Marcia Angle
Liz Schultheis
Tomomi Suwa
Evolving to
Invade
What is evolution?
A change in a trait of a population over
time (generations).
e.g.
Hair color
Disease resistance
Chemical compound
Tail length
Frequency

Beak Depth
Large Ground Finch
Geospiza magnirostris
For evolution by natural selection
to occur we need…


Variation in the trait
The trait has a genetic basis – is passed on to
offspring
Some individual produce more offspring than others
(i.e. Natural Selection)
Individual birds
# offspring

Evolution of
increased beak size!
Beak Size
Where does variation come from?



Mutation
Recombination
Migration
Evolution by
Natural Selection
Trait: body color
Selection agent: birds
Evolution of body color!
evolution.berkeley.edu
At what level does evolution occur?
•
•
•
Individual
Population (a group of interbreeding individuals)
Species (a group of potentially interbreeding
individuals – usually includes many populations)
At what level does evolution occur?
•
•
•
Individual
Population (a group of interbreeding individuals)
Species (a group of potentially interbreeding
individuals – usually includes many populations)
What is an invasive species?
Introduced from another country by people
 Grows and takes over an area



Can harm native species
Cost people a lot of time and money
“Nothing in biology makes sense except in the
light of evolution.”
-Theodosius Dobzhansky (1973)
Discussion: how will evolution affect a new
invasive species?
 Think back to the elements
necessary for evolution to occur:



Variation
Trait is genetic and passed down from parents to offspring
Selection on the trait. Survival and ability to reproduce depends
on trait value.
Discussion: how will evolution affect a new
invasive species?




There might be low genetic variation at first
But multiple introduction increases genetic variation
Invaders experience new selection in introduced range
Invaders evolve to adapt to a new environment
Game: understanding evolution in a
new invasive species
Our species – purple
loosetrife
 Individual plants have
seeds with different
numbers of barbs,
which predators can
use to collect the seeds

Trait Variation
Game:
Number of individuals in population
Graph ___ ___
10
9
8
7
6
5
4
3
2
1
0
1
2
3
4
Trait Value
(# of Velcro pieces)
5
Selection on Trait
Seed
predator 1
Game: Evolution in the native range
1
Average
trait =
2.5
1
1
A
2
C
B
1
3
D
Selection on Trait
Seed
predator 2
Game: Evolution in the invasive range
2
Average
trait =
3.4
2
2
A
2
C
B
2
2
D
How did evolution affect our invasive species?




Low genetic variation at first in invasive range
Multiple introductions increased genetic variation
Invader experienced new type of selection in
introduced range (from different type of predator)
Invader evolved and adapted to a new environment