Ecologie et macroévolution

1. Ecologie et macroévolution IHPSTPhilbio 20/03/2008 Julien Delord CERES-ERTI

2. Neutral Theories in Ecology and Evolution • Introduction: Do ecologicalcommunitiesexist (and evolve)? • 1. Presentation of the UnifiedNeutralTheory of Biodiversity (UNTBB) • 2. The (epistemological) non-neutrality of neutralmodels - Neutrality and falsity (in biology) - Neutrality as a strategytowardsgenerality and unification • 3. Neutrality and the unification of evolutionarytheory - Neutraltheories in genetics and in ecology - « L-neutrality » and « L+1 neutrality » - « Grand Unification » or « domain unification »? - Communities as evolutionnaryentities • Conclusion - Theory change in ecology

3. « Are phenomenological communities causal systems? » (Sterelny 2006) = Are communities structured, functionally organized with effects on the fate of populations they are composed of? (downward causation) 3 criteria: - Boundedness - Internal regulation - Emergent property effects  For Sterelny, they fail to meet these criteria…  For most ecologists, communities are structured by niche competition and niche assembly rules!!!

4. Dynamiques des communautés végétales Organicisme vs. Individualisme Henry GLEASON (1882-1975) « Le phénomène de la végétation dépend complètement des phénomènes des espèces individuelles »  Assemblage des végétations au hasard Frederic CLEMENTS (1874-1945) « Comme un organisme, la formation naît, croît, mûrit et meurt. En outre chaque formation climacique [ayant atteint le climax] est capable de se perpétuer, en reproduisant avec une fidélité absolue les étapes de son développement », 1916.  Déterminisme des successions végétales

5. Introduction : Do ecologicalcommunities exist and evolve ? A B C D Community 1 A: 25% B: 25% C: 25% D: 25% Community 2 A: 80% B: 5% C: 5% D: 10% EcologicalCommunity Group of populations fromdifferentspeciesinteractingwitheachother and sharing the samespatio-temporalframework. SpeciesRichness Relative SpeciesAbundance

6. 27 different models of Species Abundance Distribution McGill Brian J. et al., “Species abundance distributions: moving beyond single prediction theories to integration within an ecological framework”, Ecology Letters, 10, 2007, p. 995-1015.

7. Jared Diamond (1975) a été le premier à explorer l’idée selon laquelle il existe des règles qui gouvernent l’assemblage des communautés: La diversité des communautés dépend de leur structuration Ressources restantes

8. 1. The Unified Neutral Theory of Biodiversity and Biogeography (UNTBB) • How to explainspeciesbiodiversity in ecologicalcommunities? • How to explain the curves of relatives speciesabundance? • -Is the niche concept • necessary ? • -From case-study • rules to general • deductivelaws !

9. Courbes SAD (Surface Abundance Distribution)

10. Principles of UNTBB Definition: Ecologicalcommunity : Group of trophicallysimilar and sympatricspecies Conservation law: Neutrality : The assumption of a completeidentity of ecological interactions affectingcommunityorganisms, i. e. a per capita ecologicalequivalence (in terms of reproduction and death rates +speciation) among all individuals of everyspecies. Dependant Variables: Relative speciesabundance and speciesnumber Parameters: Reproduction rates, death rates, speciation rates, community size (= number of individuals), limits to dispersal.

11. Principles of UNTBB (Cont’d) Hypothesis: « Communities are open, nonequilibrium assemblages of species largely thrown together by chance, history and random dispersal » (Hubbell, 2001, p.8) Process: Ecological drift: demographic stochasticity in a neutral community (~ genetic drift) Result: Curves of relative species abundance at equilibrium between speciation and extinction (stationary dynamics)

12. Markovian process

13. Theoretical developments Random walk of the abundance of ith species under ecological drift (The initial relative species abundance is 0.5 - ergodic )case)

14. A brief reminder of population genetics: how to calculate the proportion of homozygotes at equilibrium between mutation and drift.

