WP 6: Ecological Networks

1
WP 6 Ecological Networks

• Principal investigators
• Jordi Bascompte (Sevilla)
• Joan Saldaña (Girona)
• Postdoc investigator
• Josep-Lluís Garcia (Girona)

2
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)

3
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

4
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

5
Population complexity
Complexity in Ecology (III)
Example of complex life cycle
6
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.)

7
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, ...

8
Trophic interactions in the web
Complexity in Ecology (VI)

• Interaction motifs in food webs

predator
consumer
resource
9
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

10
Complexity in Ecology (VIII)

• Examples of food webs

Montoya Solé (2003)
11
Complexity in Ecology (IX)

• Statistical description of food webs

Montoya Solé (2003)
12
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

13
Popul. complexity Metapop (II)
transition / migration 1 ? 2
stage/popul. 2
stage/popul. 1
stage/popul. 3
14
Popul. complexity Metapop (III)

• Population dynamics in discrete time
• where P(t)P(N(t)) is given by
• structured population
• metapopulations

survival
fecundity
transition
dispersal matrix
reproduction matrix
15
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 equa-lise the actual fitnesses in different
  stages / habitats

16
Metapopulations food webs
local food chain
local population
metapopulation
Melián, Bascompte Jordano (2005)
17
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 metapopu-lation (and
  vegetation) dynamics