Geoscience Reference
In-Depth Information
A Species-averaged PPMR
B Link-averaged PPMR
Predator
Predator
M
M
predator-preyA
predator-preyB
M
3
M
4
M
1
M
1
M
M
3
M
4
predator
M
2
M
2
m
1
m
4
m
5
m
1
m
4
m
5
m
3
m
3
m
2
m
2
M
preyB
M
preyB
M
preyA
M
preyA
Prey A
Prey A
Prey B
Prey B
PPMR :
M
predator
/
M
preyA
,
M
predator
/
M
PPMR :
M
predator-preyA
/
M
preyA
,
M
predator-preyB
/
M
preyB
preyB
C Individual-predator PPMR
D Individual-link PPMR
Predator
Predator
M
1
M
1
M
3
M
4
M
3
M
4
M
2
M
2
m
1
m
4
m
5
m
1
m
4
m
5
m
3
m
3
m
2
m
2
Prey A
Prey B
Prey A
Prey B
PPMR :
M
1
/
m
1
,
M
2
/
m
2
,
M
3
/
m
3
,
M
4
/((
m
4
+
m
5
)/2)
PPMR :
M
1
/
m
1
,
M
2
/
m
2
,
M
3
/
m
3
,
M
4
/
m
4
,
M
/
m
Figure 1
The four definitions of PPMR. Here, we use an example where four
individuals of one predator species consume five individuals of two prey species
(A and B, respectively). Dots and circles indicate individual and species identity,
respectively. Arrows represent individual feeding links. M
i
and m
i
denote the body
masses of predator and prey individuals, respectively. (A) Species-averaged PPMR is
calculated as M
predator
/M
preyA
and M
predator
/M
preyB
, where M
predator
and M
preyA
(or
M
preyB
) denote the mean body masses of the predator and prey species, respectively.
(B) Link-averaged PPMR is calculated as M
predator-preyA
/M
preyA
and M
predator-preyB
/
M
preyB
, where M
predator-preyA
(or M
predator-preyB
) denotes the mean body mass of
predator individuals that consume prey species A (or B). (C) Individual-predator
PPMR is calculated by using individual-predator mass M
i
and the average prey mass
(e.g. (m
4
and m
5
)/2 for a predator). (D) Individual-link PPMR is calculated for each
predation event. Grey regions indicate different analytical scales from individual to
link to species resolution.
(ii) link-averaged PPMR, (iii) individual-predator PPMR, and (iv) individu-
al-link PPMR, respectively (
Figure 1
).
The first definition, species-averaged PPMR, is measured by using the
average body sizes of predator and prey species (
Figure 1
A):
Mean mass of predator individuals of a species
Mean mass of prey individuals of a species
ð
Þ
Species-averaged PPMR
¼
1a
The estimation of species-averaged PPMR only requires descriptive informa-
tion about predator and prey species and independent information of represen-
tative body sizes. In contrast to the other three types of PPMR, species-averaged
PPMRdoes not necessarily require individual-level gut content information and
