BIO220 Lecture 16 Flashcards
Ecology & evolution of harvested populations
General harvesting stragety
harvest out the recruitment and leave the stock alone
recruitment
new additions to the population
stock
current population
logistic equation of population growth
dN/dt = rN[(K-N)/K]
= Change in abundance / change in time
= rate of population growth
r = intrinsic rate of population growth of the species K = carrying capacity N = number of individuals in population
What is the logistic equation of population growth saying?
As number of individuals in population nears the carrying capacity of that population (N = K), rate of population growth is slow (logistic growth)
What happens when N -> 0 (logistic population growth equation)
dN/dt = rN
= exponential growth
____ growth rate can limit population size
density-dependent
example of density-dependent population
Tern (type of seagull) on islands is limited by nesting space
- Bird island
- Ram island
- Penikese island
logistic curves can be used to predict…
harvesting & its consequences
- what would give us the best yield without harvesting the stock?
Ideal harvesting strategy would be to harvest ____ individuals per year. This ensures ____
K/2;
Max growth rate
calculation: overall rate of population increase
per capita rate of increase x population size = overall rate of population increase
How do we know that we should harvest K/2 individuals per year?
inflection point on “overall rate of population increase”
= max rate of population increase is at K/2
Recruitment axis = ___ axis
harvest amount
A “best case scenario” for harvesting does not account for…
- random chance
- weather
- seasonal year-to-year fluctuations
- predation
MEY
max economic yield
= max profit (benefit - cost)
MEY is good for business // species populations?
business & fishermen
MSY
max sustained yield
= point of max population growth
= K/2
MSY is good for business // species populations?
species population
The fisheries tend to fish to the ___ point. Why?
break even point
- incentive to catch more fish until benefit doesn’t > cost
- fish as long as there is positive profit
Cons of the break even point
- not max profit
- populations have low growth rates
- high effort
- more harvest short-term, but screwed long-term
why do fisheries harvest to the break even point, not MSY or MEY?
constant financial pressure to harvest more
Effect of new technologies on fishing curve
- decrease slope of cost curve
- no effect on population dynamics curve
what can be found on the fishing curve?
- population dynamics (“n” parabola)
2. cost of harvesting (“/” slope)
3 methods to improve the overfishing situtation
- fixed quota (set at MSY)
- fixed effort (time, size of net…)
- fixed escapement (allow some fish to escape fishery before fishing begins)
