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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
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
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