Patterns of Evolution
Jan 19, 2016
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