Predicting the Distribution of the Invasive Cactus Moth, Cactoblastis cactorum, and its Major Host...
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Predic'ng the Distribu'on of the Invasive Cactus Moth, Cactoblas)s cactorum, and its Major Host Plant, Opun)a stricta, in
Florida
Kristen E. Sauby, Mary C. Christman, and Robert D. Holt Department of Biology University of Florida
Ecological Society of America Annual Mee'ng
Sacramento, California August 11, 2014
Florida Opun)a and Their Specialist Insect Herbivores Invasive Cactus Moth, Cactoblas)s cactorum
Na've Cactus Moth, Melitara prodenialis
Na've Cactus Bug, Chelinidea vi7ger
Na've Cactus Scale, Dactylopius sp.
O. stricta O. pusilla O. humifusa var. ammophila
The invasive cactus moth, Cactoblas)s cactorum, “blas'ng” its host species,
Opun)a stricta, in Florida
Background
• Opun%a are na&ve to the New World (North and South America)
• Including the phylogeny and “puta&ve dispersal pathways of Opun%a clades”
(Majure et al., American Journal of Botany, 2012)
First introduced into Australia to control invasive cac&
1957
Early 1930s 1925
The Path to the North American Introduc'on of the Invasive Cactus Moth
Approx. na&ve range of moth
Successful Biological Control in Australia
Before… ARer.
• Quotes from Dodd (1940) • Photos from Osmond et al. 2008 (Journal of Experimental Botany)
“In August 1930, for 150 miles [240 km] along the river the pest [O. stricta] was in its full vigour, its con&nuity almost unbroken by cleared land; the pastoral proper&es had been overrun and mainly deserted.”
“…in August 1932, 90 percent of the [prickly] pear had collapsed. The change in exactly two years was extraordinary.”
Source: USDA APHIS, h`p://www.aphis.usda.gov/plant_health/plant_pest_info/cactoblas&s/spread.shtml, accessed 21 March 2009
Most recent detec&ons: Jefferson, Lafourche, and Terrebonne Parishes, Louisiana (2009)
Distribu'on of the Invasive Cactus Moth in the Southeastern United States
South Carolina, 2004
Louisiana, 2009
First detec'on, Florida Keys, 1989
NE Florida, 2000
Ques'ons
• How prevalent is the invasive cactus moth and moth damage?
• How important are different factors in structuring varia&on in cactus and invasive cactus moth occurrence? – Abio&c factors (eleva&on) – Bio&c factors (plant density, canopy cover) – Spa&al factors
The invasive moth is found primarily on O. humifusa var. ammophila and O. stricta (Sauby et al. 2012)
Sampling at the Guana Tolomato Matanzas Na'onal Estuarine Research Reserve (GTMNERR)
• Plot Surveys
• Plant Surveys
• Set up 1-‐meter2 plots according to a stra&fied random adap&ve cluster sampling scheme 1. Stra&fied Random Sampling (SRSWOR): plots randomly distributed across
(a) 5 islands and (b) two habitat patches (524 plots) 2. Adap&ve Cluster Sampling: If a plot had cac&, adjacent plots were also
surveyed (c) (829 plots)
• Surveyed plots at least twice a year (May 2012 – present) • Then aggregated data for analysis
Sampling Scheme – Plot Surveys
• Set up 1-‐meter2 plots according to a stra&fied random adap&ve cluster sampling scheme 1. Stra&fied Random Sampling (SRSWOR): plots randomly distributed across
(a) 5 islands and (b) two habitat patches (524 plots) 2. Adap&ve Cluster Sampling: If a plot had cac&, adjacent plots were also
surveyed (c) (829 plots)
• Surveyed plots at least twice a year (May 2012 – present) • Then aggregated data for analysis
Sampling Scheme – Plot Surveys
(c)
• Set up 1-‐meter2 plots according to a stra&fied random adap&ve cluster sampling scheme 1. Stra&fied Random Sampling (SRSWOR): plots randomly distributed across
(a) 5 islands and (b) two habitat patches (523 plots) 2. Adap&ve Cluster Sampling: If a plot had cac&, adjacent plots were also
surveyed (c) (824 plots)
• Surveyed plots at least twice a year (May 2012 – present) • Aggregated data for analysis (c)
Sampling Scheme – Plot Surveys
Sampling Scheme – Plant Surveys • Mapped and marked individual cactus plants in a random subset
of plots (287 plots; 1089 O. stricta and 1087 O. pusilla plants) • Surveyed all at least twice a year (Jan. 2013 – present) • Aggregated data for analysis
• Propor&on of area occupied by each cactus species
• O. humifusa var. ammophila was rare (found in only 1 plot)
Prevalence of Cac' in SRSWOR Plots
100
200
300
400
500
Absent Present
Num
ber o
f plo
ts
O. stricta
100
200
300
400
500
Absent Present
O. pusilla
75/523 = 14.3% 45/523 =
8.6%
• Increased the number of plots with cac&
Sample Size of Plots with Cac' aRer Adap've Cluster
Sampling
100
200
300
400
500
600
700
800
900
1000
1100
Absent Present
Num
ber o
f plo
ts
O. stricta
100
200
300
400
500
600
700
800
900
1000
1100
Absent Present
O. pusilla
447/1347= 33.2%
324/1347= 24.1%
50
100
150
200
250
300
350
400
