Connecting eastern monarch population dynamics across their migratory cycle Leslie Ries, Univ. of MD...

Connecting eastern monarch population dynamics across their migratory cycle

Leslie Ries, Univ. of MDKaren Oberhauser, Univ. of MN

Elise Zipkin, USGS (Patuxent)Doug Taron, IL BMS

Eduardo Rendon, WWF-Mexico

Monarchs have a complex migratory cycle that makes tracking population dynamics challenging

Stage 1: Overwintering

Stage 2: Spring migration and breeding

Stage 3: Summer expansion and breeding

Stage 4: Fall migration

• Dynamics in one stage have carry-over effects into subsequent stages• On the other hand, it is largely one population, rather than a series of loosely connected “sub” populations

Understanding monarch population dynamics is critical for their conservation

• Notable patterns:– Eastern monarchs may be declining,

but examining different life stages suggests different patterns

– Monarch populations show large fluctuations from year to year

• Underlying mechanisms– REGIONAL CONNECTIONS: How do

dynamics in one phase of the migratory cycle influence dynamics in subsequent phases?

– ENVIRONMENTAL INFLUENCE: How much do environmental factors influence the connection between these phases?

SUMMER MONITORING DATA

FALL MONITORING DATA

WINTER MONITORING DATA

How can we track dynamics through each life stage?

Surviving overwinter adults

Gen 3/4 eggs

Gen 2 adultsGen 2 eggs

Gen 1 eggs

Gen 1 adults

Gen 3/4 adults

Migrants going south

Adults arriving in Mexico

Journey Northstarted ‘99

Monarch Larvae Monitoring

Projectstarted ‘99

Migrants going north

Cape May Roosts

started ‘92

WWF-Mexico• started ’96

• started tracking overwinter mortality in 2003

N. American Bfly Assoc.

started 1975Ohio BMSstarted ’96

Journey Southstarted ’99

Monarch Watchstarted ’92

Peninsula Point Roosts

started ‘96

Monarch Health

started ‘99

Illinois BMSstarted ’87

Florida BMSstarted ’03

Expansion

Data Available for Analysis

•Cape May (CM)•WWF-Mexico (MEX)•(’95 winter start; ‘04 winter end)

Monarch Larvae Monitoring Project (MLMP)

North American Butterfly Association Counts (NABA)

Illinois Butterfly Monitoring Scheme (IL)

Ohio Butterfly Monitoring Scheme (OH)

Mexican sites

Data Available for Analysis

Monarch Larvae Monitoring Project (MLMP)

North American Butterfly Association Counts (NABA)

Mexican sites

South

N-Central

N-East

•Cape May (CM)•WWF-Mexico (MEX)•(’95 winter start; ‘04 winter end)

Ohio Butterfly Monitoring Scheme (OH)

Tracking the population through each region and stage

1. Do the number of adults surviving the winter in Mexico relate to the number of adults arriving in the Texas area in spring?

2. Do the number of spring arriving adults relate to the number of 1st gen eggs that are recorded?

Mexican sites


Mexican sites



3. How do the number of spring adults or eggs relate to the number of 1st generation arrivals in the northern regions?

Mexican sites




4. Can the number of 1st generation adults / 2nd generation eggs predict numbers in subsequent generations?


Mexican sites





5. Can the size of the population at the last stages of the breeding cycle predict the number of fall migrants?


Mexican sites





5. Can the size of the population at the last stages of the breeding cycle predict the number of fall migrants?

6. Can the size of the population at the last stages of the breeding cycle predict the number of Mexican arrivals?


Q1 and Q2. How do overwintering numbers relate to the number of arriving adults and how do arriving adults influence the number of eggs we see in the spring?

A non-existent (or weak) relationship between the number of adults leaving Mexico and the number arriving in Texas and surrounding areas in the spring. And no hint of a relationship between spring adults and eggs. But there are few data available to rigorously make these comparisons!!

0 1 2 3 4 5 6 70

0.5

1

1.5

2

2.5

MEX – monarch area covered (ha)

NAB

A de

tecti

ons (

spr –

Sou

th)

Mexican migrants and spring adults

0 0.5 1 1.5 2 2.50

0.20.40.60.8

11.21.41.61.8

2

NABA detections (South)

MLM

P eg

g de

nsity

(Sou

th)

Spring adults and spring eggsr=0.5 p=0.25 r=0.34 p=0.51

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3

2nd

gen

MLM

P eg

g de

nsit

y (N

-Cen

tral

)

1st gen MLMP egg density (South)

00.20.40.60.8

11.21.41.61.8

2

0 0.5 1 1.5 2 2.5N

ABA

1st

Gen

adu

lts (

N-E

ast)

NABA spring migrants (South)

Q3. How do the number of spring adults or eggs relate to the number of 1st generation arrivals in the northern regions?

