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J. M. Cushing
Department of Mathematics Interdisciplinary Program in Applied Mathematics
University of Arizona Tucson, Arizona, USA
Difference Equations Arising in
Evolutionary Population Dynamics
Simon Maccracken
Department of Ecology & Evolutionary Biology University of Arizona Tucson, Arizona, USA
Support by the National Science Foundation
ICDEA 2012 Barcelona
OUTLINE
1/30
Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
1
1
( , )
( , )
t t t t
t t t t
J b J A A
A s J A J
0R sb
inherent net reproductive number
( expected offspring per individual per life time )
b
s
inherent (low density) adult fertility
inherent (low density) juvenile survival
1
2
2
: [0, )
: (0,1)
(0,0)
RC
R
are
where open
(0,0) (0,0) 1
Density dependence
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Iteroparous Juvenile-Adult Models
ICDEA 2012 Barcelona
1
1
( , )
( , ) ( , )
t t t t
t j j t t t a a t t t
J b J A A
A s J A J s J A A
1
2
2
: [0, )
, : (0,1)
(0,0)
j a
RC
R
are
where open
(0,0) (0,0) (0,0) 1j a
0j a
b
s s
inherent adult fertility
inherent juvenile survival, inherent adult survival
01
j
a
sR b
s inherent net reproductive number
( expected offspring per individual per life time )
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Iteroparous Juvenile-Adult Models
ICDEA 2012 Barcelona
1
1
( , )
( , ) ( , )
t t t t
t j j t t t a a t t t
J b J A A
A s J A J s J A A
Define :
0 0 0 0 0 0
1 1 1 1 1
j j ja a
a a a a a
J j A A a J A j J a
s s ss s
s s s s sa
Within-class competitive effects
Between-class competitive effects
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Iteroparous Juvenile-Adult Models
ICDEA 2012 Barcelona
1
1
( , )
( , ) ( , )
t t t t
t j j t t t a a t t t
J b J A A
A s J A J s J A A
Fundamental Bifurcation Theorem
1. Origin is stable if R0 < 1 and unstable if R0 > 1.
2. Positive equilibria (transcritically) bifurcate from the origin at R0 = 1.
Assume a+ ≠ 0.
3. Stability depends on the direction of bifurcation:
Right (forward) bifurcating positive equilibria are stable.
Left (backward) bifurcating positive equilibria are unstable.
4. a+ < 0 => right ( hence stable ) bifurcation
a+ > 0 => left ( hence unstable ) bifurcation
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Iteroparous Juvenile-Adult Models
ICDEA 2012 Barcelona
1
1
( , )
( , ) ( , )
t t t t
t j j t t t a a t t t
J b J A A
A s J A J s J A A
Notes
A right (stable) bifurcation occurs if there are
no positive feedback effects (at low density),
i.e. if there are no positive derivatives
Positive feedback terms (positive derivatives)
are called Allee effects.
0 0 0 0, , ,J A J A .
A left (unstable) bifurcation can only occur in the
presence of strong Allee effects.
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ICDEA 2012 Barcelona
Lloyd & Dybas (1966, 1974)
Hoppensteadt & Keller (1976)
Bulmer (1977)
May (1979)
Ebenman (1987, 1988)
JC & Li (1989, 1992)
Wikan & (1996)
Nisbet & Onyiah (1994)
Wikan & Mjølhus (1997)
Behncke (2000)
Davydova (2004)
Davydova, Diekmann & van Gils (2003, 2005)
Mjølhus, Wikan & Solberg (2005)
JC (1991, 2003, 2006, 2010)
Kon (2005, 2007)
Diekmann & Yan (2008)
JC & Henson (2012)
Semelparous Juvenile-Adult Models
1
1
( , )
( , )
t t t t
t t t t
J b J A A
A s J A J
7/30
ICDEA 2012 Barcelona
Plants
Monocarpic perennials
Vertebrates
Species of :
Fish Lizards
Amphibians Marsupials
… even a
mammal !
Invertebrates
Species of Insects
Arachnids Molluscs
13, 17 year cycles
Periodical Insects
Magicicada spp.
