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

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 (IV)

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

Interaction motifs in food websComplexity in Ecology (VI)

predator

consumer

resource

Questions at the community level

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 (VII)

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)

stage/popul. 1

stage/popul. 2

stage/popul. 3

transition / migration 1 → 2

Popul. complexity & Metapop (III)

Population dynamics in discrete time:

where P(t)=P(N(t)) is given by

structured population

metapopulations

)()()1( tNtPtN

)()()( tFtTStP

)()()( tRtDtP

transition fecundity

dispersal matrix reproduction matrix

survival

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

Metapopulations + food webs

Melián, Bascompte & Jordano (2005)

local population

local food chain

metapopulation

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