Omnivory Driven by Pulse Resources in White-footed Mouse Peromyscus leucopus
description
Transcript of Omnivory Driven by Pulse Resources in White-footed Mouse Peromyscus leucopus
Pei-Jen LeeUniversity of Virginia
Portland, 2004
Omnivory Driven by Pulse Resources
in White-footed Mouse Peromyscus leucopus
The Question: What drives omnivory in a trophic generalist
species?
Dose pulse resources drive the behavioral switching between generalist and specialist strategy?
Coll and Guershon (2002):
nutrition balance / toxics dilution obligate omnivores
food supplementation / competition avoidance opportunistic omnivores
Ostfeld and Keesing (2000)
Background: Optimal Foraging Theory (Fretwell, 1972)
Original Resource DistributionSpecialized
Consumption
Resource Distribution after Specialized Consumption
Generalized Consumption
Resource Quality Gradientoptimal
Ab
un
dan
ce /
Co
nsu
mp
tio
n
The Study System: white-footed mouse in oak masting forests
(Whitaker 1966; Wolff 1985)
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1
2
3
4
5
summer fall winter yearInse
ct :
Pla
nt ra
tio in
die
ts
Eatsern Deciduous Forest Agricultural Field
Tools and Assumptions I: Stable isotopes and carbon isotopic mixing
xE (‰) = [(xE/ yE)sample / (xE/ yE)std – 1 ]*1000
13Cstd (‰): 15Nstd (‰):
Pee Dee Belemnite Atmospheric N2
-- Mixing equation:
Δ 13Cmouse (‰) = fc4 x (13Cc4 – 13Cc3)
-- Carbon isotope mixing effect: i.e. C3 versus C4 plants
Assumptions: constant fractionation, equilibrium with food etc.
Tools and Assumptions II : Trophic level based on nitrogen isotopes
Let 15Ndiet-mouse = 2.7 ‰
15Ndiet - intermediate consumer = 3 ‰
15Nplant = a ‰
15Nmouse = x ‰
Consumer trophic level: x-a
Deviation from typical omnivory: |x-(a+3.9)|
mouse
Intermediate Consumers
Producers
P 1-PHerbivore Insectivore Omnivore
P=0,1-P=1 P=1,1-P=0 P=1-P=0.5
a+2.4 a+3+2.4 a+3.9
-- Nitrogen isotopic trophic effect:
Experiment in 2003: simulation of seed mast event across two habitat
types
-3
0
3
6
9
-35-30-25-20-15-10
δ13C %o
δ15N %o
Result I:Fraction of diet derived from millet seeds
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0.1
0.2
0.3
0.4
1 week 7 weekFrac
tiona
of m
illet s
eeds
in d
iets
control
food addition
Food addition effect: p=.01
Time effect: p<.0001
Food by Time: p=.01
Result II:Intra-population divergence in trophic levels
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10
20
30
40
50
Before 1 weeks 7 weeks 15 weeksCV
of n
itrog
en is
otop
ic ra
tios
control food addition
Start End p= .02
Result III:Individual became specialized at millet seeds
Pearson r = .7, p=.05
0.00.20.40.60.81.01.21.41.6
0.0 0.1 0.2 0.3 0.4
Fraction of millet seeds in diets
Dev
iatio
n fro
m o
mni
vory
.
Pearson r = .7, p=.02
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1
2
3
4
5
0.0 0.1 0.2 0.3 0.4
Fraction of millet seeds in diets
Trop
hic le
vel
Summary
Pulse resources could drive the switching between generalist and specialist
strategy in trophic generalist consumers.
Generalist consumers could trace the changes in food abundance efficiently
at population level.
Intra-population trophic divergence (CV of nitrogen isotopes) is greater in poor
environment and smaller in rich environment.
Deviation from omnivory and trophic level of individual consumers are directly
related to the fraction of pulse resource in their diets.
Acknowledgement
Roulston, T’ai
Wilbur, Henry
Swap, Bob
Funding:
Blandy Experimental Farm / Virginia Museum of Natural
History
Carr, Dave / Morris, Clay
Drummond, Brie / Sheu, Yu-Cheng
ALL Blandy Farmers!
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5
10
15
20
25
before 1 week 7 weeks 15 weeks
po
pu
lati
on
de
ns
ity
control
mast