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Chapter 10 (Brief Overview)

Chapter 10 (Brief Overview). But first, review…. Joseph Grinnell. Resource Utilization Curve How is it related to the niche? Niche discussion… How is it related to acclimation? Not a constant set of environmental conditions Questions about this stuff?. Charles Elton. GE Hutchinson.

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Chapter 10 (Brief Overview)

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  1. Chapter 10 (Brief Overview)

  2. But first, review… Joseph Grinnell • Resource Utilization Curve • How is it related to the niche? • Niche discussion… • How is it related to acclimation? • Not a constant set of environmental conditions • Questions about this stuff? Charles Elton GE Hutchinson

  3. What is life history? • The life history is the schedule of an organism’s life, including: • age at maturity • number of reproductive events • allocation of energy to reproduction • number and size of offspring • life span

  4. Elephant Life span: >50y Age at 1st reproduction: 13-20yrs Gestation: 21-22m # young: 1 Parental care: ♂ - none ♀ - herd consists of matriarch, male and female offspring until >12y, then male offspring leave herd, female offspring stay. Salmon Life span: 1-8y Age at 1st reproduction: 1-8y Gestation: how long it takes to swim from ocean to spawning grounds # young (eggs): 2500 - 7000 Parental care: ♂ - none ♀ - none Compare

  5. Survivorship curves

  6. What influences life histories? • Life histories are influenced by: • body plan and life style of the organism • evolutionary responses to many factors, including: • physical conditions • food supply • predators • other biotic factors, such as competition

  7. A Classic Study • David Lackof Oxford University first placed life histories in an evolutionary context: • tropical songbirds lay fewer eggs per clutch than temperate counterparts • Lack speculated that this difference was based on different abilities to find food for the chicks: • Temperate breeders have longer days in which to find food than tropical breeders Snow bunting Red-headed manakin

  8. Lack’s Proposal • Lack made 3 key points: • because life history traits (i.e. # of eggs/clutch) contribute to reproductive success they influence evolutionary fitness • life histories vary in a consistent way with respect to factors in the environment (reaction norms) • hypotheses about life histories are subject to experimental tests • Therefore: Life history is shaped by natural selection and are amenable to scientific method

  9. An Experimental Test • Lack: • Artificially increase # of eggs/clutch. • There would be no reduction in success. • Therefore, the number of offspring is limited by food supply • This proposal has been tested repeatedly: • Gören Hogstedt (1980) manipulated clutch size of European magpies: • maximum number of chicks fledged corresponded to normal clutch size of seven

  10. Recapture probability 2 8 14 Brood Size • Hogstedt (1980) – Magpies (Pica pica) • Perrins and Moss (1975) – Great tits (Parus major) Expected w/ No resource limitations Predicted by Lack Observed

  11. Components of Fitness • Generic: # offspring in next and future gens. • Genetic: proportion of alleles in next and future gens. • Fitness, ultimately dependent on producing successful offspring • Components: • maturity (age at first reproduction) • parity (number of reproductive episodes) • fecundity (number of offspring per reproductive episode) • aging (total length of life)

  12. Life Histories: A Case of Trade-Offs • Organisms face a problem of allocation of scarce resources (time, energy, materials): • the trade-off: resources used for one function cannot be used for another function • Remember: • Altering resource allocation affects fitness. • Consider the possibility that an oak tree might somehow produce more seed: • how does this change affect survival of seedlings? • how does this change affect survival of the adult? • how does this change affect future reproduction?

  13. principal n = years FV = P(1 + r)n Future Value r - Interest rate Concept of renewal Now = P Year 1 = P(1+r) Year 2 = P(1+r)2 Year 3 = P(1+r)3 Choices… Self survival? Parental care? How often do I breed? Few large? Many small? How fast growth and maturity?

  14. Life histories resolve conflicting demands. • Life histories represent trade-offs among competing functions: • a typical trade-off involves the competing demands of adult survival and allocation of resources to reproduction: • kestrels with artificially reduced or enlarged broods exhibited enhanced or diminished adult survival, respectively • Hence: parental cost.

  15. The life table…

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