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Population ecology

Population ecology. Gauguin. Demographic data. 15 populations (various patch sizes) Time since fire: 0 to >30 years 9 years (1994-2004) >80 individuals per population each year Over 7000 plants in study through 2004 Censuses twice per year

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Population ecology

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  1. Population ecology Gauguin

  2. Demographic data • 15 populations (various patch sizes) • Time since fire: 0 to >30 years • 9 years (1994-2004) • >80 individuals per population each year • Over 7000 plants in study through 2004 • Censuses twice per year • 6 stage classes defined by optimization algorithm • Field and greenhouse experiments (seed and seedling dynamics)

  3. nt nt+1= +Bt -Dt +It -Et Change in population size

  4. Growth Reproductive effort Mortality Stages se seedlings v vegetative s small reproductive m medium reproductive l large reproductive Time since fire (years) 2 3-6 9-14 >20 Quintana-Ascencio et al. (2003)

  5. 2 II I 2 11 1 3 3 1 3 3 4 4 5 4 3 5 1 3 III 5- 5 5 5 IV V VI 5 4

  6. Quintana-Ascencio et al. (2003) Population Matrix Population in patch 45 (1996-1997), 11 years

  7. Population structure (3 yr post-fire) Lambda=5.52 Stable stage distribution Observed stage distribution

  8. Population structure (24 yr post-fire) Lambda=0.587 Stable stage distribution Observed stage distribution

  9. How many offspring does an average individual produce in its lifetime? • The net reproductive rate • Ro= l1F1+ l2F2+ … +lnFn=Σ liFi • Li=probability of surviving from the first census to the xth census (P1P2…Pn) • Fi= Fecundity of an average individual in age class x

  10. Reproductive value Individuals of different stages do not make equivalent contributions to future population growth. The reproductive value of different stages or ages give us a measure of the effects of different kinds of individuals on future population growth

  11. Reproductive value • R.V. = Proportion of future births in the population to individuals now in age x Proportion of the population now in age x Numerator =Σ (liFi/lambdai), from i=x to infinite Denominator =lx/lambdax-1

  12. Hypericum cumulicola: Ln (lambda) on time since fire Population growth & fire Quintana-Ascencio et al. (2003)

  13. Year 3 matrix 3.1 Year 3 matrix 3.2 Modeling samples from matrices by time since fire. In this (simplified) example, the fire return interval is 3 years: Year 0 fire matrix Use this: Year 1 matrix 1.1 Year 1 matrix 1.2 or or Year 1 matrix 1.3 Choose 1: Weighted interpolation between yrs 1 and 3 if no yr 2 matrix... or Use this: Beyond interpolation, input pooled matrices reset fire

  14. Projected median cumulative aboveground plant density Median observed cumulative aboveground plant density Population dynamics & fire Quintana-Ascencio et al. (2003)

  15. Extinction probability Simulation interval (years) No fire

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