photo of american bison skulls from wikipedia overexploitation
TRANSCRIPT
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Photo of American bison skulls from Wikipedia
Overexploitation
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N
Time
Exponential growth∆N
∆t= r • N
Occurs when growth rate is proportional to population size;
Requires unlimited resources
Population Dynamics
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N
b
d
r
Equilibrium (= carrying capacity, K)
or d
b
Notice that per capita fitness increases with
decreases in population size from K
Population Dynamics
Density-dependent per capita birth (b) and death (d) rates
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N
Time
Logistic growth∆N
∆t= r • N • (1 – )
N
K
K = carrying capacity
∆N
∆tis maximized
∆N
∆t= 0
∆N
∆t= 0
Population Dynamics
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Yield(Y)
N
oroverexploitation (overharvesting)
Sustainable yield
K
Rate of net production
of new individuals
Exploitation (harvesting)
Population Dynamics & MaximumSustainable Yield (MSY)
∆N
∆t
or
∆N
∆t=
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N
K½ K
MSY
Sustainable yield
Constant quota exploitation
Yield(Y)
Population Dynamics & MaximumSustainable Yield (MSY)
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N
Constant quota exploitation
MSY quota
Low quota
High quota
This is very rarely truly sustainable (since it is
difficult to obtain demographic information to make the predictions and half of the possible
intersections on the curve are unstable)
Yield(Y)
Population Dynamics & MaximumSustainable Yield (MSY)
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N
Proportional or “constant effort”
exploitation
Removing a constant fraction of the pop. is more
often truly sustainable (since most yields intersect
the curve stably), even if there is error in estimating
demographic rates Yield(Y)
MSY exploitation
Lowexploitation
Very highexploitation
Population Dynamics & MaximumSustainable Yield (MSY)
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Photo of lekking Attwater’s prairie chickens in Texas from www.nationalgeographic.com
Population Dynamics & Allee Effects
Allee Effects occur when per capita fitness declines as a population becomes smaller
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Logging
Subsistence hunting
Sport hunting
Pest management
Fishing
Shelling
Non-timber forest products
Trapping
Pet trade
Photo of mahogany from www.cites.org; photo of coyotes on fence from www.life.com
Examples of Exploitation of Target Species
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Photo of Dall porpoise entangled in a fishing net from Wikipedia
Collateral Damage
~30% of marine fisheries “landings” are by-catch
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Photo of Giant ground sloth bones from www.corbis.com
Paleolithic human hunters may have caused the
extinction of many species of megafauna (large-
bodied birds and mammals)
Pleistocene Overkill Hypothesis
Pleistocene = 1.8 million to 10,000 yr before present
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Photo of at least one too many deer in Pennsylvania from www.nrcdeer.com
The Double-Edged Sword of Hunting
The Pleistocene Overkill Hypothesis illustrates the potential negative impacts of too much hunting
Remember trophic cascades (e.g., the consequences of removing top predators); now consider the potential positive impacts of well-managed
hunting
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Policy as a Tool to Combat Overexploitatione.g., legislation on trade in endangered species
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Photo from Greg Dimijian
Policy as a Tool to Combat Overexploitatione.g., legislation on trade in endangered species
Tim Wright et al. (2001) Cons. Biol.
This also indicated that legal and illegal trade in parrots are positively linked
(as opposed to speculation that the two are inversely proportional to one another)
Poaching rates of Neotropical parrots were significantly lower after U.S. Wild Bird
Conservation Act of 1992 banned trade in wild-caught CITES-listed birds
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Image of domestic water buffalo from Wikipedia; case study from Ted Groves (UCSD), pers. comm.
Economic Incentives to Combat Overexploitatione.g., conservation agreement between Conservation International (CI)
& Chumnoab Commune, Cambodia
Commune members agreed to several specific measures of
good land stewardship in their pathwork landscape of
agriculture (rice) & protected forests (wildlife & timber)
CI agreed to provide economic incentives, including 8 water
buffalo after 1 year (5/25/06 – 5/24/07)
Threat: overharvesting of wildlife (e.g., crocodiles) & timber
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Image of domestic water buffalo from Wikipedia; case study from Ted Groves (UCSD), pers. comm.
Economic Incentives to Combat Overexploitatione.g., conservation agreement between Conservation International (CI)
& Chumnoab Commune, Cambodia
12 ha cleared illegally by commune members; after
renegotiation, 6 water buffalo were provided by CI
Collectively, the commune eagerly entered into new
contracts in subsequent years
Compliance monitoring conducted by Cambodia
Forestry Administration, an independent party
Threat: overharvesting of wildlife (e.g., crocodiles) & timber
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Economic Incentives to Combat Overexploitatione.g., conservation agreement between Tetepare Descendants’
Association (TDA) & villagers in the Solomon Islands
Image of leatherback turtle digging a nest from Wikipedia; case study from Ted Groves (UCSD), pers. comm.
Villagers agreed to protect sea turtles by reporting to sea
turtle monitors
Threat: overharvesting leatherback sea turtle females & eggs
Villagers & monitors receive compensation upon initial report & upon successful
hatching
So successful that TDA seeks to build an endowment to fund
future payments
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Photo of Northern bluefin tuna from Wikipedia
Seafood Watch
Use the pocket guides to gauge the status of
seafood:
Web site
Marine Example
~75% of marine fisheries are considered to be fully fished or overexploited (FAO 2002)
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Image from http://oceanworld.tamu.edu/resources/oceanography-book/marinefoodwebs.htm
Marine Examples
“The Perils of Overfishing – Part 1” - NPR interview with Daniel Pauly
Time
Tro
phic
leve
l
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Image of Orange Roughy, a.k.a. Slimehead (Hoplostethus atlanticus) from Wikipedia
Marine Examples
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Image of Hagfish (family Myxinidae) from http://www.mnn.com
Marine Examples
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Image of Chilean Sea Bass, a.k.a. Patagonian Toothfish (Dissostichus eleginoides) from Wikipedia
Marine Examples
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Image of Monkfish, a.k.a. Headfish (genus Lophius) from Wikipedia
Marine Examples
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Image of Alaska Pollock, a.k.a. Walleye Pollock (Theragra chalcogramma) from Wikipedia
Marine Examples
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Image of Atlantic Cod (Gadus morhua) from Wikipedia
Marine Examples
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Image of Peruvian anchovy, a.k.a. Anchoveta (Engraulis ringens) from Wikipedia
Marine Examples
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Image from http://oceanworld.tamu.edu/resources/oceanography-book/marinefoodwebs.htm
Marine Examples
“The Perils of Overfishing – Part 2” - NPR interview with Daniel Pauly
Time
Tro
phic
leve
l
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Image of salmon from Wikipedia
Marine Examples
Salmon are carnivores, so farmed salmon are fed fish meal (ground up fish)
Pauly encourages us to eat wild-caught salmon(if you live close to a salmon fishery)
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Image of a catfish from Wikipedia
Marine Examples
Catfish are often fed soy meal and are often farmed sustainably
Pauly encourages us to eat farmed catfish
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Image of a fried tilapia (one of several members of the fish tribe Tilapiini) from Wikipedia
Marine Examples
Tilapia are often farmed sustainably (but also often become invasive)
Pauly recommends Tilapia for the table
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Image of an oyster from Wikipedia
Marine Examples
Shellfish (clams, mussels, oysters) are often managed sustainably
Pauly also recommends shellfish
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Image of a herring from Wikipedia
Marine Examples
Small shoaling fish generally feed low on the food chain
Pauly also recommends anchovies (Anchoa etc.), herring (Clupea), sardines (Sardina)