BIOS 3010: Ecology Lecture 14: Life Histories: 2. Components of life histories: Growth, fecundity and survivorship. 3. Components of life histories:

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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 1 2. Components of life histories: Growth, fecundity and survivorship (i) Growth Balance between the benefits and costs of large and small sized individuals: (Figs & 4.16). Development Development can be varied independently of growth. Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 2 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. Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 3 1

2 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 4 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 R o. Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 5 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). Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 6 2

3 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 & Fig. 4.23). This figure also shows the cost of reproduction (Fig. 4.22). Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 7 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 8 9. Characteristics of r and K- selected individuals: r-selected individuals K-selected individuals Habitat: unstable, unpredictable stable, predictable Individual size: smaller larger Timing of reproduction: earlier later Parity: semelparous iteroparous Reproductive allocation: higher lower Number of offspring: many few Size of offspring: small large Parental care: no yes Survivorship investment Low (little defense, poor competitor) High (good defense, highly competitive) See Figure and Table 4.7 Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 9 3

4 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 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. Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 11 Figure 14.1 (3 rd ed.): Larger female crabs produce more offspring. Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 12 4

5 Figure 4.16: Predicted male damselfly size corresponds to population mode. Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 13 Figure 14.3 (3 rd ed.): Percentage allocation of calories to parts of annual plants, (a) Senecio, (b) Chrysanthemum (see Fig th ed.) Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 14 Figure 14.4 (3 rd ed.): Change in reproductive value with age in (a) Phlox and (b) grey squirrels. (see fig. 4.18, 4th ed.) Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 15 5

6 Figure 4.19: Life history tradeoffs 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 Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 16 Figure 4.23: Trade-offs in (a) goldenrod spp., (b) Hawaiian fruit flies, (c) Sceloporus lizards 3 = Solidago canadensis Predictable pollen Leaf bacteria Unpredictable yeast Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 17 Figure 4.22: Cost of reproduction in Senecio (deaths above line) Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 18 6

7 Figure (3 rd 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, 4 th ed.) Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 19 Table 4.7: (North Dakota) (Texas) Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 20 Table 4.6: Large fish predator Small fish predator Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 21 7

8 Figure 4.29: Lack clutch size (a) prediction based on offspring fitness trade-off, (b) inclusion of cost of reproduction and maximum net benefit Dr. S. Malcolm BIOS 3010: Ecology Lecture 14: slide 22 8