Geoscience Reference
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of convergence between ecological and evolutionary dynamics requires a
broad framework able to accommodate individual-level data that have suffi-
cient resolution and number of species to permit inference at individual,
population, community and food web levels simultaneously.
We here present a fine-grained analysis linking a large individual-based
food web with a combined population genetics, community and food web
model to generate a framework that can evaluate the patterns of intraspecific
variation with convergent ecological and evolutionary dynamics. Our main
goal has been to develop a general framework, but we also have tested a
neutral model using processes of individual organisms—death driven by
pairwise trophic interactions, mating with genetic constraints to have viable
offspring with mutations and genetic-distance-based speciation to quantify
individual feeding rate, species-level diversity and food web connectivity.
Using the predictions of simulated food webs, we test the patterns in species
diversity and individual connectivity produced by these basic mechanisms
against the observed number of individual prey per predator and estimates of
abundance in space and time. We also infer the speciation rate values given
by the basic mechanisms that genetic and ecological drift take into account.
We start analysing the number of observed prey as a consequence of
sampling effort in predator populations. The trophic spectrum of the popu-
lations sampled in the Guadalquivir estuary does not saturate, even after
sampling more than 1000 individuals for some populations. This highlights
the need of individual-based models in food webs to study the mechanisms
driving such high variance in individual diets and its implications for food
web structure and dynamics. We then proceed to analyse the prey consump-
tion of individual predators and found that the observed individual rank
connectivity curves depart significantly from the model expectation in all
environmental situations (
Figures 5 and 6
).
There is a growing literature on the role of body size in structuring meta-
communities (
De Roos, 2008; O'Dwyer et al., 2009
) and food webs (
Andersen
and Beyer, 2006; Beckerman et al., 2006; Woodward and Warren, 2007
), and
so we considered whether the size of predators could account for the variation
in the number of prey items per individual predator. We found that most
individual fish caught were small-sized, including mainly postlarvae and juve-
niles. Given this narrow size spectrum sampled, body size only partially
explains the variance in the number of prey per individual predator. We
found that individual size can predict the maximum number of prey items
but not the trend of the variance within each size class (
Figures 7 and 8
). This
suggests complementary mechanisms to predict prey consumption rate are
required. This also suggests more than one dimension is required to predict
more accurately individual trophic diets (
Allesina et al., 2008; Jacob et al.,
2011
). This dataset represents a large sampling effort with several replicates in
different environmental conditions and seasons, but each of these replicates is
