Evolving to Invade

Marcia AngleLiz SchultheisTomomi Suwa

A change in a trait of a population over time (generations). e.g.

Hair colorDisease resistanceChemical compoundTail length Fr

eque

ncy

Beak Depth

Large Ground FinchGeospiza magnirostris

What is evolution?

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)

# off

sprin

g

Beak Size

Individual birds

Evolution of increased beak

size!

Where does variation come from? Mutation Recombinatio

n Migration

Evolution by Natural Selection

evolution.berkeley.eduEvolution of body

color!

Trait: body colorSelection agent: birds

At what level does evolution occur?

• Individual• Population (a group of interbreeding individuals)• Species (a group of potentially interbreeding

individuals – usually includes many populations)

• Individual• Population (a group of interbreeding individuals)• Species (a group of potentially interbreeding

individuals – usually includes many populations)

At what level does evolution occur?

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)

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

Discussion: how will evolution affect a new invasive species?

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: 10987654321

0 1 2 3 4 5

Num

ber o

f ind

ivid

uals

in p

opul

atio

n

Trait Value (# of Velcro pieces)

Graph ___ ___

Selection on Trait

Seed predator 1

Game: Evolution in the native range1 A 1 B 1 D

Average trait =

2.5 2

1 C

3

Selection on Trait

Seed predator 2

2 A 2 B 2 D

Average trait =

3.4 2

2 C

Game: Evolution in the invasive range

2

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

How did evolution affect our invasive species?