Biological Invasions and

Herpetology

4/18/13

Chris Thawley

What are some invasive species?

http://news.discovery.com/animals/videos/animals-jumping-carp-attack-explained.htm

What is an “Invasive” species?

• Outside its native

range

• Transported by

humans

• Destructive?

• Detrimental?

Exotic? Non-native? Alien?

Why do we care?

• Economic consequences:– >$120 BILLION/year

– Agriculture, forestry, healthcare, fisheries

– Cost of control

• Ecological consequences:– 2nd leading threat to

biodiversity

– Capable of disrupting whole communities

Case Study: Burmese Python

• Native to SE Asia

• Introduced to S.

Florida and ENP

• Probably due to

Hurricane Andrew

• Expanding

population

Python Effects on Community

• Find lots of

incidental past

datasets to study

effects

– No one was

looking to study

effects before

they knew about

problem!

Burmese Pythons in FL

• Pythons

tracked via

radiotransmitter

• Found with

dogs and on

roads

• Very difficult to

count/study in

ENP

Python Patterns

A little more complexity…

• Rodents may decline

due to python

predation

– BUT may prosper

due to removal of

predators

• Pythons kept in check

in native range by

predation

– Prospects in FL?

Common Characteristics of

Invasive Species

• Generalists

• Quick reproduction/generation time

• Lots of offspring

• Mature quickly

• Less related to native taxa (Strauss et al 2006)

• Aggressive competitors

• Disperse easily

Which groups of

herps might be

most invasive and

why?

How do Invasions Spread?

• Stowaways

– Cargo

– Vehicles

– People

– Ballast Water

– Feces

• Pet Trade

• Biocontrol Agents

• Deliberate Introduction

Difficulties Facing Invaders

Many factors working against successful

invasions

• Low density

– Hard to find mate

– Stochastic effects

• Low genetic diversity

– Bottleneck

– Inbreeding

http://eattheinvaders.org/

Brown Anole Case Study

• Jason Kolbe (Kolbe et al 2004)

• Brown anole invasion of SE US

Brown Anole Invasion

• Native to Caribbean

• Generalist Lizard

• Relative of Green

Anole

• More

aggressive/larger

• Displace native

anoles

Brown Anole Spread

Invasive Range

– More variation

within populations

– Alleles from

different areas of

the native range

mixed in invasive

range

– Newer invasion

sites have higher

diversity

Controlling/Managing Invasions

• Often nearly

impossible

• People may want

invaders

• Killing/removing very

difficult

• By the time presence

noticed, may be too

late

Brown Tree Snake Case Study

• Native to Australia

and Pacific islands

• Introduced to Guam

via airplane during

WWII

• One native snake:

Brown Tree Snakes on Guam

• 1950’s

– First detection

• 1968

– Occupies island

• Late 1960’s

– Bird declines

begin

• 1984

– Most native birds

extinct

Total Annihilation

Attempts to Control Populations

More Management

Areas Vulnerable to Invasions

Islands

– Hawaii

– Caribbean

– Guam

Disturbed Habitats

– S. Florida

Why?

– Fewer Competitors

– “Unfilled” Niches

– Less chance native

species will be pre-

adapted

– Temperate climate

– Propagule pressure

Invasion as an Opportunity

Each One Is An Incredibly

Large, Unethical Experiment

Why do Invasions Succeed?

• Niche

– The biotic and abiotic conditions under which

an organism can survive and reproduce

• Ecological Release

– The removal of a previously limiting condition

which allows a population to grow

larger/faster or expand its niche

Predicting Invasions

Species distributions

determined by:

• Physiography

• Climate

• Geographic barriers

• Ecology

• Long time-scale

historical processes

Predicting Invasions

Invasive species

distributions also

determined by:

• Location and number

of introductions

• Vectors

• Dispersal time

• Genetic diversity

• Adaptation

?

?

??

?

Kolbe et al 2004

ContextProblem: Invasions depend on complex

factors which may make predictions difficult

Case Study

– Two species of anurans in Cuba and SE U.S.

