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Systematics • Study of pattern and processes associated with biological diversity and diversification • Taxonomy – study of classification (hierarchy, naming Diversity) • Phylogenetics – study of evolutionary relationships between species and groups (Diversification) Species Concept • • • • Biological species concept – definition All species concepts have limitations Classification is a human construct Importance of defining a species Phylogenetics • Homologies Phylogenetics • Convergence Phylogenetics • Apomorphy – derived trait • Pleisomorphy – primitive trait Subspecies Populations – coat color of subspecies match local substrate Evolution • Macroevolution – lineages of species and major groups, changes in diversity • Microevolution – changes in species, short and longer term; contemporary species • Not segregated; difference in scale Macroevolution • Evolution does not proceed at a uniform rate • Bradytelic – lineages changing at slower rates than typical • Tachytelitic – faster rates than typical • Horotelic - typical Punctuated Equilibrium • Proposed abrupt changes in lineages following long periods of stasis • Mass extinctions adaptive radiation • Does not contradict natural selection; still a key process in punctuated equilibrium • Gradualism also occurs Gradualism Macroevolution • Rapid Radiation not always with mass extinctions • Cambrian Explosion • Mass extinctions may not be random • Species selection (large sp. end Cretacrous Mechanisms of Evolution • • • • Mutation Genetic drift Gene flow Natural selection Adaptation and Range Expansion • Range of a species includes range of populations • Populations on edge of range may adapt to a limiting condition • Some species may not have capacity to adapt morphologically, physiologically, or behaviorally peripheral conditions Adaptation and Gene Flow • Gene flow changes allele frequencies of populations • Can, however, homogenize gene pool through exchanges between populations • Restricts further adaptation to local conditions • Other limitations to adaptation limit range expansion (not all species have wide ranges) • Distribution of karyotypes of Palestine mole rat (Nannospalax ehrenbergei) • Lack of overlap reduced gene flow Geographic Variation • Geographic isolation facilitates genetic drift and natural selection • Impedes gene flow • Genetic drift – isolation of small populations • Founder effect • Divergence of monarch flycatcher • Founder effect – colonizers of islands created gene pool for each Allopatric Speciation • Speciation resulting from geographic isolation • Broader definition applying environmental and physical barriers • Dispersal barriers in heterogeneous environment • Geographic isolation after dispersing to another habitat (e.g., island to island) Allopatric Speciation: Vicariance Endemic Mad. All in Family Ranidae Sympatric Speciation and Adaptive Radiation Extinction • Changing of the guard (dominance in given niches) • Cephalopod molluscs teleost fishes • Dinosaurs & reptiles birds and mammals • Species are eliminated or supplanted in their lineages Extinction • Probability of extinction independent of evolutionary age • Is related to taxonomic and ecological status • Small, herbivorous mammals lower extinction rates than large carnivores • Same true for marine invertebrates • Ties back to point about more niches for small organisms? Extinction of Species • Primary causal mechanisms for extinction • Reduction of population sizes • Habitat changes What pushes numbers of a species down to the point where it is pushed to extinction? Fossil Record and Mass Extinctions • Many events, many hypotheses • Pleistocene – megafauna of N. and S. Amer. 8,000 – 15,000 yr ago • Once thought to be climate change from recession of glaciers • More evidence that human colonization was a major contributor Fossil Record and Mass Extinctions • Permian-Triassic 250 mya • 96% of marine species lost • Causal Agent? – Climate change but how – Glaciation – Global warming – Massive volcanic activity – Continental drift > 100 Species 4 - 5 Species Seabed in P-T before and after mass extinction Species Selection • What leads to species surviving and radiating after extinctions? • Appear to be key traits • Remaining species in range also a factor • Expansion of mammals after K-T extinction (65 mya) • Filled niches left behind by dinosaurs and reptiles pushed to extinction Placental Mammals • Found globally in fossil record • Few extant species in N. & S. America • Australian marsupials • Why? • Adaptive radiation in absence of dominant reptiles • Later natural and human intro of placentals Dispersal Advantage Replacement