15. Theoretical developments How to calculate the probability of drawing two individuals from the same species at equilibrium between speciation and ecological drift. Let  be the speciation rate per generation and JMthe number of individuals in metacommunity M.

16. Theoretical developments F2 = 1 / 1+ 2 JM  Feq = 1 / 1 + 2Nμ  = 2 JM  is named by Hubbell the fundamental biodiversity number because this dimensionless number controls not only the equilibrium species richness but also the equilibrium relative species abundance in the metacommunity.

17. Some results and predictions of UNT on biodiversity dynamics By generalization, Hubbell extends this rationale to the case of 3 individuals randomly chosen in JM , etc., then J individuals belonging to S species.

18. Etienne R., Alonso D., McKane A. J., « The zero-sum assumption in neutral biodiversity theory », Journal of Theoretical Biology, 248, 2007, p. 522-536.

20. Dornelas M. et al., “Coral reef diversity refutes the neutral theory of biodiversity”, Nature, 440, 2006, p. 80-82.

21. Epistemological questions: • Ecology and its recurrent « Physics envy » • In search for laws, regularities and generality •  The concept of generality: from universality (spatio-temporal unboundedness) to invariance (Van Fraassen, Laws and Symmetry, 1991) • Invariance as a conservation law (when a certain value is conserved through time despite the changes of the system) •  Neutral models as a quest for invariance in ecology •  Generality should enhance unification

22. 2. The (epistemological) non-neutrality of neutral models - Neutrality and falsity (in biology) Conservation law in physics (sub-atomic level) vs. conservation law in ecology (macroscopic world)  In particle physics, conservation laws (i. e. conservation of energy) give rules to make sense of the data and to define the ontology of particles.  In ecology, the ontology is already defined but the rules are not known. They are interpreted in light of the discrepancy between expected patterns and empirical data. Problems: 1. Theoretical: the underdetermination of theories 2. Empirical: the confirmation of the neutral model

23. 3. Neutrality and the unification of evolutionary theory Neutral theories in genetics and in ecology Comparative approach of neutrality in genetics and in ecology

24. Hu X.-S., He F. & Hubbel S. P. (2006), “Neutral theory in macroecology and population genetics”, Oikos, 113, 3, p. 548-56.

25. Neutral theory of evolution Natural selection Neutral Theory of Biodiversity Community Evolver Niche ??? Espèce Species Class of individuals Species Evolver Espèce Interactor Individu Replicator Individu Individual Individual -Interactor Type d’Allèle Class of Alleles Type d’Allèle Replicator Allèle Allele Allèle -Interactor

26. UNT and phylogeny Last consequence of Hubbell ’s theory for phylogeny (but not the least), UNT models show thatthe organization of biodiversityatdifferentscalesisintrinsically fractal.

27. UNT and phylogeny • On the fractal dimension of biodiversity : • Hubbell : “ If biodiversityis a perfectlyhomogeneous fractal, thisimpliesthat a satisfactoryanswer to the question - how manyspecies are there ? – cannotreallybeansweredexceptoperationally. • It requires a definition of the scale of aggregationthatwe call species! »  (p.263) •  This implies a pluralist or arbitrary fixation of the level of “ ranking ”for the species.

28. Are neutrality in genetics and ecology comparable? Historical differences :  The neutral theory of molecular evolution appeared as a solution to a problematic in evolutionary genetics and as a consequence of new developments in molecular biology (high protein polymorphism). “The theory of molecular evolution by mutation and random drift led to Kimura’s prediction that those amino acids or nucleotide changes that have the least consequence would evolve faster” (J. Crow, Neutral models in biology, 1987, p. 13).  UNTBB as an elaborated null model??? What is selection for UNT ? (Rules of niche assembly ?)

