Transcript Life history and growth

WFSC 448 – Fish Ecophysiology
Life History Theory
(assembled and modified from publicly available material)
•
•
•
•
•
•
•
Growth
Change of form (development)
Dispersal
Timing of reproduction
Size at birth or germination
Number, size and parity of offspring
Age at death; variability of same
• Growth – for at least part of their life history,
all organisms grow by assimilating energy and
nutrients – final body size species-specific
• Think through equivalancies in fish
Fish growth
• Typically fish show a deterministic, asymptotic growth schedule
• Overall,
• Each species has a characteristic size-at-age path
• There is individual variability in size-at-age
• Each species can only attain a species-specific maximum size
Fish growth
• Standard length – several periods (phases) of growth
Onset of maturity
Rapid growth of young fish
Reduced growth of adults
Change of Form
• Change of form - many organisms have dramatically
different forms or stages in their life cycle
• Again, think through equivalencies in fish
• Don’t get stuck in categorical thinking
Dispersal
• At some time in their lives, most organisms go
through dispersal – enhances reproductive success.
Spiders
Milkweed
Oviparous sharks
The embryo is completely nourished by the yolk found in its egg.
Viviparous sharks
The embryo also lives completely off the yolk, but the fully developed pup is born alive. When sharks bear
living offspring and their eggs have only a very thin shell, we speak of lecithotrophic viviparity (lŽkithos,
gr. = yolk; trophŽ = food, vivipar = living offspring).
When the offspring receive additional nourishment from the mother following a phase of living off the
egg yolk prior to birth, one speaks of matrotrophic viviparity (m‡ter, lat. = mother). The amount of food
supplied by the mother can vary, depending on the shark species.
Life History Strategies
Patterns of lifespan and reproduction
• Different species may have different
characteristic LHS
• LH variation may also present within species
◊ due to genetic difference
◊ due to environmental contingencies
• LHSs and plasticity in LHS are crafted
by natural selection
• LHS may take many forms
◊ countergradient variation
◊ alternative mating strategies in bluegill
Life History Strategies—Parity
Semelparous
species
Mayfly
Agave
Iteroparous
species
Based on what you know about evolution by natural
selection, you can predict that species that semelparous
species may have evolved this strategy because:
A) semelparous parents produce more offspring if they invest all
their resources in reproduction, compared to if they saved
resources to survive until they can reproduce again
B) semelparous parents produce offspring that are more likely to
survive than offspring produced by iteroparous parents
C) iteroparous parents are more likely to die before they can
reproduce than are semelparous parents
(all of these make sense)
Two factors influence evolution
of semelparity vs iteroparity:
• Survival probability of offspring
• Probability that adults will survive to reproduce
again
Both probabilities are low in harsh or unpredictable
environments, so semelparity will be favored
• What else?
Life History Strategies—Fecundity
Think to yourself and write a contrast:
list a highly fecund and low fecundity species
Life History Strategies—Parental Investment
Think to yourself and write a contrast:
list a high and low investment fish species
Life History Strategies—Offspring Size
Think to yourself and write a contrast:
list a large and small offspring size fish species
• Practice transference of concepts.
• Often to really remove myself from my disciplinary
specialization I often think of plants
• Some plants produce a large number of small seeds, ensuring
that at least some of them will grow and eventually reproduce.
•
Other plants produce
fewer large seeds
that provide a large store
of energy that helps seedlings
become established.
General Relationship between Offspring Size
and Number of Offspring
Many
Number
of
Offspring
Few
Small
Large
Offspring Size
Reproduction vs Survival (Mortality)
Parents surviving the following winter (%)
How does caring for offspring
affect parental survival in kestrels?
100
Male
Female
80
60
40
20
0
Reduced
brood size
Normal
brood size
Enlarged
brood size
Fig. 53-13
Reproductive Trade-offs:
a) Reproduction vs Future Survival
a) Reproduction vs Future Growth
b) Current vs Future Reproduction
Annual Meadowgrass
Reproduction vs Future
Growth
Current vs Future
Reproduction
Variations in fish life cycles
Within this basic strategy there is some variation, even across large pelagic
species taken by tuna fisheries. Two well known species groups with very
contrasting life histories are the tunas and sharks.
Big implications for population dynamics and for resilience to fishing.
107
Sharks (generalised)
Tuna (generalised)
Adults
104
Juveniles
Numbers
105
Eggs/Larvae
106
103
102
101
Days
Months
Years
Why does M fluctuate?
• Natural mortality varies throughout the life-cycle of a
species
• Size/age – fish may “out-grow” predators (e.g. range of
predators of larval v juvenile v adult marlin)
• Senescence processes and Reproductive stresses
• Movement away from areas of high mortality
• Behavioural changes (e.g. formation of schools)
• Changes in ecosystem status (e.g. prey availability, habitat
availability)
• Changes in abundance (e.g. density-dependence
influences, like cannibalism, prey limitations
A few, large offspring.
Parental care in carrion beetles;
unusual in insects.
Fish analogues?