Photo of American bison skulls from Wikipedia

1
Overexploitation
Photo of American bison skulls from Wikipedia
2
Population Dynamics
?N
Exponential growth
r N
?t
Occurs when growth rate is proportional to
population size Requires unlimited resources
N
Time
3
Population Dynamics
Density-dependent per capita birth (b)
and death (d) rates
Notice that per capita fitness increases with
decreases in population size from K
b
b
r
or d
d
Equilibrium ( carrying capacity, K)
N
4
Population Dynamics
?N
N
Logistic growth
r N (1 )
?t
K
K carrying capacity
0
N
is maximized
0
Time
5
Population Dynamics Maximum Sustainable Yield
(MSY)
Exploitation (harvesting)
or overexploitation (overharvesting)
?N
?t
or
Sustainable yield
Yield (Y)
Rate of net production of new individuals
?N

?t
K
N
6
Population Dynamics Maximum Sustainable Yield
(MSY)
Constant quota exploitation
MSY
Sustainable yield
Yield (Y)
K
½ K
N
7
Population Dynamics Maximum Sustainable Yield
(MSY)
Constant quota exploitation
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)
MSY quota
Low quota
Yield (Y)
N
8
Population Dynamics Maximum Sustainable Yield
(MSY)
Proportional or constant effort exploitation
MSY exploitation
Very high 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
Low exploitation
Yield (Y)
N
9
Population Dynamics Allee Effects
Allee Effects occur when per capita fitness
declines as a population becomes smaller
Photo of lekking Attwaters prairie chickens in
Texas from www.nationalgeographic.com
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Population Dynamics Allee Effects
Allee Effects occur when per capita fitness
declines as a population becomes smaller
b
?
b
or d
?
d
K
N
Zone of Allee Effects
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Examples of Exploitation of Target Species
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
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Pleistocene Overkill Hypothesis
Pleistocene 1.8 million to 10,000 yr before
present
Paleolithic human hunters may have caused the
extinction of many species of megafauna
(large-bodied birds and mammals)
Photo of Giant ground sloth bones from
www.corbis.com
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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
Photo of at least one too many deer in
Pennsylvania from www.nrcdeer.com
14
Policy as a Tool to Combat Overexploitatione.g.,
legislation on trade in endangered species
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Policy as a Tool to Combat Overexploitatione.g.,
legislation on trade in endangered species
Tim Wright et al. (2001) Cons. Biol.
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
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)
Photo from Greg Dimijian
16
Economic Incentives to Combat Overexploitatione.g
., conservation agreement between Conservation
International (CI) Chumnoab Commune, Cambodia
Threat overharvesting of wildlife (e.g.,
crocodiles) timber
Commune members agreed to several specific
measures of good land stewardship in their
patchwork 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)
Image of domestic water buffalo from Wikipedia
case study from Ted Groves (UCSD), pers. comm.
17
Economic Incentives to Combat Overexploitatione.g
., conservation agreement between Conservation
International (CI) Chumnoab Commune, Cambodia
Threat overharvesting of wildlife (e.g.,
crocodiles) timber
Compliance monitoring conducted by Cambodia
Forestry Administration, an independent party
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
Image of domestic water buffalo from Wikipedia
case study from Ted Groves (UCSD), pers. comm.
18
Economic Incentives to Combat Overexploitatione.g
., conservation agreement between Tetepare
Descendants Association (TDA) villagers in the
Solomon Islands
Threat overharvesting leatherback sea turtle
females eggs
Villagers agreed to protect sea turtles by
reporting to sea turtle monitors
Villagers monitors receive compensation upon
initial report upon successful hatching
So successful that TDA seeks to build an
endowment to fund future payments
Image of leatherback turtle digging a nest from
Wikipedia case study from Ted Groves (UCSD),
pers. comm.
19
Marine Example
75 of marine fisheries are considered to be
fully fished or overexploited (FAO 2002)
Seafood Watch Use the pocket guides to gauge the
status of seafood
Web site
Photo of Northern bluefin tuna from Wikipedia
20
Marine Example of Collateral Damage
30 of marine fisheries landings are by-catch
Photo of Dall porpoise entangled in a fishing net
from Wikipedia
21
Marine Examples of Fishing Down Food Webs
Trophic level
Time
The Perils of Overfishing Part 1 - NPR
interview with Daniel Pauly
Image from http//oceanworld.tamu.edu/resources/oc
eanography-book/marinefoodwebs.htm
22
Marine Examples
Image of Orange Roughy, a.k.a. Slimehead
(Hoplostethus atlanticus) from Wikipedia
23
Marine Examples
Image of Hagfish (family Myxinidae) from
http//www.mnn.com
24
Marine Examples
Image of Chilean Sea Bass, a.k.a. Patagonian
Toothfish (Dissostichus eleginoides) from
Wikipedia
25
Marine Examples
Image of Monkfish, a.k.a. Headfish (genus
Lophius) from Wikipedia
26
Marine Examples
Image of Alaska Pollock, a.k.a. Walleye Pollock
(Theragra chalcogramma) from Wikipedia
27
Marine Examples
Image of Atlantic Cod (Gadus morhua) from
Wikipedia
28
Marine Examples
Image of Peruvian anchovy, a.k.a. Anchoveta
(Engraulis ringens) from Wikipedia
29
Marine Examples
Trophic level
Time
The Perils of Overfishing Part 2 - NPR
interview with Daniel Pauly
Image from http//oceanworld.tamu.edu/resources/oc
eanography-book/marinefoodwebs.htm
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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)
Image of salmon from Wikipedia
31
Marine Examples
Catfish are often fed soy meal and are often
farmed sustainably
Pauly encourages us to eat farmed catfish
Image of a catfish from Wikipedia
32
Marine Examples
Tilapia are often farmed sustainably (but also
often become invasive)
Pauly recommends Tilapia for the table
Image of a fried tilapia (one of several members
of the fish tribe Tilapiini) from Wikipedia
33
Marine Examples
Shellfish (clams, mussels, oysters) are often
managed sustainably
Pauly also recommends shellfish
Image of an oyster from Wikipedia
34
Marine Examples
Small shoaling fish generally feed low on the
food chain
Pauly also recommends anchovies (Anchoa etc.),
herring (Clupea), sardines (Sardina)
Image of a herring from Wikipedia