adaptive changes in harvested populations: plasticity and evolution of maturation
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Adaptive Changes in Harvested Populations: Plasticity and Evolution of Maturation. Bruno Ernande Fisheries Department IFREMER Port-en-Bessin, France. The potential for fisheries-induced adaptive changes. - PowerPoint PPT PresentationTRANSCRIPT
Bruno Ernande, NMA Course, Bergen
Adaptive Changes in Harvested Populations:Plasticity and Evolution of Maturation
Bruno Ernande
Fisheries Department
IFREMER
Port-en-Bessin, France
Bruno Ernande, NMA Course, Bergen
The potential for fisheries-induced adaptive changes
∎The commercial exploitation of fish stocks may not only have demographic consequences on the target species, but may also induce adaptive changes in their life history because fishing is by essence selective (Stokes et al. 1993, Palumbi 2001, Ashley et al. 2003 ).
∎Adaptive changes can have two different origins (Rijnsdorp 1993, Law 2000): Phenotypic plasticity: most species can modify their phenotype in the short term in
response to environmental variation; Evolution: the prerequisites for contemporary fisheries-induced evolution are met:
― Fisheries selective pressure is strong: fishing mortality on average 2 to 3 times higher than natural mortality (Law 2000)
― most life history traits have sufficient heritability to evolve and micro-evolutionary changes have been proven to occur within a few generations in controlled and field experiments (Reznick et al. 1990; Conover & Munch 2002)
∎Phenotypic plasticity and evolution have very different implications for management purposes: plasticity can be reversed within a generation whereas to mitigate adverse evolutionary changes requires many such generations.
Bruno Ernande, NMA Course, Bergen
Environment
Phen
otyp
e
Plasticchange
Phenotypic plasticity or evolution
∎With empirical data, one has to disentangle plastic and evolutionary response. Evolutionary changes in life history traits can be assessed by modifications in their reaction norms.
Bruno Ernande, NMA Course, Bergen
Environment
Phen
otyp
e
Evolutionarychange
∎With empirical data, one has to disentangle plastic and evolutionary response. Evolutionary changes in life history traits can be assessed by modifications in their reaction norms.
Phenotypic plasticity or evolution
Bruno Ernande, NMA Course, Bergen
Objectives
∎Modifications of reaction norms have been recently shown for age and size at maturation in commercially exploited fish stocks, e.g., North East Artic cod (Heino et al. 2002), North Sea plaice (Grift et al. 2003), Georges Bank cod (Barot et al. 2003), and Nothern cod (Olsen et al. 2003).
∎We propose a theoretical approach for modelling the evolution of maturation reaction norms in exploited populations in order to tackle three specific points:
Can harvesting be really responsible for evolutionary changes in maturation reaction norms?
Can we evaluate the evolutionary impact of different harvesting practices and the potentiality of different management policies?
What are the consequences of evolutionary changes on population abundance and sustainability?
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Bivariate reaction norm
∎The historical view: ∎univariate reaction norms
∎ {zi1, zi2, zi3, zi4, zi5}
∎Another view: ∎bivariate reaction norms
∎ {yi(xi1), yi(xi2), yi(xi3)}
E
gi
1 2 3 4 5
zi1
zi2
zi3
zi5
zi4
zE1
E2E3
Phen
otyp
e y
Phenotype x
gi
grow
th 1
grow
th 2
growth
3
agesi
ze
e.g., maturationreaction norm
Bruno Ernande, NMA Course, Bergen
Age
E1 E2 E3
Environment
Larval stage
Stock life cycle
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Larval stage
Immature stage
Metamorphosis
Age
E1 E2 E3
Environment
Stock life cycle
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Larval stage
Immature stage
Metamorphosis
Mature stage
Maturation
Age
E1 E2 E3
Environment
Stock life cycle
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Larval stage
Reproduction
Immature stage
Metamorphosis
Mature stage
Maturation
Age
E1 E2 E3
Environment
Random distribution
Habitat selection
Stock life cycle
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Random distribution
Larval stage
Reproduction
Immature stage
Metamorphosis
Mature stage
Maturation
Age
E1 E2 E3
Environment
Variation in growth and mortality rates
Habitat selection
Stock life cycle
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Δ
migration to a new environment
growth trajectory
Trade-off between reproduction and
somatic growth rate
metamorphosisEnvironmental variability
in growth trajectories
maturation reaction norm
juveniles
larvae
adults
Maturation process
∎Maturation process: maturation occurs when the growth trajectory intersects with the maturation reaction norm
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
0
1
Stock Biomass
Fish
ing
Mor
talit
y
positivedensity-dependence
negativedensity-dependence
density-independence
Quotas
Stock Size
Harvesting and management rules
∎ Mortality rates increase because of harvesting. Three management rules:Fixed Quotas: positive density-dependence Constant Harvesting Rate: density-independenceConstant Stock Size or Constant Escapement: negative density-dependence
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
)( PLS e,e,an m
0
0
)(
)()( )(
mam
mmmammS
S,δεSf
S,SfS,δεSflimaDf
m
mm
'm
'mSm
'mmSSmm daaga,anaS
dt
dmm )()( )( 2
1
PLS
PLSPLS,SPLS,SS,S
dededan
e,e,ane,e,ade,e,abf
'm
'm
m'mm
'mm
'm
)(
)()( )(
Evolutionary dynamics
∎Structured population dynamics with age and environmental trajectory as individual state variables. Size is fully determined by age and environmental trajectory.
