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C O M M O N W E A LT H
S E C R E A R I AT
M2.2 Life histories and
ecological adaptations
Assessing the status of fish stock for
management: the collection and use of basic
fisheries data and statistics
27 November -8 December 2006,
University of the South Pacific,
Suva, Fiji Islands
Content
• Life histories, life history traits, trophic
levels, species interaction.
• The principles of mortality, growth,
maturity and their relation to ecological
and evolutionary strategies
• r versus K selection.
Life histories
• Life history traits are the underlying
determinants for population response to
environmental (both biotic and abiotic)
forcing.
– On top of this natural variation will be a
modification of the response due to fishing
removals.
King and McFarlane (2003)
Life histories
The perfect organism (fish) would:
•
•
•
•
Mature early
Be large
Live long
Produce numerous
large offspring
 to start reproducing
 to avoid predation
 to produce more
 to increase offspring
and protect each from
predation
Why is this not possible?
Life histories – trade offs
If the perfect organism (fish) would:
•
•
•
•
Mature early
Be large
Live long
Produce numerous
large offspring
 would impede growth
 take time and energy
 future predictable
 many and large at the
same time takes too
much energy
You have to „choose‟ a strategy
Egg size - fecundity
• Many small eggs
• Few large eggs
• Live-born young
Fecundity
Fecundity
Relative fecundity
• Fecundity increases exponentially with length. If
fecundity increases faster than weight then
relative fecundity also increases with size.
Frequency distributions of age-of-maturity, clutch size, egg diameter
and parental care for marine and fresh water fish species Winemiller & Rose (1992)
Life history and environment
Dying is more certain than giving birth!
Most ecological processes and life history traits can
be related to the prevailing mortality pattern:
• The unstable environment: characterised by
discrete, density independent, non-predictive, nonselective mortality induced by physical changes
• The stable environment: characterised by
continuous, density-dependent, predictive, and sizeselective mortality induced by the biotic community.
Mean size of organisms
Cope‟s rule
Stable period
Stable period
Stable period
Stable period
Geological time
Cope's rule states that evolution tends to increase body size
over geological time in a lineage of populations.
But the precondition is geological stability. During unstable
periods with mass extinction the large lineages are more
susceptible. Investment in age (size) is investment in future.
Predator or prey?
Predation mortality
Instantaneous predation mortality
(M2) on Cod by other species in
the North Sea
Modified from ICES (1997).
Life history „trade offs‟
Blueweiss et al. (1978)
The intrinsic rate of natural increase: r = 0.025 ∙ Wmax-0.26
Life history „trade offs‟
Modified from Banse & Mosher (1980)
Log P/B ratio is a linear function of log body size
Life history invariants
= constant trade off between traits
Examples of Invariants
• – Ratio of lifespan (E) to age-at-first reproduction (a)
This ratios is similar for elephant and squirrels, but different from fish
(Charnov et al. 2001. Proc. Nat. Acad. Of Sci. 98:9460-9464)
Jensen (1997, CJFAS 54:987-989) Proposed the following invariants
• 1. Natural mortality (M) and age at maturation (Tm)
M∙Tm = 1.65
• 2. Natural mortality (M) and VBGF „coefficient‟ (K)
M = 1.5 K
• 3. Length at maturity [ Lm ] and maximum length (L∞)
Lm = 0.66 L∞
• 4. Growth „coefficient‟ (K) and maximum length (L∞)
L∞ = K-0.33
Life history strategies
Environment seasonal
or with large scaled
spatial variation
Fecundity
Environment unstable
or with large scaled
spatial variation
Periodic
Opportunistic
Age of Maturity
r-selection
K-selection
Equilibrium
Winemiller & Rose (1992)
Environment stable
with fine scaled spatial
variation
Life history strategies
Winemiller (2005)
Phylogentic life history variables
•
•
•
•
•
•
•
•
•
growth rate (K, yr-1 and L∞, cm)
max size (Lmax, cm) and max age (Tmax, years)
age at maturity (Tm, years)
length at maturity (Lm, cm)
length-at-5%-survival (L.05, cm)
time-to-5%-survival (T.05, years)
slope of the log-log fecundity-length relationship (Fb)
fecundity the year of maturity (Fm)
egg size (mm)
• egg volume (egg, mm3)
Life histories: The phylogenetic
comparative approach
Winemiller & Rose (1992), McCann & Shuter(1997)
Life History Strategies
1. Opportunistic strategists
fast-growing; short-lived; intermediate fecundity
2. Periodic strategists
slow-growing, long-lived, high fecundity
