1 / 11

Harvesting of Populations

Harvesting of Populations. Avoid overexploitation. Avoid underexploitation (economic, conservation). How much? How often?. Harvesting of Populations. AJ Nicholson (1895-1969). Nicholson’s Blowflies. Carrying Capacity. BHT, table 16.6. harvest reduce population size.

tulia
Download Presentation

Harvesting of Populations

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. Harvesting of Populations • Avoid overexploitation • Avoid underexploitation • (economic, conservation) • How much? How often?

  2. Harvesting of Populations AJ Nicholson (1895-1969) Nicholson’s Blowflies Carrying Capacity BHT, table 16.6 • harvest reduce population size • harvest reduce competition… • … thereby increasing fecundity, survivorship and lifespan • high yields if populations are below carrying capacity! Low intraspecific competition High intraspecific competition

  3. Harvesting of Populations Maximum Sustainable Yield (MSY): fixed quota Fixed-quota harvesting Unstable MSY (risky business!) High quota Medium quota Low quota Stable Low recruitment rate (high competition) Low recruitment rate (few individuals) BHT, fig 16.11 MSY: the highest harvesting rate that the population can match with its own recruitment

  4. Harvesting of Populations Maximum Sustainable Yield (MSY): fixed quota model The logistic equation K = 1000 r = 0.6 Carrying capacity Population size (N) Intrinsic rate of increase

  5. Harvesting of Populations Maximum Sustainable Yield (MSY): fixed quota model The logistic equation with harvest K = 1000 r = 0.6 – h Harvest quota Population size (N) Sustainable yield: dN/dt = 0

  6. Harvesting of Populations Maximum Sustainable Yield (MSY): fixed quota model The logistic equation with harvest K = 1000 r = 0.6 – h Harvest quota Population size (N) hm=150 h Sustainable yield: dN/dt = 0 =500 Nm K N Max sustainable yield: dh/dN = 0 Nm = = 0 • MSY harvested from a population size of K/2 … • … to yield (rK/4) animals per year

  7. Harvesting of Populations Maximum harvesting frequency: at what N? harvest ... The logistic equation: N = K/2 Highest frequency BHT, fig 16.12

  8. Harvesting of Populations Maximum Sustainable Yield (MSY): fixed quota extinction! Nm BHT, fig 6.12 Fixed-quota: not a very safe management strategy Population size – h(…) Effort (/days) Efficiency (catch/vessel)

  9. Harvesting of Populations Maximum Sustainable Yield (MSY): fixed effort Effort h(…) = q E N Population size Efficiency Stable MSY Economy is important! Stable SY cost Large net yield BHT, fig 16.14a Fixed-effort: a much safer management strategy (requires monitoring of N which can be expensive) BHT, fig 16.14b

  10. Harvesting of Populations K = 1000 r = 0.6 Population size (N) hm=150 h =500 Nm K N Maximum Sustainable Yield (MSY): fixed effort model Effort h(…) = q E N Population size Em = 0.3 Efficiency Finding Em: The logistic equation

  11. Harvesting of Populations Instability of harvested populations: climate BHT, fig 16.17

More Related