Source population is important

– Use ENMs to generate predictions of suitable

habitat and ID source populations

– Use phylogeographic methods to identify

source populations and patterns of diversity

Cuban Treefrog – Osteopilus septentrionalis

•Native to Cuba, Caymans, and Bahamas

• Invasive in FL, Caribbean

•Often associated with human activity

•Major threat to native treefrogs James Harding

Greenhouse Frog – Eleutherodactylus

planirostris

• Native to Cuba

• Invasive in Coastal

Plain, Caribbean,

Hawai’i, Guam

• Threat level probably

low

• Often transported via

nursery plantsJames Harding

E. planirostris - Invasion History in US

1875

1889

19101939

19441964

Georgia

•Savannah - 1998

•Brunswick Co. – 1998

•Thomasville/Valdosta -

2007

Alabama

•Mobile – 1982

Mississippi - 2004

Louisiana

•SE – 1975

Hawai’i – 1999

Guam - 2003

Creating an ENM

-Select environmental

layers

•Precipitation

•Temperature

-Add point locality data

(GPS, NHC, etc.)

-Run modelling process

(Maxent, etc.)

Maxent

• A machine-learning algorithm working on

the principle of maximum entropy

• Essentially a maximum likelihood

approach to modelling a niche

• Output: a continuous probability surface

representing probability of

occurrence/habitat suitability

ENM Construction

•Point locality data from field collections

and online databases (GBIF, Herpnet)

•BioClim environmental layers – 10

variables representing temperature and

water availability

•Models created in Maxent with native or

invasive locality data and trained over the

extent of the southeastern U.S. and Cuba

O. septentrionalis – Invasive Range Model

0.1612

E. planirostris – Invasive Range Model

0.1612

Sequencing Overview

O. septentrionalis

• 600 bp sequence of

cyt b

• 38 locations in

Cuba and Florida

• 66 individuals

E. planirostris

• 700 bp sequence of

cyt b

• 31 locations in

Coastal Plain

• 69 individuals

•Native range data

from Heinicke et al

2011

Sequencing – O. septentrionalis

• 2 lineages

• 24 total haplotypes

– 8 in FL

– 5 unique to FL

• Pairwise divergence

– 2.9% - FL

– 1% - W. Cuba

– 1.7% - Mainland

Cuba

• ≥ 2 introductions

Sequencing – E. planirostris

• 4 lineages in Cuba

• 2 lineages in SE US

• 5 haplotypes in SE US

• Pairwise divergence

– 0.3 – 1.1%

across Cuba

– 0.3% - SE US

• ≥ 2 introductionsHeinicke et al 2011

Source Populations – O. septentrionalis

Source Populations – E. planirostris

Results Summary

• Both species show phylogenetic structure in native but not invasive ranges

• Both methods identify the same source populations

• Source populations are in the north of Cuba and close to Havana, suggesting that human trade may be a vector

Future Spread?

• E. planirostris seems to be approaching northern limit of range but may become continuous across the southern Gulf Coast

• O. septentrionalis may continue expanding northward along Atlantic Coast, but spread along the Gulf Coast seems limited

• Is adaptation taking place?

Is Physiological Adaptation

Occurring?

Thawley, Unpublished DataPhysiology

A

B

C

A

A

B

B

C

C

Invasion and Climate Change2009

Predicted Range of Burmese Pythons

(Current/2010)

Predicted Range of Burmese Pythons (2100)