MothAbsent
MothPresent
Num
ber o
f plo
ts
O. stricta
50
100
150
200
250
300
350
400
MothAbsent
MothPresent
O. pusilla
Prevalence of the Invasive Cactus Moth
54/447 = 12.1%
1/324 = 0.31%
Aggregated Plot Survey Data (May 2012 – present)
Presence = moth larvae and/or eggs were found at least once Absence = moth larvae and/or eggs never observed
50
100
150
200
250
300
350
400
MothAbsent
MothPresent
Num
ber o
f plo
ts
O. stricta
50
100
150
200
250
300
350
400
MothAbsent
MothPresent
O. pusilla
100
200
300
400
500
600
700
800
900
1000
1100
MothAbsent
MothPresent
Num
ber o
f pla
nts
O. stricta
Prevalence of the Invasive Cactus Moth
35/1089 = 3.2%
Aggregated Plot Survey Data (May 2012 – present)
Aggregated Plant Survey Data (January 2013 – present)
54/447 = 12.1%
1/324 = 0.31%
Presence = moth larvae and/or eggs were found at least once Absence = moth larvae and/or eggs never observed
Prevalence of Damage from Past Moth Infesta'ons
54/449 = 12%
50
100
150
200
250
300
350
DamageAbsent
DamagePresent
Num
ber o
f plo
ts
O. stricta
50
100
150
200
250
300
350
DamageAbsent
DamagePresent
O. pusilla
334/447 = 75%
• An es&mate of cumula&ve prevalence of cactus moths • Many plants are infested at some point in their lives • Es&mates may be biased low because only live plants are surveyed • Caveat: damage may be from either the invasive and/or na&ve cactus moths
122/324 = 38%
cac& N
t
invasive cactus moth
Hypothesized Dynamics of Cactus Moth Invasion
Current state of invasion
Generalized Linear Mixed Models to Explain Paherns of O. stricta Occurrence
Analyzed in SAS v. 9.4 using GLIMMIX procedure Dependent Variables • O. stricta presence Fixed Effects • Eleva&on (meters) • Vegeta&on Class (five categories) • Vegeta&on Density (scale of 0 – 4) • Detritus Density (scale of 0 – 4) • Canopy (yes/no) Random Effects • Habitat Patch • Network (the adap&ve cluster to which a plot belongs)
Results -‐ Generalized Linear Mixed Models to Explain Paherns of Cactus Occurrence
Tests of Fixed Effects
Effect Es'mate St. Error Pr > F Canopy 0.17 0.33 0.5970 Vegeta&on Class -‐ -‐ 0.0007 Vegeta&on Density 0.38 0.12 0.0010 Detritus Density 0.42 0.11 <.0001
Eleva&on (m) 0.037 0.10 0.7153
Least Squares Means
Vegeta'on Class Mean Prob(Y=1) Standard Error t Value Pr > |t|
Marsh plants 0.0097 0.0081 -‐5.50 <.0001
Mixed forbs 0.16 0.059 -‐3.78 0.0002
Overhanging cedar/mixed forbs 0.14 0.057 -‐3.83 0.0001
Palm/palme`o 0.00014 0.0022 -‐0.57 0.57
Shrubs/vines 0.083 0.039 -‐4.64 <.0001
Results – Rela'onship Between Vegeta'on Class and O. stricta Occurrence
• Limited analysis to plots containing O. stricta • Analyzed in SAS v. 9.4 using GLIMMIX procedure
Dependent Variable • Invasive Cactus Moth presence Fixed Effects • O. stricta maximum height • O. stricta percent cover • Eleva&on (meters) • Vegeta&on Class (seven categories) • Vegeta&on Density (scale of 0 – 4) • Detritus Density (scale of 0 – 4) • Canopy (yes/no) Random Effects • Network (the adap&ve cluster to which a plot belongs)
• Did NOT include Habitat Patch because it was not sta&s&cally significant in a model with only random effects
Generalized Linear Mixed Model to Explain Paherns of Invasive Cactus Moth Occurrence on O. stricta
Results -‐ Generalized Linear Mixed Model to Explain Paherns of Invasive Cactus Moth Occurrence on O. stricta
Effect Es'mate St. Error Pr > F
Canopy 0.21 0.7751 0.79
Vegeta'on Class -‐ -‐ 0.52
O. stricta Height 0.042 0.016 0.011
O. stricta Percent Cover 0.038 0.018 0.037
Eleva'on 0.23 0.094 0.013
Detritus 0.046 0.22 0.84
Conclusions • Abio&c and bio&c factors can be used to explain pa`erns of cactus and cactus moth occurrence
O. stricta occurrence • Posi&ve rela&onship with detritus and vegeta&on density
• Significant varia&on among vegeta&on classes
Conclusions
Invasive cactus moth occurrence • Cumula&ve damage is much greater than present rates of infesta&on
• Rare on O. pusilla • Posi&vely related to O. stricta height and percent cover as well as eleva&on
Spa&al factors • Habitat patch and Network included in models of cactus occurrence as random effects
Invasive Species Management
• Important to consider the rela&ve threat of the species
• Important to account for spa&al varia&on in risk of invasion and costs of surveillance (Epanchin-‐Niell et al., Ecol. Le;., 2012)
Future Work
• Assess temporal and spa&al autocorrela&on in: – the dynamics of cactus and cactus moth occupancy
• Assess threat of the invasive cactus moth to cac& using demographic models
Acknowledgments University of Florida
• Michael Barfield • James Nifong • Doria Gordon • Robert Fletcher • Jose Miguel Poncianco • Jake Ferguson • Rosana Zenil-‐Ferguson • Polly Harding (pictured)
GTMNERR • Ka'e Petrinec • Mah Welsh
Feel free to contact me at [email protected]