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Announcements

Announcements. Error in Term Paper Assignment Originally: Would . . . a 25% reduction in carrying capacity . . . Corrected: Would . . . a 25% increase in carrying capacity . . . Homework 3 Assigned. Extinction Risk as a Function Density. Demographic stochasticity 50-100 individuals

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Announcements

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  1. Announcements • Error in Term Paper Assignment • Originally: Would . . . a 25% reduction in carrying capacity . . . • Corrected: Would . . . a 25% increase in carrying capacity . . . • Homework 3 Assigned

  2. Extinction Risk as a Function Density • Demographic stochasticity • 50-100 individuals • Environmental stochasticity • 1000-10,000 to buffer against • Natural catastrophes • > 1 population • Genetic stochasticity • 50- 500

  3. Spotted Owl Recovery • How many breeding pairs are necessary? • What management manipulation is most likely to prevent extinction? • What stages of the life-cycle have the largest impact on population dynamics?

  4. “Minimum Viable Population” (MVP) • How large must a population be for it to have a reasonable chance of survival for a reasonably long period of time? • Reasonable chance often taken as 95%. • Reasonably long period, 100 years.

  5. Population Viability Analysis (PVA) • The science of determining the probability that a population will persist for a given time. • We will use VORTEX

  6. PVA as Population Ecology Applied • Model • Nt+1 = Nt+B-D+I-E • B&D may be influenced by genetic factors • I&E • Closed population vs. metapopulation • Differences • Focal species • Implications

  7. Stochastic vs. Deterministic Models • B&D fixed • Deterministic models allow us to identify population trajectory and “critical” life-history stages. • B&D variable • We cannot predict population size with certainty. We can only specify the probability of particular outcomes. • Stochastic models allow us evaluate the probability of extinction.

  8. Deterministic Model for Spotted Owls Hatchlings 0.26 0.07 Juveniles (age 1) 0.84 0.21 Sub-Adults (age 2) 0.84 0.34 0.84 Adults (age 3-20)

  9. Life Table: Spotted Owl

  10. Management Plan: Spotted Owl • Double juvenile survivorship • Increase adult survivorship by 10% • Double adult fecundity

  11. “Sensitivity Analysis” Click here for Excel file

  12. What About Extinction • r is either greater than or less than 0. • Risk of extinction is independent of population size. • Fecundity of adult females = 0.34 exactly every single year.

  13. 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

  14. 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”

  15. 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%

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

  17. 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

  18. “Last Ditch” Estimate of S.D. • For example where mean value (e.g. fecundity) = 34% • “highly tolerant of EV” • let SD = 34%*.05 • “very vulnerable to EV” • let SD = 35%*.50 • “intermediate tolerance” • let SD = 35%*.25

  19. 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.

  20. Catastrophes: Harbor Seals • Disease outbreaks in 1931, 1957, 1964, and 1980 • 445 seals out of 600 (part of a larger population ~10,000) died. • “Few” seals reproduce J. R. Geraci et al., Science215, 1129-1131 (1982).

  21. 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)

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