a wandering monarch in a milkweed patch: some ideas for butterfly conservation. myron (‘meron’)...
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A Wandering Monarch in a Milkweed Patch: some
ideas for butterfly conservation.Myron (‘Meron’) P. ZaluckiSchool of Integrative Biology
The University of Queensland, Australia
Acknowledgments
Lincoln Brower, Mike Bull, Tony Clarke, Hugh Dingle, Jane Hughes, Roger Kitching, Duncan Mackay, Steve Malcolm, Tim Paine, Wayne Rochester, Yoshito Suzuki, … and many others
Monarchs “down-under”
Applied entomology
Basic entomology
Will monarchs go extinct ?
Already an endangeredphenomenon! Will Bt corn, climate change, & herbicides impact on monarchs?
Climate & changes in abundance
Milkweed abundance at a landscape level & host plant search - metapopulations & habitat
Modelling risk…
What determines large scale fluctuations in monarch
abundance?
Climate...
• Affects milkweed• Affects reproduction & survival• Will have a strong influence on seasonal &
year to year abundance & distribution
+- D.plexippus
D.petilia
in North America
Year to year variation in climatic suitability
Expect large scale variation in abundance…
Milkweed
The distribution and abundance of host plant patches will have a dramatic effect on
monarch abundance
Metapopulation of interconnected milkweed patch ‘habitats’
Habitat?
Milkweed patch and surrounding ‘highish’ density of single plants defines breeding habitat.
Metapopulation of interconnected milkweed patch ‘habitats’
Space between is NOT empty!
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Age in Degree days (dz=11.5oC)
Monarch Reproduction
Zalucki. 1981. Res Pop Ecol 23: 318 - 27
Rules for egg layingIf (‘habitat’) lay all eggsIf (‘not habitat’) depends on isolated plants found
And that all depends on distribution and abundanceof milkweed and the monarchs ability to find these
What happens as the single plant density (SPD) increases in non-patch areas?
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Proportion of eggs laid as single plant density (SPD) increases in non-patch areasSearch parameter same for patches and singles
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SPD = 0.01
SPD = 0.2
SPD = 0.1
Change in Proportion eggs laid
Search parameterH ---------------->L
Search parameterL ---------------->H
Prop Patch
H--->LSearch parameterH ---------------->L
Prop
Pat
ch
L--->
H
Returns on eggs will depend on factors affecting immature monarch survival
Zalucki, Clarke & MalcolmAnn Rev Ent 47: 361-393
Patches: 10%Singles: 20%
Predators?
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egg I II
Stage
Early stage monarch survivalEarly stage survival & patch size: egg to II instar
Large larval survival:III to V instar
Patch plants 50%Single plants 33%
Food limitation?
Parasitism levels range from11-80 % in
winter/springto
38-99.9 % in summer/autumn
Patch plants 58%Single plants 36%
So putting eggs onsingle plants gives a higher return…
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P(e
gg
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id)
NR
R
Sea
rch tim
e
Patch search
Random search for singles
Population persistencedepends very much onability to find plants bothas patches & singles
Proportion landscape withmilkweed patch habitat
Density of single plantsoutside milkweed patchhabitat
Population viability analysis of migratory monarch butterflies exposed to genetically
modified maize
Continental-scale resource use
Malcolm, Cockrell, & Brower, 1993
migration
Primary target of GM Bt-maize is the European corn borer
http://www.ent.iastate.edu/pest/cornborer/intro/intro.html
Non-target effects of Bt-maize pollen:
• Losey, Rayor & Carter, 1999. Nature 399: 214.– Larval mortality increased
44% in greenhouse.
• Hansen Jesse & Obrycki. 2000. Oecologia 125: 241-248.– 17-20% increase in
mortality of larvae exposed in the laboratory to Bt corn pollen deposited naturally on A. syriaca leaves.
Risk assessment• Sears et al. 2001 (PNAS 98) measured risk in Iowa as:
– R = Pe x Pt
• Risk = probability of exposure x probability of toxic effect– For Bt176 pollen:
• R = 0.0042 x 0.9 = 0.0038 (0.38%)– For Mon810 and Bt11 pollen:
• R = 0.0168 x 0.007 = 0.00012 (0.012%)– At 80% adoption this becomes:
• R = 0.067 x 0.007 = 0.00047 (0.047%)
• These estimates of R were revised by Dively et al. 2004 (Environ. Entomol. 33) to:– At 37% Bt corn use in Iowa, R = 0.0124 (1.24%)
• mortality of 2nd generation in Iowa.– At maximum 80% Bt corn use, R = 0.0261 (2.6%)
• Where Pe = proportion monarchs from maize (l) x overlap of pollen shed (o) x adoption rate of Bt maize (a).
What does this ‘low’ risk mean for monarch butterflies?
• We use the risk measures for monarch generation 2 of Dively et al. 2004 in a spatially discrete model of 4 linked generations where:– Gi = (Gi-1Ri + iGi-2Ri)SeSlSp
• G = generation size.• = proportion overlap
varies from 0 to 0.1.
• R = average realized fecundity.
• S = survivorship of eggs, larvae &
pupae.
G1
G2
G3
G4
time
lati
tud
e
overwinteringspring migration
autumnmigration
G3=Bt
Stochastic density independent models were run for 100 simulations
of 100 yearsMexico
0
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100000000
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200000000
250000000
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350000000
400000000
450000000
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97
Year
Nu
mb
er
Mexico
Model 1 with random normally varying
reproduction and no Bt corn effect onsurvival in G3
with variable generation overlap[R = Pe x Pt = 0.0 x 0.07 = 0.0]
mean = 0/500 OW<500,000 (N=100)
Mexico
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1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97
Year
Nu
mb
er
Mexico
Model 1 with random normally varyingreproduction and Bt corn effect on
survival in G3 and effect onreproduction in G4
with variable generation overlap[R = Pe x Pt = 0.024 x 0.07 = 0.002]mean = 0/500 OW<500,000 (N=100)
% extinction at overwintering threshold of
1 million monarchs vs exposure to Bt maize
Percentage of simulations in which N fell below theshold
0%
10%
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90%
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Pe (Proportion exposed to Bt) in DD Random 4
Pe
rce
nta
ge
10% carryover + 50% fecundity reduction
no carryover
Percentage of simulations in which N fell below threshold
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Pe (Proportion exposed to Bt) in DI Random 1
Perc
en
tag
e
10% carryover + 50%
no carryoverDensity independentmodel 1
Density dependentmodel 4
10% overlap + 50% fecundity reduction
no overlap
10% overlap + 50% fecundity reduction
no overlap
Will monarchs go extinct?• During the 2004/5 winter monarch overwintering
populations were the lowest recorded at 2.1 ha of overwintering forest in Mexico.– 10% of the largest recorded area of 21 ha in 1996/97.
Overwintering colony areas (hectares)(redrawn from Rendon and Galindo-Leal, 2005)
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Overwintering season
Num
ber
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are
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Will monarchs go extinct?
• The conclusion of Sears et al. 2001 and Dively et al. 2004 that Bt maize poses low risk to monarchs is premature.
• Require more spatially and temporally relevant life-history data before reaching a conclusion.
Will monarchs go extinct?
• Need to determine the impact of added mortality from GM crops on the population dynamics of monarchs.
• A range of simulations suggests that the impact of Bt maize is not trivial.
• We also propose to address the impact of herbicide-tolerant soya beans.
Will monarchs go extinct ?
Don’t know … willdepend in part onclimate & hostplant distributionacross theLandscape & risks
For this wanderer in a milkweed patch