Chapter 10 (Brief Overview)

But first, review… 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? Joseph Grinnell Charles Elton GE Hutchinson

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

Compare Elephant –Life span: >50y –Age at 1 st reproduction: yrs –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 1 st reproduction: 1-8y –Gestation: how long it takes to swim from ocean to spawning grounds –# young (eggs): –Parental care: ♂ - none ♀ - none

Survivorship curves

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

A Classic Study David Lack of 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

Lack’s Proposal Lack made 3 key points: 1.because life history traits (i.e. # of eggs/clutch) contribute to reproductive success they influence evolutionary fitness 2.life histories vary in a consistent way with respect to factors in the environment (reaction norms) 3.hypotheses about life histories are subject to experimental tests –Therefore: Life history is shaped by natural selection and are amenable to scientific method

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

Hogstedt (1980) – Magpies (Pica pica) Perrins and Moss (1975) – Great tits (Parus major) Brood Size Recapture probability 2814 Expected w/ No resource limitations Predicted by Lack Observed

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)

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?

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

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.

The life table…