Melontha spp. 3, 4, 5 year cycles
Lasiocampa quercus var
1, 2 year cycles
Annuals
Semelparity
“Poster-child” species
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ICDEA 2012 Barcelona
Semelparous Juvenile-Adult Models
1
1
( , )
( , )
t t t t
t t t t
J b J A A
A s J A J
Define :
0 0 0 0
J j A J j Aa s s
Within-class competitive effects
Between-class competitive effects
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Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
Fundamental bifurcation Theorem
JC & Jia Li (1989), JC (2006), JC & Henson (2012)
1
1
( , )
( , )
t t t t
t t t t
J b J A A
A s J A J
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Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
Fundamental bifurcation Theorem
0 0 0 0 J As (or ) right (or left) bifurcation
3. Synchronous 2-cycles also bifurcate from the origin at R0 = 1.
2. Positive equilibria bifurcate from the origin at R0 = 1.
1. Origin is stable if R0 = sb < 1 and unstable if R0 > 1.
Assume a+ ≠ 0.
4. (a) Left bifurcations are unstable.
(b) A right bifurcation is stable if the other bifurcation is to the left.
(c) If both bifurcations are to the right, then
0 0 a (or ) right (or left) bifurcation
0 a equilibria stabl & 2 - cycles une stable
0 a equilibria unstab 2 - cycles le st & ableDynamic
Dichotomy
1
1
( , )
( , )
t t t t
t t t t
J b J A A
A s J A J
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Notes
Weak between-class competition gives stable equilibria Strong between-class competition gives stable synchronous 2-cycles
0 0 0 0 0J j A J j Aa s s
0 0 0 0 0J j A J j Aa s s
If there are no Allee effects, that is, no positive derivatives
then Dynamic Dichotomy occurs.
0 0 0 0, , ,J A J A
Between-class (nymph) competition is leading hypothesis for periodical cicada dynamics Dichotomy observed in experiments with Tribolium castaneum
JC et al., Chaos in Ecology, Academic Press (2003) King, Costantino, JC, Henson, Desharnais & Dennis, Proc Nat Acad Sci (2003) Dennis, Desharnais, JC, Henson & Costantino, Ecol Monogr (2001) Costantino, JC, Dennis & Desharnais, Science (1997)
ICDEA 2012 Barcelona 12/30
Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
Typical example for which the Dynamic Dichotomy occurs:
1
1
( , )
( , )
t t t t
t t t t
J b J A A
A s J A J
11 12 21 22
1 1( , ) , ( , )
1 1J A J A
c J c A c J c A
Leslie-Gower-type competition interaction functionals
… a natural extension of discrete logistic ( or Beverton-Holt )
equation for an unstructured population.
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Evolutionary Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
u U trait interval
max ( ) 1.U u
Ub
Assume
Then maximum adult fertility ( over the trait interval )
(0,0, ) 1
(0,0, ) 1
u
u
1
1
( ) ( , , )
( ) ( , , )
t t t t
t t t t
J b u J A u A
A s u J A u J
14/30
u mean of a phenotypic trait subject to Darwinian evolution
Evolutionary Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
1 0
0
1
2ln ( , , )
( , , ) ( ) ( ) ( , , ) ( , , )
t t uu u v R J A u
R J A u b u s u J A u J A u
v trait variance ( assumed constant in time )
Using Evolutionary Game Theory Methodology
Vincent & Brown 2005
1
1
( ) ( , , )
( ) ( , , )
t t t t t t
t t t t t t
J b u J A u A
A s u J A u J
(0,0, ) 1
(0,0, ) 1
u
u
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Evolutionary Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
What are the dynamics of this model ?
When v = 0 the Fundamental Bifurcation Theorem applies and the Dynamics Dichotomy is a possibility. What happens when v > 0 (i.e. when evolution is present)?
1
1ln[ ( ) ( ) ( , , ) ( , , )]
2t t uu u v b u s u J A u J A u
(0,0, ) 1
(0,0, ) 1
u
u
1
1
( ) ( , , )
( ) ( , , )
t t t t t t
t t t t t t
J b u J A u A
A s u J A u J
16/30
Evolutionary Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
Extinction Equilibria & Critical Traits
An extinction equilibrium (J, A, u) is an equilibrium with J = A = 0.
A critical trait u satisfies 0(0,0, ) 0.uR u
Easy to see that …
(0, 0, u) is an extinction equilibrium if and only if u is a critical trait.
