BIOS 3010: Ecology Lecture 14: Life Histories
Transcript of BIOS 3010: Ecology Lecture 14: Life Histories
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 1
BIOS 3010: Ecology Lecture 14: Life Histories:
• Lecture summary: – Components of life
histories: • Growth. • Fecundity. • Survivorship.
– Reproductive value. – Trade-offs. – r- and K-selection. – Habitat templates. – Clutch size.
Dendrobates, M & P. Fogden, Rainforests, A Celebration
Linnet, D. Attenborough (1998), Life of Birds, Princeton.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 2
2. Components of life histories:
• Growth, fecundity and survivorship – (i) Growth
• Balance between the benefits and costs of large and small sized individuals:
– (Figs. 14.1 & 4.16). • Development
– Development can be varied independently of growth.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 3
3. Components of life histories:
• (ii) Fecundity – Rapid development can lead to early reproduction – Timing important (pre-reproductive period length). – Duration and frequency of reproduction is also
important (semelparity and iteroparity). • Offspring size
– variation in parental investment in individual offspring.
• Number of offspring – variation in numbers.
• Parental care – variation in how much parents look after offspring.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 4
4. Components of life histories:
• (iii) Survivorship – Variation in mortality, affected by:
• Energy storage: – Valuable for irregularly supplied resources.
– Dispersal in space and time: • Like migration across space and diapause
through time to escape periods of resource shortage.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 5
5. Reproductive effort:
• “Proportion of the available resource input that is allocated to reproduction over a defined period of time.”
• E.g., the allocation of energy or dry weight to different parts at various stages of development (Fig. 14.3).
• "Natural selection favours those individuals that make the greatest proportionate contribution to the future of the population to which they belong.”
– Begon et al., 2006, p 111. – Life histories are evolutionary attempts to maximize fecundity
and survival and these can be compared as a single "currency” » The reproductive value as a measure of fitness » Such as the intrinsic rate of natural increase r, or the basic
reproductive rate Ro.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 6
6. Reproductive value:
• (i) Reproductive value at a stage or age is the sum of the current reproductive output and the future reproductive value.
• (ii) Future reproductive value includes both future survival and expected fecundity.
• (iii) Future contribution of an individual is determined relative to the contribution of others.
• (iv) The life history favored by natural selection will be the one with the highest sum of contemporary output plus future output (Fig. 14.4).
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 7
7. Trade-offs:
• Life histories are balances of costs and benefits: – One characteristic can result in increased
benefits that are associated with decreased benefits from another characteristic (Fig. 4.19 & Fig. 4.23).
– This figure also shows the cost of reproduction (Fig. 4.22).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 8
8. r and K selection:
• After MacArthur & Wilson (1967) based on parameters of the logistic equation: – r-selected individuals:
• Favored for the ability to reproduce rapidly (high r - values) in r-selecting habitats (more unstable).
– K-selected individuals: • Favored for the ability to make a large proportional
contribution to a population which remains at its carrying capacity (K) in K-selecting habitats (more stable).
– These are extremes of a continuum.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 9
9. Characteristics of r and K- selected individuals:
See Figure 14.20 and Table 4.7
r-selected individuals K-selected individualsHabitat: unstable, unpredictable stable, predictable
Individual size: smaller largerTiming of reproduction: earlier later
Parity: semelparous iteroparousReproductive allocation: higher lower
Number of offspring: many fewSize of offspring: small large
Parental care: no yesSurvivorship investment Low (little defense,
poor competitor)High (good defense,highly competitive)
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 10
10. Habitat and life history
• Habitat is the templet (template) to which individuals fit their life history (Southwood, 1977).
• For example, guppies in Trinidad streams: – Selection by different fish predators influences the
cost of reproduction in guppies (Table 4.6) and selects for:
• Shift in offspring sizes. • Change in reproductive allocation.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 11
11. Clutch size:
• How many eggs should a bird lay? • “Lack clutch size”
– Balance between number produced & subsequent survival to maturity (Fig. 4.29).
– Lack’s predictions not supported because: • (1) Inadequate assessment of offspring fitness:
– Subsequent survival of added eggs not measured - so Lack may be correct?
• (2) Cost of reproduction (Fig 4.29) not considered: – Impact of present reproduction on future reproduction in
iteroparous species.
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Figure 14.1 (3rd ed.): Larger female crabs produce more offspring.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 13
Figure 4.16: Predicted male damselfly size corresponds to population mode.
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Figure 14.3 (3rd ed.):
Percentage allocation of calories to parts of annual plants, (a) Senecio, (b) Chrysanthemum (see Fig. 4.17 4th ed.)
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Figure 14.4 (3rd ed.): Change in reproductive value with age in (a) Phlox and (b) grey squirrels.
(see fig. 4.18, 4th ed.)
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 16
Figure 4.19:
Life history trade-offs in: (a) migratory fruit flies, (b) douglas fir, (c) male fruit flies with 8 virgin, 1 virgin + 7 mated or 0 virgin + 8 mated females
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Figure 4.23: Trade-offs in (a) goldenrod spp., (b) Hawaiian fruit flies, (c) Sceloporus lizards
Predictable pollen
Unpredictable yeast
Leaf bacteria
3 = Solidago canadensis
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Figure 4.22: Cost of reproduction in Senecio (deaths above line)
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 19
Figure 14.20 (3rd ed.):
Plants and the r/K continuum: (a) Reproductive allocation (b) Seed weight (c) age of reproduction variation with life span (see fig 4.30, 4th ed.)
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Table 4.7:
(North Dakota) (Texas)
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Table 4.6:
Large fish���predator Small fish���
predator
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Figure 4.29: “Lack clutch size” (a) prediction based on offspring fitness trade-off, (b) inclusion of cost of reproduction and maximum net benefit