Isotopic Tracing of Resource Movement by Animal Consumers
Lee, P-J., S. A. Macko and M. A. Bowers
University of Virginia
TWS2004, Calgary, Canada
Background: Pulse resource in space and time
0
1
2
3
4
1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000acor
n pr
oduc
tion
inde
x
Data: Virginia Department of Wildlife and Inland Fisheries
-- acorn mast in Quercus spp.
Background: Isotopic tracing of resource movement
xE (‰) = [(xE/ yE)sample / (xE/ yE)std – 1 ]*1000
13Cstd (‰): PDB
15Nstd (‰): Atmospheric N2
Stapp and Polis (2003)
Marine resources penetrate
inland areas through predator
spillover effects and subsidize
Peromyscus maniculatus
populations
Methods: Mast simulation with C4 millet seeds
-3
0
3
6
9
12
-35-30-25-20-15-10
13C
15N
millet seeds
background plants
Timing: September-October 2003
Intensity: 50 pounds of seed / 0.25 hectare / 10days
Total amount: 200 pounds of seed / 0.25 hectare
Methods : Mice sampling and isotopic analysis
capture-recapture
trapping grids in forests and fields
Isotopic analysis
taking blood and hair samples
Methods : Quantifying resource taken by mice
Mixing equation:
Δ xE (‰) = fb x (xEb) + (fm) x (xEm)
where (fb + fm) = 1
(MacAvoy et al. 2003)
Isotopic turnover in mouse (Mus musculus) blood
13C 15N
Half-life 17 20
Equilibrium 70 56
Methods : applying mouse turnover to P. leucopus
R2 = 0.92
10
15
20
25
30
0 3 6 9 12 15ln(body mass)
ha
lf-lif
e o
f 13
C in
blo
od
(d
ays
).
Black bear(Ursus americanus)
Mink(Mustela vison)
Mouse
Body mass of P. leucopus is similar to that of Mouse = 20grams
Result: Fraction in adult diets derived from millet seeds
Forest
0
0.1
0.2
0.3
0.4
0.5
0.6
0 25 50 75 100 125
Days
Frac
tion
of m
illet s
eeds
in m
ouse
di
et (l
east
squ
are
trans
form
ed)
control
mast
Field
0
0.1
0.2
0.3
0.4
0.5
0.6
0 25 50 75 100 125
Days
Frac
tion
of m
illet s
eeds
in m
ouse
die
t (lea
st s
quar
e tra
nsfo
rmed
)
control
mast
Result: seed mast penetration into neighboring areas
--no immigration from control grids to mast grids detected:
mice commute to gain access to resources
mast resources
could penetrate
~140 meters into
neighboring areas
in forests
y = -0.0034x + 0.4782
R2 = 0.7743
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 50 100 150Distance from masting patch (m)
Fra
ctio
n of
mill
et s
eeds
in
mou
se d
iets
Forest
Field
Result : Mice population density and reproduction output
Forest
0
5
10
15
20
25
30
35
10 50 105 305
days
Mic
e de
nsity
(pe
r grid
)
controlmast
Field
0
5
10
15
20
25
30
35
10 50 105
Days
Mic
e de
nsity
(pe
r gr
id)
controlmast
-- Equal number of juveniles per adult female between mast and control grids
-- Juvenile mice incorporate equal amount of millet-derived nutrients
towards hair tissue synthesis: 32%
Conclusions
--Resource transport efficiency via consumer movements
patchy resources could penetrate hundreds of meters
--Mode of resource movement across neighboring food webs
mice commute to mast grids at a scale of hundreds of meters
--Reproductive output is equal between control and mast grids
local patchy resources could promote regional population dynamics
Acknowledgement
Stephen McAvoy
Clay Morris
Kimberly Spalding
Blandy staff
Funding:
Blandy Experimental Farm
Virginia Museum of Natural History
The Wildlife Society student travel grant
Questions?
Top Related