Michael J. CramerUniversity of Notre DameEnvironmental Research Center

Important plant-animal interaction

Plant perspective Directly affects fitness Anti-predator strategies Some need predators to aid in

dispersal Animal perspective

Seeds are high energy and nutrient-rich

Easily harvested, stored and defended

Common interaction in forest systems, with small mammals playing major role

Uncertainty of knowing which species are removing seeds

What is the ultimate fate of the seed?

Eaten seed predators

Cached seed dispersers (potentially)

Study of preferences in laboratory

Much research on sciurid seed predation Other rodents also effective seed predators

Two species

Peromyscus maniculatus gracilis (forest deer mouse)

Peromyscus leucopus (white-footed mouse)

Major seed predators Ecological effects commonly

pooled Identification tricky

Morphologically similar P.m. gracilis ear

length ≥ 18 mm Confirmed by rt-PCR

and sequencing No misidentifications for

2009 captures

Misidentifications 2012▪ P. maniculatus 2/235

▪ P. leucopus 3/78

0

20

40

60

80

100

120

13 14 15 16 17 18 19 20 21

Fre

qu

en

cy

Ear Length (mm)

maniculatus

leucopus

0

20

40

60

80

100

78.1

78.3

78.5

78.7

78.9

79.1

79.3

79.5

Fre

qu

en

cy

COIII Melting Temperature (C)

maniculatus

leucopus

Photo by David Chan

Sugar Maple (Acer saccharum)

Red Maple (Acer rubrum)

Determine feeding preferences for both Peromyscus species

Expectations

No difference between species in terms of seed preference or amount eaten

A. saccharum should be preferred over A. rubrum

▪ Larger seeds more energy

▪ Mouse populations respond to changes in sugar maple seed crops

5 grids in 2009, 8 grids in 2011

5 x 5 grids with 15 m spacing

Data collected

Individual marks

Species

Sex

Weight

Ear length

Subjects held overnight

Starved 5 hours prior to test

Provided with 5 g of each type of Acer seed

Seeds sorted and weighed the following morning

Data standardized prior to analysis

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

P.maniculatus P.leucopus

Ma

ss E

ate

n(g

/)/B

od

y M

ass

(g

)

Species

F1,76 = 3.049, P = 0.085

Species x Seed:F1,76 = 14.661

P < 0.001

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2009 2011

Se

lect

ivit

y In

de

x

Year

A.rubrum

A.saccharum

Seed x Year:F1,40 = 9.888

P = 0.003

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2009 2011

Se

lect

ivit

y In

de

x

Year

A.rubrum

A.saccharum

Seed x Year:F1,36 = 4.230

P = 0.047

P. MANICULATUS

Preferences consistent Always consumed more

red than sugar maple Difference in selectivity

more extreme in 2011

P. LEUCOPUS

Preferences not consistent Consumed more red than

sugar maple in 2011 No preference for either

seed in 2009

Mice population effects

• Different abundances between years

• Could lead to selection of differing food resources

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

P.maniculatus P.leucopus

Po

pu

lati

on

Est

ima

te

Species

2009

2011

Species x Year:F1,12 = 0.628, P = 0.444

Seeds obtained from distributors Lower consumption of A. saccharum

compared to A. rubrum A. rubrum seeds restocked in 2011 Potential difference in seed viability by 2011

for A. saccharum P. leucopus may have consumed more A.

rubrum in 2011 because A. saccharum seeds were too old

Difference between mouse species

P. leucopus habitat generalists

P. maniculatus more specialized

P. maniculatus more selective

Ate more A. rubrum seeds

Why?

Optimal foraging considerations

Change foraging strategy for different seeds

Nutrient and secondary compounds may differ between Acer species

A. saccharum is larger but also has thicker seed coat Differences in energy content and handling time =

differences in food quality

Decide to consume A. rubrum immediately and save A. saccharum for later

Seasonal effect better to eat A. rubrum in summer and save A. saccharum for winter

Squirrel-oak example Mouse-maple system

A. rubrum▪ Germinate in same year▪ Produced in spring▪ Thin seed coat

A. saccharum▪ Germinate following year▪ Produced in summer▪ Thick seed coat

Next steps: Caching behavior Seasonal changes in

foraging behavior

Peromyscus species differ in foraging preferences P. maniculatus: consistent

preference for red over sugar maple

P. leucopus: preferences inconsistent

Peromyscus not ecologically equivalent

Influence previous studies of seed predation

Implications for forest composition with changes in rodent community

Fieldwork: Heidi Mahon, Matt Igleski, Natalia Colón-Rosa, Zuleika Cruz-Ramos and Kate Witkowski

Genetic analyses: Ben Ridenhour, Mary Oswald, Andrew Bantel

Discussion: David Flagel, Karen Francl, Page Klug, Gary Belovsky

Funding: University of Notre Dame Environmental Research Center