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

1. Competition between species is minimized as new species fill unique ecological niches

2. 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

1) Natural Selection favours the evolution of similar traits in similar environments

2) 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