Cane Toad Invasion and Evolution

• Introduced

intentionally in 1935

• Biocontrol of cane

beetle

• Huge effect on

many animals in Oz

• Uneradicable

Evolution of Predators

Evolution of Cane Toads

• Physiology

• Dispersal

• Morphology

– Phillips et al 2006

– Older populations

have shorter legs

– Invasion has sped

up

Evolution of Cane Toads• Spatial Sorting –

– Shine et al 2011

Red Imported Fire Ant Invasion

• Predicted to occupy

>50% of Earth’s

surface

• Major human and

agricultural pest

• Introduced in Mobile,

AL in 1920s

• Significant threat to

native species

Alex Wild

alexanderwild.com

Fence Lizard/Fire Ant System

• Both predator and prey of lizards

• Do not alter habitat use in presence of fire ants

Fence Lizard/Fire Ant System

Uninvaded Lizards

• Freeze response to

predators

Invaded Lizards

• Increase in flee

behaviors

• Increase in hind

limb length

Juvenile Lizards

• Act like invaded

Behavior mediates survival via anti-predator adaptations

Langkilde, 2009, Ecology

Fence Lizard/Fire Ant System

Invaded Lizards

• Increase in twitch

behaviors

• Removes ants

• BUT

– Predators such as

birds and snakes?

Behavior mediates survival via anti-predator adaptations

Langkilde, 2009, Ecology

Research Questions

How do fire ants exert pressure on fence

lizard populations?

•Direct Effects: Predation

•Indirect Effects: Growth, Body Condition, Behavioral Changes

Treatments

• Adults vs. Juveniles

– Vulnerability to venom

– Prey differences

– Behavior

• Invaded vs. Uninvaded populations

• Fire ant Presence vs. Absence

Enclosures

• 520 m2, Aluminum flashing

• Supplemental cover/perch objects

• Natural habitat, plenty of food

Experimental Setup

• Transplant juvenile

and adult lizards – 6

sites

• 2 weeks in paired

enclosures

• Fire ants removed

from two enclosures

• Lizards observed

daily for survival

No Fire Ants

Invn=10

UnInvn=10

Fire Ants

Invn=10

UnInvn=10

N=240

Summary of Exps

• Survival

– Daily observations → parametric survival

analysis

• Body Cond/Growth

– Measure SVL and Mass before and after

enclosures

– Body Condition

Results – Survival Analysis - Juveniles

• Uninvaded lizards have significantly

lower survival

Results – Survival Analysis - Adults

• Fire ants decrease survival in adults

• Difference based on origin?

Survival Conclusions

• No difference in

absolute survival

between adults and

juveniles

• Juveniles – Effect

of Origin

• Adults – FA cause

mortality

– Origin effect?

Growth/Body Condition

Differences in Mass, SVL, and Body Condition

• GLMs

• Body Condition as residuals from OLS regression of ln-

transformed values

Before placement in enclosures

• Juveniles

– Lower size and body condition at uninvaded sites

• Adults

– No differences

• No differences by sex

• No differences for survival

Results-Growth-Juveniles

• Juveniles in FA

enclosures grow

less

• Lower mass and

SVL gain in FA

enclosuresA

Mass:

•FA: F=15.392, p<0.001

•Inv: F=21.329, p<0.001

SVL:

•FA: F=15.229, p<0.001

•Inv: F=10.312, p=0.002

ABB

AB

A

BB

C

Results-Growth-Adults

• Interaction effect

for Mass

Difference

• No change in SVL

(no surprise)

Mass:

•FA*Inv: F=7.275, p=0.011

SVL:

•NS

Results-Body Condition

Adults

• Interaction effect

for difference in

body condition

Juveniles

• No sig effect

Body Condition Difference:

•FA*Inv: F=5.434, p=0.025

Immediate vs. Delayed Consequences

• Predation Trade-offs:

– Adults: Avoidance behaviors alter susceptibility to different predators

– Juveniles: avoiding fire ant consumption reduces envenomation and energy intake

• Body Condition:

– Overwintering Survival

– Reproductive Output

Conclusions

• FA cause increased mortality in adult lizards

• FA reduce body condition in juvenile lizards– May recover quickly in non-

FA environment

• Interaction between origin and FA in adults– Escape behavior: exposed

to predation?

– Change in diet?

Future Work• Arthropod surveys

– Does prey community

vary with FA presence?

• Fecal samples

– Do lizards eat FA and

how many?

– Do lizards eat more/ less

in presence of FA?

• Extensions:

• Stress

• Population modeling

• Epigenetics