Artificial Population Regulation

1. Artificial Population Regulation • For regulation of populations • For commercial harvest • Maximum Sustained Yield (MSY) • Based on the logistic equation: • dN/dt = rN((K-N)/K) • Generally found at 1/2 the carrying capacity (K) • Formula for MSY • H = (Kr)/4

2. Frequency of Harvest The most frequent harvests can be taken at intermediate population sizes.

3. Maximum sustainable yield (MSY) Anchovy MSY Krebs: Fig. 17.3

4. Anchovy Harvest Record

5. Optimum yield Below MSY because of other interests • Defined in the U.S. Fishery Conservation and Management Act of 1976 • “the quantity . . . (1) that will provide the greatest overall benefit to the nation, with reference to food production and recreation and • (2) that is prescribed as such on the basis of maximum sustained yield as modified by any relevant economic, social, or ecological factors.

6. Fixed Quota Harvesting

7. Reproduction curves & replacement 45o line is density independent replacement level r populations K type populations

8. Whale harvests Note the lack of whaling during WWII

9. Efficiency of whale harvest after WWII

10. Haddock & Cod fisheries

11. Predictions • Garrod & Jones (1974) • Cod fishery • Ignored by fisheries managers

12. Fixed effort harvesting

13. Multiple equilibria in harvesting Declining harvest efficiency with increased density Eo would harvest to extinction U= unstable equilibrium

14. IFQ’s • Individual fishing quota • Allowable catch divided into %’s awarded to or purchased by fisherman and companies • Avoids “fishing derby” • Can be sold or traded • High cost excludes many fishermen • Can be overcome if community quotas are allowed

15. Dynamic pool

16. Dynamic pool example • Plaice (Krebs, Fig. 17.5) • Best harvest rate would have been about 1/2 of actual level

17. Interface with economics ? - + + + - + - + - + + + + + - + + + + - - +

18. Cycle Catch + - + Effort Price Includes political pressure to increase effort

19. Biological Conservation • Population viability analysis (PVA) • How vulnerable to extinction? Includes minimum viable population (MVP) • Three general methods • Long term studies - biogeographical patterns • Subjective expert assessment • General mathematical model • Simulation models seem to hold the most promise • Problems with the analysis: • Changing conditions • Stochastic forces

20. Causes of rarity • Habitable areas are: • Short-lived • Small • Isolated • Resources sparse • Predators • Genetic variation lacking

22. Florida panther

23. Management decisions Sumatran Rhino