Environmental Engineering Reference
In-Depth Information
from the resource and (2) the subtractability of the benei ts consumed by
one individual from those available to others (Ostrom et al., 1994). These
characteristics have been considered to generate two broad problems: that
of appropriation and that of provision. The i rst relates to extracting more
than the socially optimal level.
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The dii culty of excluding others from the
use of a CPR creates the problem of ef ectively limiting use (Ostrom et al.,
1994). In the case of renewable natural resources, such as a common prop-
erty forest land, for example, the concern is that the l ow extracted will not
exceed its regeneration rate. The second problem refers to the dii culty of
investing for the 'adequate' provision of the CPR or in activities related to
its improvement or maintenance. Both these problems can be considered to
generate negative consequences for other appropriators/users.
Commonly used games for depicting CPR problems
Three main games have been used for depicting CPR problems. These
games are: (1) the prisoner's dilemma game
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(2) the chicken game
9
and
(3) the assurance game.
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The prisoner's dilemma game has been widely
used to represent the appropriation problems encountered in CPRs. When
limits for resource use cannot be established, all users of the CPR will want
to use as much as possible so as to maximize their own proi t, resulting in
over-appropriation of the resource. In the case of natural resources this
over-appropriation can lead to over-exploitation.
The prisoner's dilemma game is probably the most well-known game
with two players each having two strategies (Figure 10.4). The two avail-
able strategies for each player are to cooperate or to defect. The payof s
considered for this game are such that
c
.
a
,
d
.
c
and
a
.
d
. Thus, given
the payof s for this game, the best response strategy for each player is to
defect. This game has a unique Nash equilibrium that is: defect, defect.
Here is where the dilemma lies, since the players could both be better of if
both chose to cooperate (C) simultaneously since
a
.
d
.
In the case of resource provision, the problem arises with free-riders
benei ting from the resource (as a public good) provided without having
contributed to its provision. For example, time investments for the moni-
toring and enforcement of communitiy forestry or a commonly managed
natural reserve. This problem has been modelled, depending on the provi-
sion technology, with the prisoner's dilemma or with the assurance game,
the former having no one contributing to the resource provision (Figure
10.4) and the latter having players contributing if, and only if, the others
are to contribute (Figure 10.5). The assurance game for which the payof s
are such that
a
.
c
and
d
.
b
(Figure 10.5) thus depicts situations in
which one person's contribution is not enough to gain a collective benei t,
but the contribution of both players will result in a joint benei t. That
