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bio220 > BIO220 Lecture 16 > Flashcards

BIO220 Lecture 16 Flashcards

Ecology & evolution of harvested populations

1
Q

General harvesting stragety

A

harvest out the recruitment and leave the stock alone

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2
Q

recruitment

A

new additions to the population

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3
Q

stock

A

current population

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4
Q

logistic equation of population growth

A

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
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5
Q

What is the logistic equation of population growth saying?

A

As number of individuals in population nears the carrying capacity of that population (N = K), rate of population growth is slow (logistic growth)

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6
Q

What happens when N -> 0 (logistic population growth equation)

A

dN/dt = rN

= exponential growth

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7
Q

____ growth rate can limit population size

A

density-dependent

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8
Q

example of density-dependent population

A

Tern (type of seagull) on islands is limited by nesting space

  • Bird island
  • Ram island
  • Penikese island
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9
Q

logistic curves can be used to predict…

A

harvesting & its consequences

- what would give us the best yield without harvesting the stock?

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10
Q

Ideal harvesting strategy would be to harvest ____ individuals per year. This ensures ____

A

K/2;

Max growth rate

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11
Q

calculation: overall rate of population increase

A

per capita rate of increase x population size = overall rate of population increase

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12
Q

How do we know that we should harvest K/2 individuals per year?

A

inflection point on “overall rate of population increase”

= max rate of population increase is at K/2

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13
Q

Recruitment axis = ___ axis

A

harvest amount

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14
Q

A “best case scenario” for harvesting does not account for…

A
  • random chance
  • weather
  • seasonal year-to-year fluctuations
  • predation
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15
Q

MEY

A

max economic yield

= max profit (benefit - cost)

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16
Q

MEY is good for business // species populations?

A

business & fishermen

17
Q

MSY

A

max sustained yield
= point of max population growth
= K/2

18
Q

MSY is good for business // species populations?

A

species population

19
Q

The fisheries tend to fish to the ___ point. Why?

A

break even point

  • incentive to catch more fish until benefit doesn’t > cost
  • fish as long as there is positive profit
20
Q

Cons of the break even point

A
  • not max profit
  • populations have low growth rates
  • high effort
  • more harvest short-term, but screwed long-term
21
Q

why do fisheries harvest to the break even point, not MSY or MEY?

A

constant financial pressure to harvest more

22
Q

Effect of new technologies on fishing curve

A
  • decrease slope of cost curve

- no effect on population dynamics curve

23
Q

what can be found on the fishing curve?

A
  1. population dynamics (“n” parabola)

2. cost of harvesting (“/” slope)

24
Q

3 methods to improve the overfishing situtation

A
  1. fixed quota (set at MSY)
  2. fixed effort (time, size of net…)
  3. fixed escapement (allow some fish to escape fishery before fishing begins)
25
Q

Problems with fixed quota harvesting strategy

A

In a bad year, population won’t grow as fast. Next year, stock will be harvested. Eventually deplete population.
- Do not account for the random factors influencing population growth

26
Q

requirements for using fixed effort harvesting strategy

A

define “effort” strictly

27
Q

Problem with fixed effort harvesting strategy

A
  • political pressure to change “effort” leads to rachet effect
  • Good years: increased pressure to harvest more
  • Bad years: political & economic pressure will always increase harvest, never decrease
28
Q

Rachet effect

A

Political pressure to harvest more when there is a good year, but no pressure to harvest less when there are bad/normal years in the future

29
Q

What is the ideal harvesting curve?

A

Set so that break-even point (B=C) is @ MSY

- fisheries will harvest to MSY

30
Q

What does the fishing curve look like when there is over-harvesting?

A

When cost curve is very steep

31
Q

What does the fishing curve look like when there is under-harvesting?

A

Cost curve is very flat

32
Q

What further complicates fixed effort harvesting strategy?

A

multiple fish caught in the same net
- different fishing curves for different fish, so cost curve of 1 fish can’t be applied to the other without some kind of consequence

33
Q

What is the best solution to overfishing (currently)?

A

Fixed escapement

34
Q

fixed escapement works best with…

A

salmon & migratory fisheries

35
Q

Benefit of fixed escapement

A

ensures that a fraction of the population escapes into the wild to spawn every generation

36
Q

Cons of fixed escapement

A
  • expensive & complicated

- not useful for non-migratory fish

bio220 (24 decks)

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