3. Equilibrium strategists
fast-growing, long-lived, low fecundity
4. Salmonic strategists
opportunistic strategists but with freshwater and marine
phase
King and McFarlane 2003
Principal Components Analysis
(PCA) on life history traits
King and McFarlane 2003
PCA groups on life history traits
King and McFarlane 2003
Typical population dynamics
Opportunistic strategist
King and McFarlane 2003
Typical population dynamics
Periodic strategist
King and McFarlane 2003
Typical population dynamics
Equilibrium strategist
King and McFarlane 2003
r-K selection
• r-selected species:
– Small
– Rapid growth
– Early maturation
– No parental care
– Opportunistic
– Colonisers
– Unstable environment
– Resilient
• K-selected species
– Large
– Slow growth
– Late maturation
– Parental care
– Specialised
– Competitors
– Stable environment
– Vulnerable
Logistic growth: r-K selection
Carrying capacity = B∞ = K
K
2
dB
dt
r B
dB
dt
B
r B1
K
Equilibrium
Periodic
Opportunistic
Winemiller (2005)
Population dynamics
in relation to carrying
capacity and the
relative strength and
frequency of density
dependence for three
life history strategies
Life history traits at the community
level
Increased mortality has different impact depending on the trophic level. Traits that
make species vulnerable covary both between and within trophic levels. Body size
(size of the circles) of top carnivore species tends to be larger than that of species at
lower trophic levels. Range of body sizes and number of species are larger at lower
trophic levels. From Raffaelli (2004)
Life history and communities
• Traits such as body size and its covariates such as home range and
tolerance to stress, together with differences in species richness
between trophic levels, will determine the impact on ecosystems of
different biodiversity loss scenarios:
• Top predators with their large body size, low abundance, and large
range requirements are particularly vulnerable to habitat
fragmentation or destruction, but less susceptible to pollution stress,
which affects smaller species disproportionately.
• In contrast, the higher species richness at lower trophic levels,
provides more “insurance” against the effects of species losses.
These species also have greater capacity for adaptive change due to
their shorter life-spans and faster turnover rates.
• With respect to species traits, extinction is unlikely to occur
randomly. Raffaelli (2004)
The r-K selection principle as a
function of mortality pattern
Abundance (Log N)
Increased juvenile mortality
= K-selection
Slope = total mortality rate Z = r
Increased adult mortality
= r-selection
Age (size)
Kolding (1993)
K-selection: Stable environment, biotic mortality (predation) – predictive, size selective
r-selection: Unstable environment, abiotic mortality – non-predictive, non-selective
The biomass-size distribution
Biomass
A Lindeman pyramid illustrating
a fish community.
Size
The biomass-size distribution is an important indicator in both
single species and community studies.
Changes in intercept is informative about changes in biomass
While changes in slope is informative about mortality pattern
Biomass-size distributions in
different environments
Detrivores, Herbivores, Zooplanktivores,
Macro-invertebrate feeders
Piscivores
Energy
A
Competition
Predation
Constant systems
Biomass
B
Biomass-size distributions:
Slope = Z = r = P/B
Pulsed systems
Size of individual fish
Fishing pressure
„Production‟ = Z∙ Biomass
= area ∙ slope
Trophic interactions:
Top down versus
Bottom up control.
Cascading effects
Response of
zooplankton and
phytoplankton
community biomass
to:
- fish (top down)
- nutrient (bottom up)
- combined
treatments (N = 11).
Brett & Goldman 1997
Predator-prey relationships:
Cascading effects
Predator-preys often have time
lagged oscillations due to density
dependent responses.
Left Fig:Dynamics of shrimp and
cod biomass in the Barents Sea from
1982-1998. Berenboim et al. 2000 J.
Northw. Atl. Fish. Sci., Vol. 27
Predator-prey relationships:
Cascading effects
Inverse biomass trends as an illustration of a trophic
cascade in the Black Sea (from Daskalov 2002)
Final comments
• Life histories are evolved and shaped by
different mortality patterns
• Mortality due to environmental variations and
habitat destructions are typically discrete, nonselective, non predictive, and increase mortality
on all size groups.
• Mortality due to predation is typically continuous,
highly selective, predictive, and predominantly
affects young and small individuals.
Predation and fishing on cod
Man is selecting opposite all other predators!!
From ICES (1997).