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Biological Control of Invasive Species
Why doesn’t it work?
The Control Freaks
Aaron Lim,
Georgi Kapitanov,
Britta Teller,
Verónica Crespo Pérez
Biological invasions
•  Introduction and spread of exotic
organisms in regions outside of their
native range
–  advances in technology → increase in
worldwide movement of humans and their
goods
Second largest cause of current biodiversity
loss after habitat destruction
(Keane & Crawley 2002)
Stages of invasions
Liebhold & Tobin 2008
1)  Arrival
2)  Establishment
3)  Spread
1.
2.
3.
Enemy Release
Hypothesis
“Introduced species should experience a
decrease in regulation by natural enemies,
resulting in an increase in distribution and
abundance”
(Keane & Crawley 2002)
Controlling invasive
species
Chemical
Physical
Biological
control
Biological control
Natural
enemies
Invaded range
time
Native range
The abundance of an invasive species may be
rapidly reduced by introducing specialist enemies
from the native range
Biological Control in Practice
Purple loosestrife
(Lythrum salicaria)
Problems with biological control:
Nontarget effects
Rhinocilus conicus
Galerucella pusilla
Biological Control in Practice
Spotted knapweed
(Centaurea maculosa)
Problems with biological control:
Naturalization
Urophora affenis
Peromyscus maniculatus
Our Objectives
•  Build a model to evaluate the potential of a
“perfect biological control”
–  Assumes that the biological control is
completely dependant on the invasive for
reproduction.
•  Evaluate the parameter values over which
equilibria exist and decide if they are
biologically relevant
Our Model
Control
Invasive
Native
Equilibrium Conditions
Assumed parameter estimates
Parameter
Value
βN
Birth rate of N
1
µN
Death rate of N
0.1
βI
Birth Rate of I
50
µI
Death Rate of I
0.1
K
Carrying capacity
5000
κ1
Number of births of C
per (attack related) death
of I
0.5
αN
Attack rate of N on I
.0001
αI
Attack rate of I on N
0< αI <1
αC
Attack rate of C on I
0< αC <1
µc
Death rate of C
0< µc <1
Graphical Representations
Equilibrium Density
Parameter Constraints
µc=0.2
µc=0.5
µc=0.8
What happens if the biological
control is “leaky”?
Our Model
Control
Invasive
Native
Equilibrium Conditions
Assumed parameter estimates
Parameter
Value
βN
Birth rate of N
1
µN
Death rate of N
0.1
βI
Birth Rate of I
50
µI
Death Rate of I
0.1
K
Carrying capacity
5000
κ1
Number of births of C per
(attack related) death of I
0.5
αN
Attack rate of N on I
.0001
αI
Attack rate of I on N
0< αI <1
αC
Attack rate of C on I
0< αC <1
µc
Death rate of C
0< µc <1
k2
Benefit of C by N
0.5
lc
Attack rate of C on N
0.5 * αC
Graphical Representations
Equilibrium Density
Parameter Constraints
Conclusions
•  In a “perfect” biological control scenario, the
control is effective at achieving a 3 species
equilibrium when the biological control is
aggressive and has a low death rate.
•  In the “leaky” biological control scenario the
biological control is effective at achieving a 3
species equilibrium however, there is overlap in
the equilibrium parameter space and it is
sensitive to initial values.
Future Directions
•  Compensatory growth
•  Evolution
•  Poor estimates of parameters
(all of which lead to the persistence of the
invasive, control or both)
References
RM. Callaway, TH. DeLuca, WM. Belliveau (1999) BIOLOGICAL-CONTROL
HERBIVORES MAY INCREASE COMPETITIVE ABILITY OF THE
NOXIOUS WEED CENTAUREA MACULOSA. Ecology: Vol. 80, No. 4, pp.
1196–1201.
R.M. Keane, M.J. Crawley (2002) EXOTIC PLANT INVASIONS AND THE
ENEMY RELEASE HYPOTHESIS. TRENDS in Ecology & Evolution: Vol.
17, No.4, pp. 164–170.
A.M. Liebhold, P.C. Tobin (2008) POPULATION ECOLOGY OF INSECT
INVASIONS AND THEIR MANAGEMENT. Annual Reviews of Entomology:
Vol. 53, pp. 387–408.
S. Louda, Kendall D, Connor J, Simberloff D (1997) ECOLOGICAL EFFECTS
OF AN INSECT INTRODUCED FOR THE BIOLOGICAL CONTROL OF
WEEDS. Science: Vol. 277, No. , pp. 1087–90.
H Müller-Schärer, U Schaffner, and T Steinger (2004) EVOLUTION IN
INVASIVE PLANTS: IMPLICATIONS FOR BIOLOGICAL CONTROL.
Trends in Ecology & Evolution: Vol. 19, No. 8, pp. 417–422.
D. E. Pearson, K. S. McKelvey and L. F. Ruggiero (2000) NON-TARGET
EFFECTS OF AN INTRODUCED BIOLOGICAL CONTROL AGENT ON
DEER MOUSE ECOLOGY . Oecologia: Vol. 122, No. 1, pp. 121–8.
Images
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http://plants.usda.gov/maps/large/LY/LYSA2.png
http://plants.usda.gov/maps/large/CE/CESTM.png
http://www.missouriplants.com/Pinkalt/Centaurea_maculosa_involucre.jpg
http://www.missouriplants.com/Pinkalt/Centaurea_maculosa_plant.jpg
http://www.fs.fed.us/r9/forests/white_mountain/ecosystems/WMEDN/
nnis_plants/images/purple_loostrife_flower_les.jpg
http://www.invasive.org/weedcd/images/1536x1024/5358645.jpg
http://freshcutspro.com/yahoo_site_admin/assets/images/CrepeMyrtle.
96124546_large.jpg
http://www.zin.ru/Animalia/Coleoptera/images/kv_mak/
galerucella_pusilla.jpg
http://www.fsoe.se/bilder/rhinocyllus_conicus.jpg
http://www.cedarcreek.umn.edu/mammals/midsize/peromyscusmaniculatus.jpg
http://upload.wikimedia.org/wikipedia/commons/thumb/6/63/Green_bug.svg/
548px-Green_bug.svg.png
http://www.landcareresearch.co.nz/education/weeds/images/pullweed1.gif
http://www.extertronic.com/image/insect-protection/fly-natural-control.jpg
http://img0.gmodules.com/ig/cache/ca/a1/
caa179188c1529420e032145a86af7cc.png
http://cipm.ncsu.edu/ent/biocontrol/images/banner_main.gif
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