questions 12

13 Order: Chelonia Family: Testudinidae Genus: Gopherus Species: Gopherus agassizii Monachus schauinslandi (monk seals) Cladistics or evolutionary systematics? 13

14 A D C B E What can you say? 14