Patterns of Evolution

Looking for Patterns We’ve examined homologous and vestigial structures We’ve examined genetic drift and the founder effect Can we recognize larger patterns of evolution for new species?

Before we start… Niche - The role or function of an organism or species in an ecosystem

Adaptive Radiation Adaptive Radiation: Relatively fast evolution of one species into a number of distinct but related species Each new species fills a previously empty ecological niche

Example: Darwin’s Finches One species millions of years ago It has evolved into 13 separate species Assume an initial medium-sized, medium-beaked species in South America Competition on the mainland (S. America) probably drove stabilizing selection of these traits

Example: Darwin’s Finches On the island, there was much less competition from other birds Their only competition was from each other The islands already had insects and plant species, but relatively few predators When the finches arrived, they found new food sources to exploit

Example: Darwin’s Finches A finch with a larger beak would not face competition from the medium-beaked birds, and could exploit the new food source A finch that could eat insects would not face competition from a finch that ate nuts We now know of 7 seed-eating species 6 insect-eating species

Example: African Rift Lakes Another powerful example of adaptive radiation Several lakes that are isolated from each other Each lake has hundreds of unique species, all descended from a very few Each species fills a unique niche, feeding on something different

Example: African Rift Lakes Lake Malawi, for example, has over one thousand species of African cichlids (fish), all descended from a few initial species The Toronto Zoo: recreation of Lake Victoria

Adaptive Radiation Review Start with one, or a few, species in a new environment This species adapts to the new environment by filling different niches By filling different niches, each new species has less competition for resources Leads to many new species evolving

Ecological Roles There are so many different roles to fill in any ecosystem Consumers and producers, for example Each role must be filled by one or more species

Example: Herbivores Herbivores come in a huge variety of shapes and sizes Natural selection has directed their evolution into many different species

Divergent Evolution Divergent Evolution: the large-scale evolution of a group into many different species

Example: Rodents Rodents are the largest group of mammals, many of them found here in Ontario They all descended from a common ancestor They underwent adaptive radiation in order to fill different ecological roles Rodents provide an excellent example of divergent evolution

Red Squirrels and Flying Squirrels For example: Red squirrels: active during the day Flying squirrels: similar niche, but active at night

Porcupines and Beavers Porcupines climb trees to eat bark and twigs Beavers cut down trees to eat bark and twigs

Outcomes of Divergent Evolution Competition between species is minimized as new species fill unique ecological niches New species continue to evolve until most available resources are used

Analogous Features Remember: Analogous features? What causes analogous features to evolve?

Convergent Evolution Convergent Evolution: occurs when two different species evolve to fill similar ecological niches distantly related species develop similar traits in order to do so

Convergent Evolution Why would a species fill a similar niche as another? Wouldn’t this mean they’re now competing with each other? The best examples of convergent evolution occur in different geographic regions

Convergent Evolution in Plants Cacti: evolved in South American deserts Euphorbia: evolved in African and Asian deserts - Both have evolved features to deal with desert conditions

Why are they Convergent? Although they look similar and fill similar niches, there are differences: Cacti: spikes evolved spikes from leaves Euphorbia: evolved spikes from the stem

Example: Sharks and Dolphins Both have evolved similar features, and fill similar niches (high speed carnivores) Sharks evolved from primitive fish Dolphins evolved from land mammals

Convergent Evolution and Analogous Features What’s the difference? Convergent evolution leads to analogous features

Outcomes of Convergent Evolution Natural Selection favours the evolution of similar traits in similar environments While some features will converge in function, each species will retain other features that indicate their distinct evolutionary past

Co-evolution Co-evolution: A process in which a species evolves in response to the evolution of another species

Co-evolution Plants evolve hard shells to prevent animals from eating their seeds Herbivores evolve more powerful jaws and beaks to break the shells This is known as an evolutionary arms race

Example: Coconut Crab

Effects of Co-evolution One species may become dependent on the other So a threat to one species can also be a threat to the other

Co-evolution and Symbiotic Relationships Coevolution can be best seen in symbiotic relationships Darwin’s Orchid and the Madagascan Hawk Moth Each has become so dependent on the other – for food and for pollination – that extinction of one would mean extinction for the other

Honeyguides

Convergent, Divergent or Co-evolution?!

Convergent, Divergent or Co-evolution?!

Convergent, Divergent or Co-evolution?!

Convergent, Divergent or Co-evolution?!

Convergent, Divergent or Co-evolution?!

Convergent, Divergent or Co-evolution?!

Homework PG. 345 #1,2,7