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mating (
Figure 1
B and C). As in the model for one metacommunity, the
dynamics of the speciation rate in the resource-predator individual-based
food web model is controlled by the birth-death process, mutation rate (
m
P
and
m
R
, respectively) and the minimum genetic similarity value to have viable
offspring (q
min
P
and q
min
R
, respectively).
B. Study Area and Sampling Methods of a Large
Individual-Based Food Web
1. Study Area
Estuaries have an important role as a nursery, thus species with part of their
life cycle in the Guadalquivir estuary have a strong migratory and genetic flow
with the Atlantic Ocean (
Fern´ndez-Delgado et al., 2007
). Despite the high
level of connectance between the ocean and the estuary, testing the model may
detect the importance of factors like dispersal limitation, environmental
fluctuations and spatial heterogeneity. Stomach contents and estimates of
abundance were collected monthly from February 1998 to January 1999 at
three locations in the estuary of the Guadalquivir river, southern Spain.
Samples were taken across a range of different environmental conditions,
with seasonal variations in temperature and spatial variations in salinity.
Sampling effort was maintained constant across the whole study period and
more than 1000 individuals were sampled in some species (
Figure 2
). The
number of individual captures for each species was correlated with the inde-
pendent estimation of local species abundance (
Figure 3
). The cumulative
estimations of abundance we have analysed have approximately 9
10
6
and
10
6
fish andmysid individuals, respectively. The cumulative diet sampling
we have analysed has 23989 individuals (5725 individual fish predators, 159
individual fish preys and 18,105 individual mysid preys). From this data, we can
extract the observed number of individual prey per predator and the species
rank abundance curves for the fish and the mysid communities under a range of
temperature and salinity conditions. Sampled predator individuals show the
prey individuals that have not yet been digested, and because we focus on prey
like mysids that are quickly digested, the observed data represents the 'instan-
taneous' rate or the very recent predation events of each predator individual.
Note also that the instantaneous rate has been replicated almost 100 times
across all the seasons between February 1998 and January 1999.
The Guadalquivir river estuary (SW Spain: 37
15
0
-36
45
0
N, 6
00
0
-
6
22
0
W) is vertically mixed, shows a longitudinal salinity gradient and a
completely mixed water column (
Vann´y, 1970
). As most temperate and
well-mixed estuaries, its maximum turbidity zone is in the oligohaline region.
The tidal influence reaches about 110 km up stream from the river mouth,
and the mean tidal range is 3.5 m in the outer estuary.
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