Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Storage effect wikipedia , lookup
Occupancy–abundance relationship wikipedia , lookup
Biodiversity action plan wikipedia , lookup
Introduced species wikipedia , lookup
Island restoration wikipedia , lookup
Latitudinal gradients in species diversity wikipedia , lookup
Molecular ecology wikipedia , lookup
Theoretical ecology wikipedia , lookup
LECTURE 15 COEVOLUTION AND MUTUALISM pg. 381-383; 385-386; 389-396 MAJOR CONCEPTS 1) Coevolution involves mutual evolutionary responses by interacting populations. 2) Diffuse coevolution may be more common than strict coevolution. 3) Constraints restrict evolution of strict mutualisms. 4) Coevolution in plant-pathogen systems reveals genotype-genotype interactions and involves a gene-for-gene concept and an ‘evolutionary arms race’. 5) Evidence for coevolution can arise from inference, circumstantial evidence, or experimentation. 6) Mutualists have complementary functions; they involve trophic, defensive, and dispersive functions. Types of pairwise interspecific interactions Mutualism (+/+) Predation (+/-) Competition (-/-) Commensalism (+/0) Amensalism (-/0) Fluidity in type of relationship Symbioses Intimate, often obligatory association of two species Usually involving coevolution May be parasitic or mutualistic Coevolution Interacting species evolve in response to each other Each species acts as selective agent on other species Traits of each species affect fitness of other species Traits have genetic basis May be mutualistic or antagonistic Strict coevolution Limited to pair of species Specialized response May be rare and limited to very strong interactions Diffuse coevolution Response to many other species Generalized response Gene-for-gene concept and evolutionary ‘arms race’ Occurs in plant-pathogen and host-parasite systems Based on single gene conferring resistance to host or virulence to pathogen Back and forth selection between genotype of host and genotype of pathogen Interaction escalates as more and more traits are added Evidence for coevolution Inference from closely related herbivores feeding on closely related plants Suggests long evolutionary history of interaction Based on parallel phylogenetic relationships Experimentation Circumstantial evidence e.g. character displacement of competing species when in sympatry but not when in allopatry; infer that competition drives coevolution Mutualism Two species specialized to perform positive function for each other Trophic: partners complement food/nutrients for each other Defensive: species receive food and/or shelter in return for defending against natural enemies Dispersive: animal vectors move pollen or seeds in return for food rewards Pollination examples Seed dispersal examples Mixed systems Yucca and its pollinator moth acting as both mutualist and seed predator When is it coevolution? Preadaptation: some adaptations present before establishment of mutualism Some adaptations occur in close relatives that are not mutualists Constraints on evolution of strict mutualism Community diversity diffuses selection from single species. Changes in species’ ranges or disturbance change selection over time/space. Genetic complexities cause uneven rates of evolution between mutualists.