1
1ln[ ( ) ( ) ( , , ) ( , , )]
2t t uu u v b u s u J A u J A u
(0,0, ) 1
(0,0, ) 1
u
u
1
1
( ) ( , , )
( ) ( , , )
t t t t t t
t t t t t t
J b u J A u A
A s u J A u J
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Evolutionary Semelparous Juvenile-Adult Models
ICDEA 2012 Barcelona
Synchronous 2-cycles
1 2
0
0
J
A
u u
1
1ln[ ( ) ( ) ( , , ) ( , , )]
2t t uu u v b u s u J A u J A u
(0,0, ) 1
(0,0, ) 1
u
u
1
1
( ) ( , , )
( ) ( , , )
t t t t t t
t t t t t t
J b u J A u A
A s u J A u J
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Main Theorem
ICDEA 2012 Barcelona
(b) If ∂uuR0(0 ,0, u*) > 0 then the equilibria (extinction & positive) equilibria
and the synchronous 2-cycles are all unstable.
2. ∂uuR0(0 ,0, u*) ≠ 0
(a) If ∂uuR0(0 ,0, u*) < 0 then the Fundamental Bifurcation Theorem
and the Dynamic Dichotomy hold
… using R0(0 ,0, u*) as a bifurcation parameter.
NOTE: R0(0, 0, u) = bb(u)s(u)
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Assume … 1. There exists a critical trait u* : ∂uR0(0, 0, u*) = 0
0 0 0 0 0 00 0J j A J j A J Aa s s s 3. and
Then …
Examples
ICDEA 2012 Barcelona
11 12 21 22
1 1( , ) , ( , )
1 1
0, 0 ij ii
J A J Ac J c A c J c A
c cat least one
• No trait dependence in these density feedback terms • No Allee effects • Dynamic Dichotomy holds in absence of evolution • Dynamic dichotomy holds occurs in the presence of evolution if
∂uuR0(0 ,0, u*) < 0
Leslie-Gower Nonlinearities
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Examples
ICDEA 2012 Barcelona
Mathematically:
s(u) and b (u) have opposite monotonicity
( ) ( ) 2 ( ) ( ) ( ) ( ) 0u s u u s u u s u
Trade-offs are of fundamental biological interest:
Survival & fertility change in opposite manner as u increases.
Dynamic Dichotomy criterion:
Critical trait equation: 0
0(0,0, ) 0uR u
( ) ( ) ( ) ( ) 0u s u u s u
0(0,0, ) ( ) ( )R u b u s u
Net reproductive number:
0
0(0,0, ) 0uuR u
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1
[ ( ) ( )]1
2 ( ) ( )
u t tt t
t t
u s uu u v
u s u
21 22
11 12
1
1
1
1
1
1
( )
( )t
t t t
t t
t t t
t
c J c A
c J c A
J b u A
A s u J
Examples
ICDEA 2012 Barcelona
( ) ( ) 2 ( ) ( ) ( ) ( ) 0u s u u s u u s u
Dynamic Dichotomy criterion:
Critical trait equation: 0
0(0,0, ) 0uR u
( ) ( ) ( ) ( ) 0u s u u s u
0(0,0, ) ( ) ( )R u b u s u
Net reproductive number:
0
0(0,0, ) 0uuR u
Stability critieria:
21 12 11 22[ ( *) ] [ ( *) ] 0
a c s u c c s u c
stable equilibria
21 12
11 22
( *)
( *)
c s u cc
c s u c
competition ratio
22/30
1
[ ( ) ( )]1
2 ( ) ( )
u t tt t
t t
u s uu u v
u s u
21 22
11 12
1
1
1
1
1
1
( )
( )t
t t t
t t
t t t
t
c J c A
c J c A
J b u A
A s u J
Examples
ICDEA 2012 Barcelona
( ) ( ) 2 ( ) ( ) ( ) ( ) 0u s u u s u u s u
Dynamic Dichotomy criterion:
Critical trait equation: 0
0(0,0, ) 0uR u
( ) ( ) ( ) ( ) 0u s u u s u
0(0,0, ) ( ) ( )R u b u s u
Net reproductive number:
21 22
11 12
1
1
1
1
1
1
( )
( )t
t t t
t t
t t t
t
c J c A
c J c A
J b u A
A s u J
0
0(0,0, ) 0uuR u
Stability critieria:
21 12
11 22
( *)
( *)
c s u cc
c s u c
competition ratio
1 c stable equilibria
1 c stable 2 - cycles
22/30
1
[ ( ) ( )]1
2 ( ) ( )
u t tt t
t t
u s uu u v
u s u
ICDEA 2012 Barcelona
b (u)
s(u)
R0(0,0,u)
u u
Dynamical Dichotomy holds at critical trait
u* = 1
