Transcript lecture14
Selection and community interaction Selection: composite of the forces that limit the reproductive success of the genotype Fitness: comparative ability of a genotype to withstand selection Frequency dependent selection: selection against a gene depends on its frequency within the population Batesian mimicry Batesian mimicry: a palatable species mimics an unpalatable species and gains protection from predation Monarch butterfly (distasteful) Viceroy butterfly (tasty) Muellerian mimicry Muellerian mimicry: 2+ unpalatable species share similar aposematic coloration both species distasteful Selection & industrial melanism Peppered moth http://web.nmsu.edu/~wboeckle/biston.html Departure from highest fitness it is quite as dangerous to be conspicuously above a certain standard of organic excellence as it is to be conspicuously below the standard Bumpus 1899 Departure from highest fitness Human birth weight Selection modes - stabilizing Selection modes - directional Selection modes - disruptive Community interactions If some of these many species become modified and improved, others will have to be improved in a corresponding degree or they will be exterminated Darwin 1859 Community interactions Red Queen hypothesis organisms have to evolve as fast as they can just to stay in the same place Through the looking glass Lewis Carroll "Now, here, you see, it takes all the running you can do, to keep in the same place." Community interactions species B species A - 0 + predation commensalism 0 amensalism neutralism - competition + mutualism Community interactions Competition - two groups depend on same limited resource so each group leads to a demonstrable reduction in numbers of the other Community interactions Resource partitioning - species minimize harmful effects of direct competition by using different aspects of their common environment Character displacement measurable phenotypic differences accompany resource partitioning Community interactions Competitive exclusion two groups cannot coexist in the same ecological niche Community interactions Owing to the high geometrical rate of increase of all organic beings, each area is already fully stocked with inhabitants; and it follows from this, that as the favored forms increase in number, so generally will the less favored decrease and become rare Darwin, 1859 Coevolution Coevolution: evolutionary changes in 1+ species in response to changes in other species in the same community -can lead to an evolutionary ‘arms race’ Coevolution Coevolution Cospeciation: speciation process that occurs in 2 interacting species simultaneously