29. Neutrality • Neutrality in a hierarchical systems • Neutrality relative to level L+1 (replicator <> interactor) • Neutrality relative to level L (replicator-interactor) • Example of « contextual » neutrality: genetic drift and transposons

30. « L neutrality » and « L+1 neutrality »

31. Kimura’s neutral theory was defined as a « L+1 neutrality » with respect to natural selection • Hubbell’s neutral theory of biodiversity was defined as a « L neutrality » with respect to differential replication

32. - « Grand Unification » or « domain unification »? Is a neutral synthesis of evolutionary theory possible ? Ecological drift vs deterministic “rules” of niche assembly Genetic drift vs natural selection Incompatibility Incompatibility • Ecological drift requires non-neutral mutations • Ecological drift would induce different speeds of genetic drift

34. Gould’shierarchicalmacroevolutionarytheory

35. Vrba and Gould « The hierarchical expansion of sorting and selection: sorting and selection cannot be equated », Paleobiology, 12, 1986, p. 217-28.

36. Stephen J. Gould’sapproach • Speciesselection: • Emergent species-level trait • Emergent species-level fitness • Aggregate traits • Neutral traits • 2 Confusions : • The nature of extinction (whydissymetrybetweenspeciation and extinction???) (p. 669) • Speciesdrifting and clade drifting (p. 718)  « True » species selection

37. Gould’sanalogybetween micro- and macroevolution

38. Gould’sanalogybetween micro- and macroevolution

39. Hiérarchies historiques et fonctionnelles

40. « Domain unification » in Evolution UNTBB is both a macroecological and a macroevolutionary theory : Evolution at the community level is ecology!!! (The equivalent of genetics at the community level is ecology)

41. Conclusion: 2 macro-ecoevolutionarystrategies Alleles Organism Species Genus or family

42. Conclusion • 3 major challenges for the UNTBB: • 1. Ecology: • “Neutral theory is limited because it is incapable of predicting which species are rare or abundant” (Tilman, 2004)… • Frustration for disappearance of causes, forces, etc: • Opportunity for ecologists to move from typological to population thinking!! •  Challenge of the reconciliation with the niche perspective, like the niche construction: from idealized invariant to ceteris paribus laws. • Dynamics of species substitution

43. Conclusion • 2. Evolution: • How to test the neutral nature of species substitution at the community level ? • Community invasion rate as a test for species substitution??? • The unification of macro-and microevolution !!! • More collaboration between paleoevolution and community ecology with regard to species evolution (for a better contribution to the emergent property/emergent fitness debate)?????

44. Bibliography • - Dornelas M., Connolly S. R., Hughes T. P., “Coral reef diversity refutes the neutral theory of biodiversity”, Nature, 440, 2006, p. 80-82. • - Etienne R., Alonso D., McKane A. J., « The zero-sum assumption in neutral biodiversity theory », Journal of Theoretical Biology, 248, 2007, p. 522-536. • - Holt Robert D., “Emergent neutrality”, Trends in Ecology and Evolution, 21, 10, 2006, p. 531-533. • - Hu X.-S., He F. & Hubbel S. P., 2006, “Neutral theory in macroecology and population genetics”, Oikos, 113, 3, p. 548-56. • - Hubbell Stephen P., 2001, The Unified Neutral Theory of Biodiversity and Biogeography, Princeton and Oxford, Princeton University Press. • - Leigh Jr. E. G., « Neutral theory: a historical perspective », Journal of Evolutionary Biology, 20, 2007, p. 2075-2091. • - McGill Brian J. et al., “Species abundance distributions: moving beyond single prediction theories to integration within an ecological framework”, Ecology Letters, 10, 2007, p. 995-1015. • Sterelny, K., Local Ecological Communities, Philosophy of Science, 73, 2006, p. 215-231. • - Tilman, D., “Niche tradeoffs, neutrality, and community structure: a stochastic theory of resource competition, invasion, and community assembly”, Proc. Natl. Acad. Sci., 101, 2004, p. 10854–10861. • - Volkov Igor, BanavarJayanth R., Hubbell Stephen P., Maritan Amos,“A neutral theory and relative species abundance in ecology”, Nature, 424, 2003, p. 1035-1037. • - Volkov Igor, BanavarJayanth R., Hubbell Stephen P., Maritan Amos,“Patterns of relative species abundance in rainforests and coral reefs”, Nature, 450, 1 november 2007, p. 45-49.