The document discusses the application of equilibrium theory to community assembly on remote islands, emphasizing the unique flora and fauna shaped by in situ evolution and biogeographic isolation. It outlines key concepts in island biogeography, including species saturation, colonization dynamics, and the impact of geological history on species richness and diversification. The text also highlights ongoing research efforts and collaborations aimed at enhancing the understanding of species richness determinants and evolutionary processes in island ecosystems.

1. Community Assembly on Remote Islands
Does Equilibrium Theory apply?
Christophe Thébaud
University of Toulouse
ISLANDS
2012-2015

2. Islands are important systems to understand how organisms
came to be and why they are distributed the way they are
remote oceanic islands have very limited faunas and
floras
similarities between island fauna and flora and nearby
continents
uniqueness of island fauna and flora - in situ evolution
Alfred Russell Wallace

3. CONTINENT
ISLANDS
Island Biogeography in the 1960s • 3
of geographic variation. They turned out to be mostly specialized on mar-
ginal habitats, those inhabited by relatively small numbers of species.
In Melanesia, the marginal habitats include littoral environments of the
coastal shore, river-edge forests, and savannas. Such are places that are
happenstance staging areas for between-island dispersal. Local populations
Figure 1.1. E. O. Wilson with guard crossing the lower Mongi River, Papua New
Guinea, April 1955.
MelanesiaSoutheastern Asia
Time
Marginal
Habitats
Inner
Rain
Forest
1
2
4
3
5
6
Figure 1.2. The taxon cycle in the Melanesian ant fauna (Wilson 1965, modified
from Wilson 1959).
E.O. Wilson 1955 Papua New Guinea
Wilson 1961
« It can be inferred that, as a rule, new species can
invade an island only if resident species are
exJnguished to make room for them »
Wilson’ s concept of species saturation and island size

4. Species numbers decrease with increasing distance
from the nearest land mass (source of colonisation)
« The open sea is like a sieve which let pass
only certain adapted elements » (Mayr
1940)
Vanikoro White-eye

5. Species numbers decrease with increasing distance
from the nearest land mass (source of colonisation)
« The open sea is like a sieve which let pass
only certain adapted elements » (Mayr
1940)
Vanikoro White-eye
Near
Far

6. What explains species numbers on discrete areas
with hard boundaries like islands?

7. 1967
1963

8. Island Biogeography Theory
Equilibrium model of a biota of a single island
Dynamic steady state in which species continually
disappear from islands only to be replaced at an equal
rate by new colonists
Changing intersections (equilibria)
predicting the area and distance effects

9. Huge impact on the study of the distribution organisms,
present, past, and future
Key to the integration of ecology, population biology, evolution, and paleontology
Metapopulation theory; r/K selection; taxon cycles; neutral theory
Important implications for conservation of species
Refuge design, extinction risk of small populations
Confirmed Darwin and Wallace’s insights that island and archipelagos provide discrete,
manageable, and replicated microcosms of the rest of the world
A very powerful conceptual framework in ecology and evolution, ever since MacArthur
and Wilson 1963

10. Premises of CESAB-ISLANDS
A primary element that is missing from the original conception of the model is the
role of evolutionary divergence and species formation on islands
Speciation may play a role analogous to immigration in adding species to communities, and this might
be especially likely on distant islands (because immigration is rare)
However,
This will in some way depend on a given organism’s ability to disperse, which may determine the
likelihood of colonization as well as opportunities for speciation.
This will also depend on the geological and geographical history of an island system, where the size,
number, elevation and isolation of islands may vary through time, leading to nonequilibrium situations
(mass extinctions, peaks of colonization, …)

11. Aims of CESAB-ISLANDS
Species richness
Determinants Habitat Diversity
Island Isola2on
Island Eleva2on
Island Geology
Precipita2on
Soil type diversity
La2tude
…

12. Aims of CESAB-ISLANDS
Species richness
Determinants Habitat Diversity
Island Isola2on
Island Eleva2on
Island Geology
Precipita2on
Soil type diversity
La2tude
…
Species richness
Realized
Diversifica3on
Realized
Coloniza3on
Diversifica3on
Timing
Time since
Coloniza3on
Determinants
Diversification = speciation minus extinction

13. Use replicated phylogeneJc (Jme-calibrated) data to go beyond the
study of mere species richness
Use staJsJcal models allowing the direct use of actual data
Use a plasJc staJsJcal framework for further development
Approach
t
Number and richness of island lineages
Speciation times

14. 355 island lineages iden,fied from the literature

15. Importance of the interplay between immigration
history and diversification dynamics
Major outcomes
Josselin Cornuault

16. Importance of non equilibrium
processes
Bird species have accumulated at
slow rates, through both new
arrivals and in situ speciation, and
total diversity is far from
asymptotic phase
Major outcomes
Luis Valente

17. STAN MCMC Bayesian so,ware
Build 2me-calibrated
phylogeny with Beast
Major outcomes

18. STAN MCMC Bayesian so,ware
Build 2me-calibrated
phylogeny with Beast
r T
DNA P(DNA | x, T)
P(r | D, β) P(T | D, β)
x
P(x, N | r, T)
S
h N
P(S | N, h)
Determinants
ri: Diversifica,on rate of lineage i
Ti: Time since coloniza,on of lineage i
xi: (Incomplete) phylogeny of lineage i
Ni: Species richness of lineage i
S: Distribu,on of sampled species
h: Parameters of S distribu,on
Data
Parameters
Stochas,c rela,onship
Implement
Diversity-Dependent Diversifica@on
Major outcomes

19. Conceptual challenges
What has been done
What remains to be done
Major outcomes
Ben H. Warren

20. Team & disciplinary scope
Core group of 10 but a total of 22 people took part to at
least one meeting
Members from USA (Berkeley, Missouri, Tennessee), UK
(Oxford, Imperial College), Spain (CSIC), Greece (Athens),
Portugal (CIBIO), Netherlands (Amsterdam), Switzerland
(Zurich) and France (CNRS & Universities)
Key players : Josselin Cornuault, Luis Valente, Ben Warren,
Bob Ricklefs, Brent Emerson, Rosie Gillespie, Fabien
Condamine
Basic research in ecology and evolutionary biology

21. Acknowledgments
FRB & its founding members for funding through CESAB
CESAB Directors : Alison Specht, Eric Garnier and Claire Salomon
CESAC Staff : Magali Grana and Baptiste Laporte