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Reading - Tuesday & Thursday lectures chapter 20: Coevolution & Mutualism (p. 381-383; 389-390) chapter 21: Community Structure (p. 399-407) chapter 22: Community Development (entire chapter) -lots of photos easy reading. chapter 23: Biodiversity Co-evolution of Competitors Ricklefs 2001: chapter 20 How do species avoid competition? Evolve different niches. This would be favoured by natural selection. Interacting populations evolve in response to each other • European rabbits introduced into Australia in 1859 became a major pest • To decrease populations, introduced the myxoma virus in 1950… epidemic of myxomatosis transmitted by arthropods Myxoma virus seen with an electron microscope Initially 99.8% of rabbits killed, but mortality declined with additional treatments…some rabbits had genetic resistance Ricklefs 2001 Fig. 20.1 Co-evolution: each species influences the evolution of all species with which it interacts • rabbit-virus system left on its own would have resulted in an equilibrium, but…various strains used as control agents. Species avoid competition by evolving different niches Niches of 2 species % 5 7 Food Size (mm) In evolutionary time, the populations (species)diverge to avoid competition. 5 7 Reduction of niche overlap allows species to coexist without severe competition. 3 9 Food Size (mm) Conditions favouring this... Species #1 Species #2 Allopatry Allopatry Sympatry Competition can only occur in sympatry Ricklefs 2001, Fig. 20.12 Character traits of two closely related species differ more in sympatric regions than in allopatric regions of their geographic ranges. A common example of character displacement is the size & shape of a food gathering a apparatus Morphological changes