Ecologie et macrovolution

1
Ecologie et macroévolution

• IHPST Philbio
  20/03/2008

Julien Delord
CERES-ERTI
2
Neutral Theories in Ecology and Evolution

• Introduction Do ecological communities exist
  (and evolve)?
• 1. Presentation of the Unified Neutral Theory of
  Biodiversity (UNTBB)
• 2. The (epistemological) non-neutrality of
  neutral models
• - Neutrality and falsity (in biology)
• - Neutrality as a strategy towards generality
  and unification
• 3. Neutrality and the unification of evolutionary
  theory
• - Neutral theories in genetics and in ecology
• -  L-neutrality  and  L1 neutrality 
• -  Grand Unification  or  domain
  unification ?
• - Communities as evolutionnary entities
• 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 ecological communities exist
and evolve ?

Ecological Community Group of populations from
different species interacting with each other and
sharing the same spatio-temporal
framework. Species Richness Relative
Species Abundance
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 lidée selon laquelle il existe des
règles qui gouvernent lassemblage 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 explain species biodiversity in
  ecological communities ?
• How to explain the curves of relatives species
  abundance ?
• -Is the niche concept
• necessary ?
• -From case-study
• rules to general
• deductive laws !

9
Courbes SAD (Surface Abundance Distribution)
10
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 number Parameters R
eproduction rates, death rates, speciation rates,
community size ( number of individuals), limits
to dispersal.
11
Principles of UNTBB (Contd)
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 JM the 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.
19
(No Transcript)
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
Natural selection
Neutral Theory of Biodiversity
Neutral theory of evolution
Community
Evolver
Niche ???
Species Class of individuals
Espèce
Species
Espèce
Evolver
Individu
Interactor
Replicator
Individu
Individual
Individual
-Interactor
Type dAllèle
Class of Alleles
Type dAllèle
Allèle
Replicator
Allele
Allèle
-Interactor
26
UNT and phylogeny Last 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.
27
UNT 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.
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 Kimuras 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 L1 (replicator
  ltgt interactor)
• Neutrality relative to level L
  (replicator-interactor)
• Example of  contextual  neutrality genetic
  drift and transposons

30
 L neutrality  and  L1 neutrality 
31

• Kimuras neutral theory was defined as a  L1
  neutrality  with respect to natural selection
• Hubbells 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

33
(No Transcript)
34
Goulds hierarchical macroevolutionary theory
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. Goulds approach

• Species selection
• Emergent species-level trait
• Emergent species-level fitness
• Aggregate traits
• Neutral traits
• 2 Confusions
• The nature of extinction (why dissymetry between
  speciation and extinction???) (p. 669)
• Species drifting and clade drifting (p. 718)

?  True  species selection
37
Goulds analogy between micro- and macroevolution
38
Goulds analogy between 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-ecoevolutionary strategies
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.
  1085410861.
• - 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.

45
(No Transcript)