Nicolas Loeuille - présentation MEE2013
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Transcript of Nicolas Loeuille - présentation MEE2013
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Nicolas LoeuilleLaboratoire Ecologie & Evolution,
Université Pierre et Marie [email protected]
Effects of local negative feedbacks on the evolution of species within
metacommunities
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Starting with an old debate
Gause 1934
Hutchinson 1961
How do we explain the maintenance of diversity within a group of species ?
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Spatial components in the maintenance of diversity
● Total « regional » diversity :– Colinization-Competition Trade-off (Tilman 1994)
– Spatial heterogeneity and niche partitioning (Leibold et al. 2004)
– Storage effects (Chesson 1994)
– Random speciation, ecological drift (Hubbell 2001)
● Local diversity– Mass effects (source-sink relationships) Mouquet &
Loreau (2004)
– Janzen-Connell (Janzen 1970)
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The puzzling diversity of tropical forests
● Neutral dynamics
Speciation, migration, ecological drift (Hubbell 2001)
● Niche deterioration
Competitive hierarchy, mediated by enemy attraction (Janzen 1970)
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The Janzen-Connell hypothesis
Janzen 1970
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Local negative feedbacks
Enemy presence
Presence of one individual
Decrease in survival, decrease in competitive ability
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An illustrative example
Diez et al. 2010
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Importance for community structure and diversity
Klironomos et al. 2002
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Consumption constraints also yield local negative feedback (1/2)
Plant N:P=12:1
SoilN:P=15:1
Nu
trie
nt u
pta
keN
itrog e
n re
lease
N:P in soil increasesFavors incoming competitor species with a higher N:P
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Consumption constraints also yield local negative feedback (2/2)
P
BA
P
BA
Habitat becomes less suitable for predator AAn alternative predator with high affinity for B would be favored
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Critical conditions under which feedbacks act on diversity
1)Local environment is largely driven by the species presence (vs, eg, external abiotic constraints): niche construction (Laland et al. 1999, Kylafis & Loreau 2008)
2)Spatial constraints: low diffusion of enemies or nutrient compared to the species dispersal
3)Evolutionary constraints: Evolutionary dynamics lag behind ecological dynamics
What is the amount of diversity emerging from the interplay of these three constraints?
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Ecological dynamics of the model● 30*30 patches on a torus
● Each patch i has an environmental state zi
● Each morph has a trait xi
● (a) Extinction, with probability e● (b) Colonization from neighbor with probability c,
success if the invader j is better adapted (xj closer to
zi)
Initial Situation(a)
(b)
Ecological Dynamics
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Evolutionary dynamics
● Each local population has a probabilityμ to undergo a beneficial mutation.
● (c) If so, the new trait of the population xi becomes
closer to environmental state zi by less than dx
Initial Situation
(c)
Evolutionary Dynamics
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Environmental dynamicsLocal environment z
i changes :
d) Away from xi by a fixed step
dz if the patch is full (negative feedback)
d) Toward 0 by a step dz if the patch is empty (global averaging)
e) Toward the local average by a step αdz in all instances (contamination)
Initial Situation
(d)
(e)
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Initial conditions and possible dynamics
● Only one population, of trait xi=0.5
● For each patch, an environmental value z is picked at random between 0 and 1
● One million time steps considered
Q1 Conditions for the emergence of diversity ?
Q2 Effects on the environmental structure ?
Q3 Effects on the community patterns at various scales ?
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Permanent generalism
One species only, generalist(here, high e)
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Permanent specialization
DiversificationMaintenance of specialist morphs(here, e=0)
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Taxon cycles
DiversificationPeriodic extinction of specialist morphs(here, intermediate e)
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On taxon cycles
Considering the occupation of islands by lizards :-one lizard species on one island-invasion by larger lizard species is possible-evolution toward smaller sizes of the ancestral species (specialization)-Same for the invader-Eventual extinction of the ancestral species
Roughgarden & Pacala 1979Ricklefs & Bermingham 2002
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Effects on the grain of the environment
Permanent Generalism
Taxon cycles
Permanent specialization
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The succession of the three patterns is deterministic
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Conditions for emerging diversity
● From the succession of the three patterns, it is possible to distinguish parameters favoring diversity (PG->TC->PS)
● Such parameters include : colonization rate c, negative feedback dz
● Parameters that prevent the emergence of structure and diversity : extinction rate e, mutation rate μ (or mutation amplitude dx), contamination from surrounding patches α
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What is the amount of diversity obtained ?
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What is the amount of diversity obtained ?
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The succession of the three patterns is deterministic
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How is diversity organized in space ?
● Species-Area relationship (Preston 1962) : D=D0As
Kodric-Brown & Brown (1993)
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How is diversity organized in space ?
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Species abundance distribution
From McGill et al. 2007
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On an arithmetic scale, the model reproduces the traditional empty curve
PGTCPS PGTCPS
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On a logarithmic scale, multimode distributions
PGTCPS PGTCPS
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Conclusions
● Negative feedbacks may allow the emergence of diversity, but not under all conditions
● Taxon cycle one possible outcome, but in fact part of a continuum
● The model also provides classical shapes for macroecological patterns (species abundance distribution, species area curve)
● Associated with the temporal dynamics of diversity, such patterns can allow more robust testing of the model (McGill et al. 2003)
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Acknowledgements
Mathew Leibold