∎ Invasion fitness of a mutant: long term growth rate of a mutant Sm’ in a resident population with reaction norm Sm
∎Selection gradient: functional derivate of invasion fitness
∎Evolutionary dynamics: Canonical equation for infinite dimensional traits
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Evolution under state-dependent harvesting
Quota Constant Rate Constant Stock Size
Immature
Mature
Q
CRCSS
age (a)
harvesting mortality H0
size
(a)
H0(Mature)
Bruno Ernande, NMA Course, Bergen
Evolution under size-dependent harvesting
Quota Constant Rate Constant Stock Size
age (a)
size
(a)
Unfished sizesUnfished sizes
Unfished sizes Unfished sizes Unfished sizes
Unfished sizes Unfished sizes Unfished sizes
Unfished sizes
H0
Bruno Ernande, NMA Course, Bergen
Sens
itivi
ty
natural morality growth rate trade-off strength
Control of the sensitivity of the evolutionary response
∎The sensitivity of the evolutionary response of maturation reaction norms to harvesting is controlled by three life history parameters: it increases as
the average natural mortality rate decreases,the average growth rate increases,the strength of the trade-off between growth and reproduction weakens.
Ernande et al. 2004. Proc Roy Soc B
Bruno Ernande, NMA Course, Bergen
Consequences for demographic characteristics
∎Evolutionary induced decrease in population biomass due to a decrease in adult mean size and population density.
Quota Constant Rate Constant Stock Size
mean adult size
population biomass
population density
mortality
Evolutionary time
Pro
port
ion
of
orig
inal
val
ue
Fishing m
ortality
Bruno Ernande, NMA Course, Bergen
Consequences for population sustainability
∎The previous insights are qualitatively the same for the three management policies.
∎The main difference between the three management policies lies in the consequences of evolutionary changes of the maturation reaction norm on population abundance.
Bruno Ernande, NMA Course, Bergen
Trade-off growth-reproduction
expressedearlier R
ela
tiv
e b
iom
ass
evolutionarytime, t
FixedQuotas
Negativedensity-dependence
evolutionarytime, t
Lo
cal
ha
rves
tin
g m
ort
alit
y
Evolutionary feedback
Consequences for population sustainability
Bruno Ernande, NMA Course, Bergen
Trade-off growth-reproduction
expressedearlier R
ela
tiv
e b
iom
ass
Evolutionarysuicide
Rel
ati
ve
den
sit
y
evolutionarytime, t
ecological time
ecological time
FixedQuotas
Negativedensity-dependence
evolutionarytime, t
Lo
cal
ha
rves
tin
g m
ort
alit
y
Consequences for population sustainability
Bruno Ernande, NMA Course, Bergen
∎Fishing can induce evolutionary modifications in the position and the shape of the maturation reaction norm.
∎The direction of these changes actually depends on the life history stage which is harvested when harvesting depends on maturity status
∎According to the sensitivity analysis, these changes could be minimized by fishing mainly adults and by focusing on species characterized by high natural mortality, low growth rate, and a strong trade-off between growth and reproduction.
∎The prevalent system of management currently, quotas, seems to be the worse management practice in terms of fisheries-induced evolution
∎The consequences of these evolutionary changes on stock abundance and sustainability may be dramatic as suggested by the example of extinction through evolutionary suicide. Simple population dynamics models would overlook this possibility, which highlights the necessity to take evolutionary trends into account in responsible management practices.
Conclusions