Post on 19-Jan-2016
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Ecologie et Ecologie et macroévolutionmacroévolution
IHPSTIHPST PhilbioPhilbio 20/03/200820/03/2008
Julien DelordJulien Delord CERES-ERTI
• Introduction: Do ecological communities exist (and Introduction: Do ecological communities exist (and evolve)?evolve)?
• 1. Presentation of the Unified Neutral Theory of 1. Presentation of the Unified Neutral Theory of Biodiversity (UNTBB)Biodiversity (UNTBB)
• 2. The (epistemological) non-neutrality of neutral models2. The (epistemological) non-neutrality of neutral models- Neutrality and falsity (in biology)- Neutrality and falsity (in biology)- Neutrality as a strategy towards generality and unification- Neutrality as a strategy towards generality and unification
• 3. Neutrality and the unification of evolutionary theory3. Neutrality and the unification of evolutionary theory - Neutral theories in genetics and in ecology- Neutral theories in genetics and in ecology- « L-neutrality » and « L+1 neutrality »- « L-neutrality » and « L+1 neutrality »- « Grand Unification » or « domain unification »?- « Grand Unification » or « domain unification »?
- Communities as evolutionnary entities- Communities as evolutionnary entities
• ConclusionConclusion- - Theory change in ecologyTheory change in ecology
Neutral Theories in Ecology and Neutral Theories in Ecology and EvolutionEvolution
« 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!!!
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
Henry GLEASON (1882-1975)
« Le phénomène de la végétation dépend complètement des phénomènes des espèces individuelles »
Assemblage des végétations au hasard
Dynamiques des communautés végétales
Organicisme vs. Individualisme
Introduction : Do ecological communities Introduction : Do ecological communities exist and evolve ?exist and evolve ?
Community 1
A: 25% B: 25% C: 25% D: 25%
Community 2
A: 80% B: 5% C: 5% D: 10%
D
C
B
A
Ecological CommunityEcological Community
Group of populations from different species interacting with each other and sharing the same spatio-temporal framework.
Species Richness
Relative Species Abundance
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.
27 different models of Species Abundance Distribution
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
- How to explain species How to explain species biodiversity in ecological biodiversity in ecological communities ?communities ?
- How to explain the curves of How to explain the curves of relatives species abundance ?relatives species abundance ?
--Is the niche Is the niche conceptconcept
necessary ?necessary ?
--From case-study From case-study rules to general rules to general deductive laws !deductive laws !
1. The Unified Neutral Theory of Biodiversity1. The Unified Neutral Theory of Biodiversity and Biogeography (UNTBB)and Biogeography (UNTBB)
Courbes SAD (Surface Abundance Distribution)
Principles of UNTBB
Definition: Ecological community : Group of trophically similar and sympatric species
Conservation law: Neutrality : The assumption of a complete identity of ecological interactions affecting community organisms, i. e. a per capita ecological equivalence (in terms of reproduction and death rates + speciation) among all individuals of every species.
Dependant Variables:Relative species abundance and species numberParameters:Reproduction rates, death rates, speciation rates, community size (= number of individuals), limits to dispersal.
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)
Markovian process
Theoretical developments
Random walk of the abundance of ith species under ecological drift
(The initial relative species abundance is 0.5 - ergodic )case)
A brief reminder of population genetics:
how to calculate the proportion of homozygotes at equilibrium between mutation and drift.
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 JM the number of individuals in metacommunity M.
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.
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.
Etienne R., Alonso D., McKane A. J., « The zero-sum assumption in neutral biodiversity theory », Journal of Theoretical Biology, 248, 2007, p. 522-536.
Dornelas M. et al., “Coral reef diversity refutes the neutral theory of biodiversity”, Nature, 440, 2006, p. 80-82.
Epistemological questions: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
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
2. The (epistemological) non-neutrality 2. The (epistemological) non-neutrality of neutral modelsof neutral models
- Neutrality and falsity (in biology)- Neutrality and falsity (in biology)
3. Neutrality and the unification of 3. Neutrality and the unification of evolutionary theoryevolutionary theory
Neutral theories in genetics and in ecologyNeutral theories in genetics and in ecology
Comparative approach of neutralityComparative approach of neutrality
in genetics and in ecologyin genetics and in ecology
Hu X.-S., He F. & Hubbel S. P. (2006), “Neutral theory in macroecology and population genetics”, Oikos, 113, 3, p. 548-56.
