Chapter 10 (Brief Overview) But first, review Resource Utilization Curve How is it related to the niche? Niche discussion Joseph Grinnell Charles Elton GE Hutchinson How is it related to acclimation? Not a constant set of environmental conditions Questions about this stuff?
What is life history? The life history is the schedule of an organisms 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 1st reproduction: 1320yrs 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 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: Snow bunting 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 Red-headed manakin Lacks 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: Gren 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)
Recapture probability Expected w/ No resource limitations Predicted by Lack Observed 2 8 Brood Size 14
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 principal FV = P(1 + r)n Future Value n = years r - Interest rate
Now = P Year 1 = P(1+r) Year 2 = P(1+r)2 Year 3 = P(1+r)3 Choices Self survival? Parental care? Few large? Many small? How fast growth and maturity?
How often do I breed? 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
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