Ecological Effects of Leaf Mining Plant Performance and Trophic Dynamics
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Transcript of Ecological Effects of Leaf Mining Plant Performance and Trophic Dynamics
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Ecological Effects of Leaf MiningPlant Performance and Trophic Dynamics
Diane Wagner
LTER SymposiumFebruary 2014
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Acknowledgements
• Collaborators– Pat Doak– Knut Kielland– Tom Clausen– Linda Defoliart– Jenny Schneiderheinze
• Graduate students – Brian Allman– Brent Mortensen– Jonathon Newman– Adam Watson– Brian Young
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Local leaf miner and chewers densities on deciduous trees
BC LTER: Defoliating Insect Population Levels – Werner & Kruse
Year
Num
ber insects m-2
0
50
100
150
200
250
Leaf minersExternal chewers
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Major leaf miner outbreaks across Alaska
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000 Aspen leaf miner Willow leaf blotch miner
Area
infe
sted
(ha)
Aerial Insect Detection Survey – USFS
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Outline
• Why did ALM outbreak last so long?• What caused the end of the ALM outbreak? • How does aspen leaf miner (ALM) affect aspen
performance?• New experiment: Long term ecosystem
consequences of insect herbivory, mammalian browsing, and their interaction
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Aspen leaf miner moth (Phyllocnistis populiella)
North American native One generation per year Larvae consume epidermal
cell layer Restricted to one side of a
single leaf until adulthood Adults emerge in June,
overwinter under spruce
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Why did the ALM outbreak last so long?
• High plant tolerance of herbivory– Nutrient stores
• Insect behavior– Larvae unable to attack foliage produced late in growing
season (one generation, larvae immobile)– Aggression towards conspecifics prevents decimation of
food supply
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Competition
20062007
20082009
20102011
2012
010203040506070
Leaf area mined (%)
20062007
20082009
20102011
2012
02468
101214
Eggs per leaf
max n survivors
Initial number of larvae
Pro
babi
lity
of
indi
vidu
al s
urvi
val
Per
cent
of l
eaf
surfa
ce m
ined
Pup
al m
ass
(mg)
(a)
(b)
(c)
Est
imat
ed n
umbe
r su
rviv
ing
0.00.20.40.60.81.01.21.4
0.0
0.1
0.2
0.3
0.4
0.5
0
0.2
0.4
0.6
0.8
1
0 5 10 15
Pupal mass of survivors (mg)
Initial larvae per leaf Doak & Wagner in review
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Competition
20062007
20082009
20102011
2012
010203040506070
Leaf area mined (%)
20062007
20082009
20102011
2012
02468
101214
Eggs per leaf
max n survivors
Initial number of larvae
Pro
babi
lity
of
indi
vidu
al s
urvi
val
Per
cent
of l
eaf
surfa
ce m
ined
Pup
al m
ass
(mg)
(a)
(b)
(c)
Est
imat
ed n
umbe
r su
rviv
ing
0.00.20.40.60.81.01.21.4
0.0
0.1
0.2
0.3
0.4
0.5
0
0.2
0.4
0.6
0.8
1
0 5 10 15
Pupal mass of survivors (mg)
Initial larvae per leaf
Intense interference competition:• Prevents food limitation• Allows some larvae to survive leaf
overpopulation• Preserves leaf function
Doak & Wagner in review
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What ended the outbreak?
• Phenological mis-match• Adult overwintering survival• Egg mortality• Larval parasitism• Larval and pupal predation (ants, birds)• Larval and pupal mortality (other predators,
pathogens)
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What ended the outbreak?
• Phenological mis-match• Adult overwintering survival• Egg mortality• Larval parasitism• Larval and pupal predation (ants, birds)• Larval and pupal mortality (other predators,
pathogens)
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20062007
20082009
20102011
2012
Percent of individuals
0
20
40
60
80
100
Dead in leafRemovedParasitizedSurvived
What ended the outbreak?
20062007
20082009
20102011
20122013
Survivors per leaf
0.0
0.2
0.4
0.6
0.8
1.0
Indirect effect of WLBM increase?
Doak & Wagner in review
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How does leaf mining affect aspen performance?
Methodology• Experimental suppression of leaf miner density on
aspen < 2m• 2 sites: Bonanza Creek and Ester Dome; mixed stands• 7 years
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How does leaf mining affect aspen performance?
• Mortality– No effect of leaf miner suppression
• Growth and size– Strong effects
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Effects of leaf mining across 7 years
2005 2012
Height (cm)
20
40
60
80
100
120
140
160
InsecticideControl
Wagner & Doak 2013
2005 2012
Diameter at 20 cm (mm)
6
8
10
12
14
16
18
20
Implications for browsing, competition
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Mechanisms of ALM-caused aspen decline
• Early leaf abscission (Wagner et al. 2008)
• Leaf mining reduces photosynthesis by disrupting stomatal function (Wagner et al. 2008)
• Mining disrupts water balance (unpubl.)
• Mining induces ineffectual defenses– Phenolic glycosides (Young et al. 2007)
– Extrafloral nectar (Newman & Wagner 2013) – Both increase costs
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Willow leaf blotch miner(Micrurapteryx salicifoliella)
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Willow leaf blotch miner(Micrurapteryx salicifoliella)
One generation Multiple Salix hosts Larvae consume mesophyll Mobile – will move to new leaves within plant
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Wide variation in susceptibility among willow species
Willow species
% Leaf mining
0
20
40
60
80
10020102011
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Questions• What are the individual and combined effects of invertebrate
and vertebrate herbivores on the early successional plant community & ecosystem?
• Do invertebrate and vertebrate herbivore interact indirectly through effects on plants:– Production– Plant chemistry / palatability
• E.g. Summer insect leaf herbivory may affect availability or palatability of willow species preferred by mammals in winter
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Experiment: Impact of, and interactions between, invertebrate & vertebrate herbivores
• Started spring 2012; ~10 year duration • Invertebrate suppression (insecticide) x exclusion of
moose/hares (fencing)• Dependent variables:
– Willow herbivory, browse, production, chemistry– Community composition– Soil nutrients, decomposition
Tanana River
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Impact of, and interactions between, insect & vertebrate herbivores
• Preliminary results– Suppressing insect herbivory increased production
of woody tissues (~ 50% in 2012)– No notable changes in community composition– No evidence that insect herbivory wood chemistry– No effect of insect suppression on mammalian
browsing to date
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Conclusions• Why did ALM outbreak last so long? Tolerance, intense interference competition
• What caused the end of the ALM outbreak? Increased larval and pupal mortality by biotic agent
• How does aspen leaf miner (ALM) affect plant performance? Weak effects on mortality; strong negative effects on plant size
• New experiment: Long term consequences of invertebrate herbivory, vertebrate browsing, and their interaction
Underway
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Implications of insect outbreaks
• NPP
• Successional sequence
• Source of uncertainty in ecosystem projections