b/4
0 2
1( ) , ( )
1 1
[0, )
(0,0, )(1 )
us u u
u u
U
uR u b
u
trait interval :
Example 1
21 22
11 12
1
1
1 1
1 1
1
1 1
t
t
t t
t t
t t
t t
t
u c J c A
u
u c J c A
J b A
A J
1
11
2 (1 )
tt t
t t
uu u v
u u
23/30
Example 1
ICDEA 2012 Barcelona
Sample Time Series
R0(0,0,1) = 0.75
Extinction
R0(0,0,1) = 2
c < 1
Stable Equilibrium
R0(0,0,1) = 2
c > 1
Stable 2-cycle
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Example 2
ICDEA 2012 Barcelona
b (u)
s(u)
R0(0,0,u)
u u
Large a > a0
a = s′′(0)
2
2 2
1
2
0 2 2
2 2( ) , ( )
1 2
0, 0 , 1
2 2(0,0, )
1 2
m us u u
au u
m
U R
m uR u b
au u
trait interval :
2
2
21 22
1
1 2
11 12
2 1
2 1
2 1
1 1
t
t t t
t t
t t
t t t
u
u c J c AJ b A
mA A
au c J c A
2
2 21
1 2 2
(1 )(1 )
t
t t
t t
u
u uu u vu
25/30
2
2
21 22
1
1 2
11 12
2 1
2 1
2 1
1 1
t
t t t
t t
t t
t t t
u
u c J c AJ b A
mA A
au c J c A
2
2 21
1 2 2
(1 )(1 )
t
t t
t t
u
u uu u vu
Example 2
ICDEA 2012 Barcelona
b (u)
s(u)
R0(0,0,u)
u u
Dynamical Dichotomy holds at critical trait
u* = 0
a = s′′(0)
2
2 2
1
2
0 2 2
2 2( ) , ( )
1 2
0, 0 , 1
2 2(0,0, )
1 2
m us u u
au u
m
U R
m uR u b
au u
trait interval :
Large a > a0
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Example 1
ICDEA 2012 Barcelona
Sample Time Series
R0(0,0,0) = 1.5
c < 1
Stable Equilibrium
R0(0,0,0) = 1.5
c > 1
Stable 2-cycle
26/30
Example 2
ICDEA 2012 Barcelona
b (u)
s(u)
u u
Small a < a0 R0(0,0,u)
2
2 2
1
2
0 2 2
2 2( ) , ( )
1 2
0, 0 , 1
2 2(0,0, )
1 2
m us u u
au u
m
U R
m uR u b
au u
trait interval :a = s′′(0)
2
2
21 22
1
1 2
11 12
2 1
2 1
2 1
1 1
t
t t t
t t
t t
t t t
u
u c J c AJ b A
mA A
au c J c A
2
2 21
1 2 2
(1 )(1 )
t
t t
t t
u
u uu u vu
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2
2
21 22
1
1 2
11 12
2 1
2 1
2 1
1 1
t
t t t
t t
t t
t t t
u
u c J c AJ b A
mA A
au c J c A
2
2 21
1 2 2
(1 )(1 )
t
t t
t t
u
u uu u vu
Example 2
ICDEA 2012 Barcelona
b (u)
s(u)
u u
Small a < a0 R0(0,0,u)
Dynamical Dichotomy holds at
2 critical traits u*
2
2 2
1
2
0 2 2
2 2( ) , ( )
1 2
0, 0 , 1
2 2(0,0, )
1 2
m us u u
au u
m
U R
m uR u b
au u
trait interval :a = s′′(0)
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Example 2
ICDEA 2012 Barcelona
Sample Time Series
R0(0,0, u*) = 1.5
c < 1
Stable Equilibrium
R0(0,0,u*) = 1.5
c > 1
Stable 2-cycle
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u will equilibrate at negative critical trait
for other initial
conditions
ICDEA 2012 Barcelona
Summary
The Fundamental Bifurcation Theorem holds at critical traits u*
where inherent (low density) fitness has a local maximum :
∂uR0(0,0,u*) = 0, ∂uuR0(0,0,u*) < 0
Positive equilibria & synchronous 2-cycles bifurcate at R0(0,0,u*) = 1.
The Dynamic Dichotomy holds.
For example, when no Allee effects are present.
For the EGT semelparous juvenile-adult model :
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ICDEA 2012 Barcelona
Open Problems
What are the properties of the bifurcation at R0 = 1 for Leslie semelparous of dimensions 3 and higher
without evolution ? with evolution?
Global stability results? Especially for Leslie-Gower nonlinearities.
What happens to bifurcating branches for large R0 >> 1 ?
EGT Leslie semelparous models with 2 or more phenotypic traits
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