NOTE: There are eight combinations of comparisons here, none show significant relationships (the strongest patterns are shown below).

A weak, or non-existent, relationship between the spring generation and summer arrivals in the north could be due to lack of data, or swamping out by environmental factors.

1st gen eggs in south to 2nd gen eggs North Migrant adults in south to 1st gen adult arrivals

r=0.5 p=0.13 r=0.69 p=0.12

0

1

2

3

4

5

6

7

8

0 1 2 3

Sum

mer

NA

BA d

etec

tions

(N-C

entr

al)

1st Gen Spring arrivals NABA (N-Central)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.01 0.1 1

Sum

mer

MLM

P eg

g de

ns (N

-Cen

tral

)

2nd gen MLMP egg density (N-Central)

Q3. Can the number of 1st generation adults / 2nd generation eggs predict numbers in subsequent generations?

YES: This suggests that the number of arrivals in the northern breeding grounds from the southern spring generation has a strong influence on the ultimate size of that year’s population.

0

1

2

3

4

5

6

0.001 0.01 0.1 1Su

mm

er N

ABA

det

ectio

ns (N

-Eas

t)2nd gen MLMP egg density (N-East)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.001 0.01 0.1 1

Sum

mer

MLM

P eg

g de

nsit

y (N

-Eas

t)

2nd gen MLMP egg density (N-East)

N-East: r=0.899 p=<0.0001 r=0.85 p=0.004

r=0.7925 p=<0.0001 r=0.73 p=0.005

N-Central:

Tracking climate’s impacts on the migratory monarch butterfly

Overwintering site

Approximate limit of breeding

center of summer recruitment

a)

b)

Years of data1-4

5-910-13

We examined the impacts on population growth in Ohio of:1. Spring temperature (in

Texas)2. Spring precipitation (in

Texas)3. Summer temperature (in

Ohio)4. Summer precipitation (in

Ohio)

Patterns based on simple climate metrics aren’t informative

2 3 4 5 6 7 8 9 10 11 120

5

10

15

20

Texas rainfall (cm)

500 550 600 650 700 750 80002468

1012141618

Texas GDD (weeks 4-9)

1500 1700 1900 2100 2300 250002468

1012141618

Ohio GDD (weeks 10-28)

-4 -3 -2 -1 0 1 2 3 4 50

5

10

15

20

Ohio PDI (through week 28)

Mea

n nu

mbe

r mon

arch

s/hr

(wee

ks 2

6-28

)

a) b)

c) d)

Spring precipitation (Texas)

Spring temperature (GDD in Texas) Summer temperature (GDD in Ohio)

Summer drought index (Ohio)

Sum

mer

pea

k po

pula

tion

size

(Ohi

o)

Meaningful patterns emerge when patterns are evaluated in a multiple regression framework, taking

site characteristics into account

0

5

10

15

20

10 15 20 25

-1.0

-0.5

0.0

0.5

1.0

1.5

Week

Sp

rin

g P

reci

pita

tion

in T

X (

sta

nd

ard

ize

d)

0

1

2

3

4

5

6

10 15 20 25

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Week

Sp

rin

g G

DD

in T

X (

sta

nd

ard

ize

d)

b)

a)

Sprin

g G

DD

in T

X (s

tand

ardi

zed)

Week

0

2

4

6

8

10

10 15 20 25

-3

-2

-1

0

1

2

3

week

GD

Ddi

ff (s

tand

ardi

zed)

Location with min average GDD

0

2

4

6

8

10

10 15 20 25

-3

-2

-1

0

1

2

3

week

GD

Dd

iff (

sta

nda

rdiz

ed)

Location with mean average GDD

0

2

4

6

8

10

10 15 20 25

-3

-2

-1

0

1

2

3

week

GD

Ddi

ff (s

tan

da

rdiz

ed

)

Location with max average GDD

Sum

mer

GD

D in

OH

(sta

ndar

dize

d)

Sprin

g pr

ecip

itatio

n (c

m) i

n TX

(sta

ndar

dize

d)

Week

Coolest sites

Avg site

Warmest sitesSt

anda

rdiz

ed s

umm

er G

DD

in O

hio

Stan

dard

ized

spr

ing

GD

D in

TX

Stan

dard

ized

spr

ing

Prec

ip in

TX

Zipkin et al. (in press): Global Change Biology

The story so far…• No relationship between adults leaving Mexico, arriving in the South, and laying eggs

• Weak (or non-existent) relationship between adults arriving in the South, next generation arrivals in the North and egg-laying

• The disconnect may be due to the importance of spring climate on the ultimate population size (and/or health) of migrants to the North

• A strong relationship between the numbers arriving in the North and laying eggs and the size of the population at the end of the summer.

