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9 Cards in this Set
- Front
- Back
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who coined the term coevolution
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erlich and raven
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janzen 1980 definition
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evolutionary change in a trait of the individuals in one population in response to a trait of the individuals of a second population, followed by an evolutionary response by the second population to the change in the first
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Reciprocal evolutionary change
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driving force behind diversification.
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how does it work
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Evolution of plant chemical defences releases animals from herbivory and they increase in abundance, evolve and become counter adapted to the plant defence. Changes in attack and defence allow them to move into new adaptive zones within which evolutionary divergence occurs.
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geographical mosaic theory
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coevolution driven by geographical variation in spp interactions. Selection mosaic- different evo outcomes in different populations. Coevolutionary hotspot created when interacting spp impose selection on each other and its reciprocal.
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what is wrong with many coevolution studies
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Many studies short term local studies, cannot accurately test theory, ignore ecological dynamics and geographical variation of populations (thomspon 1999).
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red squirrels crossbills and pine cones
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Red squirrels common in rocky mountain range, superior competitors for seeds in pine cones, crossbills uncommon. Evolution of cone structure driven by selection frm squirrels, crossbills adapt to average cone size. Red squirrels absent in some mtn ranges, crossbills more abundant. Pine cones have lost defences against squirrels, crossbills primary consumers, exert selection. Favoured evolution of crossbills with larger bills. Continual arms race. Same found in south hills, cypress hills, newfoundland black spruce, led to evolution of new species of crossbill, distinct from South Hills spp. Geographic variation- geographic mosaic model.
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Darwin 1862
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evolution of tongue length and corolla depth, driven by natural selection due to benefits flower and insect derived. Star orchid of Madagascar, spur of 11. 3 inches, 1903, discovered pollinator Xanthopan morganii praedicta. Alternative hypothesis- L.T. Wasserthal- longer tongues avoidance of predators, hawkmoths swing hovering behaviour, couldn’t insert tongue into long tubed tobacco flowers, behaviour induced by predator stimuli. They are generalist feeders, exploit small shallow flowers, spiders pursue shivering/ hovering moths. Tongues- adaptions against predators. Refuted based on lack of evidence (Nilsson 1998). Jermy (1999)- no mutual dependence btw two spp, nilsson’s arguments made on speculation, wasserthal’s explanation more plausible.
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Euglossine bees in panama
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forage at any flower from which they can extract nectar, only one bee with long tongue being specialist on longer tubes. Those with longer tongues visited higher number of nectar hosts, flowers with longer tubes, fewer visitors. Long tubes exclude shrot tongued bees, provide more nectar to longer tongued bees, longer tongue bees include them in their daily traplines, they didn’t evolve through coevolution, but due to comp with flowers for inclusion on trapline.
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