Download 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