WP 6: Ecological Networks

Principal investigators:
Jordi Bascompte (Sevilla)
&
Joan Saldaña (Girona)

Postdoc investigator:
Josep-Lluís Garcia (Girona)
Related research topics of PIs

Structured population dynamics (JS)

Adaptive dynamics (JS)

Habitat destruction & metapop. dynamics (JB, JS)

Food-web structure and dynamics (JB)

Spatial dimension of community dynamics (JB)

Plant-animal coevolutionary networks (JB)
Complexity in Ecology

Since the 70s it is well known that simple
models can display complex dynamics
Dinamical complexity

Several ways of introducing complexity
into ecological models to capture the
structural complexity of natural systems
Complexity in Ecology (II)

At the population level:
Individuals can be classified according to internal
variables (age, size, rank, stage, ...) rellevant for their
physiological state
Populations are not described by a number but by a
density of individuals with respect to the internal
variables
Individuals can also be located in the space → density
with respect to the space and the internal variables
Population complexity
Example of complex life cycle:
Complexity in Ecology (III)
Questions at the population level
Complexity in Ecology (IV)



Role of hierarchical / asimetrical competition
in the ecological stability (rank vs scramble
competition)
Effects of the population structure on the
food-chain dynamics (persistence, stabilizing
effect)
Evolutionary stable traits (strategies)
(f.ex., optimal transition rates among individual stages,
optimal resource allocation, etc.)
Complexity in Ecology (V)

At the community level:
Community = a highly interconnected
assemblage of species characterized by
recurrent food-web structures (motifs)
= complex network of interactions
Sorts of interactions: predation, competition,
mutualism, ...
Trophic interactions in the web
Complexity in Ecology (VI)

Interaction motifs in food webs
predator
consumer
resource
Questions at the community level
Complexity in Ecology (VII)

Topological properties of static food
webs (connectivity vs number of species, degree
distribution, degree correlations, interaction strenght motifs, ...)

Food-web structure and stability
→ The diversity-stability debate
→ The role of body size in the trophic interations

Growing food webs: assembly models
and evolutionary models
Complexity in Ecology (VIII)

Examples of food webs:
Montoya & Solé
(2003)
Complexity in Ecology (IX)

Statistical
description
of food
webs:
Montoya & Solé
(2003)
Population complexity & Metapop

The structured population formalism is
similar to the one used in metapopulations
individual stage → local population
population → metapopulation
transition rate → migration rate
Popul. complexity & Metapop (II)
transition / migration
1→2
stage/popul. 2
stage/popul. 1
stage/popul. 3
Popul. complexity & Metapop (III)

Population dynamics in discrete time:
N (t  1)  P(t ) N (t )
where P(t)=P(N(t)) is given by
survival
fecundity
transition
P(t )  TS (t )  F (t )
structured population
P(t )  D(t ) R(t )
metapopulations
dispersal matrix
reproduction matrix
Popul. complexity & Metapop (IV)

What are the evolutionarily stable transition rates /
dispersal rates in the previous model?
Ideal free distribution among stages / populations
The ideal free distribution (Fretwell & Lucas, 1970) is a hypothesis about how
organisms would distribute themselves in a space composed of habitats of
different suitability if they were free to move so as to maximize their fitness
→ Individuals will so distribute themselves as to equalise the actual fitnesses in different stages / habitats
Metapopulations + food webs
local food chain
local population
metapopulation
Melián, Bascompte
& Jordano (2005)
Research objectives of the WP

Analytical results on persistence theory
in food webs: study of the effect of different
nonlinearities in food-web models on the dynamical
properties of the solutions

Mean-field approximation to metapopulation (and vegetation) dynamics