Type d’Allèle
Individu
Natural selection Neutral Theory of Biodiversity
Species
Class of individuals
Community
Individual
Espèce
Allèle
Type d’Allèle
Individu
Espèce
Allèle
Class of Alleles
Individual
Species
Allele
Evolver
Interactor
Replicator-Interactor
Niche ???
Neutral theory of evolution
Evolver
Replicator-Interactor
UNT and phylogenyUNT and phylogenyLast consequence of Hubbell ’s theory for
phylogeny (but not the least), UNT models show that the organization of biodiversity at different
scales is intrinsically fractal.
UNT and phylogenyUNT and phylogeny
On the fractal dimension of biodiversity :
Hubbell : “ If biodiversity is a perfectly homogeneous fractal, this implies that a satisfactory answer to the question - how many species are there ? – cannot really be answered except operationally.It requires a definition of the scale of aggregation that we call species! » (p.263)
This implies a pluralist or arbitrary fixation of the level of “ ranking ”for the species.
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 ?)
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
NeutralityNeutrality
Level Level L+1L+1
(species)(species)
Level LLevel L
(individuals)(individuals)
YesYes NoNo
YesYes UNTBBUNTBBApparent Apparent neutralityneutrality
NoNo « free » « free » replicatorsreplicators
Species Species selectionselection
« L neutrality » and « L+1 « L neutrality » and « L+1 neutrality »neutrality »
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
- « Grand Unification » or « domain unification »?- « 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
- Ecological drift requires non-neutral mutations- Ecological drift would induce different speeds of genetic drift
Incompatibility
Gould’s hierarchical Gould’s hierarchical macroevolutionary macroevolutionary
theorytheory
Vrba and Gould « The hierarchical expansion of sorting and selection: sorting and selection cannot be equated », Paleobiology, 12, 1986, p. 217-28.
Stephen J. Gould’s approach
Species selection: Species selection:
- Emergent species-level trait- Emergent species-level fitness
- Aggregate traits- Neutral traits
- 2 Confusions : 2 Confusions : - The nature of extinction (why dissymetry between speciation and extinction???) (p. 669)- Species drifting and clade drifting (p. 718)
« True » species
selection
Gould’s analogy between micro- and
macroevolution
Gould’s analogy Gould’s analogy between micro- between micro-
and and macroevolution macroevolution
Hiérarchies historiques et Hiérarchies historiques et fonctionnellesfonctionnelles
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)
« Domain unification » in Evolution« Domain unification » in Evolution
MacroevolutioMacroevolutionn
MegaevolutionMegaevolution - - Fauna and floraFauna and flora- Geological times- Geological times
Punctuated equilibrium theory,Punctuated equilibrium theory,fractal dynamics, etc.fractal dynamics, etc.
MesoevolutionMesoevolution -Communities et meta- Communities et meta- communitiescommunities
- Ecological times- Ecological times
UNTBBUNTBB
Interspecific competitionInterspecific competition between between neutral individuals neutral individuals OrOr Niche assemblyNiche assembly
MicroevolutioMicroevolutionn
Darwinian Darwinian evolutionevolution
- Populations- Populations- Adaptations- Adaptations
Natural selectionNatural selection(mutation, sélection, migration)(mutation, sélection, migration)
Intraspecific competitionIntraspecific competition
Molecular evolutionMolecular evolution - Populations- Populations- Neutral variations- Neutral variations
Neutral theory of molecular Neutral theory of molecular evolutionevolution(mutation, genetic drift)(mutation, genetic drift)
Interallelic competitionInterallelic competition
Alleles
Organism
Species
Genus or family
Conclusion: 2 macro-ecoevolutionary strategiesConclusion: 2 macro-ecoevolutionary strategies
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
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)?????
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, Banavar Jayanth R., Hubbell Stephen P., Maritan Amos, “A neutral theory and relative species abundance in ecology”, Nature, 424, 2003, p. 1035-1037.- Volkov Igor, Banavar Jayanth R., Hubbell Stephen P., Maritan Amos, “Patterns of relative species abundance in rainforests and coral reefs”, Nature, 450, 1 november 2007, p. 45-49.
- 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, Banavar Jayanth R., Hubbell Stephen P., Maritan Amos, “A neutral theory and relative species abundance in ecology”, Nature, 424, 2003, p. 1035-1037.- Volkov Igor, Banavar Jayanth R., Hubbell Stephen P., Maritan Amos, “Patterns of relative species abundance in rainforests and coral reefs”, Nature, 450, 1 november 2007, p. 45-49.