Geoscience Reference
In-Depth Information
X
S
F
¼
; m
F
;
;
N
ðÞ
o
N
S
ðÞ
o
q
min
F
log PN
ðÞ
o
N
ðÞ
q
min
F
'
;
...
;
jm
F
;
j
ð
32
Þ
i
¼
1
X
S
M
¼
; m
M
;
;
N
ðÞ
o
N
S
ðÞ
o
q
min
M
log PN
ðÞ
o
N
ðÞ
q
min
M
'
;
...
;
jm
M
;
j
ð
33
Þ
i
¼
1
where S
F
and S
M
are the number of species in the fish and mysid community,
respectively, N
ð
o
and N
(i)
are the observed and the model prediction of the
number of individuals of species i, and
m
M
, q
mi
F
and q
mi
M
are the mutation
rate and the minimum genetic similarity value for the fish and mysid com-
munity, respectively.
Simulations were carried out using Eq.
(26)-(28)
with a system size,
J
P
¼
m
F
,
10
3
individuals (J
P
and J
R
represent the number of individual fish
and mysids, respectively). This size was sufficient to recover the rank species
in abundance for the 10 and 3 most common sampled fish and mysid species,
respectively (see
Section III
). Results were obtained after 2
J
R
¼
10
3
generations
of a single model run, where a generation is an update of J
P
and J
R
time steps.
At this stage, species diversity had reached a steady state confirmed by
studying the equilibrium between speciation and extinction rate. Metacom-
munity size was kept constant by assuming zero-sum dynamics. A practical
advantage of assuming zero-sum dynamics is that it is computationally more
efficient, resulting in a substantial decrease in computing time for the simula-
tions. Zero-sum models are equivalent to their non zero-sum counterparts at
stationarity (
Etienne et al., 2007
).
For the fish and mysid communities, we tested 800 combinations of the key
parameters:
[10
4
,10
2
] and q
min
R
q
min
P
[0.75, 0.98]. The values
of the minimum genetic similarity required to complete reproductive isola-
tion were chosen to satisfy the speciation condition, q
min
m
R
¼m
P
2
¼
2
Q
*
. The values of
the parameters are within the range of the observed values of mutation rate
for eukaryotes,
>
[10
6
,10
4
](
Drake et al., 1998
) and genetic divergence
values between species in the range of [5, 10] times greater than genetic
divergence within species to have complete reproductive isolation in the
context of large genomes (
Hickerson et al., 2006
). At each parameter combi-
nation, 100 replicate simulations were completed.
m2
5. Sampling Effort and Species Level Food Web Connectance
A significant body of literature on food webs has explored the sensitivity of
species-level connectance and other species-level food web properties to the
effect of aggregation of different species to the same 'node'. Different meth-
ods of aggregation exist, using different measures of qualitative and quanti-
tative trophic similarity (
Bersier et al., 1999; Goldwasser and Roughgarden,
1997; Martinez, 1991
).