• This suggests that the size of that first generation produced in the spring that arrives in the North is an important contributor to yearly population sizes and (again) that spring climate is important

Next up: Population connections on the return trip

0 1 2 3 4 5 60

20

40

60

80

100

120

N-east summer adult population (NABA detections)

Cape

May

Roo

st S

ize

Q5. Can the size of the population at the last stages of the breeding cycle predict the number of fall migrants?

r=0.61 p=0.005

02468

101214161820

0 2 4 6

Ove

rwin

ter c

olon

y si

ze in

Nov

(ha)

N-east summer adult population (NABA detections)

02468

101214161820

0 2 4 6 8

Ove

rwin

ter c

olon

y si

ze in

Nov

(ha)

N-central summer adult population (NABA detections)

Q6. Can the size of the population at the last stages of the breeding cycle predict the number of Mexican arrivals?

r=0.00 p=0.99 r=-0.01 p=0.69

NO? This lack of relationship is surprising given results of past (admittedly smaller) analyses, and deserves further examination.

Conclusions and future directions• Growth during the summer breeding season is the most important

factor driving yearly population sizes– The number (or health) of migrants arriving from the southern US into the

north is a key driver of population growth and this may be driven by climate– Summer climate also influences summer growth

• There seems to be little congruence between winter colony size and the spring and summer detection rates from butterfly surveys– Loss of milkweed (not captured by surveys) may be influencing winter, but not

summer, values (Pleasants and Oberhauser, in press)

• We will continue to develop this “regional connections” framework– Include data from other programs– Repeat analyses as data resources grow– Continue to develop mechanistic models that explore environmental impacts on

specific stages or linkages

Acknowledgements• All members of

MonarchNet• NCEAS monarch

working group

• Program coordinators and the thousands of volunteers!!!

• Funding:Monarch Joint VentureCECSESYNC

Results: Winter counts are related to the previous summer (but not vice-versa)

0

0.5

1

1.5

2

2.5

3

3.5

0 0.5 1 1.5 2 2.5 3

ln (Previous Summer Counts + 1)

ln (

Fo

llo

win

g W

inte

r M

exic

an C

ou

nts

+

1) Illinois

Ohio

4-Jul

Linear (Ohio)

Linear (Illinois)

0

0.5

1

1.5

2

2.5

3

3.5

0 0.5 1 1.5 2 2.5 3 3.5

ln (Previous Winter Mexican Counts)

LN

(F

oll

ow

ing

Su

mm

er C

ou

nts

)

Illinois

Ohio

4-Jul

Illinois: r = 0.72, p = 0.005Ohio: r = 0.80, p = 0.0094July: r = 0.38, p = 0.21*

Illinois: r = 0.13, p = 0.68Ohio: r = 0.08, p = 0.834July: r = 0.17, p = 0.60

*Data can be expanded to their full range and for the full 30 years of winter data

Gen 2-4 adults

Overwintering adults

Gen 2-4 adults

Overwintering adults

Two main questions

Stage 1: Overwintering

Stage 2: Spring migration and breeding

Stage 3: Summer expansion and breeding

Stage 4: Fall migration

•REGIONAL CONNECTIONS ANALYSIS: How do dynamics in one phase of the migratory cycle influence dynamics in subsequent phases?• CLIMATE ANALYSIS: How much do environmental factors influence the connection between these phases?

Monarch Net: A network of monarch monitoring groups

For more information, see monarchnet.org and the Butterfly Monitoring Poster

How can we track dynamics through each life stage?

Surviving overwinter adults

Gen 3/4 eggs

Gen 2 adultsGen 2 eggs

Gen 1 eggs

Gen 1 adults

Gen 3/4 adults

Migrants going south

Adults arriving in Mexico

Monarch Larvae Monitoring

Projectstarted ‘99

Migrants going north

Cape May Roosts

started ‘92

WWF-Mexico• started ’96

• started tracking overwinter mortality in 2005

N. American Bfly Assoc.

started 1975

Expansion

Connecting eastern monarch population dynamics across their migratory cycle Leslie Ries, Univ. of MD...

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