🦚Section One: Life History Basics and Trade-offs🪺

what life history is and relevant experiments in regards to trade offs.

🦚Life history

🪺The schedule of how an organism allocates resources to growth, development, defense and reproduction over its lifetime.

🦚Three key properties of life histories

🪺They are genetically based and heritable, subject to natural selection, and considered to maximize fitness.

🦚Fecundity

🪺The number of offspring produced per reproductive episode.

🦚Parity

🪺The number of reproductive episodes an organism has in its lifetime.

🦚Semelparous

🪺Reproduces only once, then dies (e.g., Pacific salmon).

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🪺Reproduces multiple times during its life (e.g., humans, most birds).

🦚Parental investment

🪺The amount of time and energy parents give to each offspring.

🦚Longevity

🪺The life span (life expectancy) of an organism.

🦚Annual vs. perennial

🪺Annuals live one year; perennials live more than one year.

🦚Principle of allocation

🪺Resources are limited, so energy devoted to one function (growth, defense or reproduction) cannot be used for another. This is why life histories involve trade-offs.

🦚Goldenrod seed graph

🪺Shows a trade-off between offspring number and offspring size: plants that make bigger seeds make fewer of them.

🦚Magpie clutch experiment (Högstedt 1980)

🪺Researchers added or removed eggs. Nests with 7 eggs (the natural average) fledged the most chicks, supporting the idea that natural clutch size maximizes fitness. Too many eggs meant parents couldn't feed them all.

🦚Kestrel brood experiment (Dijkstra et al. 1990)

🪺Adding chicks increased the number fledged but lowered parent survival; removing chicks did the opposite. Shows a trade-off between current reproduction and parent survival (future reproduction).

🦚What the kestrel experiment shows about males vs. females

🪺Females had lower survival than males in every treatment, suggesting they pay a higher cost of reproduction.