1. 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

2. 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

3. Fish growth
4/26/2017
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
Deterministic means outcome that can be easily, accurately predicted.

4. Fish growth Standard length – several periods (phases) of growth
4/26/2017
Standard length – several periods (phases) of growth
Onset of maturity
Reduced growth of adults
Rapid growth of young fish

5. 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

6. 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.

7. 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

8. Life History Strategies—Parity
Semelparous
species
Mayfly
Agave
Mayflies in order Ephemeroptera (“ephemeral”) – live only 24 hrs, do not even feed
Iteroparous
species

9. (all of these make sense)
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)
Answer: a

10. Two factors influence evolution of semelparity vs iteroparity:
Survival probability of offspring
Probability that adults will survive to reproduce again
What else?
Both probabilities are low in harsh or unpredictable environments, so semelparity will be favored

11. Life History Strategies—Fecundity
Think to yourself and write a contrast:
list a highly fecund and low fecundity species

12. Life History Strategies—Parental Investment
Think to yourself and write a contrast:
list a high and low investment fish species

13. Life History Strategies—Offspring Size
Think to yourself and write a contrast:
list a large and small offspring size fish species

14. Other plants produce 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.

15. Number of Offspring Offspring Size
General Relationship between Offspring Size
and Number of Offspring
Many
Number of
Offspring
Few
Small Large
Offspring Size

16. Reproduction vs Survival (Mortality)

17. How does caring for offspring affect parental survival in kestrels?
100
Male
Female 80 60
Parents surviving the following winter (%) 40 20
Reduced
brood size
Normal
brood size
Enlarged
brood size
Fig

18. Reproductive Trade-offs:
Reproduction vs Future Survival
Reproduction vs Future Growth
Current vs Future Reproduction

19. Annual Meadowgrass Current vs Future Reproduction vs Future
Growth

20. Variations in fish life cycles
4/26/2017
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)
106
Eggs/Larvae
105
Juveniles
Adults
Numbers
104
103
102
101
Days
Months
Years

21. Why does M fluctuate?
4/26/2017
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

22. A few, large offspring.
Parental care in carrion beetles;
unusual in insects.
Fish analogues?