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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