1. Harvesting of Populations
TerrEco_Lec ppt
Biologisk InstitutKøbenhavns Universitet
Avoid overexploitation
Avoid underexploitation
(economic, conservation)
How much? How often?

2. Nicholson’s Blowflies
Harvesting of Populations
AJ Nicholson
( )
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!
High intraspecific
competition
Low intraspecific
competition

3. Fixed-quota harvesting
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
Population size (N)
r Intrinsic rate of increase
K Carrying capacity

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
Harvest quota
Population size (N)
hm=150 h
Sustainable yield: dN/dt = 0 Nm
=500 K N
Max sustainable yield: dh/dN = 0
Nm =
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
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
Maximum Sustainable Yield (MSY): fixed effort model
Population size (N)
K = 1000
r = 0.6 h N K Nm
hm=150
=500
Effort
h(…) = q E N
Population size
Efficiency
Em = 0.3
Finding Em: The logistic equation

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