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