Natural Resources Ecology - Chapter 8: Life Histories

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Module 2: Organisms Chapter 8
- By Friday: Short quizzes for Chapters 6, 7, 8 on D2L. These open Thursday at 12:15 pm and close Friday at 11:59 pm.
- By Friday: Handout for individual phenology project due. Instructions are on D2L (Content $\to$ Module 0 $\to$ Phenology Project). Submit via email to your assigned instructor (Taylor or Flurin).

The process of evolution is dependent on genetic variation.
Evolution can occur through either random processes or natural selection.
Microevolution operates at the population level, focusing on changes in allele frequencies within a species.
Macroevolution operates at the species level and at higher levels of taxonomic organization, dealing with divergence and the formation of new species.

Life history traits represent the entire schedule of an organism’s life, from birth through reproduction to death.
Life history traits are inherently shaped by evolutionary trade-offs, where investment in one trait often compromises investment in another.
Organisms exhibit variation in the number of times they reproduce throughout their lives, but all organisms eventually experience senescence, a gradual decline in function.
An organism's life history is highly sensitive and responsive to prevailing environmental conditions.

Life history is defined as the schedule of an individual's life, encompassing timings of growth, reproduction, and survival.
Trade-off in allocation: This refers to how an organism strategically invests its finite time and energy among three critical functions: growth, reproduction, and survival. The goal is to maximize fitness.
Fitness: Represents an individual's genetic contribution to the next generation (e.g., number of surviving offspring).
Life history strategies are driven by both extrinsic factors (ecological conditions, e.g., predation, resource availability) and intrinsic factors (phylogeny, physiology, developmental constraints).

Fecundity: Typically produces 1 offspring per reproductive episode.
Parity: Engages in 7-9 reproductive episodes over its lifespan.
Parental Investment: Requires substantial time and energy, approximately 5 months of care for offspring.
Longevity/Life Expectancy: Averages 15-20 years.
Only 19\% of Emperor Penguins survive their first year. After this initial high mortality, the average yearly survival rate for adults is high, at 95\%.
Data from 2009 to 2018 shows existing colonies with varying average population sizes, with some exceeding 25,000 individuals. The global population also saw changes between 2010 and 2018.

Emperor Penguin:
- Fecundity: 1 offspring.
- Investment: 64 days of incubation plus extensive parental care.
- Average adult survival: 95\%.
- This represents a strategy of high parental investment and high adult survival, compensating for low fecundity.
Krill:
- Fecundity: Up to 10,000 offspring.
- Investment: 0 parental investment after egg laying.
- Average adult survival: < 30\%.
- This represents a strategy of extremely high fecundity with no parental investment, leading to very low adult survival.
This comparison highlights a classic fecundity/survival trade-off: organisms often face a choice between producing many offspring with little investment (and low survival) or fewer offspring with high investment (and higher survival).

Variation in one life history trait is often correlated with variation in other life history traits.
- For example, the number of offspring is typically negatively correlated with the size of offspring (organisms producing many offspring usually produce small ones).
This continuum describes two general strategies:
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