1 / 17

Understanding Population Extinction Predictors: Demographic, Environmental, & Genetic Stochasticity

Explore factors like carrying capacity, growth rate, and stochastic events affecting population persistence. Learn to calculate SD, predict catastrophes, & genetic stochasticity impacts.

brooksw
Download Presentation

Understanding Population Extinction Predictors: Demographic, Environmental, & Genetic Stochasticity

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Announcements • HW Addendum for CONS670 • Reading assignment for BSCI363

  2. Mean r = 0, P(extinction) = ? Population Density (Ln) pop “a” pop “b” pop “e” pop “g” pop “c” pop “d” pop “h” pop “f” TIME

  3. General Predictors of Extinction Current population size + Population Growth - Population Size

  4. General Predictors of Extinction • Carrying capacity / population size. • Maximum growth rate. • Variation in growth rate • Demographic stochasticity • Environmental stochasticity • Genetic stochasticity

  5. Variation in B&D: Demographic Stochasticity • “Transparent” in VORTEX • Probabilistic nature of births and deaths, males and females • Function of • Birth and death rates • Fecundity = 0.34? • Sex ratio

  6. Variation in B&D: Demographic Stochasticity

  7. Variation in B&D: EV • Fecundity of adult spotted owls = 0.34 • In a “normal” year: 34% of adult females have 1 female offspring. • In a “bad” year, EV results in decreased r: e.g., births = 34% - “x” • In a “good” year, EV results in increased r: e.g., births = 34% + “x”

  8. Yearly Variation in Fecundity X= 34% frequency s.d. s.d. s.d. s.d. 14 24 34 44 54 % of females producing offspring ~68% ~95%

  9. Calculating S.D. from Data (> 5 yrs.)

  10. Calculating S.D. from Data (> 5 yrs.)

  11. Calculating S.D. From Data (Range) • Average fecundity = .34 (range .14 – .54) • Calculate S.D., based on years / data points • For N ~ 10, assume range defines +/- 1.5 SD. • For N ~ 25, assume range defines +/- 2SD • For N ~ 50, assume range defines +/- 2.25 SD • For N ~ 100, assume range defines +/- 2.5 SD • For N ~ 200, assume range defines +/- 2.75 SD • For N ~ 300, assume range defines +/- 3 SD

  12. “Last Ditch” Estimate of S.D. • Where mean value (e.g. fecundity) = 34% • “highly tolerant of EV” • let SD = 34%*.05 • “very vulnerable to EV” • let SD = 34%*.50 • “intermediate tolerance” • let SD = 34%*.25

  13. Variation in B&D: Catastrophes • Defined by VORTEX as episodic effects that occasionally depress survival or reproduction. • Types (up to 25, start with 1) • Independent causes of mass mortality. • Probability based on data (# per 100 years). • Loss due to catastrophe (= % surviving) • 0 = no survivors. • 1 = no effect.

  14. Catastrophes: Harbor Seals • Disease outbreaks in 1931, 1957, 1964, and 1980 • 1980: 445 seals out of ~10,000 died. • “Few” seals reproduce J. R. Geraci et al., Science215, 1129-1131 (1982).

  15. Disease outbreaks in 1931, 1957, 1964, and 1980 445 seals out of ~10,000 died. “Few” seals reproduce Probability of catastrophe: 26, 12, 14 years between outbreaks Average time between outbreaks = 17 years. 1 every 17 years or 6 every 100 years. Loss (e.g., % surviving) 9,555 / 10,000 ~ 95% Reproduction = ? Catastrophes: Harbor Seals J. R. Geraci et al., Science215, 1129-1131 (1982).

  16. Catastrophes: More Info • Mangel, M., and C. Tier. 1994. Four facts every conservation biologist should know about persistence. Ecology 75:607-614. • General background • Young, T. P. 1994. Natural die-offs of large mammals: implications for conservation. Conservation Biology 8:410-418. • Possible reference or starting point for term-paper • Access through JSTOR (www.jstor.org)

  17. Variation in B&D: Genetic Stochasticity Aa x Where a is deleterious Aa Homozygous recessive is lethal (Recessive Allele Model) Presence of “a” allele decreases fitness Reduced fitness = sum of lethal equivalents (Heterosis Model)

More Related